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Posted to commits@commons.apache.org by si...@apache.org on 2011/05/14 00:22:03 UTC
svn commit: r1102911 - in /incubator/ognl/trunk: ./ docbook/ docs/ src/site/
src/site/resources/ src/site/resources/images/ src/site/xdoc/ www/
Author: simonetripodi
Date: Fri May 13 22:22:03 2011
New Revision: 1102911
URL: http://svn.apache.org/viewvc?rev=1102911&view=rev
Log:
[OGNL-10] Update the User/Developer guide according the Commons standard
Added:
incubator/ognl/trunk/src/site/
incubator/ognl/trunk/src/site/resources/
incubator/ognl/trunk/src/site/resources/images/
incubator/ognl/trunk/src/site/site.xml (with props)
incubator/ognl/trunk/src/site/xdoc/
incubator/ognl/trunk/src/site/xdoc/developer-guide.xml (with props)
incubator/ognl/trunk/src/site/xdoc/index.xml (with props)
incubator/ognl/trunk/src/site/xdoc/language-guide.xml (with props)
Removed:
incubator/ognl/trunk/docbook/
incubator/ognl/trunk/docbook.properties
incubator/ognl/trunk/docbook.xml
incubator/ognl/trunk/docs/
incubator/ognl/trunk/www/
Added: incubator/ognl/trunk/src/site/site.xml
URL: http://svn.apache.org/viewvc/incubator/ognl/trunk/src/site/site.xml?rev=1102911&view=auto
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+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+ Licensed to the Apache Software Foundation (ASF) under one or more
+ contributor license agreements. See the NOTICE file distributed with
+ this work for additional information regarding copyright ownership.
+ The ASF licenses this file to You under the Apache License, Version 2.0
+ (the "License"); you may not use this file except in compliance with
+ the License. You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+-->
+<project name="OGNL">
+
+ <bannerRight>
+ <name>Commons OGNL</name>
+ <src>/images/logo.png</src>
+ <href>/index.html</href>
+ </bannerRight>
+
+ <body>
+ <menu name="Discovery">
+ <item name="Overview" href="/index.html" />
+ <item name="Download" href="http://commons.apache.org/ognl/download_ognl.cgi" />
+ <item name="Release Notes (4.0-incubating)" href="http://www.apache.org/dist/commons/ognl/RELEASE-NOTES.txt" />
+ <item name="Language Guide" href="/language-guide.html" />
+ <item name="Developer Guide" href="/developer-guide.html" />
+ </menu>
+
+ <menu name="Development">
+ <item name="Mailing Lists" href="/mail-lists.html" />
+ <item name="Issue Tracking" href="/issue-tracking.html" />
+ <item name="Source Repository" href="/source-repository.html" />
+ <item name="Building" href="/building.html" />
+ <item name="Javadoc (SVN latest)" href="apidocs/index.html" />
+ </menu>
+ </body>
+
+</project>
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Added: incubator/ognl/trunk/src/site/xdoc/developer-guide.xml
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--- incubator/ognl/trunk/src/site/xdoc/developer-guide.xml (added)
+++ incubator/ognl/trunk/src/site/xdoc/developer-guide.xml Fri May 13 22:22:03 2011
@@ -0,0 +1,275 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+ Licensed to the Apache Software Foundation (ASF) under one or more
+ contributor license agreements. See the NOTICE file distributed with
+ this work for additional information regarding copyright ownership.
+ The ASF licenses this file to You under the Apache License, Version 2.0
+ (the "License"); you may not use this file except in compliance with
+ the License. You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+-->
+<document xmlns="http://maven.apache.org/XDOC/2.0"
+ xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+ xsi:schemaLocation="http://maven.apache.org/XDOC/2.0 http://maven.apache.org/xsd/xdoc-2.0.xsd">
+
+ <properties>
+ <title>Apache Commons OGNL - Developer Guide</title>
+ </properties>
+
+ <body>
+ <section name="Introduction">
+ <p><acronym>OGNL</acronym> as a language allows for the navigation of Java objects through a concise syntax that allows for specifying, where possible, symmetrically settable and gettable values. The language specifies a syntax that
+ attempts to provide as high a level of abstraction as possible for navigating object graphs; this usually means specifying paths through and to JavaBeans properties, collection indices, etc. rather than directly accessing property getters and
+ setters (collectively know as <i>accessors</i>).</p>
+
+ <p>The normal usage of OGNL is to embed the language inside of other constructs to provide a place for flexible binding of values from one place to another. An example of this is a web application where values need to be bound from a model
+ of some sort to data transfer objects that are operated on by a view. Another example is an XML configuration file wherein values are generated via expressions which are then bound to configured objects.</p>
+ </section>
+
+ <section name="Embedding OGNL">
+ <p>The <code>org.apache.commons.ognl.Ognl</code> class contains convenience methods for evaluating <acronym>OGNL</acronym> expressions. You can do this in two stages, parsing an expression into an internal form and then using that internal form
+ to either set or get the value of a property; or you can do it in a single stage, and get or set a property using the String form of the expression directly. It is more efficient to pre-compile the expression to it's parsed form,
+ however, and this is the recommended usage.</p>
+
+ <p>OGNL expressions can be evaluated without any external context, or they can be provided with an execution environment that sets up custom extensions to modify the way that expressions are evaluated.</p>
+
+ <p>The following example illustrates how to encapsulate the parsing of an OGNL expression within an object so that execution will be more efficient. The class then takes an <code>OgnlContext</code> and a root object to
+ evaluate against.</p>
+
+ <source>import org.apache.commons.ognl.Ognl;
+import org.apache.commons.ognl.OgnlContext;
+
+public class OgnlExpression
+{
+
+ private Object expression;
+
+ public OgnlExpression( String expressionString )
+ throws OgnlException
+ {
+ super();
+ expression = Ognl.parseExpression( expressionString );
+ }
+
+ public Object getExpression()
+ {
+ return expression;
+ }
+
+ public Object getValue( OgnlContext context, Object rootObject )
+ throws OgnlException
+ {
+ return Ognl.getValue( getExpression(), context, rootObject );
+ }
+
+ public void setValue( OgnlContext context, Object rootObject, Object value )
+ throws OgnlException
+ {
+ Ognl.setValue(getExpression(), context, rootObject, value);
+ }
+
+}</source>
+ </section>
+
+ <section name="Extending OGNL">
+ <p>OGNL expressions are not evaluated in a static environment, as Java programs are. Expressions are not compiled to bytecode at the expression level based on static class reachability. The same expression can have multiple paths
+ through an object graph depending upon the root object specified and the dynamic results of the navigation. Objects that are delegated to handle all of the access to properties of objects, elements of collections, methods of objects,
+ resolution of class names to classes and converting between types are collectively known as <i>OGNL extensions</i>. The following chapters delve more deeply into these extensions and provide a roadmap as to how they are used
+ within OGNL to customize the dynamic runtime environment to suit the needs of the embedding program.</p>
+ </section>
+
+ <section name="Property Accessors">
+ <p>When navigating an <acronym>OGNL</acronym> expression many of the elements that are found are properties. Properties can be many things depending on the object being accessed. Most of the time these property names resolve to JavaBeans
+ properties that conform to the set/get pattern. Other objects (such as <code>Map</code>) access properties as keyed values. Regardless of access methodology the OGNL syntax remains the same. Under the hood, however, there are
+ <code>PropertyAccessor</code> objects that handle the conversion of property name to an actual access to an objects' properties.</p>
+
+ <source>public interface PropertyAccessor
+{
+
+ Object getProperty( Map context, Object target, Object name )
+ throws OgnlException;
+
+ void setProperty( Map context, Object target, Object name, Object value )
+ throws OgnlException;
+
+}</source>
+
+ <p>You can set a property accessor on a class-by-class basis using <code>OgnlRuntime.setPropertyAccessor()</code>. There are default property accessors for <code>Object</code> (which uses JavaBeans patterns to extract
+ properties) and <code>Map</code> (which uses the property name as a key).</p>
+ </section>
+
+ <section name="Method Accessors">
+ <p>Method calls are another area where OGNL needs to do lookups for methods based on dynamic information. The MethodAccessor interface provides a hook into how OGNL calls a method. When a static or instance method is requested the
+ implementor of this interface is called to actually execute the method.</p>
+
+ <source>public interface MethodAccessor
+{
+
+ Object callStaticMethod( Map context, Class targetClass, String methodName, List args )
+ throws MethodFailedException;
+
+ Object callMethod( Map context, Object target, String methodName, List args )
+ throws MethodFailedException;
+
+}</source>
+
+ <p>You can set a method accessor on a class-by-class basis using <code>OgnlRuntime.setMethodAccessor()</code>. The is a default method accessor for <code>Object</code> (which simply finds an appropriate method based
+ on method name and argument types and uses reflection to call the method).</p>
+ </section>
+
+ <section name="Elements Accessors">
+ <p>Since iteration is a built-in function of OGNL and many objects support the idea of iterating over the contents of an object (i.e. the <code>object.{ ... }</code> syntax) OGNL provides a hook into how iteration is done. The
+ <code>ElementsAccessor</code> interface defines how iteration is done based on a source object. Simple examples could be a <code>Collection</code> elements accessor, which would simply</p>
+
+ <source>public interface ElementsAccessor
+{
+
+ Enumeration getElements( Object target )
+ throws OgnlException;
+
+}</source>
+
+ <p>You can set a method accessor on a class-by-class basis using <code>OgnlRuntime.setElementsAccessor()</code>. There are default elements accessors for <code>Object</code> (which returns an <code>Enumeration</code>
+ of itself as the only object), <code>Map</code> (which iterates over the values in the <code>Map</code>), and Collection (which uses the collection's <code>iterator()</code>). One clever use of
+ <code>ElementsAccessor</code>s is the <code>NumberElementsAccessor</code> class which allows for generating numeric sequences from 0 to the target value. For example the expression <code>(100).{ #this }</code> will
+ generate a list of 100 integers ranged 0..99.</p>
+ </section>
+
+ <section name="Class References">
+ <p>In the sections on accessing static field and static methods it stated that classes must be full-specified in between the class reference specifier (<code>@<classname>@<field|method>@</code>).
+ This is not entirely true; the default <code>ClassResolver</code> simply looks up the name of the class and assumes that it is fully specified. The <code>ClassResolver</code> interface is included in the
+ <acronym>OGNL</acronym> context to perform lookup of classes when an expression is evaluated. This makes it possible to specify, for example, a list of imports that are specific to a particular <code>setValue()</code> or
+ <code>getValue()</code> context in order to look up classes. It also makes class references agreeably short because you don't have to full specify a class name.</p>
+
+ <source>public interface ClassResolver
+{
+
+ Class classForName( Map context, String className )
+ throws ClassNotFoundException;
+
+}</source>
+
+ <p>You can set a class resolver on a context basis using the <code>Ognl</code> methods <code>addDefaultContext()</code> and <code>createDefaultContext()</code>.</p>
+ </section>
+
+ <section name="Type Conversion">
+ <p>When performing set operations on properties or calling methods it is often the case that the values you want to set have a different type from the expected type of the class. <acronym>OGNL</acronym> supports a context variable (set by
+ <code>OgnlRuntime.setTypeConverter(Map context, TypeConverter typeConverter)</code>) that will allow types to be converted from one to another. The default type converter that is uses is the <code>ognl.DefaultTypeConverter</code>,
+ which will convert among numeric types <code>(Integer</code>, <code>Long</code>, <code>Short</code>, <code>Double</code>, <code>Float</code>, <code>BigInteger</code>,
+ <code>BigDecimal</code>, and their primitive equivalents), string types (<code>String</code>, <code>Character</code>) and <code>Boolean</code>. Should you need specialized type conversion (one popular
+ example is in Servlets where you have a <code>String[]</code> from an <code>HttpServletRequest.getParameters()</code> and you want to set values with it in other objects; a custom type converter can be written (most likely
+ subclassing <code>ognl.DefaultTypeConverter</code>) to convert <code>String[]</code> to whatever is necessary.</p>
+
+ <source>public interface TypeConverter
+{
+
+ Object convertValue( Map context,
+ Object target,
+ Member member,
+ String propertyName,
+ Object value,
+ Class toType );
+
+}</source>
+
+ <p>Note that <code>ognl.DefaultTypeConverter</code> is much easier to subclass; it implements <code>TypeConverter</code> and calls it's own <code>convertValue(Map context, Object value, Class toType)</code>
+ method and already provides the numeric conversions. For example, the above converter (i.e. converting <code>String[]</code> to <code>int[]</code> for a list of identifier parameters in a request) implemented as a subclass
+ of <code>org.apache.commons.ognl.DefaultTypeConverter</code>:
+
+ <source>HttpServletRequest request;
+Map context = Ognl.createDefaultContext( this );
+
+/* Create an anonymous inner class to handle special conversion */
+Ognl.setTypeConverter( context, new org.apache.commons.ognl.DefaultTypeConverter() {
+
+ public Object convertValue( Map context, Object value, Class toType )
+ {
+
+ Object result = null;
+
+ if ( (toType == int[].class) && (value instanceof String[].class) ) {
+ String sa = (String[])value;
+ int[] ia = new int[sa.length];
+
+ for ( int i = 0; i < sa.length; i++) {
+ Integer cv;
+
+ cv = (Integer) super.convertValue( context,
+ sa[i],
+ Integer.class );
+ ia[i] = cv.intValue();
+ }
+ result = ia;
+ } else {
+ result = super.convertValue( context, value, toType );
+ }
+ return result;
+ }
+});
+/* Setting values within this OGNL context will use the above-defined TypeConverter */
+Ognl.setValue( "identifiers",
+ context,
+ this,
+ request.getParameterValues( "identifier" ) );</source></p>
+ </section>
+
+ <section name="Member Access">
+ <p>Normally in Java the only members of a class (fields, methods) that can be accessed are the ones defined with public access. <acronym>OGNL</acronym> includes an interface that you can set globally (using <code>OgnlContext.setMemberAccessManager()</code>)
+ that allows you to modify the runtime in Java 2 to allow access to private, protected and package protected fields and methods. Included in the <acronym>OGNL</acronym> package is the <code>DefaultMemberAccess</code> class. It
+ contains a constructor that allows you to selectively lower the protection on any private, protected or package protected members<code> using the AccessibleObject</code> interface in Java2. The default class can be subclasses to
+ select different objects for which accessibility is allowed.</p>
+
+ <source>public interface MemberAccess
+{
+
+ Object setup( Member member );
+
+ void restore( Member member, Object state );
+
+ boolean isAccessible( Member member );
+
+}</source>
+ </section>
+
+ <section name="Null Handler">
+ <p>When navigating a chain sometimes properties or methods will evaluate to null, causing subsequent properties or method calls to fail with <code>NullPointerException</code>s. Most of the time this behaviour is correct (as it is
+ with Java), but sometimes you want to be able to dynamically substitute another object in place of <code>null</code>. The <code>NullHandler</code> interface allows you to specify on a class-by-class basis how nulls are
+ handled within OGNL expressions. Implementing this interface allows you to intercept when methods return <code>null</code> and properties evaluate to <code>null</code> and allow you to substitute a new value. Since you are
+ given the source of the method or property a really clever implementor might write the property back to the object so that subsequent invocations do not return or evaluate to <code>null</code>.</p>
+
+ <source>public interface NullHandler
+{
+
+ Object nullMethodResult( Map context, Object target, String methodName, List args );
+
+ Object nullPropertyValue( Map context, Object target, Object property );
+
+}</source>
+
+ <p><code>NullHandler</code> implementors are registered with <acronym>OGNL</acronym> using the <code>OgnlRuntime.setNullHandler()</code> method.</p>
+ </section>
+
+ <section name="Other API features">
+ <subsection name="Tracing Evaluations">
+ <p>As of OGNL 2.5.0 the <code>OgnlContext</code> object can automatically tracks evaluations of expressions. This tracking is kept in the <code>OgnlContext</code> as <code>currentEvaluation</code> during the
+ evaluation. After execution you can access the last evaluation through the <code>lastEvaluation</code> property of <code>OgnlContext</code>.</p>
+
+ <p><b>Note</b>: The tracing feature is turned off by default. If you wish to turn it on there is a <code>setTraceEvaluations()</code> method on <code>OgnlContext</code> that you can call.</p>
+
+ <p>Any <i>method accessor</i>, <i>elements accessor</i>, <i>type converter</i>, <i>property accessor</i>
+ or <i>null handler</i> may find this useful to give context to the operation being performed. The <code>Evaluation</code> object is itself a tree and can be traversed up, down and left and right
+ through siblings to determine the exact circumstances of an evaluation. In addition the <code>Evaluation</code> object tracks the node that was performing the operation, the source object on which that operation was being
+ performed and the result of the operation. If an exception is thrown during execution the user can get the last evaluation's last descendent to find out exactly which subexpression caused the error. The execption is also tracked in
+ the <code>Evaluation</code>.</p>
+ </subsection>
+ </section>
+ </body>
+
+</document>
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--- incubator/ognl/trunk/src/site/xdoc/index.xml (added)
+++ incubator/ognl/trunk/src/site/xdoc/index.xml Fri May 13 22:22:03 2011
@@ -0,0 +1,85 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+ Licensed to the Apache Software Foundation (ASF) under one or more
+ contributor license agreements. See the NOTICE file distributed with
+ this work for additional information regarding copyright ownership.
+ The ASF licenses this file to You under the Apache License, Version 2.0
+ (the "License"); you may not use this file except in compliance with
+ the License. You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+-->
+<document xmlns="http://maven.apache.org/XDOC/2.0"
+ xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+ xsi:schemaLocation="http://maven.apache.org/XDOC/2.0 http://maven.apache.org/xsd/xdoc-2.0.xsd">
+
+ <properties>
+ <title>Apache Commons OGNL - Object Graph Navigation Library</title>
+ </properties>
+
+ <body>
+
+ <section name="Apache Commons OGNL - Object Graph Navigation Library">
+ <p>
+ OGNL stands for Object-Graph Navigation Language; it is an expression language for getting and setting
+ properties of Java objects, plus other extras such as list projection and selection and lambda expressions.
+ You use the same expression for both getting and setting the value of a property.
+ </p>
+
+ <p>
+ The <code>Ognl</code> class contains convenience methods for evaluating OGNL expressions. You can do this in two
+ stages, parsing an expression into an internal form and then using that internal form to either set or get the
+ value of a property; or you can do it in a single stage, and get or set a property using the String form of the
+ expression directly.
+ </p>
+
+ <p>
+ OGNL started out as a way to set up associations between UI components and controllers using property names. As the
+ desire for more complicated associations grew, Drew Davidson created what he called KVCL, for Key-Value Coding
+ Language, egged on by Luke Blanshard. Luke then reimplemented the language using ANTLR, came up with the new name,
+ and, egged on by Drew, filled it out to its current state. Later on Luke again reimplemented the language using
+ JavaCC. Further maintenance on all the code is done by Drew (with spiritual guidance from Luke).
+ </p>
+
+ <p>
+ We pronounce OGNL as a word, like the last syllables of a drunken pronunciation of "<i>orthogonal</i>".
+ </p>
+ </section>
+
+ <section name="Introduction">
+ <p>
+ Many people have asked exactly what <code>OGNL</code> is good for. Several of the uses to which <code>OGNL</code>
+ has been applied are:
+ </p>
+ <ul>
+ <li>
+ A binding language between GUI elements (textfield, combobox, etc.) to model objects. Transformations are made
+ easier by <code>OGNL</code>'s TypeConverter mechanism to convert values from one type to another (String to
+ numeric types, for example);
+ </li>
+ <li>
+ A data source language to map between table columns and a Swing TableModel;
+ </li>
+ <li>
+ A binding language between web components and the underlying model objects;
+ </li>
+ <li>
+ A more expressive replacement for the property-getting language used by the Apache Commons BeanUtils package or
+ JSTL's EL (which only allow simple property navigation and rudimentary indexed properties).
+ </li>
+ </ul>
+ <p>
+ Most of what you can do in Java is possible in <code>OGNL</code>, plus other extras such as list <i>projection</i>,
+ <i>selection</i> and <i>lambda expressions</i>.
+ </p>
+ </section>
+
+ </body>
+
+</document>
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@@ -0,0 +1,1237 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+ Licensed to the Apache Software Foundation (ASF) under one or more
+ contributor license agreements. See the NOTICE file distributed with
+ this work for additional information regarding copyright ownership.
+ The ASF licenses this file to You under the Apache License, Version 2.0
+ (the "License"); you may not use this file except in compliance with
+ the License. You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+-->
+<document xmlns="http://maven.apache.org/XDOC/2.0"
+ xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+ xsi:schemaLocation="http://maven.apache.org/XDOC/2.0 http://maven.apache.org/xsd/xdoc-2.0.xsd">
+
+ <properties>
+ <title>Apache Commons OGNL - Language Guide</title>
+ </properties>
+
+ <body>
+ <section name="Syntax">
+ <p>
+ Basic <acronym>OGNL</acronym> expressions are very simple. The language has become quite rich with features, but
+ you don't generally need to worry about the more complicated parts of the language: the simple cases have
+ remained that way. For example, to get at the name property of an object, the <acronym>OGNL</acronym> expression
+ is simply <code>name</code>. To get at the <code>text</code> property of the object returned by the headline
+ property, the <acronym>OGNL</acronym> expression is <code>headline.text</code>.
+ </p>
+
+ <p>
+ What is a property? Roughly, an <acronym>OGNL</acronym> property is the same as a bean property, which means that
+ a pair of get/set methods, or alternatively a field, defines a property (the full story is a bit more complicated,
+ since properties differ for different kinds of objects; see below for a full explanation).
+ </p>
+
+ <p>
+ The fundamental unit of an <acronym>OGNL</acronym> expression is the navigation chain, usually just called
+ "chain." The simplest chains consist of the following parts:
+ </p>
+
+ <table>
+ <thead>
+ <tr>
+ <th>Expression Element Part</th>
+ <th>Example</th>
+ </tr>
+ </thead>
+ <tbody>
+ <tr>
+ <td>Property names</td>
+ <td>like the <code>name</code> and <code>headline.text</code> examples above</td>
+ </tr>
+ <tr>
+ <td>Method Calls</td>
+ <td><code>hashCode()</code> to return the current object's hash code</td>
+ </tr>
+ <tr>
+ <td>Array Indices</td>
+ <td><code>listeners[0]</code> to return the first of the current object's list of listeners</td>
+ </tr>
+ </tbody>
+ </table>
+
+ <p>
+ All <acronym>OGNL</acronym> expressions are evaluated in the context of a current object, and a chain simply uses
+ the result of the previous link in the chain as the current object for the next one. You can extend a chain as
+ long as you like. For example, this chain:
+ </p>
+
+ <source>name.toCharArray()[0].numericValue.toString()</source>
+
+ <p>
+ This expression follows these steps to evaluate:
+ </p>
+
+ <ul>
+ <li>extracts the <code>name</code> property of the initial, or root, object (which the user provides to
+ <acronym>OGNL</acronym> through the <acronym>OGNL</acronym> context);</li>
+ <li>
+ calls the <code>toCharArray()</code> method on the resulting <code>String</code>;
+ </li>
+ <li>
+ extracts the first character (the one at index <code>0</code>) from the resulting array;
+ </li>
+ <li>
+ gets the <code>numericValue</code> property from that character (the character is represented as a
+ <code>Character</code> object, and the <code>Character</code> class has a method called
+ <code>getNumericValue()</code>);
+ </li>
+ <li>
+ calls <code>toString()</code> on the resulting <code>Integer</code> object. The final result of this expression
+ is the <code>String</code> returned by the last <code>toString()</code> call.
+ </li>
+ </ul>
+
+ <p>
+ Note that this example can only be used to get a value from an object, not to set a value. Passing the above
+ expression to the <code>Ognl.setValue()</code> method would cause an <code>InappropriateExpressionException</code>
+ to be thrown, because the last link in the chain is neither a property name nor an array index.
+ </p>
+
+ <p>
+ This is enough syntax to do the vast majority of what you ever need to do.
+ </p>
+ </section>
+
+ <section name="Expressions">
+ <p>
+ This section outlines the details the elements of <acronym>OGNL</acronym>'s expressions.
+ </p>
+
+ <subsection name="Constants">
+ <p>
+ <acronym>OGNL</acronym> has the following kinds of constants:
+ </p>
+
+ <ul>
+ <li>
+ String literals, as in Java (with the addition of single quotes): delimited by single- or double-quotes,
+ with the full set of character escapes;
+ </li>
+ <li>
+ Character literals, also as in Java: delimited by single-quotes, also with the full set of escapes;
+ </li>
+ <li>
+ Numeric literals, with a few more kinds than Java. In addition to Java's ints, longs, floats and doubles,
+ <acronym>OGNL</acronym> lets you specify BigDecimals with a "b" or "B" suffix, and BigIntegers
+ with an "h" or "H" suffix (think "huge"---we chose "h" for BigIntegers because
+ it does not interfere with hexadecimal digits);
+ </li>
+ <li>
+ Boolean (<code>true</code> and <code>false</code>) literals;
+ </li>
+ <li>
+ The <code>null</code> literal.
+ </li>
+ </ul>
+ </subsection>
+
+ <subsection name="Referring to Properties">
+ <p>
+ <acronym>OGNL</acronym> treats different kinds of objects differently in its handling of property references.
+ Maps treat all property references as element lookups or storage, with the property name as the key.
+ Lists and arrays treat numeric properties similarly, with the property name as the index, but string properties
+ the same way ordinary objects do. Ordinary objects (that is, all other kinds) only can handle string properties
+ and do so by using "get" and "set" methods (or "is" and "set"), if the object
+ has them, or a field with the given name otherwise.
+ </p>
+
+ <p>
+ Note the new terminology here. Property "names" can be of any type, not just Strings. But to refer to
+ non-String properties, you must use what we have been calling the "index" notation. For example, to get
+ the length of an array, you can use this expression:
+ </p>
+
+ <source>array.length</source>
+
+ <p>
+ But to get at element 0 of the array, you must use an expression like this:
+ </p>
+
+ <source>array[0]</source>
+
+ <p>
+ Note that Java collections have some special properties associated with them.
+ </p>
+ </subsection>
+
+ <subsection name="Indexing">
+ <p>
+ As discussed above, the "indexing" notation is actually just property reference, though a computed form
+ of property reference rather than a constant one.
+ </p>
+
+ <p>
+ For example, <acronym>OGNL</acronym> internally treats the "array.length" expression exactly the same as
+ this expression:
+ </p>
+
+ <source>array["length"]</source>
+
+ <p>
+ And this expression would have the same result (though not the same internal form):
+ </p>
+
+ <source>array["len" + "gth"]</source>
+
+ <!-- sub-subsection -->
+ <p>
+ <b>Array and List Indexing</b>
+ </p>
+
+ <p>
+ For Java arrays and Lists indexing is fairly simple, just like in Java.
+ An integer index is given and that element is the referrent. If the index is out of bounds of the array or List
+ and IndexOutOfBoundsException is thrown, just as in Java.
+ </p>
+
+ <!-- sub-subsection -->
+ <p>
+ <b>JavaBeans Indexed Properties</b>
+ </p>
+
+ <p>
+ JavaBeans supports the concept of Indexed properties. Specifically this means that an object has a set of
+ methods that follow the following pattern:
+ </p>
+ <ul>
+ <li>
+ <code>public <i>PropertyType</i>[] get<i>PropertyName</i>();</code>
+ </li>
+ <li>
+ <code>public void set<i>PropertyName</i>(<i>PropertyType</i>[] anArray);</code>
+ </li>
+ <li>
+ <code>public <i>PropertyType</i> get<i>PropertyName</i>(int index);</code>
+ </li>
+ <li>
+ <code>public void set<i>PropertyName</i>(int index, <i>PropertyType</i> value);</code>
+ </li>
+ </ul>
+
+ <p>OGNL can interpret this and provide seamless access to the property through the indexing notation.
+ References such as</p>
+
+ <source>someProperty[2]</source>
+
+ <p>
+ are automatically routed through the correct indexed property accessor (in the above case through
+ <code>getSomeProperty(2)</code> or <code>setSomeProperty(2, value)</code>). If there is no indexed property
+ accessor a property is found with the name <code>someProperty</code> and the index is applied to that.
+ </p>
+
+ <!-- sub-subsection -->
+ <p>
+ <b>OGNL Object Indexed Properties</b>
+ </p>
+
+ <p>
+ OGNL extends the concept of indexed properties to include indexing with arbitrary objects, not just integers as
+ with JavaBeans Indexed Properties. When finding properties as candidates for object indexing, OGNL looks for
+ patterns of methods with the following signature:
+ </p>
+ <ul>
+ <li><code>public <i>PropertyType</i> get<i>PropertyName</i>(<i>IndexType</i> index);</code></li>
+ <li><code>public void set<i>PropertyName</i>(<i>IndexType</i> index, <i>PropertyType</i> value);</code></li>
+ </ul>
+
+ <p>
+ The <code>PropertyType</code> and <code>IndexType</code> must match each other in the corresponding set and get
+ methods. An actual example of using Object Indexed Properties is with the Servlet API: the Session object has
+ two methods for getting and setting arbitrary attributes:
+ </p>
+
+ <source>public Object getAttribute(String name) public void setAttribute(String name, Object value)</source>
+
+ <p>
+ An OGNL expression that can both get and set one of these attributes is:
+ </p>
+
+ <source>session.attribute["foo"]</source>
+ </subsection>
+ </section>
+
+ <section name="Calling Methods">
+ <p><acronym>OGNL</acronym> calls methods a little differently from the way Java does, because
+ <acronym>OGNL</acronym> is interpreted and must choose the right method at run time, with no extra type
+ information aside from the actual arguments supplied. <acronym>OGNL</acronym> always chooses the most specific
+ method it can find whose types match the supplied arguments; if there are two or more methods that are equally
+ specific and match the given arguments, one of them will be chosen arbitrarily.</p>
+
+ <p>
+ In particular, a null argument matches all non-primitive types, and so is most likely to result in an unexpected
+ method being called.
+ </p>
+
+ <p>
+ Note that the arguments to a method are separated by commas, and so the comma operator cannot be used unless it is
+ enclosed in parentheses. For example,
+ </p>
+
+ <source>method( ensureLoaded(), name )</source>
+
+ <p>
+ is a call to a 2-argument method, while
+ </p>
+
+ <source>method( (ensureLoaded(), name) )</source>
+
+ <p>
+ is a call to a 1-argument method.
+ </p>
+ </section>
+
+ <section name="Variable References">
+ <p>
+ <acronym>OGNL</acronym> has a simple variable scheme, which lets you store intermediate results and use them
+ again, or just name things to make an expression easier to understand. All variables in <acronym>OGNL</acronym>
+ are global to the entire expression. You refer to a variable using a number sign in front of its name, like this:
+ </p>
+
+ <source>#var</source>
+
+ <p>
+ <acronym>OGNL</acronym> also stores the current object at every point in the evaluation of an expression in the
+ this variable, where it can be referred to like any other variable. For example, the following expression operates
+ on the number of listeners, returning twice the number if it is more than 100, or 20 more than the number otherwise:
+ </p>
+
+ <source>listeners.size().(#this > 100? 2*#this : 20+#this)</source>
+
+ <p>
+ <acronym>OGNL</acronym> can be invoked with a map that defines initial values for variables. The standard way of
+ invoking <acronym>OGNL</acronym> defines the variables <code>root</code> (which holds the initial, or root,
+ object), and <code>context</code> (which holds the <code>Map</code> of variables itself).
+ </p>
+
+ <p>
+ To assign a value to a variable explicitly, simply write an assignment statement with a variable reference on the
+ left-hand side:
+ </p>
+
+ <source>#var = 99</source>
+ </section>
+
+ <section name="Parenthetical Expressions">
+ <p>
+ As you would expect, an expression enclosed in parentheses is evaluated as a unit, separately from any surrounding
+ operators. This can be used to force an evaluation order different from the one that would be implied by
+ <acronym>OGNL</acronym> operator precedences. It is also the only way to use the comma operator in a method
+ argument.
+ </p>
+ </section>
+
+ <section name="Chained Subexpressions">
+ <p>
+ If you use a parenthetical expression after a dot, the object that is current at the dot is used as the current object throughout the parenthetical expression. For example,</p>
+
+ <source>headline.parent.(ensureLoaded(), name)</source>
+
+ <p>traverses through the <code>headline</code> and <code>parent</code> properties, ensures that the <code>parent</code> is loaded and then returns (or sets) the parent's <code>name</code>.</p>
+
+ <p>Top-level expressions can also be chained in this way. The result of the expression is the right-most expression element.</p>
+
+ <source>ensureLoaded(), name</source>
+
+ <p>This will call <code>ensureLoaded()</code> on the root object, then get the <code>name</code> property of the root object as the result of the expression.</p>
+ </section>
+
+ <section name="Collection Construction">
+ <subsection name="Lists">
+ <p>To create a list of objects, enclose a list of expressions in curly braces. As with method arguments, these expressions cannot use the comma operator unless it is enclosed in parentheses. Here is an example:</p>
+
+ <source>name in { null,"Untitled" }</source>
+
+ <p>This tests whether the <code>name</code> property is <code>null</code> or equal to <code>"Untitled"</code>.</p>
+
+ <p>The syntax described above will create a instanceof the <code>List</code> interface. The exact subclass is not defined.</p>
+ </subsection>
+
+ <subsection name="Native Arrays">
+ <p>Sometimes you want to create Java native arrays, such as <code>int[]</code> or <code>Integer[]</code>. <acronym>OGNL</acronym> supports the creation of these similarly to the way that constructors are normally called, but allows
+ initialization of the native array from either an existing list or a given size of the array.</p>
+
+ <source>new int[] { 1, 2, 3 }</source>
+
+ <p>This creates a new <code>int</code> array consisting of three integers 1, 2 and 3.</p>
+
+ <p>To create an array with all <code>null</code> or <code>0</code> elements, use the alternative size constructor</p>
+
+ <source>new int[5]</source>
+
+ <p>This creates an <code>int</code> array with 5 slots, all initialized to zero.</p>
+ </subsection>
+
+ <subsection name="Maps">
+ <p>Maps can also be created using a special syntax.</p>
+
+ <source>#{ "foo" : "foo value", "bar" : "bar value" }</source>
+
+ <p>This creates a Map initialized with mappings for <code>"foo"</code> and <code>"bar"</code>.</p>
+
+ <p>Advanced users who wish to select the specific Map class can specify that class before the opening curly brace</p>
+
+ <source>#@java.util.LinkedHashMap@{ "foo" : "foo value", "bar" : "bar value" }</source>
+
+ <p>The above example will create an instance of the JDK 1.4 class <code>LinkedHashMap</code>, ensuring the the insertion order of the elements is preserved.</p>
+ </subsection>
+ </section>
+
+ <section name="Projecting Across Collections">
+ <p><acronym>OGNL</acronym> provides a simple way to call the same method or extract the same property from each element in a collection and store the results in a new collection. We call this "projection," from the database
+ term for choosing a subset of columns from a table. For example, this expression:</p>
+
+ <source>listeners.{delegate}</source>
+
+ <p>returns a list of all the listeners' delegates. See the coercion section for how <acronym>OGNL</acronym> treats various kinds of objects as collections.</p>
+
+ <p>During a projection the <code>#this</code> variable refers to the current element of the iteration.</p>
+
+ <source>objects.{ #this instanceof String ? #this : #this.toString()}</source>
+
+ <p>The above would produce a new list of elements from the objects list as string values.</p>
+ </section>
+
+ <section name="Selecting From Collections">
+ <p><acronym>OGNL</acronym> provides a simple way to use an expression to choose some elements from a collection and save the results in a new collection. We call this "selection," from the database term for choosing a subset of
+ rows from a table. For example, this expression:</p>
+
+ <source>listeners.{? #this instanceof ActionListener}</source>
+
+ <p>returns a list of all those listeners that are instances of the <code>ActionListener</code> class.</p>
+
+ <subsection name="Selecting First Match">
+ <p>In order to get the first match from a list of matches, you could use indexing such as <code>listeners.{? true }[0]</code>. However, this is cumbersome because if the match does not return any results (or if the result
+ list is empty) you will get an <code>ArrayIndexOutOfBoundsException</code>.</p>
+
+ <p>The selection syntax is also available to select only the first match and return it as a list. If the match does not succeed for any elements an empty list is the result.</p>
+
+ <source>objects.{^ #this instanceof String }</source>
+
+ <p>Will return the first element contained in objects that is an instance of the <code>String</code> class.</p>
+ </subsection>
+
+ <subsection name="Selecting Last Match">
+ <p>Similar to getting the first match, sometimes you want to get the last element that matched.</p>
+
+ <source>objects.{$ #this instanceof String }</source>
+
+ <p>This will return the last element contained in objects that is an instanceof the <code>String</code> class</p>
+ </subsection>
+ </section>
+
+ <section name="Calling Constructors">
+ <p>You can create new objects as in Java, with the <code>new</code> operator. One difference is that you must specify the fully qualified class name for classes other than those in the java.lang package.</p>
+ <p>This is only true with the default ClassResolver in place. With a custom class resolver packages can be mapped in such a way that more Java-like references to classes can be made. Refer to the
+ OGNL Developer's Guide for details on using <code>ClassResolver</code> class (for example, <code>new java.util.ArrayList()</code>, rather than simply <code>new ArrayList()</code>).</p>
+
+ <p><acronym>OGNL</acronym> chooses the right constructor to call using the same procedure it uses for overloaded method calls.</p>
+ </section>
+
+ <section name="Calling Static Methods">
+ <p>You can call a static method using the syntax <code>@</code><code>class</code><code>@</code><code>method(args)</code>. If you leave out class, it defaults to <code>java.lang.Math</code>, to
+ make it easier to call <code>min</code> and <code>max</code> methods. If you specify the class, you must give the fully qualified name.</p>
+
+ <p>If you have an instance of a class whose static method you wish to call, you can call the method through the object as if it was an instance method.</p>
+
+ <p>If the method name is overloaded, <acronym>OGNL</acronym> chooses the right static method to call using the same procedure it uses for overloaded instance methods.</p>
+ </section>
+
+ <section name="Getting Static Fields">
+ <p>You can refer to a static field using the syntax <code>@</code><code>class</code><code>@</code><code>field</code>. The class must be fully qualified.</p>
+ </section>
+
+ <section name="Expression Evaluation">
+ <p>If you follow an <acronym>OGNL</acronym> expression with a parenthesized expression, without a dot in front of the parentheses, <acronym>OGNL</acronym> will try to treat the result of the first expression as another expression to
+ evaluate, and will use the result of the parenthesized expression as the root object for that evaluation. The result of the first expression may be any object; if it is an AST, <acronym>OGNL</acronym> assumes it is the parsed form of an
+ expression and simply interprets it; otherwise, <acronym>OGNL</acronym> takes the string value of the object and parses that string to get the AST to interpret.</p>
+
+ <p>For example, this expression</p>
+
+ <source>#fact(30H)</source>
+
+ <p>looks up the <code>fact</code> variable, and interprets the value of that variable as an <acronym>OGNL</acronym> expression using the <code>BigInteger</code> representation of <code>30</code> as the
+ <code>root</code> object. See below for an example of setting the <code>fact</code> variable with an expression that returns the factorial of its argument. Note that there is an ambiguity in <acronym>OGNL</acronym>'s
+ syntax between this double evaluation operator and a method call. <acronym>OGNL</acronym> resolves this ambiguity by calling anything that looks like a method call, a method call. For example, if the current object had a fact property
+ that held an <acronym>OGNL</acronym> factorial expression, you could not use this approach to call it</p>
+
+ <source>fact(30H)</source>
+
+ <p>because <acronym>OGNL</acronym> would interpret this as a call to the <code>fact</code> method. You could force the interpretation you want by surrounding the property reference by parentheses:</p>
+
+ <source>(fact)(30H)</source>
+ </section>
+
+ <section name="Pseudo-Lambda Expressions">
+ <p><acronym>OGNL</acronym> has a simplified lambda-expression syntax, which lets you write simple functions. It is not a full-blown lambda calculus, because there are no closures---all variables in <acronym>OGNL</acronym> have global
+ scope and extent.</p>
+
+ <p>For example, here is an <acronym>OGNL</acronym> expression that declares a recursive factorial function, and then calls it:</p>
+
+ <source>#fact = :[#this<=1? 1 : #this*#fact(#this-1)], #fact(30H)</source>
+
+ <p>The lambda expression is everything inside the brackets. The <code>#this</code> variable holds the argument to the expression, which is initially <code>30H</code>, and is then one less for each successive call to the
+ expression.</p>
+
+ <p><acronym>OGNL</acronym> treats lambda expressions as constants. The value of a lambda expression is the <code>AST</code> that <acronym>OGNL</acronym> uses as the parsed form of the contained expression.</p>
+ </section>
+
+ <section name="Pseudo-Properties for Collections">
+ <p>There are some special properties of collections that <acronym>OGNL</acronym> makes available. The reason for this is that the collections do not follow JavaBeans patterns for method naming; therefore the <code>size()</code>,
+ <code>length()</code>, etc. methods must be called instead of more intuitively referring to these as properties. <acronym>OGNL</acronym> corrects this by exposing certain pseudo-properties as if they were built-in.</p>
+
+ <table>
+ <caption>Special Collections Pseudo-Properties</caption>
+ <thead>
+ <tr>
+ <th>Collection</th>
+ <th>Special Properties</th>
+ </tr>
+ </thead>
+ <tbody>
+ <tr>
+ <td><code>Collection</code> (inherited by <code>Map</code>, <code>List</code> & <code>Set</code>)</td>
+ <td>
+ <ul>
+ <li><code>size</code>: The size of the collection</li>
+ <li><code>isEmpty</code>: Evaluates
+ to <code>true</code> if the collection is empty</li>
+ </ul>
+ </td>
+ </tr>
+ <tr>
+ <td>List</td>
+ <td>
+ <ul>
+ <li><code>iterator</code>: Evalutes to an <code>Iterator</code> over the <code>List</code>.</li>
+ </ul>
+ </td>
+ </tr>
+ <tr>
+ <td>Map</td>
+ <td>
+ <ul>
+ <li><code>keys</code>: Evalutes to a <code>Set</code> of all keys in the <code>Map</code></li>
+ <li><code>values</code>: Evaluates to a <code>Collection</code> of all values in the <code>Map</code></li>
+ </ul>
+ <b>Note</b> These properties, plus <code>size</code> and <code>isEmpty</code>,
+ are different than the indexed form of access for <code>Map</code>s (i.e. <code>someMap["size"]</code> gets the <code>"size"</code> key from the map, whereas <code>someMap.size</code>
+ gets the size of the <code>Map</code>
+ </td>
+ </tr>
+ <tr>
+ <td>Set</td>
+ <td>
+ <ul>
+ <li><code>iterator</code>: Evalutes to an <code>Iterator</code> over the <code>Set</code></li>
+ </ul>
+ </td>
+ </tr>
+ <tr>
+ <td>Iterator</td>
+ <td>
+ <ul>
+ <li><code>next</code>: Evalutes to the next object from the <code>Iterator</code></li>
+ <li><code>hasNext</code>: Evaluates to <code>true</code> if there is a next object available from the <code>Iterator</code></li>
+ </ul>
+ </td>
+ </tr>
+ <tr>
+ <td>Enumeration</td>
+ <td>
+ <ul>
+ <li><code>next</code>: Evalutes to the next object from the <code>Enumeration</code></li>
+ <li><code>hasNext</code>: Evaluates to <code>true</code> if there is a next object available from the <code>Enumeration</code></li>
+ <li><code>nextElement</code>: Synonym for <code>next</code></li>
+ <li><code>hasMoreElements</code>: Synonym for <code>hasNext</code></li>
+ </ul>
+ </td>
+ </tr>
+ </tbody>
+ </table>
+ </section>
+
+ <section name="Operators that differ from Java's operators">
+ <p>For the most part, <acronym>OGNL</acronym>'s operators are borrowed from Java and work similarly to Java's operators. See the <acronym>OGNL</acronym> Reference for a complete discussion. Here we describe <acronym>OGNL</acronym>
+ operators that are not in Java, or that are different from Java.</p>
+
+ <ul>
+ <li>The comma (,) or sequence operator. This operator is borrowed from C. The comma is used to separate two independent expressions. The value of the second of these expressions is the value of the comma expression. Here is an
+ example:
+
+ <source>ensureLoaded(), name</source>
+
+ When this expression is evaluated, the ensureLoaded method is called (presumably to make sure that all parts of the object are in memory), then the name property is retrieved (if getting the value) or replaced (if setting).</li>
+ <li>List construction with curly braces ({}). You can create a list in-line by enclosing the values in curly braces, as in this example:
+
+ <source>{ null, true, false }</source></li>
+ <li>The <code>in</code> operator (and <code>not in</code>, its negation). This is a containment test, to see if a value is in a collection. For example,
+
+ <source>name in {null,"Untitled"} || name</source></li>
+ </ul>
+ </section>
+
+ <section name="Setting values versus getting values">
+ <p>As stated before, some values that are gettable are not also settable because of the nature of the expression. For example,</p>
+
+ <source>names[0].location</source>
+
+ <p>is a settable expression - the final component of the expression resolves to a settable property.</p>
+
+ <p>However, some expressions, such as</p>
+
+ <source>names[0].length + 1</source>
+
+ <p>are not settable because they do not resolve to a settable property in an object. It is simply a computed value. If you try to evaluate this expression using any of the <code>Ognl.setValue()</code> methods it will fail with
+ an <code>InappropriateExpressionException</code>.</p>
+
+ <p>It is also possible to set variables using get expressions that include the '<code>=</code>' operator. This is useful when a get expression needs to set a variable as a side effect of execution.</p>
+ </section>
+
+ <section name="Coercing Objects to Types">
+ <p>Here we describe how <acronym>OGNL</acronym> interprets objects as various types. See below for how <acronym>OGNL</acronym> coerces objects to booleans, numbers, integers, and collections.</p>
+
+ <subsection name="Interpreting Objects as Booleans">
+ <p>Any object can be used where a boolean is required. <acronym>OGNL</acronym> interprets objects as booleans like this:</p>
+ <ul>
+ <li>If the object is a <code>Boolean</code>, its value is extracted and returned;</li>
+ <li>If the object is a <code>Number</code>, its double-precision floating-point value is compared with zero; non-zero is treated as <code>true</code>, zero as <code>false</code>;</li>
+ <li>If the object is a <code>Character</code>, its boolean value is <code>true</code> if and only if its char value is non-zero;</li>
+ <li>Otherwise, its boolean value is <code>true</code> if and only if it is non-<code>null</code>.</li>
+ </ul>
+ </subsection>
+
+ <subsection name="Interpreting Objects as Numbers">
+ <p>Numerical operators try to treat their arguments as numbers. The basic primitive-type wrapper classes (Integer, Double, and so on, including Character and Boolean, which are treated as integers), and the "big" numeric
+ classes from the java.math package (BigInteger and BigDecimal), are recognized as special numeric types. Given an object of some other class, <acronym>OGNL</acronym> tries to parse the object's string value as a number.</p>
+
+ <p>Numerical operators that take two arguments use the following algorithm to decide what type the result should be. The type of the actual result may be wider, if the result does not fit in the given type.</p>
+
+ <ul>
+ <li>If both arguments are of the same type, the result will be of the same type if possible;</li>
+ <li>If either argument is not of a recognized numeric class, it will be treated as if it was a <code>Double</code> for the rest of this algorithm;</li>
+ <li>If both arguments are approximations to real numbers <code>(Float</code>, <code>Double</code>, or <code>BigDecimal</code>), the result will be the wider type;</li>
+ <li>If both arguments are integers <code>(Boolean</code>, <code>Byte</code>, <code>Character</code>, <code>Short</code>, <code>Integer</code>, <code>Long</code>, or
+ <code>BigInteger</code>), the result will be the wider type;</li>
+ <li>If one argument is a real type and the other an integer type, the result will be the real type if the integer is narrower than "int"; <code>BigDecimal</code> if the integer is <code>BigInteger</code>;
+ or the wider of the real type and <code>Double</code> otherwise.</li>
+ </ul>
+ </subsection>
+
+ <subsection name="Interpreting Objects as Integers">
+ <p>Operators that work only on integers, like the bit-shifting operators, treat their arguments as numbers, except that <code>BigDecimal</code>s and <code>BigInteger</code>s are operated on as
+ <code>BigInteger</code>s and all other kinds of numbers are operated on as Longs. For the <code>BigInteger</code> case, the result of these operators remains a <code>BigInteger</code>; for the
+ <code>Long</code> case, the result is expressed as the same type of the arguments, if it fits, or as a <code>Long</code> otherwise.</p>
+ </subsection>
+
+ <subsection name="Interpreting Objects as Collections">
+ <p>The projection and selection operators (<code>e1.{e2}</code> and <code>e1.{?e2}</code>), and the <code>in</code> operator, all treat one of their arguments as a collection and walk it. This is done
+ differently depending on the class of the argument:</p>
+
+ <ul>
+ <li>Java arrays are walked from front to back;</li>
+ <li>Members of <code>java.util.Collection</code> are walked by walking their iterators;</li>
+ <li>Members of <code>java.util.Map</code> are walked by walking iterators over their values;</li>
+ <li>Members of <code>java.util.Iterator</code> and <code>java.util.Enumeration</code> are walked by iterating them;</li>
+ <li>Members of <code>java.lang.Number</code> are "walked" by returning integers less than the given number starting with zero;</li>
+ <li>All other objects are treated as singleton collections containing only themselves.</li>
+ </ul>
+ </subsection>
+ </section>
+
+ <section name="Appendix: OGNL Language Reference">
+ <p>This section has a fairly detailed treatment of <acronym>OGNL</acronym>'s syntax and implementation. See below for a complete table of <acronym>OGNL</acronym>'s operators, a section on how <acronym>OGNL</acronym> coerces objects
+ to various types, and a detailed description of <acronym>OGNL</acronym>'s basic expressions.</p>
+
+ <subsection name="Operators">
+ <p><acronym>OGNL</acronym> borrows most of Java's operators, and adds a few new ones. For the most part, <acronym>OGNL</acronym>'s treatment of a given operator is the same as Java's, with the important caveat that
+ <acronym>OGNL</acronym> is essentially a typeless language. What that means is that every value in <acronym>OGNL</acronym> is a Java object, and <acronym>OGNL</acronym> attempts to coerce from each object a meaning appropriate to the
+ situation it is used in (see the section on coercion).</p>
+
+ <p>The following table lists <acronym>OGNL</acronym> operators in reverse precedence order. When more than one operator is listed in the same box, these operators have the same precedence and are evaluated in left-to-right order.</p>
+
+ <table>
+ <caption>OGNL Operators - operators are listed in reverse precedence order</caption>
+ <thead>
+ <tr>
+ <th>Operator</th>
+ <th><tt>getValue()</tt> Notes</th>
+ <th><tt>setValue()</tt> Notes</th>
+ </tr>
+ </thead>
+
+ <tbody>
+ <tr>
+ <td>
+ <div>
+ <dl>
+ <dt><span><i><tt>e1</tt></i><tt>,</tt> <i><tt>e2</tt></i></span></dt>
+
+ <dd>
+ <p>Sequence operator</p>
+ </dd>
+ </dl>
+ </div>
+ </td>
+
+ <td>Both <tt>e1</tt> and <tt>e2</tt> are evaluated with the same
+ source object, and the result of <tt>e2</tt> is returned.</td>
+
+ <td><tt>getValue</tt> is called on <tt>e1</tt>, and then
+ <tt>setValue</tt> is called on <tt>e2</tt>.</td>
+ </tr>
+
+ <tr>
+ <td>
+ <div>
+ <dl>
+ <dt><span><i><tt>e1</tt></i> <tt>=</tt> <i><tt>e2</tt></i></span></dt>
+
+ <dd>
+ <p>Assignment operator</p>
+ </dd>
+ </dl>
+ </div>
+ </td>
+
+ <td><tt>getValue</tt> is called on <tt>e2</tt>, and then
+ <tt>setValue</tt> is called on <tt>e1</tt> with the result of <tt>e2</tt> as the target object.</td>
+
+ <td>Cannot be the top-level expression for <tt>setValue</tt>.</td>
+ </tr>
+
+ <tr>
+ <td>
+ <div>
+ <dl>
+ <dt><span><i><tt>e1</tt></i> <tt>?</tt> <i><tt>e2</tt></i> <tt>:</tt> <i><tt>e3</tt></i></span></dt>
+
+ <dd>
+ <p>Conditional operator</p>
+ </dd>
+ </dl>
+ </div>
+ </td>
+
+ <td><tt>getValue</tt> is called on <tt>e1</tt> and the result is interpreted as a boolean.
+ <tt>getValue</tt> is then called on either <tt>e2</tt> or <tt>e3</tt>, depending on whether the result of
+ <tt>e1</tt> was <tt>true</tt> or <tt>false</tt> respectively, and the result is returned.</td>
+
+ <td><tt>getValue</tt> is called on <tt>e1</tt>, and then
+ <tt>setValue</tt> is called on either <tt>e2</tt> or <tt>e3</tt>.</td>
+ </tr>
+
+ <tr>
+ <td>
+ <div>
+ <dl>
+ <dt><span><i><tt>e1</tt></i> <tt>||</tt> <i><tt>e2</tt></i>,</span> <span>e1 <tt>or</tt> <i><tt>e2</tt></i></span></dt>
+
+ <dd>
+ <p>Logical <tt>or</tt> operator</p>
+ </dd>
+ </dl>
+ </div>
+ </td>
+
+ <td><tt>getValue</tt> is called on <tt>e1</tt> and the result is
+ interpreted as a boolean. If
+ <tt>true</tt>, that result is returned; if <tt>false</tt>, <tt>getValue</tt> is called on <tt>e2</tt> and its value is returned.</td>
+
+ <td><tt>getValue</tt> is called on <tt>e1</tt>; if <tt>false</tt>, <tt>setValue</tt> is called on <tt>e2</tt>. Note that
+ <tt>e1</tt> being <tt>true</tt> prevents any further setting from taking
+ place.</td>
+ </tr>
+
+ <tr>
+ <td>
+ <div>
+ <dl>
+ <dt><span><i><tt>e1</tt></i> <tt>&&</tt>
+ <i><tt>e2</tt></i>,</span> <span><i><tt>e1</tt></i>
+ <tt>and</tt> <i><tt>e2</tt></i></span></dt>
+
+ <dd>
+ <p>Logical <tt>and</tt> operator</p>
+ </dd>
+ </dl>
+ </div>
+ </td>
+
+ <td><tt>getValue</tt> is called on <tt>e1</tt> and the result is
+ interpreted as a boolean. If
+ <tt>false</tt>, that result is returned; if true, <tt>getValue</tt> is called
+ on e2 and its value is returned.</td>
+
+ <td><tt>getValue</tt> is called on <tt>e1</tt>; if <tt>true</tt>, <tt>setValue</tt> is called on <tt>e2</tt>. Note that
+ <tt>e1</tt> being <tt>false</tt> prevents any further setting from taking
+ place.</td>
+ </tr>
+
+ <tr>
+ <td>
+ <div>
+ <dl>
+ <dt><span><i><tt>e1</tt></i> <tt>|</tt> <i><tt>e2</tt></i>,</span> <span><i><tt>e1</tt></i>
+ <tt>bor</tt> <i><tt>e2</tt></i></span></dt>
+
+ <dd>
+ <p>Bitwise <tt>or</tt> operator</p>
+ </dd>
+ </dl>
+ </div>
+ </td>
+
+ <td><tt>e1</tt> and <tt>e2</tt> are interpreted as integers and the result is an integer.</td>
+
+ <td>Cannot be the top-level expression passed to <tt>setValue</tt>.</td>
+ </tr>
+
+ <tr>
+ <td>
+ <div>
+ <dl>
+ <dt><span><i><tt>e1</tt></i> <tt>^</tt> <i><tt>e2</tt></i>,</span> <span><i><tt>e1</tt></i>
+ <tt>xor</tt> <i><tt>e2</tt></i></span></dt>
+
+ <dd>
+ <p>Bitwise exclusive-or operator</p>
+ </dd>
+ </dl>
+ </div>
+ </td>
+
+ <td><tt>e1</tt> and <tt>e2</tt> are interpreted as integers and the result is an integer.</td>
+
+ <td>Cannot be the top-level expression passed to <tt>setValue</tt>.</td>
+ </tr>
+
+ <tr>
+ <td>
+ <div>
+ <dl>
+ <dt><span><i><tt>e1</tt></i> <tt>&</tt> <i><tt>e2</tt></i>,</span> <span><i><tt>e1</tt></i>
+ <tt>band</tt> <i><tt>e2</tt></i></span></dt>
+
+ <dd>
+ <p>Bitwise and operator</p>
+ </dd>
+ </dl>
+ </div>
+ </td>
+
+ <td><tt>e1</tt> and <tt>e2</tt> are interpreted as integers and the result is an integer.</td>
+
+ <td>Cannot be the top-level expression passed to <tt>setValue</tt>.</td>
+ </tr>
+
+ <tr>
+ <td>
+ <div>
+ <dl>
+ <dt><span><i><tt>e1</tt></i> <tt>==</tt> <i><tt>e2</tt></i>,</span> <span><i><tt>e1</tt></i>
+ <tt>eq</tt> <i><tt>e2</tt></i></span></dt>
+
+ <dd>
+ <p>Equality test</p>
+ </dd>
+
+ <dt><span><i><tt>e1</tt></i> <tt>!=</tt> <i><tt>e2</tt></i>,</span> <span><i><tt>e1</tt></i>
+ <tt>neq</tt> <i><tt>e2</tt></i></span></dt>
+
+ <dd>
+ <p>Inequality test</p>
+ </dd>
+ </dl>
+ </div>
+ </td>
+
+ <td>Equality is tested for as follows. If either value is <tt>null</tt>, they are
+ equal if and only if both are <tt>null</tt>. If they are the same object or the <tt>equals()</tt>
+ method says they are equal, they are equal. If they are both <tt>Number</tt>s, they are equal if their values as
+ double-precision floating point numbers are equal.
+ Otherwise, they are not equal. These rules make numbers compare equal more readily than they would normally, if
+ just using the equals method.</td>
+
+ <td>Cannot be the top-level expression passed to <tt>setValue</tt>.</td>
+ </tr>
+
+ <tr>
+ <td>
+ <div>
+ <dl>
+ <dt><span><i><tt>e1</tt></i> <tt><</tt> <i><tt>e2</tt></i>,</span> <span><i><tt>e1</tt></i>
+ <tt>lt</tt> <i><tt>e2</tt></i></span></dt>
+
+ <dd>
+ <p>Less than comparison</p>
+ </dd>
+
+ <dt><span><i><tt>e1</tt></i> <tt><=</tt> <i><tt>e2</tt></i>,</span> <span><i><tt>e1</tt></i>
+ <tt>lte</tt> <i><tt>e2</tt></i></span></dt>
+
+ <dd>
+ <p>Less than or equals comparison</p>
+ </dd>
+
+ <dt><span><i><tt>e1</tt></i> <tt>></tt> <i><tt>e2</tt></i>,</span> <span><i><tt>e1</tt></i>
+ <tt>gt</tt> <i><tt>e2</tt></i></span></dt>
+
+ <dd>
+ <p>Greater than comparison</p>
+ </dd>
+
+ <dt><span><i><tt>e1</tt></i> <tt>>=</tt> <i><tt>e2</tt></i>,</span> <span><i><tt>e1</tt></i>
+ <tt>gte</tt> <i><tt>e2</tt></i></span></dt>
+
+ <dd>
+ <p>Greater than or equals comparison</p>
+ </dd>
+
+ <dt><span><i><tt>e1</tt></i> <tt>in</tt> <i><tt>e2</tt></i></span></dt>
+
+ <dd>
+ <p>List membership comparison</p>
+ </dd>
+
+ <dt><span><i><tt>e1</tt></i> <tt>not in</tt> <i><tt>e2</tt></i></span></dt>
+
+ <dd>
+ <p>List non-membership comparison</p>
+ </dd>
+ </dl>
+ </div>
+ </td>
+
+ <td>The ordering operators compare with <tt>compareTo()</tt> if their arguments
+ are non-numeric and implement <tt>Comparable</tt>; otherwise, the arguments are interpreted
+ as numbers and compared numerically. The in operator is not from Java; it tests for inclusion of e1 in e2,
+ where e2 is interpreted as a collection. This test is not efficient: it iterates the collection. However, it
+ uses the standard OGNL equality test.</td>
+
+ <td>Cannot be the top-level expression passed to <tt>setValue</tt>.</td>
+ </tr>
+
+ <tr>
+ <td>
+ <div>
+ <dl>
+ <dt><span><i><tt>e1</tt></i> <tt><<</tt> <i><tt>e2</tt></i>,</span> <span><i><tt>e1</tt></i>
+ <tt>shl</tt> <i><tt>e2</tt></i></span></dt>
+
+ <dd>
+ <p>Bit shift left</p>
+ </dd>
+
+ <dt><span><i><tt>e1</tt></i> <tt>>></tt> <i><tt>e2</tt></i>,</span> <span><i><tt>e1</tt></i>
+ <tt>shr</tt> <i><tt>e2</tt></i></span></dt>
+
+ <dd>
+ <p>Bit shift right</p>
+ </dd>
+
+ <dt><span><i><tt>e1</tt></i> <tt>>>></tt>
+ <i><tt>e2</tt></i>,</span> <span><i><tt>e1</tt></i>
+ <tt>ushr</tt> <i><tt>e2</tt></i></span></dt>
+
+ <dd>
+ <p>Logical shift right</p>
+ </dd>
+ </dl>
+ </div>
+ </td>
+
+ <td><tt>e1</tt> and <tt>e2</tt> are interpreted as integers and the result is an integer.</td>
+
+ <td>Cannot be the top-level expression passed to <tt>setValue</tt>.</td>
+ </tr>
+
+ <tr>
+ <td>
+ <div>
+ <dl>
+ <dt><span><i><tt>e1</tt></i> <tt>+</tt> <i><tt>e2</tt></i></span></dt>
+
+ <dd>
+ <p>Addition</p>
+ </dd>
+
+ <dt><span><i><tt>e1</tt></i> <tt>-</tt> <i><tt>e2</tt></i></span></dt>
+
+ <dd>
+ <p>Subtraction</p>
+ </dd>
+ </dl>
+ </div>
+ </td>
+
+ <td>The plus operator concatenates strings if its arguments are non-numeric; otherwise it interprets its arguments as numbers and adds
+ them. The minus operator always works on numbers.</td>
+
+ <td>Cannot be the top-level expression passed to <tt>setValue</tt>.</td>
+ </tr>
+
+ <tr>
+ <td>
+ <div>
+ <dl>
+ <dt><span><i><tt>e1</tt></i><tt>*</tt> <i><tt>e2</tt></i></span></dt>
+
+ <dd>
+ <p>Multiplication</p>
+ </dd>
+
+ <dt><span><i><tt>e1</tt></i> <tt>/</tt> <i><tt>e2</tt></i></span></dt>
+
+ <dd>
+ <p>Division</p>
+ </dd>
+
+ <dt><span><i><tt>e1</tt></i> <tt>%</tt> <i><tt>e2</tt></i></span></dt>
+
+ <dd>
+ <p>Remainder</p>
+ </dd>
+ </dl>
+ </div>
+ </td>
+
+ <td>Multiplication, division, which interpret their arguments as numbers, and remainder, which interprets its arguments as integers.</td>
+
+ <td>Cannot be the top-level expression passed to <tt>setValue</tt>.</td>
+ </tr>
+
+ <tr>
+ <td>
+ <div>
+ <dl>
+ <dt><span><tt>+</tt> <i><tt>e</tt></i></span></dt>
+
+ <dd>
+ <p>Unary plus</p>
+ </dd>
+
+ <dt><span><tt>-</tt> <i><tt>e</tt></i></span></dt>
+
+ <dd>
+ <p>Unary minus</p>
+ </dd>
+
+ <dt><span><tt>!</tt> <i><tt>e</tt></i>,</span>
+ <span><tt>not</tt> <i><tt>e</tt></i></span></dt>
+
+ <dd>
+ <p>Logical not</p>
+ </dd>
+
+ <dt><span><tt>~</tt> <i><tt>e</tt></i></span></dt>
+
+ <dd>
+ <p>Bitwise not</p>
+ </dd>
+
+ <dt><span><i><tt>e</tt></i> <tt>instanceof</tt>
+ <i><tt>class</tt></i></span></dt>
+
+ <dd>
+ <p>Class membership</p>
+ </dd>
+ </dl>
+ </div>
+ </td>
+
+ <td>Unary plus is a no-op, it simply returns the value of its argument. Unary minus interprets its argument as a
+ number. Logical not interprets its argument as a
+ boolean. Bitwise not interprets its
+ argument as an integer. The <i><tt>class</tt></i> argument to instanceof is the fully
+ qualified name of a Java class.</td>
+
+ <td>Cannot be the top-level expression passed to <tt>setValue</tt>.</td>
+ </tr>
+
+ <tr>
+ <td>
+ <div>
+ <dl>
+ <dt><i><tt>e</tt></i><tt>.</tt><i><tt>method</tt></i><tt>(</tt><i><tt>args</tt></i><tt>)</tt></dt>
+
+ <dd>
+ <p>Method call</p>
+ </dd>
+
+ <dt><i><tt>e</tt></i><tt>.</tt><i><tt>property</tt></i></dt>
+
+ <dd>
+ <p>Property</p>
+ </dd>
+
+ <dt><i><tt>e1</tt></i><tt>[</tt> <i><tt>e2</tt></i> <tt>]</tt></dt>
+
+ <dd>
+ <p>Index</p>
+ </dd>
+
+ <dt><i><tt>e1</tt></i><tt>.{</tt> <i><tt>e2</tt></i>
+ <tt>}</tt></dt>
+
+ <dd>
+ <p>Projection</p>
+ </dd>
+
+ <dt><i><tt>e1</tt></i><tt>.{?</tt> <i><tt>e2</tt></i>
+ <tt>}</tt></dt>
+
+ <dd>
+ <p>Selection</p>
+ </dd>
+
+ <dt><i><tt>e1</tt></i><tt>.(</tt><i><tt>e2</tt></i><tt>)</tt></dt>
+
+ <dd>
+ <p>Subexpression evaluation</p>
+ </dd>
+
+ <dt><i><tt>e1</tt></i><tt>(</tt><i><tt>e2</tt></i><tt>)</tt></dt>
+
+ <dd>
+ <p>Expression evaluation</p>
+ </dd>
+ </dl>
+ </div>
+ </td>
+
+ <td>Generally speaking, navigation chains are evaluated by evaluating the first expression, then
+ evaluating the second one with the result of the first as the source object.</td>
+
+ <td>Some of these forms can be passed as top-level expressions to <tt>setValue</tt> and others cannot.
+ Only those chains that end in property references (e.property),
+ indexes (<tt>e1[e2]</tt>), and subexpressions (<tt>e1.(e2)</tt>) can be; and
+ expression evaluations can be as well. For the chains, <tt>getValue</tt> is called on the
+ left-hand expression (<tt>e</tt> or <tt>e1</tt>), and then <tt>setValue</tt> is called on the rest with the result as the target object.</td>
+ </tr>
+
+ <tr>
+ <td>
+ <div>
+ <dl>
+ <dt><i><tt>constant</tt></i></dt>
+
+ <dd>
+ <p>Constant</p>
+ </dd>
+
+ <dt><tt>(</tt>
+ <i><tt>e</tt></i> <tt>)</tt></dt>
+
+ <dd>
+ <p>Parenthesized expression</p>
+ </dd>
+
+ <dt><i><tt>method</tt></i><tt>(</tt><i><tt>args</tt></i><tt>)</tt></dt>
+
+ <dd>
+ <p>Method call</p>
+ </dd>
+
+ <dt><i><tt>property</tt></i></dt>
+
+ <dd>
+ <p>Property reference</p>
+ </dd>
+
+ <dt><tt>[</tt> <i><tt>e</tt></i> <tt>]</tt></dt>
+
+ <dd>
+ <p>Index reference</p>
+ </dd>
+
+ <dt><tt>{</tt> <i><tt>e</tt></i><tt>,</tt> ... <tt>}</tt></dt>
+
+ <dd>
+ <p>List creation</p>
+ </dd>
+
+ <dt><tt>#</tt><i><tt>variable</tt></i></dt>
+
+ <dd>
+ <p>Context variable reference</p>
+ </dd>
+
+ <dt><tt>@</tt><i><tt>class</tt></i><tt>@</tt><i><tt>method</tt></i><tt>(</tt><i><tt>args</tt></i><tt>)</tt></dt>
+
+ <dd>
+ <p>Static method reference</p>
+ </dd>
+
+ <dt><tt>@</tt><i><tt>class</tt></i><tt>@</tt><i><tt>field</tt></i></dt>
+
+ <dd>
+ <p>Static field reference</p>
+ </dd>
+
+ <dt><tt>new</tt> <i><tt>class</tt></i><tt>(</tt><i><tt>args</tt></i><tt>)</tt></dt>
+
+ <dd>
+ <p>Constructor call</p>
+ </dd>
+
+ <dt><tt>new</tt> <i><tt>array-component-class</tt></i><tt>[] {</tt> <i><tt>e</tt></i><tt>,</tt> ... <tt>}</tt></dt>
+
+ <dd>
+ <p>Array creation</p>
+ </dd>
+
+ <dt><tt>#{</tt> <i><tt>e1</tt></i> <tt>:</tt> <i><tt>e2</tt></i><tt>,</tt> ... <tt>}</tt></dt>
+
+ <dd>
+ <p>Map creation</p>
+ </dd>
+
+ <dt><tt>#@</tt><i><tt>classname</tt></i><tt>@{</tt> <i><tt>e1</tt></i> <tt>:</tt> <i><tt>e2</tt></i><tt>,</tt> ... <tt>}</tt></dt>
+
+ <dd>
+ <p>Map creation with specific subclass</p>
+ </dd>
+
+ <dt><tt>:[</tt> <i><tt>e</tt></i> <tt>]</tt></dt>
+
+ <dd>
+ <p>Lambda expression definition</p>
+ </dd>
+ </dl>
+ </div>
+ </td>
+
+ <td>Basic expressions</td>
+
+ <td>Only property references (<tt>property</tt>), indexes (<tt>[e]</tt>), and variable references
+ (<tt>#variable</tt>) can be passed as top-level
+ expressions to <tt>setValue</tt>. For indexes, <tt>getValue</tt> is called on
+ <tt>e</tt>, and then the result is used as the property "name" (which might be a <tt>String</tt> or any other
+ kind of object) to set in the current target object. Variable and property
+ references are set more directly.</td>
+ </tr>
+ </tbody>
+ </table>
+ </subsection>
+ </section>
+ </body>
+
+</document>
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