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Posted to commits@nifi.apache.org by jo...@apache.org on 2018/01/12 21:00:25 UTC
svn commit: r1821033 [33/46] - in /nifi/site/trunk/docs: nifi-docs/
nifi-docs/components/ nifi-docs/components/org.apache.nifi/
nifi-docs/components/org.apache.nifi/nifi-ambari-nar/
nifi-docs/components/org.apache.nifi/nifi-ambari-nar/1.5.0/ nifi-docs/...
Added: nifi/site/trunk/docs/nifi-docs/html/developer-guide.html
URL: http://svn.apache.org/viewvc/nifi/site/trunk/docs/nifi-docs/html/developer-guide.html?rev=1821033&view=auto
==============================================================================
--- nifi/site/trunk/docs/nifi-docs/html/developer-guide.html (added)
+++ nifi/site/trunk/docs/nifi-docs/html/developer-guide.html Fri Jan 12 21:00:14 2018
@@ -0,0 +1,3655 @@
+<!--
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+ http://www.apache.org/licenses/LICENSE-2.0
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+</head>
+<body class="article">
+<div id="header">
+<h1>NiFi Developer’s Guide</h1>
+<div class="details">
+<span id="author" class="author">Apache NiFi Team</span><br>
+<span id="email" class="email"><a href="mailto:dev@nifi.apache.org">dev@nifi.apache.org</a></span><br>
+</div>
+<div id="toc" class="toc">
+<div id="toctitle">Table of Contents</div>
+<ul class="sectlevel1">
+<li><a href="developer-guide.html#introduction">Introduction</a></li>
+<li><a href="developer-guide.html#components">NiFi Components</a></li>
+<li><a href="developer-guide.html#processor_api">Processor API</a>
+<ul class="sectlevel2">
+<li><a href="developer-guide.html#supporting_api">Supporting API</a></li>
+<li><a href="developer-guide.html#AbstractProcessor">AbstractProcessor API</a></li>
+<li><a href="developer-guide.html#component-lifecycle">Component Lifecycle</a></li>
+<li><a href="developer-guide.html#component-notification">Component Notification</a></li>
+<li><a href="developer-guide.html#restricted">Restricted</a></li>
+<li><a href="developer-guide.html#state_manager">State Manager</a></li>
+<li><a href="developer-guide.html#reporting-processor-activity">Reporting Processor Activity</a></li>
+</ul>
+</li>
+<li><a href="developer-guide.html#documenting-a-component">Documenting a Component</a>
+<ul class="sectlevel2">
+<li><a href="developer-guide.html#documenting-properties">Documenting Properties</a></li>
+<li><a href="developer-guide.html#documenting-relationships">Documenting Relationships</a></li>
+<li><a href="developer-guide.html#documenting-capability-and-keywords">Documenting Capability and Keywords</a></li>
+<li><a href="developer-guide.html#documenting-flowfile-attribute-interaction">Documenting FlowFile Attribute Interaction</a></li>
+<li><a href="developer-guide.html#documenting-related-components">Documenting Related Components</a></li>
+<li><a href="developer-guide.html#advanced-documentation">Advanced Documentation</a></li>
+</ul>
+</li>
+<li><a href="developer-guide.html#provenance_events">Provenance Events</a></li>
+<li><a href="developer-guide.html#common-processor-patterns">Common Processor Patterns</a>
+<ul class="sectlevel2">
+<li><a href="developer-guide.html#ingress">Data Ingress</a></li>
+<li><a href="developer-guide.html#data-egress">Data Egress</a></li>
+<li><a href="developer-guide.html#route-based-on-content-one-to-one">Route Based on Content (One-to-One)</a></li>
+<li><a href="developer-guide.html#route-based-on-content-one-to-many">Route Based on Content (One-to-Many)</a></li>
+<li><a href="developer-guide.html#route-streams-based-on-content-one-to-many">Route Streams Based on Content (One-to-Many)</a></li>
+<li><a href="developer-guide.html#route-based-on-attributes">Route Based on Attributes</a></li>
+<li><a href="developer-guide.html#split-content-one-to-many">Split Content (One-to-Many)</a></li>
+<li><a href="developer-guide.html#update-attributes-based-on-content">Update Attributes Based on Content</a></li>
+<li><a href="developer-guide.html#enrich-modify-content">Enrich/Modify Content</a></li>
+</ul>
+</li>
+<li><a href="developer-guide.html#error-handling">Error Handling</a>
+<ul class="sectlevel2">
+<li><a href="developer-guide.html#exceptions-within-the-processor">Exceptions within the Processor</a></li>
+<li><a href="developer-guide.html#exceptions-within-a-callback-ioexception-runtimeexception">Exceptions within a callback: IOException, RuntimeException</a></li>
+<li><a href="developer-guide.html#penalization-vs-yielding">Penalization vs. Yielding</a></li>
+<li><a href="developer-guide.html#session-rollback">Session Rollback</a></li>
+</ul>
+</li>
+<li><a href="developer-guide.html#general-design-considerations">General Design Considerations</a>
+<ul class="sectlevel2">
+<li><a href="developer-guide.html#consider-the-user">Consider the User</a></li>
+<li><a href="developer-guide.html#cohesion-and-reusability">Cohesion and Reusability</a></li>
+<li><a href="developer-guide.html#naming-convensions">Naming Conventions</a></li>
+<li><a href="developer-guide.html#processor-behavior-annotations">Processor Behavior Annotations</a></li>
+<li><a href="developer-guide.html#data-buffering">Data Buffering</a></li>
+</ul>
+</li>
+<li><a href="developer-guide.html#controller-services">Controller Services</a>
+<ul class="sectlevel2">
+<li><a href="developer-guide.html#developing-controller-service">Developing a ControllerService</a></li>
+<li><a href="developer-guide.html#interacting-with-controller-service">Interacting with a ControllerService</a></li>
+</ul>
+</li>
+<li><a href="developer-guide.html#reporting-tasks">Reporting Tasks</a>
+<ul class="sectlevel2">
+<li><a href="developer-guide.html#developing-a-reporting-task">Developing a Reporting Task</a></li>
+</ul>
+</li>
+<li><a href="developer-guide.html#ui-extensions">UI Extensions</a>
+<ul class="sectlevel2">
+<li><a href="developer-guide.html#custom-processor-uis">Custom Processor UIs</a></li>
+<li><a href="developer-guide.html#content-viewers">Content Viewers</a></li>
+</ul>
+</li>
+<li><a href="developer-guide.html#command-line-tools">Command Line Tools</a>
+<ul class="sectlevel2">
+<li><a href="developer-guide.html#tls-toolkit">tls-toolkit</a></li>
+</ul>
+</li>
+<li><a href="developer-guide.html#testing">Testing</a>
+<ul class="sectlevel2">
+<li><a href="developer-guide.html#instantiate-testrunner">Instantiate TestRunner</a></li>
+<li><a href="developer-guide.html#add-controllerservices">Add ControllerServices</a></li>
+<li><a href="developer-guide.html#set-property-values">Set Property Values</a></li>
+<li><a href="developer-guide.html#enqueue-flowfiles">Enqueue FlowFiles</a></li>
+<li><a href="developer-guide.html#run-the-processor">Run the Processor</a></li>
+<li><a href="developer-guide.html#validate-output">Validate Output</a></li>
+<li><a href="developer-guide.html#mocking-external-resources">Mocking External Resources</a></li>
+<li><a href="developer-guide.html#additional-testing-capabilities">Additional Testing Capabilities</a></li>
+</ul>
+</li>
+<li><a href="developer-guide.html#nars">NiFi Archives (NARs)</a></li>
+<li><a href="developer-guide.html#per-instance-classloading">Per-Instance ClassLoading</a></li>
+<li><a href="developer-guide.html#deprecation">Deprecating a Component</a></li>
+<li><a href="developer-guide.html#how-to-contribute-to-apache-nifi">How to contribute to Apache NiFi</a>
+<ul class="sectlevel2">
+<li><a href="developer-guide.html#technologies">Technologies</a></li>
+<li><a href="developer-guide.html#where-to-start">Where to Start?</a></li>
+<li><a href="developer-guide.html#supplying-a-contribution">Supplying a contribution</a></li>
+<li><a href="developer-guide.html#contact-us">Contact Us</a></li>
+</ul>
+</li>
+</ul>
+</div>
+</div>
+<div id="content">
+<div class="sect1">
+<h2 id="introduction"><a class="anchor" href="developer-guide.html#introduction"></a>Introduction</h2>
+<div class="sectionbody">
+<div class="paragraph">
+<p>The intent of this Developer Guide is to provide the reader with the information needed to understand how Apache NiFi
+extensions are developed and help to explain the thought process behind developing the components. It provides an introduction to
+and explanation of the API that is used to develop extensions. It does not, however, go into great detail about each
+of the methods in the API, as this guide is intended to supplement the JavaDocs of the API rather than replace them.
+This guide also assumes that the reader is familiar with Java 7 and Apache Maven.</p>
+</div>
+<div class="paragraph">
+<p>This guide is written by developers for developers. It is expected that before reading this
+guide, you have a basic understanding of NiFi and the concepts of dataflow. If not, please see the <a href="overview.html">NiFi Overview</a>
+and the <a href="user-guide.html">NiFi User Guide</a> to familiarize yourself with the concepts of NiFi.</p>
+</div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="components"><a class="anchor" href="developer-guide.html#components"></a>NiFi Components</h2>
+<div class="sectionbody">
+<div class="paragraph">
+<p>NiFi provides several extension points to provide developers the
+ability to add functionality to the application to meet their needs. The following list provides a
+high-level description of the most common extension points:</p>
+</div>
+<div class="ulist">
+<ul>
+<li>
+<p>Processor</p>
+<div class="ulist">
+<ul>
+<li>
+<p>The Processor interface is the mechanism through which NiFi exposes access to
+<a href="developer-guide.html#flowfile">FlowFile</a>s, their attributes, and their content. The Processor is the basic building
+block used to comprise a NiFi dataflow. This interface is used to accomplish
+all of the following tasks:</p>
+<div class="ulist">
+<ul>
+<li>
+<p>Create FlowFiles</p>
+</li>
+<li>
+<p>Read FlowFile content</p>
+</li>
+<li>
+<p>Write FlowFile content</p>
+</li>
+<li>
+<p>Read FlowFile attributes</p>
+</li>
+<li>
+<p>Update FlowFile attributes</p>
+</li>
+<li>
+<p>Ingest data</p>
+</li>
+<li>
+<p>Egress data</p>
+</li>
+<li>
+<p>Route data</p>
+</li>
+<li>
+<p>Extract data</p>
+</li>
+<li>
+<p>Modify data</p>
+</li>
+</ul>
+</div>
+</li>
+</ul>
+</div>
+</li>
+<li>
+<p>ReportingTask</p>
+<div class="ulist">
+<ul>
+<li>
+<p>The ReportingTask interface is a mechanism that NiFi exposes to allow metrics,
+monitoring information, and internal NiFi state to be published to external
+endpoints, such as log files, e-mail, and remote web services.</p>
+</li>
+</ul>
+</div>
+</li>
+<li>
+<p>ControllerService</p>
+<div class="ulist">
+<ul>
+<li>
+<p>A ControllerService provides shared state and functionality across Processors, other ControllerServices,
+and ReportingTasks within a single JVM. An example use case may include loading a very
+large dataset into memory. By performing this work in a ControllerService, the data
+can be loaded once and be exposed to all Processors via this service, rather than requiring
+many different Processors to load the dataset themselves.</p>
+</li>
+</ul>
+</div>
+</li>
+<li>
+<p>FlowFilePrioritizer</p>
+<div class="ulist">
+<ul>
+<li>
+<p>The FlowFilePrioritizer interface provides a mechanism by which <a href="developer-guide.html#flowfile">FlowFile</a>s
+in a queue can be prioritized, or sorted, so that the FlowFiles can be processed in an order
+that is most effective for a particular use case.</p>
+</li>
+</ul>
+</div>
+</li>
+<li>
+<p>AuthorityProvider</p>
+<div class="ulist">
+<ul>
+<li>
+<p>An AuthorityProvide is responsible for determining which privileges and roles, if any,
+a given user should be granted.</p>
+</li>
+</ul>
+</div>
+</li>
+</ul>
+</div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="processor_api"><a class="anchor" href="developer-guide.html#processor_api"></a>Processor API</h2>
+<div class="sectionbody">
+<div class="paragraph">
+<p>The Processor is the most widely used Component available in NiFi.
+Processors are the only Component
+to which access is given to create, remove, modify, or inspect
+FlowFiles (data and attributes).</p>
+</div>
+<div class="paragraph">
+<p>All Processors are loaded and instantiated using Java’s ServiceLoader
+mechanism. This means that all
+Processors must adhere to the following rules:</p>
+</div>
+<div class="ulist">
+<ul>
+<li>
+<p>The Processor must have a default constructor.</p>
+</li>
+<li>
+<p>The Processor’s JAR file must contain an entry in the META-INF/services directory named
+<code>org.apache.nifi.processor.Processor</code>. This is a text file where each line contains the
+fully-qualified class name of a Processor.</p>
+</li>
+</ul>
+</div>
+<div class="paragraph">
+<p>While <code>Processor</code> is an interface that can be implemented directly, it
+will be extremely rare to do so, as
+the <code>org.apache.nifi.processor.AbstractProcessor</code> is the base class
+for almost all Processor implementations. The <code>AbstractProcessor</code> class provides a significant
+amount of functionality, which makes the task of developing a Processor much easier and more convenient.
+For the scope of this document, we will focus primarily on the <code>AbstractProcessor</code> class when dealing
+with the Processor API.</p>
+</div>
+<div class="paragraph">
+<div class="title">Concurrency Note</div>
+<p>NiFi is a highly concurrent framework. This means that all extensions
+must be thread-safe. If unfamiliar with writing concurrent software in Java, it is highly
+recommended that you familiarize yourself with the principles of Java concurrency.</p>
+</div>
+<div class="sect2">
+<h3 id="supporting_api"><a class="anchor" href="developer-guide.html#supporting_api"></a>Supporting API</h3>
+<div class="paragraph">
+<p>In order to understand the Processor API, we must first understand -
+at least at a high level - several supporting classes and interfaces, which are discussed below.</p>
+</div>
+<div class="sect3">
+<h4 id="flowfile"><a class="anchor" href="developer-guide.html#flowfile"></a>FlowFile</h4>
+<div class="paragraph">
+<p>A FlowFile is a logical notion that correlates a piece of data with a
+set of Attributes about that data.
+Such attributes include a FlowFile’s unique identifier, as well as its
+name, size, and any number of other
+flow-specific values. While the contents and attributes of a FlowFile
+can change, the FlowFile object is
+immutable. Modifications to a FlowFile are made possible by the ProcessSession.</p>
+</div>
+<div class="paragraph">
+<p>The core attributes for FlowFiles are defined in the <code>org.apache.nifi.flowfile.attributes.CoreAttributes</code> enum.
+The most common attributes you’ll see are filename, path and uuid. The string in quotes is the value of the
+attribute within the <code>CoreAttributes</code> enum.</p>
+</div>
+<div class="ulist">
+<ul>
+<li>
+<p>Filename ("filename"): The filename of the FlowFile. The filename should not contain any directory structure.</p>
+</li>
+<li>
+<p>UUID ("uuid"): A unique universally unique identifier (UUID) assigned to this FlowFile.</p>
+</li>
+<li>
+<p>Path ("path"): The FlowFile’s path indicates the relative directory to which a FlowFile belongs and does not contain the filename.</p>
+</li>
+<li>
+<p>Absolute Path ("absolute.path"): The FlowFile’s absolute path indicates the absolute directory to which a FlowFile belongs and does not contain the filename.</p>
+</li>
+<li>
+<p>Priority ("priority"): A numeric value indicating the FlowFile priority.</p>
+</li>
+<li>
+<p>MIME Type ("mime.type"): The MIME Type of this FlowFile.</p>
+</li>
+<li>
+<p>Discard Reason ("discard.reason"): Specifies the reason that a FlowFile is being discarded.</p>
+</li>
+<li>
+<p>Alternative Identifier ("alternate.identifier"): Indicates an identifier other than the FlowFile’s UUID that is known to refer to this FlowFile.</p>
+</li>
+</ul>
+</div>
+</div>
+<div class="sect3">
+<h4 id="process_session"><a class="anchor" href="developer-guide.html#process_session"></a>ProcessSession</h4>
+<div class="paragraph">
+<p>The ProcessSession, often referred to as simply a "session," provides
+a mechanism by which FlowFiles can be created, destroyed, examined, cloned, and transferred to other
+Processors. Additionally, a ProcessSession provides mechanism for creating modified versions of
+FlowFiles, by adding or removing attributes, or by modifying the FlowFile’s content. The ProcessSession
+also exposes a mechanism for emitting <a href="developer-guide.html#provenance_events">Provenance Events</a> that provide for the ability to track the
+lineage and history of a FlowFile. After operations are performed on one or more FlowFiles, a
+ProcessSession can be either committed or rolled back.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="process_context"><a class="anchor" href="developer-guide.html#process_context"></a>ProcessContext</h4>
+<div class="paragraph">
+<p>The ProcessContext provides a bridge between a Processor and the framework. It provides information
+about how the Processor is currently configured and allows the Processor to perform
+Framework-specific tasks, such as yielding its resources so that the framework will schedule other
+Processors to run without consuming resources unnecessarily.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="property_descriptor"><a class="anchor" href="developer-guide.html#property_descriptor"></a>PropertyDescriptor</h4>
+<div class="paragraph">
+<p>PropertyDescriptor defines a property that is to be used by a
+Processor, ReportingTask, or ControllerService.
+The definition of a property includes its name, a description of the
+property, an optional default value,
+validation logic, and an indicator as to whether or not the property
+is required in order for the Processor
+to be valid. PropertyDescriptors are created by instantiating an
+instance of the <code>PropertyDescriptor.Builder</code>
+class, calling the appropriate methods to fill in the details about
+the property, and finally calling
+the <code>build</code> method.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="validator"><a class="anchor" href="developer-guide.html#validator"></a>Validator</h4>
+<div class="paragraph">
+<p>A PropertyDescriptor MUST specify one or more Validators that can be
+used to ensure that the user-entered value
+for a property is valid. If a Validator indicates that a property
+value is invalid, the Component will not be
+able to be run or used until the property becomes valid. If a
+Validator is not specified, the Component will be assumed invalid and
+NiFi will report that the property is not supported.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="validation_context"><a class="anchor" href="developer-guide.html#validation_context"></a>ValidationContext</h4>
+<div class="paragraph">
+<p>When validating property values, a ValidationContext can be used to
+obtain ControllerServices,
+create PropertyValue objects, and compile and evaluate property values
+using the Expression Language.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="property_value"><a class="anchor" href="developer-guide.html#property_value"></a>PropertyValue</h4>
+<div class="paragraph">
+<p>All property values returned to a Processor are returned in the form
+of a PropertyValue object. This
+object has convenience methods for converting the value from a String
+to other forms, such as numbers
+and time periods, as well as providing an API for evaluating the
+Expression Language.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="relationship"><a class="anchor" href="developer-guide.html#relationship"></a>Relationship</h4>
+<div class="paragraph">
+<p>Relationships define the routes to which a FlowFile may be transfered
+from a Processor. Relationships
+are created by instantiating an instance of the <code>Relationship.Builder</code>
+class, calling the appropriate methods
+to fill in the details of the Relationship, and finally calling the
+<code>build</code> method.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="supporting_api_state_manager"><a class="anchor" href="developer-guide.html#supporting_api_state_manager"></a>StateManager</h4>
+<div class="paragraph">
+<p>The StateManager provides Processors, Reporting Tasks, and Controller Services a mechanism
+for easily storing and retrieving state. The API is similar to that of ConcurrentHashMap
+but requires a Scope for each operation. The Scope indicates whether the state is to be
+retrieved/stored locally or in a cluster-wide manner. For more information, see the
+<a href="developer-guide.html#state_manager">State Manager</a> section.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="processor_initialization_context"><a class="anchor" href="developer-guide.html#processor_initialization_context"></a>ProcessorInitializationContext</h4>
+<div class="paragraph">
+<p>After a Processor is created, its <code>initialize</code> method will be called
+with an <code>InitializationContext</code> object.
+This object exposes configuration to the Processor that will not
+change throughout the life of the Processor,
+such as the unique identifier of the Processor.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="ComponentLog"><a class="anchor" href="developer-guide.html#ComponentLog"></a>ComponentLog</h4>
+<div class="paragraph">
+<p>Processors are encouraged to perform their logging via the
+<code>ComponentLog</code> interface, rather than obtaining
+a direct instance of a third-party logger. This is because logging via
+the ComponentLog allows the framework
+to render log messages that exceeds a configurable severity level to
+the User Interface, allowing those who
+monitor the dataflow to be notified when important events occur.
+Additionally, it provides a consistent logging
+format for all Processors by logging stack traces when in DEBUG mode
+and providing the Processor’s unique
+identifier in log messages.</p>
+</div>
+</div>
+</div>
+<div class="sect2">
+<h3 id="AbstractProcessor"><a class="anchor" href="developer-guide.html#AbstractProcessor"></a>AbstractProcessor API</h3>
+<div class="paragraph">
+<p>Since the vast majority of Processors will be created by extending the
+AbstractProcessor, it is the
+abstract class that we will examine in this section. The
+AbstractProcessor provides several methods that
+will be of interest to Processor developers.</p>
+</div>
+<div class="sect3">
+<h4 id="processor-initialization"><a class="anchor" href="developer-guide.html#processor-initialization"></a>Processor Initialization</h4>
+<div class="paragraph">
+<p>When a Processor is created, before any other methods are invoked, the
+<code>init</code> method of the
+AbstractProcessor will be invoked. The method takes a single argument,
+which is of type
+<code>ProcessorInitializationContext</code>. The context object supplies the
+Processor with a ComponentLog,
+the Processor’s unique identifier, and a ControllerServiceLookup that
+can be used to interact with the
+configured ControllerServices. Each of these objects is stored by the
+AbstractProcessor and may be obtained by
+subclasses via the <code>getLogger</code>, <code>getIdentifier</code>, and
+<code>getControllerServiceLookup</code> methods, respectively.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="exposing-processor-s-relationships"><a class="anchor" href="developer-guide.html#exposing-processor-s-relationships"></a>Exposing Processor’s Relationships</h4>
+<div class="paragraph">
+<p>In order for a Processor to transfer a FlowFile to a new destination
+for follow-on processing, the
+Processor must first be able to expose to the Framework all of the
+Relationships that it currently supports.
+This allows users of the application to connect Processors to one
+another by creating
+Connections between Processors and assigning the appropriate
+Relationships to those Connections.</p>
+</div>
+<div class="paragraph">
+<p>A Processor exposes the valid set of Relationships by overriding the
+<code>getRelationships</code> method.
+This method takes no arguments and returns a <code>Set</code> of <code>Relationship</code>
+objects. For most Processors, this Set
+will be static, but other Processors will generate the Set
+dynamically, based on user configuration.
+For those Processors for which the Set is static, it is advisable to
+create an immutable Set in the Processor’s
+constructor or init method and return that value, rather than
+dynamically generating the Set. This
+pattern lends itself to cleaner code and better performance.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="exposing-processor-properties"><a class="anchor" href="developer-guide.html#exposing-processor-properties"></a>Exposing Processor Properties</h4>
+<div class="paragraph">
+<p>Most Processors will require some amount of user configuration before
+they are able to be used. The properties
+that a Processor supports are exposed to the Framework via the
+<code>getSupportedPropertyDescriptors</code> method.
+This method takes no arguments and returns a <code>List</code> of
+<code>PropertyDescriptor</code> objects. The order of the objects in the
+List is important in that it dictates the order in which the
+properties will be rendered in the User Interface.</p>
+</div>
+<div class="paragraph">
+<p>A <code>PropertyDescriptor</code> object is constructed by creating a new
+instance of the <code>PropertyDescriptor.Builder</code> object,
+calling the appropriate methods on the builder, and finally calling
+the <code>build</code> method.</p>
+</div>
+<div class="paragraph">
+<p>While this method covers most of the use cases, it is sometimes
+desirable to allow users to configure
+additional properties whose name are not known. This can be achieved
+by overriding the
+<code>getSupportedDynamicPropertyDescriptor</code> method. This method takes a
+<code>String</code> as its only argument, which
+indicates the name of the property. The method returns a
+<code>PropertyDescriptor</code> object that can be used to validate
+both the name of the property, as well as the value. Any
+PropertyDescriptor that is returned from this method
+should be built setting the value of <code>isDynamic</code> to true in the
+<code>PropertyDescriptor.Builder</code> class. The default
+behavior of AbstractProcessor is to not allow any dynamically created
+properties.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="validating-processor-properties"><a class="anchor" href="developer-guide.html#validating-processor-properties"></a>Validating Processor Properties</h4>
+<div class="paragraph">
+<p>A Processor is not able to be started if its configuration is not
+valid. Validation of a Processor property can
+be achieved by setting a Validator on a PropertyDescriptor or by
+restricting the allowable values for a
+property via the PropertyDescriptor.Builder’s <code>allowableValues</code> method
+or <code>identifiesControllerService</code> method.</p>
+</div>
+<div class="paragraph">
+<p>There are times, though, when validating a Processor’s properties
+individually is not sufficient. For this purpose,
+the AbstractProcessor exposes a <code>customValidate</code> method. The method
+takes a single argument of type <code>ValidationContext</code>.
+The return value of this method is a <code>Collection</code> of
+<code>ValidationResult</code> objects that describe any problems that were
+found during validation. Only those ValidationResult objects whose
+<code>isValid</code> method returns <code>false</code> should be returned.
+This method will be invoked only if all properties are valid according
+to their associated Validators and Allowable Values.
+I.e., this method will be called only if all properties are valid
+in-and-of themselves, and this method allows for
+validation of a Processor’s configuration as a whole.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="responding-to-changes-in-configuration"><a class="anchor" href="developer-guide.html#responding-to-changes-in-configuration"></a>Responding to Changes in Configuration</h4>
+<div class="paragraph">
+<p>It is sometimes desirable to have a Processor eagerly react when its
+properties are changed. The <code>onPropertyModified</code>
+method allows a Processor to do just that. When a user changes the
+property values for a Processor, the
+<code>onPropertyModified</code> method will be called for each modified property.
+The method takes three arguments: the PropertyDescriptor that
+indicates which property was modified,
+the old value, and the new value. If the property had no previous
+value, the second argument will be <code>null</code>. If the property
+was removed, the third argument will be <code>null</code>. It is important to
+note that this method will be called regardless of whether
+or not the values are valid. This method will be called only when a
+value is actually modified, rather than being
+called when a user updates a Processor without changing its value. At
+the point that this method is invoked, it is guaranteed
+that the thread invoking this method is the only thread currently
+executing code in the Processor, unless the Processor itself
+creates its own threads.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="performing-the-work"><a class="anchor" href="developer-guide.html#performing-the-work"></a>Performing the Work</h4>
+<div class="paragraph">
+<p>When a Processor has work to do, it is scheduled to do so by having
+its <code>onTrigger</code> method called by the framework.
+The method takes two arguments: a <code>ProcessContext</code> and a
+<code>ProcessSession</code>. The first step in the <code>onTrigger</code> method
+is often to obtain a FlowFile on which the work is to be performed by
+calling one of the <code>get</code> methods on the ProcessSession.
+For Processors that ingest data into NiFi from external sources, this
+step is skipped. The Processor is then free to examine
+FlowFile attributes; add, remove, or modify attributes; read or modify
+FlowFile content; and transfer FlowFiles to the appropriate
+Relationships.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="when-processors-are-triggered"><a class="anchor" href="developer-guide.html#when-processors-are-triggered"></a>When Processors are Triggered</h4>
+<div class="paragraph">
+<p>A Processor’s <code>onTrigger</code> method will be called only when it is
+scheduled to run and when work exists for the Processor.
+Work is said to exist for a Processor if any of the following conditions is met:</p>
+</div>
+<div class="ulist">
+<ul>
+<li>
+<p>A Connection whose destination is the Processor has at least one
+FlowFile in its queue</p>
+</li>
+<li>
+<p>The Processors has no incoming Connections</p>
+</li>
+<li>
+<p>The Processor is annotated with the @TriggerWhenEmpty annotation</p>
+</li>
+</ul>
+</div>
+<div class="paragraph">
+<p>Several factors exist that will contribute to when a Processor’s
+<code>onTrigger</code> method is invoked. First, the Processor will not
+be triggered unless a user has configured the Processor to run. If a
+Processor is scheduled to run, the Framework periodically
+(the period is configured by users in the User Interface) checks if
+there is work for the Processor to do, as described above.
+If so, the Framework will check downstream destinations of the
+Processor. If any of the Processor’s outbound Connections is full,
+by default, the Processor will not be scheduled to run.</p>
+</div>
+<div class="paragraph">
+<p>However, the <code>@TriggerWhenAnyDestinationAvailable</code> annotation may be
+added to the Processor’s class. In this case, the requirement
+is changed so that only one downstream destination must be "available"
+(a destination is considered "available" if the Connection’s
+queue is not full), rather than requiring that all downstream
+destinations be available.</p>
+</div>
+<div class="paragraph">
+<p>Also related to Processor scheduling is the <code>@TriggerSerially</code>
+annotation. Processors that use this Annotation will never have more
+than one thread running the <code>onTrigger</code> method simultaneously. It is
+crucial to note, though, that the thread executing the code
+may change from invocation to invocation. Therefore, care must still
+be taken to ensure that the Processor is thread-safe!</p>
+</div>
+</div>
+</div>
+<div class="sect2">
+<h3 id="component-lifecycle"><a class="anchor" href="developer-guide.html#component-lifecycle"></a>Component Lifecycle</h3>
+<div class="paragraph">
+<p>The NiFi API provides lifecycle support through use of Java
+Annotations. The <code>org.apache.nifi.annotations.lifecycle</code> package
+contains
+several annotations for lifecycle management. The following
+Annotations may be applied to Java methods in a NiFi component to
+indicate to
+the framework when the methods should be called. For the discussion of
+Component Lifecycle, we will define a NiFi component as a
+Processor, ControllerServices, or ReportingTask.</p>
+</div>
+<div class="sect3">
+<h4 id="onadded"><a class="anchor" href="developer-guide.html#onadded"></a>@OnAdded</h4>
+<div class="paragraph">
+<p>The <code>@OnAdded</code> annotation causes a method to be invoked as soon as a
+component is created. The
+component’s <code>initialize</code> method (or <code>init</code> method, if subclasses
+<code>AbstractProcessor</code>) will be invoked after the component is
+constructed,
+followed by methods that are annotated with <code>@OnAdded</code>. If any method
+annotated with <code>@OnAdded</code> throws an Exception, an error will
+be returned to the user, and that component will not be added to the
+flow. Furthermore, other methods with this
+Annotation will not be invoked. This method will be called only once
+for the lifetime of a component.
+Methods with this Annotation must take zero arguments.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="onenabled"><a class="anchor" href="developer-guide.html#onenabled"></a>@OnEnabled</h4>
+<div class="paragraph">
+<p>The <code>@OnEnabled</code> annotation can be used to indicate a method should be called
+whenever the Controller Service is enabled. Any method that has this annotation will be
+called every time a user enables the service. Additionally, each time that NiFi
+is restarted, if NiFi is configured to "auto-resume state" and the service
+is enabled, the method will be invoked.</p>
+</div>
+<div class="paragraph">
+<p>If a method with this annotation throws a Throwable, a log message and
+bulletin will be issued for the component. In this event, the service will
+remain in an 'ENABLING' state and will not be usable. All methods with this
+annotation will then be called again after a delay. The service will not be
+made available for use until all methods with this annotation have returned
+without throwing anything.</p>
+</div>
+<div class="paragraph">
+<p>Methods using this annotation must take either 0 arguments or a single argument
+of type <code>org.apache.nifi.controller.ConfigurationContext</code>.</p>
+</div>
+<div class="paragraph">
+<p>Note that this annotation will be ignored if applied to a ReportingTask or
+Processor. For a Controller Service, enabling and disabling are considered
+lifecycle events, as the action makes them usable or unusable by other
+components. However, for a Processor and a Reporting Task, these are not
+lifecycle events but rather a mechanism to allow a component to be excluded
+when starting or stopping a group of components.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="onremoved"><a class="anchor" href="developer-guide.html#onremoved"></a>@OnRemoved</h4>
+<div class="paragraph">
+<p>The <code>@OnRemoved</code> annotation causes a method to be invoked before a
+component is removed from the flow.
+This allows resources to be cleaned up before removing a component.
+Methods with this annotation must take zero arguments.
+If a method with this annotation throws an Exception, the component
+will still be removed.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="onscheduled"><a class="anchor" href="developer-guide.html#onscheduled"></a>@OnScheduled</h4>
+<div class="paragraph">
+<p>This annotation indicates that a method should be called every time
+the component is scheduled to run. Because ControllerServices
+are not scheduled, using this annotation on a ControllerService does
+not make sense and will not be honored. It should be
+used only for Processors and Reporting Tasks. If any method with this
+annotation throws an Exception, other methods with this
+annotation will not be invoked, and a notification will be presented
+to the user. In this case, methods annotated with
+<code>@OnUnscheduled</code> are then triggered, followed by methods with the
+<code>@OnStopped</code> annotation (during this state, if any of these
+methods throws an Exception, those Exceptions are ignored). The
+component will then yield its execution for some period of time,
+referred to as the "Administrative Yield Duration," which is a value
+that is configured in the <code>nifi.properties</code> file. Finally, the
+process will start again, until all of the methods annotated with
+<code>@OnScheduled</code> have returned without throwing any Exception.
+Methods with this annotation may take zero arguments or may take a
+single argument. If the single argument variation is used,
+the argument must be of type <code>ProcessContext</code> if the component is a
+Processor or <code>ConfigurationContext</code> if the component
+is a ReportingTask.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="onunscheduled"><a class="anchor" href="developer-guide.html#onunscheduled"></a>@OnUnscheduled</h4>
+<div class="paragraph">
+<p>Methods with this annotation will be called whenever a Processor or
+ReportingTask is no longer scheduled to run. At that time, many threads
+may still be active in the Processor’s <code>onTrigger</code> method. If such a method
+throws an Exception, a log message will be generated, and the
+Exception will be otherwise
+ignored and other methods with this annotation will still be invoked.
+Methods with this annotation may take zero arguments or may take a
+single argument.
+If the single argument variation is used, the argument must be of type
+<code>ProcessContext</code> if the component is a Processor or
+<code>ConfigurationContext</code> if the
+component is a ReportingTask.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="onstopped"><a class="anchor" href="developer-guide.html#onstopped"></a>@OnStopped</h4>
+<div class="paragraph">
+<p>Methods with this annotation will be called when a Processor or
+ReportingTask is no longer scheduled to run
+and all threads have returned from the <code>onTrigger</code> method. If such a
+method throws an Exception,
+a log message will be generated, and the Exception will otherwise be
+ignored; other methods with
+this annotation will still be invoked.
+Methods with this annotation are permitted to take either 0 or 1 argument. If
+an argument is used, it must be of type ConfigurationContext if the
+component is a ReportingTask or of type ProcessContext if the
+component is a Processor.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="onshutdown"><a class="anchor" href="developer-guide.html#onshutdown"></a>@OnShutdown</h4>
+<div class="paragraph">
+<p>Any method that is annotated with the <code>@OnShutdown</code> annotation will be
+called when NiFi is successfully
+shut down. If such a method throws an Exception, a log message will be
+generated, and the
+Exception will be otherwise ignored and other methods with this
+annotation will still be invoked.
+Methods with this annotation must take zero arguments. Note: while
+NiFi will attempt to invoke methods
+with this annotation on all components that use it, this is not always
+possible. For example, the process
+may be killed unexpectedly, in which case it does not have a chance to
+invoke these methods. Therefore,
+while methods using this annotation can be used to clean up resources,
+for instance, they should not be
+relied upon for critical business logic.</p>
+</div>
+</div>
+</div>
+<div class="sect2">
+<h3 id="component-notification"><a class="anchor" href="developer-guide.html#component-notification"></a>Component Notification</h3>
+<div class="paragraph">
+<p>The NiFi API provides notification support through use of Java
+Annotations. The <code>org.apache.nifi.annotations.notification</code> package
+contains several annotations for notification management. The following
+annotations may be applied to Java methods in a NiFi component to
+indicate to the framework when the methods should be called. For the
+discussion of Component Notification, we will define a NiFi component
+as a <strong>Processor</strong>, <strong>Controller Service</strong>, or <strong>Reporting Task</strong>.</p>
+</div>
+<div class="sect3">
+<h4 id="onprimarynodestatechange"><a class="anchor" href="developer-guide.html#onprimarynodestatechange"></a>@OnPrimaryNodeStateChange</h4>
+<div class="paragraph">
+<p>The <code>@OnPrimaryNodeStateChange</code> annotation causes a method to be invoked
+as soon as the state of the Primary Node in a cluster has changed.
+Methods with this annotation should take either no arguments or one
+argument of type <code>PrimaryNodeState</code>. The <code>PrimaryNodeState</code> provides
+context about what changed so that the component can take appropriate
+action. The <code>PrimaryNodeState</code> enumerator has two possible values:
+<code>ELECTED_PRIMARY_NODE</code> (the node receiving this
+state has been elected the Primary Node of the NiFi cluster), or
+<code>PRIMARY_NODE_REVOKED</code> (the node receiving this state was the Primary
+Node but has now had its Primary Node role revoked).</p>
+</div>
+</div>
+</div>
+<div class="sect2">
+<h3 id="restricted"><a class="anchor" href="developer-guide.html#restricted"></a>Restricted</h3>
+<div class="paragraph">
+<p>A Restricted component is one that can be used to execute arbitrary unsanitized code provided by the operator
+through the NiFi REST API/UI or can be used to obtain or alter data on the NiFi host system using the NiFi OS
+credentials. These components could be used by an otherwise authorized NiFi user to go beyond the intended use of
+the application, escalate privilege, or could expose data about the internals of the NiFi process or the host
+system. All of these capabilities should be considered privileged, and admins should be aware of these
+capabilities and explicitly enable them for a subset of trusted users.</p>
+</div>
+<div class="paragraph">
+<p>A Processor, Controller Service, or Reporting Task can be marked with the @Restricted annotation. This
+will result in the component being treated as restricted and will require a user to be explicitly added to the
+list of users who can access restricted components. Once a user is permitted to access restricted components,
+they will be allowed to create and modify those components assuming all other permissions are permitted.
+Without access to restricted components, a user will be still be aware these types of components exist but will
+be unable to create or modify them even with otherwise sufficient permissions.</p>
+</div>
+</div>
+<div class="sect2">
+<h3 id="state_manager"><a class="anchor" href="developer-guide.html#state_manager"></a>State Manager</h3>
+<div class="paragraph">
+<p>From the ProcessContext, ReportingContext, and ControllerServiceInitializationContext, components are
+able to call the <code>getStateManager()</code> method. This State Manager is responsible for providing a simple API
+for storing and retrieving state. This mechanism is intended to provide developers with the ability to
+very easily store a set of key/value pairs, retrieve those values, and update them atomically. The state
+can be stored local to the node or across all nodes in a cluster. It is important to note, however, that
+this mechanism is intended only to provide a mechanism for storing very 'simple' state. As such, the API
+simply allows a <code>Map<String, String></code> to be stored and retrieved and for the entire Map to be atomically
+replaced. Moreover, the only implementation that is currently supported for storing cluster-wide state is
+backed by ZooKeeper. As such, the entire State Map must be less than 1 MB in size, after being serialized.
+Attempting to store more than this will result in an Exception being thrown. If the interactions required
+by the Processor for managing state are more complex than this (e.g., large amounts of data must be stored
+and retrieved, or individual keys must be stored and fetched individually) than a different mechanism should
+be used (e.g., communicating with an external database).</p>
+</div>
+<div class="sect3">
+<h4 id="state_scope"><a class="anchor" href="developer-guide.html#state_scope"></a>Scope</h4>
+<div class="paragraph">
+<p>When communicating with the State Manager, all method calls require that a Scope be provided. This Scope will
+either be <code>Scope.LOCAL</code> or <code>Scope.CLUSTER</code>. If NiFi is run in a cluster, this Scope provides important information
+to the framework about how the operation should occur.</p>
+</div>
+<div class="paragraph">
+<p>If state as stored using <code>Scope.CLUSTER</code>, then all nodes in the cluster will be communicating with the same
+state storage mechanism. If state is stored and retrieved using <code>Scope.LOCAL</code>, then each node will see a different
+representation of the state.</p>
+</div>
+<div class="paragraph">
+<p>It is also worth noting that if NiFi is configured to run as a standalone instance, rather than running in a cluster,
+a scope of <code>Scope.LOCAL</code> is always used. This is done in order to allow the developer of a NiFi component to write the code
+in one consistent way, without worrying about whether or not the NiFi instance is clustered. The developer should instead assume
+that the instance is clustered and write the code accordingly.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="storing-and-retrieving-state"><a class="anchor" href="developer-guide.html#storing-and-retrieving-state"></a>Storing and Retrieving State</h4>
+<div class="paragraph">
+<p>State is stored using the StateManager’s <code>getState</code>, <code>setState</code>, <code>replace</code>, and <code>clear</code> methods. All of these methods
+require that a Scope be provided. It should be noted that the state that is stored with the Local scope is entirely different
+than state stored with a Cluster scope. If a Processor stores a value with the key of <em>My Key</em> using the <code>Scope.CLUSTER</code> scope,
+and then attempts to retrieve the value using the <code>Scope.LOCAL</code> scope, the value retrieved will be <code>null</code> (unless a value was
+also stored with the same key using the <code>Scope.CLUSTER</code> scope). Each Processor’s state, is stored in isolation from other
+Processors' state.</p>
+</div>
+<div class="paragraph">
+<p>It follows, then, that two Processors cannot share the same state. There are, however, some circumstances in which it is very
+necessary to share state between two Processors of different types, or two Processors of the same type. This can be accomplished
+by using a Controller Service. By storing and retrieving state from a Controller Service, multiple Processors can use the same
+Controller Service and the state can be exposed via the Controller Service’s API.</p>
+</div>
+</div>
+<div class="sect3">
+<h4 id="unit-tests"><a class="anchor" href="developer-guide.html#unit-tests"></a>Unit Tests</h4>
+<div class="paragraph">
+<p>NiFi’s Mock Framework provides an extensive collection of tools to perform unit testing of Processors. Processor unit tests typically
+begin with the <code>TestRunner</code> class. As a result, the <code>TestRunner</code> class contains a <code>getStateManager</code> method of its own. The StateManager
+that is returned, however, is of a specific type: <code>MockStateManager</code>. This implementation provides several methods in addition to those
+defined by the <code>StateManager</code> interface, that help developers to more easily develop unit tests.</p>
+</div>
+<div class="paragraph">
+<p>First, the <code>MockStateManager</code> implements the <code>StateManager</code> interface, so all of the state can be examined from within a unit test.
+Additionally, the <code>MockStateManager</code> exposes a handful of <code>assert*</code> methods to perform assertions that the State is set as expected.
+The <code>MockStateManager</code> also provides the ability to indicate that the unit test should immediately fail if state is updated for a particular
+<code>Scope</code>.</p>
+</div>
+</div>
+</div>
+<div class="sect2">
+<h3 id="reporting-processor-activity"><a class="anchor" href="developer-guide.html#reporting-processor-activity"></a>Reporting Processor Activity</h3>
+<div class="paragraph">
+<p>Processors are responsible for reporting their activity so that users
+are able to understand what happens
+to their data. Processors should log events via the ComponentLog,
+which is accessible via the InitializationContext
+or by calling the <code>getLogger</code> method of <code>AbstractProcessor</code>.</p>
+</div>
+<div class="paragraph">
+<p>Additionally, Processors should use the <code>ProvenanceReporter</code>
+interface, obtained via the ProcessSession’s
+<code>getProvenanceReporter</code> method. The ProvenanceReporter should be used
+to indicate any time that content is
+received from an external source or sent to an external location. The
+ProvenanceReporter also has methods for
+reporting when a FlowFile is cloned, forked, or modified, and when
+multiple FlowFiles are merged into a single FlowFile
+as well as associating a FlowFile with some other identifier. However,
+these functions are less critical to report, as
+the framework is able to detect these things and emit appropriate
+events on the Processor’s behalf. Yet, it is a best practice
+for the Processor developer to emit these events, as it becomes
+explicit in the code that these events are being emitted, and
+the developer is able to provide additional details to the events,
+such as the amount of time that the action took or
+pertinent information about the action that was taken. If the
+Processor emits an event, the framework will not emit a duplicate
+event. Instead, it always assumes that the Processor developer knows
+what is happening in the context of the Processor
+better than the framework does. The framework may, however, emit a
+different event. For example, if a Processor modifies both the
+content of a FlowFile and its attributes and then emits only an
+ATTRIBUTES_MODIFIED event, the framework will emit a CONTENT_MODIFIED
+event. The framework will not emit an ATTRIBUTES_MODIFIED event if any
+other event is emitted for that FlowFile (either by the
+Processor or the framework). This is due to the fact that all
+<a href="developer-guide.html#provenance_events">Provenance Events</a> know about the attributes of the FlowFile before the
+event occurred as well as those attributes that occurred as a result
+of the processing of that FlowFile, and as a result the
+ATTRIBUTES_MODIFIED is generally considered redundant and would result
+in a rendering of the FlowFile lineage being very verbose.
+It is, however, acceptable for a Processor to emit this event along
+with others, if the event is considered pertinent from the
+perspective of the Processor.</p>
+</div>
+</div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="documenting-a-component"><a class="anchor" href="developer-guide.html#documenting-a-component"></a>Documenting a Component</h2>
+<div class="sectionbody">
+<div class="paragraph">
+<p>NiFi attempts to make the user experience as simple and convenient as
+possible by providing significant amount of documentation
+to the user from within the NiFi application itself via the User
+Interface. In order for this to happen, of course, Processor
+developers must provide that documentation to the framework. NiFi
+exposes a few different mechanisms for supplying documentation to
+the framework.</p>
+</div>
+<div class="sect2">
+<h3 id="documenting-properties"><a class="anchor" href="developer-guide.html#documenting-properties"></a>Documenting Properties</h3>
+<div class="paragraph">
+<p>Individual properties can be documented by calling the <code>description</code>
+method of a PropertyDescriptor’s builder as such:</p>
+</div>
+<div class="listingblock">
+<div class="content">
+<pre class="highlight"><code class="language-java" data-lang="java">public static final PropertyDescriptor MY_PROPERTY = new PropertyDescriptor.Builder()
+ .name("My Property")
+ .description("Description of the Property")
+ ...
+ .build();</code></pre>
+</div>
+</div>
+<div class="paragraph">
+<p>If the property is to provide a set of allowable values, those values
+are presented to the user in a drop-down field in the UI.
+Each of those values can also be given a description:</p>
+</div>
+<div class="listingblock">
+<div class="content">
+<pre class="highlight"><code class="language-java" data-lang="java">public static final AllowableValue EXTENSIVE = new AllowableValue("Extensive", "Extensive",
+ "Everything will be logged - use with caution!");
+public static final AllowableValue VERBOSE = new AllowableValue("Verbose", "Verbose",
+ "Quite a bit of logging will occur");
+public static final AllowableValue REGULAR = new AllowableValue("Regular", "Regular",
+ "Typical logging will occur");
+
+public static final PropertyDescriptor LOG_LEVEL = new PropertyDescriptor.Builder()
+ .name("Amount to Log")
+ .description("How much the Processor should log")
+ .allowableValues(REGULAR, VERBOSE, EXTENSIVE)
+ .defaultValue(REGULAR.getValue())
+ ...
+ .build();</code></pre>
+</div>
+</div>
+</div>
+<div class="sect2">
+<h3 id="documenting-relationships"><a class="anchor" href="developer-guide.html#documenting-relationships"></a>Documenting Relationships</h3>
+<div class="paragraph">
+<p>Processor Relationships are documented in much the same way that
+properties are - by calling the <code>description</code> method of a
+Relationship’s builder:</p>
+</div>
+<div class="listingblock">
+<div class="content">
+<pre class="highlight"><code class="language-java" data-lang="java">public static final Relationship MY_RELATIONSHIP = new Relationship.Builder()
+ .name("My Relationship")
+ .description("This relationship is used only if the Processor fails to process the data.")
+ .build();</code></pre>
+</div>
+</div>
+</div>
+<div class="sect2">
+<h3 id="documenting-capability-and-keywords"><a class="anchor" href="developer-guide.html#documenting-capability-and-keywords"></a>Documenting Capability and Keywords</h3>
+<div class="paragraph">
+<p>The <code>org.apache.nifi.annotations.documentation</code> package provides Java
+annotations that can be used to document components. The
+CapabilityDescription
+annotation can be added to a Processor, Reporting Task, or Controller
+Service and is intended to provide a brief description of the
+functionality
+provided by the component. The Tags annotation has a <code>value</code> variable
+that is defined to be an Array of Strings. As such, it is used
+by providing multiple values as a comma-separated list of Strings
+with curly braces. These values are then incorporated into the UI by
+allowing
+users to filter the components based on a tag (i.e., a keyword).
+Additionally, the UI provides a tag cloud that allows users to select
+the tags that
+they want to filter by. The tags that are largest in the cloud are
+those tags that exist the most on the components in that instance of
+NiFi. An
+example of using these annotations is provided below:</p>
+</div>
+<div class="listingblock">
+<div class="content">
+<pre class="highlight"><code class="language-java" data-lang="java">@Tags({"example", "documentation", "developer guide", "processor", "tags"})
+@CapabilityDescription("Example Processor that provides no real functionality but is provided" +
+ " for an example in the Developer Guide")
+public static final ExampleProcessor extends Processor {
+ ...
+}</code></pre>
+</div>
+</div>
+</div>
+<div class="sect2">
+<h3 id="documenting-flowfile-attribute-interaction"><a class="anchor" href="developer-guide.html#documenting-flowfile-attribute-interaction"></a>Documenting FlowFile Attribute Interaction</h3>
+<div class="paragraph">
+<p>Many times a processor will expect certain FlowFile attributes be set on in-bound FlowFiles in order
+for the processor to function properly. In other cases a processor may update or
+create FlowFile attributes on the out-bound FlowFile. Processor developers may document both of these
+behaviors using the <code>ReadsAttribute</code> and <code>WritesAttribute</code> documentation annotations. These attributes are used to generate documentation
+that gives users a better understanding of how a processor will interact with the flow.</p>
+</div>
+<div class="paragraph">
+<p>Note: Because Java 7 does not support
+repeated annotations on a type, you may need to use <code>ReadsAttributes</code> and <code>WritesAttributes</code> to indicate
+that a processor reads or writes multiple FlowFile attributes. This annotation can only be applied to Processors. An example is listed below:</p>
+</div>
+<div class="listingblock">
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