[jira] [Comment Edited] (JEXL-387) v3.2.1 breaks with log-related NullPointerException

["Garret Wilson (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/JEXL-387?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17640159#comment-17640159 ] 

Garret Wilson edited comment on JEXL-387 at 11/28/22 5:47 PM:
--------------------------------------------------------------

To guide you through the project unit test, look in {{io.guise.mesh.JexlMexlEvaluatorTest}}. The "MEXL" interfaces are a very thin wrapper around JEXL, just in case Mesh wants to switch to a different expression engine in the future. An example unit test looks like this:

{code:java}
@Test
public void shouldRetrieveMapValue() {
  final MeshContext context = new DefaultMeshContext();
  context.setVariable("foo", Map.of("bar", 123));
  assertThat(JexlMexlEvaluator.INSTANCE.evaluate(context, "foo.bar"), is(123));
}
{code}

You can't get much simpler than that. It works fine in JEXL 3.1, but breaks as described in JEXL 3.2.1.

In {{JexlMexlEvaluator}} you'll see we create an instance of {{JexlEngine}} using {{new JexlBuilder().strategy(RESOLVER_STRATEGY).create()}}, where {{RESOLVER_STRATEGY}} is a {{JexlUberspect.PropertyResolver}} that knows how to get properties from [URF|https://urf.io/]. That's about all there is. Even those are irrelevant details, as the problem here stems from some internal logger not getting initialized.

The question is: what did you change with your internal logger that suddenly makes me go through extra steps in order to get it initialized?


was (Author: garretwilson):
To guide you through the project unit test, look in {{io.guise.mesh.JexlMexlEvaluatorTest}}. The "MEXL" interfaces are a very thin wrapper around JEXL, just in case Mesh wants to switch to a different expression engine in the future. An example unit test looks like this:

{code:java}
@Test
public void shouldRetrieveMapValue() {
  final MeshContext context = new DefaultMeshContext();
  context.setVariable("foo", Map.of("bar", 123));
  assertThat(JexlMexlEvaluator.INSTANCE.evaluate(context, "foo.bar"), is(123));
}
{code}

You can't get much simpler than that. It works fine in JEXL 3.1, but breaks as described in JEXL 3.2.1.

> v3.2.1 breaks with log-related NullPointerException
> ---------------------------------------------------
>
>                 Key: JEXL-387
>                 URL: https://issues.apache.org/jira/browse/JEXL-387
>             Project: Commons JEXL
>          Issue Type: Bug
>         Environment: Java 17; Windows 10
>            Reporter: Garret Wilson
>            Priority: Major
>
> In my [Guise Mummy|https://github.com/globalmentor/guise-mummy] static site generator I'm using JEXL to interpret the built-in [Mesh Expression Language|https://github.com/globalmentor/guise-mummy/tree/main/mesh] (MEXL). Everything was working fine with JEXL 3.1. In fact the entire [Guise Mummy web site|https://guise.io/mummy/] itself was produced using Guise Mummy with MEXL on top of JEXL.
> But when I upgrade to JEXL 3.2.1, the unit tests break. The MEX+JEXL error message says "Error in MEXL expression `foo.bar`: io.guise.mesh.JexlMexlEvaluator.evaluate:93 undefined property 'bar'", but if you look in the stack trace, you'll see that the problem seems to be a deeper {{NullPointerException}} which {{InterpreterBase.getAttribute(…)}} catches and effectively ignores, making it look like the problem was a missing variable.
> {code:xml}
> } catch (final Exception xany) {
>   xcause = xany;
> }
> {code}
> Here's the real problem:
> {noformat}
> Caused by: java.lang.NullPointerException: Cannot invoke "org.apache.commons.logging.Log.isDebugEnabled()" because "log" is null
> 	at org.apache.commons.jexl3.internal.introspection.ClassMap.populateWithClass(ClassMap.java:296)
> 	at org.apache.commons.jexl3.internal.introspection.ClassMap.populateWithInterface(ClassMap.java:270)
> 	at org.apache.commons.jexl3.internal.introspection.ClassMap.create(ClassMap.java:229)
> 	at org.apache.commons.jexl3.internal.introspection.ClassMap.<init>(ClassMap.java:100)
> 	at org.apache.commons.jexl3.internal.introspection.Introspector.getMap(Introspector.java:315)
> 	at org.apache.commons.jexl3.internal.introspection.Introspector.getMethod(Introspector.java:146)
> 	at org.apache.commons.jexl3.internal.introspection.Introspector.getMethod(Introspector.java:133)
> 	at org.apache.commons.jexl3.internal.introspection.PropertyGetExecutor.discoverGet(PropertyGetExecutor.java:107)
> 	at org.apache.commons.jexl3.internal.introspection.PropertyGetExecutor.discover(PropertyGetExecutor.java:42)
> 	at org.apache.commons.jexl3.internal.introspection.Uberspect.getPropertyGet(Uberspect.java:263)
> 	at org.apache.commons.jexl3.internal.InterpreterBase.getAttribute(InterpreterBase.java:971)
> 	at org.apache.commons.jexl3.internal.Interpreter.visit(Interpreter.java:1108)
> 	at org.apache.commons.jexl3.parser.ASTIdentifierAccess.jjtAccept(ASTIdentifierAccess.java:104)
> 	at org.apache.commons.jexl3.internal.Interpreter.visit(Interpreter.java:1156)
> 	at org.apache.commons.jexl3.parser.ASTReference.jjtAccept(ASTReference.java:19)
> 	at org.apache.commons.jexl3.internal.Interpreter.visit(Interpreter.java:1029)
> 	at org.apache.commons.jexl3.parser.ASTJexlScript.jjtAccept(ASTJexlScript.java:58)
> 	at org.apache.commons.jexl3.internal.Interpreter.interpret(Interpreter.java:193)
> 	at org.apache.commons.jexl3.internal.Script.execute(Script.java:188)
> 	at org.apache.commons.jexl3.internal.Script.evaluate(Script.java:180)
> 	... 72 more
> {noformat}
> For some reason your internal {{ClassMap}} class is being passed a {{Log}} that is {{null}}. Looking up the stack trace, it would appear this is coming from your {{Introspector}}. (There is a similar [error on Stack Overflowhttps://stackoverflow.com/q/64927054] with no answers; I don't know if they are using JAXL.)
> * First, passing the {{Log}} around as a parameter is an antipattern. Logging is a cross-cutting concern; passing it around as a parameter is a bad idea.
> * I wish you were using {{SLF4J}} like practically everyone else instead of {{org.apache.commons.logging}}.
> * You shouldn't catch {{NullPointerException}} and turn it into a "normal" error condition, trying to say that a variable wasn't defined when really this was an internal error with the library.
> In any case, for some reason JEXL 3.2.1 isn't initializing its internal logging support.
> To reproduce this:
> # Clone [Guise Mummy 0.5.3|https://github.com/globalmentor/guise-mummy/releases/tag/v0.5.3].
> # In the overall project {{pom.xml}}, change the version of {{org.apache.commons:commons-jexl3}} from {{<version>3.1</version>}} to {{<version>3.2.1</version>}}.
> # Run {{mvn clean verify}}.



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