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POCreating a custom AbstractProcessor and integrating with Eclipse
 

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  1. POCreating a custom AbstractProcessor and integrating with Eclipse
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    <p>I'm trying to create a new annotation with which I'll do some runtime wiring, but, for a number of reasons, I'd like to verify at compile time that my wiring will be successful with some rudimentary checks.</p> <p>Suppose I create a new annotation:</p> <pre><code>@Target(ElementType.FIELD) @Retention(RetentionPolicy.RUNTIME) public @interface CustomAnnotation{ } </code></pre> <p>Now I want to do some kind of validation at compile time, like check the field that <code>CustomAnnotation</code> annotates is of a particular type: <code>ParticularType</code>. I'm working in Java 6, so I created an <code>AbstractProcessor</code>:</p> <pre><code>@SupportedAnnotationTypes("com.example.CustomAnnotation") public class CompileTimeAnnotationProcessor extends AbstractProcessor { @Override public boolean process(Set&lt;? extends TypeElement&gt; annotations, RoundEnvironment roundEnv) { Set&lt;? extends Element&gt; elements = roundEnv.getElementsAnnotatedWith(CustomAnnotation.class); for(Element e : elements){ if(!e.getClass().equals(ParticularType.class)){ processingEnv.getMessager().printMessage(Kind.ERROR, "@CustomAnnotation annotated fields must be of type ParticularType"); } } return true; } } </code></pre> <p>Then, based on some instructions I found, I created a folder <code>META-INF/services</code> and created a file <code>javax.annotation.processing.Processor</code> with contents:</p> <pre><code> com.example.CompileTimeAnnotationProcessor </code></pre> <p>Then, I exported the project as a jar.</p> <p>In another project, I built a simple test class:</p> <pre><code>public class TestClass { @CustomAnnotation private String bar; // not `ParticularType` } </code></pre> <p>I configured the Eclipse project properties as follows:</p> <ul> <li>Set Java Compiler -> Annotation Processing: "Enable annotation processing" and "Enable processing in editor"</li> <li>Set Java Compiler -> Annotation Processing -> Factory Path to include my exported jar and checked under advanced that my fully qualified class shows up.</li> </ul> <p>I clicked "apply" and Eclipse prompts to rebuild the project, I hit okay -- but no error is thrown, despite having the annotation processor.</p> <p>Where did I go wrong?</p> <hr> <p>I ran this using <code>javac</code> as</p> <pre><code>javac -classpath "..\bin;path\to\tools.jar" -processorpath ..\bin -processor com.example.CompileTimeAnnotationProcessor com\test\TestClass.java </code></pre> <p>with output</p> <blockquote> <p>@CustomAnnotation annotated fields must be of type ParticularType</p> </blockquote>
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    1. USMark Elliot
    1. USMark Elliot
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    1. COFirst, does the annotation processor work with javac outside of Eclipse?
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      1. USantlersoft
    2. CO@antlersoft: yes, it works outside of Eclipse with straight javac (edits reflect this).
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      1. USMark Elliot
    3. COHave you checked the Error Log in Eclipse (Window > Show View > Error Log in case you can't see it)? When an annotation processor fails you might not get a popup dialog with an error but you will get an error displayed in the error log. You can also try to debug your processor in Eclipse by sprinkling Messager.printMessage() with kind=NOTE in your processor, as these show up in the error log as well.
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      1. USprunge
 

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