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<p>Here are some tips on how to debug what is happening on the transition from groovy source code into the generated bytecode.</p><table class="confluenceTable"><tbody><tr><th class="confluenceTh"><p>artifact</p></th><th class="confluenceTh"><p>transformation</p></th><th class="confluenceTh"><p>artifact</p></th></tr><tr><td class="confluenceTd"><p>source (<a class="confluence-link unresolved" data-filename="hello.groovy" data-linked-resource-default-alias="hello.groovy" href="#">hello.groovy</a>)</p></td><td class="confluenceTd"><p>GroovyLexer</p></td><td class="confluenceTd"><p>antlr tokens</p></td></tr><tr><td class="confluenceTd"><p>antlr tokens</p></td><td class="confluenceTd"><p>GroovyRecognizer</p></td><td class="confluenceTd"><p>antlr ast</p></td></tr><tr><td class="confluenceTd"><p>antlr ast</p></td><td class="confluenceTd"><p>AntlrParserPlugin</p></td><td class="confluenceTd"><p>groovy ast</p></td></tr><tr><td class="confluenceTd"><p>groovy ast</p></td><td class="confluenceTd"><p>AsmClassGenerator</p></td><td class="confluenceTd"><p>bytecode (<a class="confluence-link unresolved" data-filename="hello.class" data-linked-resource-default-alias="hello.class" href="#">hello.class</a>)</p></td></tr></tbody></table><p><em>Note1</em> <a href="http://fisheye.codehaus.org/browse/groovy/trunk/groovy/groovy-core/src/main/org/codehaus/groovy/antlr/groovy.g#r17581">groovy.g</a> is used to generate <a href="http://groovy.codehaus.org/jsr/spec/GroovyLexer.html">GroovyLexer</a> and <a href="http://groovy.codehaus.org/jsr/spec/GroovyRecognizer.html">GroovyRecognizer</a></p><p><em>Note2</em> <a href="http://groovy.codehaus.org/jsr/spec/GroovyRecognizer.html">GroovyRecognizer</a> is sometimes easier to understand in its <a href="http://groovy.codehaus.org/jsr/spec/grammar/">syntax diagram</a> form</p><p><em>Note3</em> <a href="https://fisheye.codehaus.org/browse/groovy/trunk/groovy/groovy-core/src/main/org/codehaus/groovy/antlr/AntlrParserPlugin.java?hb=true">AntlrParserPlugin</a> source available.</p><h1>Example</h1><p>For these examples let's assume the file <a class="confluence-link unresolved" data-filename="hello.groovy" data-linked-resource-default-alias="hello.groovy" href="#">hello.groovy</a> contains</p><table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>class Hello {
    static void main(args) {
        println "hello world"
    }
}
</pre></td></tr></table><h1>GroovyLexer (viewing Antlr Tokens)</h1><p>To view the antlr tokens that the source code has been broken into you need to do the following in groovy-core subdirectory</p><table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>java -cp
  target/install/embeddable/groovy-all-1.6-beta-2.jar
  org.codehaus.groovy.antlr.LexerFrame
</pre></td></tr></table><p><img class="confluence-embedded-image" src="/download/attachments/231082404/tokenstreamviewer.png?version=1&amp;modificationDate=1371723091876" data-image-src="/download/attachments/231082404/tokenstreamviewer.png?version=1&amp;modificationDate=1371723091876" data-linked-resource-id="231377399" data-linked-resource-type="attachment" data-linked-resource-default-alias="tokenstreamviewer.png" data-base-url="http://docs.codehaus.org" data-linked-resource-container-id="231082404" title="null > tokenstreamviewer.png"></p><h1>GroovyRecognizer (viewing Antlr AST)</h1><p>To view the antlr AST that the recognized tokens have built</p><table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>java -cp
  target/install/embeddable/groovy-all-1.6-beta-2.jar
  org.codehaus.groovy.antlr.Main
  -showtree Hello.groovy
</pre></td></tr></table><p><img class="confluence-embedded-image" src="/download/attachments/231082404/antlrast.png?version=1&amp;modificationDate=1371723091876" data-image-src="/download/attachments/231082404/antlrast.png?version=1&amp;modificationDate=1371723091876" data-linked-resource-id="231377398" data-linked-resource-type="attachment" data-linked-resource-default-alias="antlrast.png" data-base-url="http://docs.codehaus.org" data-linked-resource-container-id="231082404" title="null > antlrast.png"></p><h1>AntlrParserPlugin (viewing Groovy AST)</h1><p>To view the Groovy AST that is one step closer to the generated bytecode you can generate <a class="confluence-link unresolved" data-filename="hello.groovy.xml" data-linked-resource-default-alias="hello.groovy.xml" href="#">hello.groovy.xml</a> using these unix commands.</p><p>This can be generated by changing the <strong>groovy.ast</strong> system property. By doing this we can diff the generated Groovy AST artifacts for debugging and migration purposes.</p><table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>$ export JAVA_OPTS="-Dgroovy.ast=xml"
$ groovyc Hello.groovy
Written AST to Hello.groovy.xml
</pre></td></tr></table><p><img class="confluence-embedded-image" src="/download/attachments/231082404/groovyast.png?version=1&amp;modificationDate=1371723091875" data-image-src="/download/attachments/231082404/groovyast.png?version=1&amp;modificationDate=1371723091875" data-linked-resource-id="231377397" data-linked-resource-type="attachment" data-linked-resource-default-alias="groovyast.png" data-base-url="http://docs.codehaus.org" data-linked-resource-container-id="231082404" title="null > groovyast.png"></p><h1>Viewing Bytecode</h1><p>One interesting bytecode viewer is <a href="http://www.ej-technologies.com/products/jclasslib/overview.html">jclasslib</a> which renders <a class="confluence-link unresolved" data-filename="hello.class" data-linked-resource-default-alias="hello.class" href="#">hello.class</a> in this manner...</p><p><img class="confluence-embedded-image" src="/download/attachments/231082404/jclasslib.png?version=1&amp;modificationDate=1371723091860" data-image-src="/download/attachments/231082404/jclasslib.png?version=1&amp;modificationDate=1371723091860" data-linked-resource-id="231377394" data-linked-resource-type="attachment" data-linked-resource-default-alias="jclasslib.png" data-base-url="http://docs.codehaus.org" data-linked-resource-container-id="231082404" title="null > jclasslib.png"></p><h1>Decompiling bytecode back to Java</h1><p>If, however, you are bamboozled by bytecode... The easiest to grok mechanism for reading the compiled code is to use a tool like <a href="http://www.kpdus.com/jad.html">JAD</a> to decompile the <a class="confluence-link unresolved" data-filename="hello.class" data-linked-resource-default-alias="hello.class" href="#">hello.class</a> into a readable <a class="confluence-link unresolved" data-filename="hello.java" data-linked-resource-default-alias="hello.java" href="#">hello.java</a></p><p><img class="confluence-embedded-image" src="/download/attachments/231082404/jad.png?version=1&amp;modificationDate=1371723091860" data-image-src="/download/attachments/231082404/jad.png?version=1&amp;modificationDate=1371723091860" data-linked-resource-id="231377393" data-linked-resource-type="attachment" data-linked-resource-default-alias="jad.png" data-base-url="http://docs.codehaus.org" data-linked-resource-container-id="231082404" title="null > jad.png"></p>