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http://db.apache.org/derby/javadoc/engine/org/apache/derby/impl/services/bytecode/BCJava.html https://builds.apache.org/job/Derby-trunk/lastSuccessfulBuild/artifact/trunk/javadoc/engine/index.html

To execute various queries, Derby generates Java classes on the fly, then executes that generated code.

To study a particular Derby issue, you may find yourself wanting to view that generated code. For example, DERBY-2352 involves understanding what code is generated for various expressions. DERBY-739 is another example.

Here's a simple technique that will allow you to view the generated code:

  • Run Derby with the argument -Dderby.debug.true=DumpClassFile:

    •  java -Dderby.debug.true=DumpClassFile org.apache.derby.tools.ij 

  • Reproduce the problem that you're interested in. It's best if you can narrow the problem down to a single statement that you can execute in your IJ session.
  • Exit IJ and look in your current directory. You'll see a file like:
    •  ac601a400fx0116x4ec6xd381x00000010e1180.class  This is the generated class file for the statement you just ran.

  • Use a decompiler to transform the generated Java class into source code. I've been successful using "jad". Others have used javap -c. Still others have used 'jode' (see below).

  • Now you can read the code!

Some other information about generated class files is documented here: https://builds.apache.org/job/Derby-trunk/lastSuccessfulBuild/artifact/trunk/javadoc/engine/index.html

A shell script for using the 'jode' decompiler

This shell script may prove useful if you are using the 'jode' decompiler to view the generated class file's code:

# Run the jode decompiler on a class. E.g.:
# runjode acf81e0010x011cxddd8xfcabx0000000feab00


. setupClasspath

export CLASSPATH=$CLASSPATH:$SW/javaDecompilers/jode/jode-1.1.2-pre1.jar:.


mkdir org
mkdir org/apache
mkdir org/apache/derby
mkdir org/apache/derby/exe

cp $classStub.class org/apache/derby/exe/

#java -cp $CLASSPATH jode.decompiler.Main --help $*
java -cp $CLASSPATH jode.decompiler.Main org.apache.derby.exe.$classStub

DumpClassFile (last edited 2014-02-13 21:28:47 by MyrnavanLunteren)