Problems debugging Java after ANT compile

Alex Staveley

Dec. 14, 11 · Java Zone · Interview

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Ok, this one is pretty easy but worth posting. I lost a few hours because of it and I don't want the same to happen to you! Suppose you want to be able to pass a switch into an ANT target which performs a javac to tell it to include debug information or not.

Your properties file will contain properties such as:

compile.debug=true
compile.debug.level=lines,vars,source

The ANT compile target then uses these properties:

<project default="help" name="my-proj">
 <property file="build.properties"></property>
 ...
 ...
 <target name="compile">
  <echo message="compiling code"></echo>
  <echo message="compile.debug=${compile.debug}"></echo>
  <echo message="compile.debug.level=${compile.debug.level}"></echo>
  <javac srcdir="${SRC.DIR}"
   destdir="${DEST.DIR}"
   debug="${compile.debug}"
   debuglevel="{compile.debug.level}">
   ...
  </javac>
 ...
 ...

However, the debug information is not there when you are debugging. You run
ant -v compile to get more information. You see:

compile:
     [echo] This target compiles everything.
     [echo] Compiling java classes...
     [echo] compile.debug=true
     [echo] compile.debug.level=lines,vars,source
    [javac] ...
    [javac] Compiling ...
    [javac] Using modern compiler
    [javac] Compilation arguments:
    [javac] '-deprecation'
    [javac] '-d'
    [javac] ...
    [javac] '-classpath'
    [javac] ...
    [javac] '-g:none'
    [javac] '-O'
    [javac]
    [javac] ...

Now, as we can see the properties are echo'd as expected. But, the "-g:none" indicates the compile won't include debug information. Before you tear your hair out, relax! You have just made a very silly mistake we all make at sometime. When ANT reads property files it reads all property values literally. This means there is a difference between "true" and "true ", i.e. boolean properties should not have trailing spaces otherwise they will not be read as boolean properties. This is what happened here. Ouch!

Ouch - trailing space!

As it states in http://ant.apache.org/manual/Tasks/property.html, regarding property files: "Trailing spaces are not stripped. It may have been what you wanted."

So rip that trailing space and re-run the ant compile target.

You should see:

[javac] '-g:lines,vars,source'

which means the compiler is going to add lines, vars and source debug information. Happy debugging!

References:
1. http://ant.apache.org/manual/Tasks/property.html

From http://dublintech.blogspot.com/2011/10/problems-debugging-java-after-ant.html

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Problems debugging Java after ANT compile

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