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Setting the target version of Java in ant javac

I need to compile a jar file using ant (1.7.0) to run under a specific version of Java (1.5). I currently have Java 1.6 on my machine. I have tried setting:

<target name="compile">
  <javac compiler="javac1.5" target="1.5" srcdir=.../>
</target>

I have also removed 

<property name="build.compiler" value="modern"/>

and there is no properties file. I am running Java 1.6 on Linux/SUSE

Also is there a simple way of determining which version of Java is expected in the jar file.

Solution

  • Use "target" attribute and remove the 'compiler' attribute. See here. So it should go something like this:

    <target name="compile">
  <javac target="1.5" srcdir=.../>
</target>

    Here's an example of using the javac command directly to achieve this. This information comes from @kon psych's link. I know and this doesn't show how did do this in an ant build.xml but it's still extremely helpful and I'd like to keep this information on the site in case that URL 404s some day.

    Cross-Compilation Example

    The following example uses javac to compile code that will run on a 1.6 VM.

    % javac -source 1.6 -target 1.6 -bootclasspath jdk1.6.0/lib/rt.jar \
            -extdirs "" OldCode.java

    The -source 1.6 option specifies that version 1.6 (or 6) of the Java programming language be used to compile OldCode.java. The option -target 1.6 option ensures that the generated class files will be compatible with 1.6 VMs. Note that in most cases, the value of the -target option is the value of the -source option; in this example, you can omit the -target option.

    You must specify the -bootclasspath option to specify the correct version of the bootstrap classes (the rt.jar library). If not, the compiler generates a warning:

    % javac -source 1.6 OldCode.java
warning: [options] bootstrap class path not set in conjunction with -source 1.6

    If you do not specify the correct version of bootstrap classes, the compiler will use the old language rules (in this example, it will use version 1.6 of the Java programming language) combined with the new bootstrap classes, which can result in class files that do not work on the older platform (in this case, Java SE 6) because reference to non-existent methods can get included.