M-x all-things-emacs

This post describes how to integrate jdee, ant, and the eclipse batch compiler to get the same warning and error messages as your Eclipse-loving friends. I am assuming that you already know your way around the jdee environment (i.e., you have it setup and configured such that you can run an ant build from within emacs), and the ant build tool.

1. Download the jdt core batch compiler. You can install the entire eclipse application if you like, but it is easier and faster to just download the batch compiler and ant adapter (the size of the download is an order of magnitude smaller for the compiler only). It is named ecj.jar. If you have eclipse installed and want to use the installed compiler, then you will need to locate the org.eclipse.jdt.core_3.2.x.xxx.jar in the plugins directory of you eclipse installation.
2. Install ant 1.7. You may be able to get away with using an older version, but the newer version allows you to specify additional parameters that you may need on the command line.
3. Place the ecj.jar file (if you downloaded the compiler and ant adapter) in the <ANT_HOME>/lib directory, or make it available on the classpath so that it is available to ant. If you are using the eclipse jdt core jar, then make it available either by copying or adding to the ant classpath. You will also need to make the jdtCompilerAdapter.jar available to ant. It is bundled inside the jdt core jar (if you went this route).

1. You are now ready to test your ant/eclipse compiler setup. Go to a java project that you want to compile. Use your normal compile target with the following additional parameter(s). Note: the ant.build.javac.target and ant.build.javac.source only need to be used if the default values are not what you desired.

ant -Dbuild.compiler=org.eclipse.jdt.core.JDTCompilerAdapter 
    -Dant.build.javac.target=1.5 
    -Dant.build.javac.source=1.5 compile

The build.compiler is self explanatory. The reason I suggested upgrading to ant version 1.7 or above is so that you have the ability to specify the source and target type on the command line. At this point you should be able to run ant with the additional properties from within emacs in whatever way you normally do, and it will use the eclipse compiler. If your ant build within emacs does not propmpt you for additional arguments, then customize the following variable: jde-ant-read-args. The first time you perform a build with the eclipse compiler, you will notice that the error messages are not formatted nicely in the compilation buffer. There are two ways that I have come up with for getting the compilation output formatted for emacs. First, you can use the compilerarg element in ant to pass compiler specific settings to the compiler. The eclipse compiler takes the parameter -Xemacs to format its output in the format the emacs compilation buffer expects. See the example below:

     <javac
          srcdir="${src}"
          destdir="${build.dir}/classes"> 
        <compilerarg 
           compiler="org.eclipse.jdt.core.JDTCompilerAdapter" 
           line="-warn:+unused -Xemacs"/>
        <classpath refid="compile.classpath" />
      </javac>

The compilerarg element also allows you to pass in additional command line args to the eclipse compiler. The downside of the compilerarg approach is that you must modify your build.xml, which may not be an option on your project. An alternative approach is to change the compilation-error-regexp-alist in emacs to handle the eclipse formatting.

(setq compilation-error-regexp-alist
  (cons '("----------\n[0-9]+. \\(ERROR\\|WARNING\\) in \\(.*\\)\n (at line \\([0-9]+\\))\n\\(\\(.*\n\\)+?\\).*^+\n\\(.*\n\\)"
         2 3)
         compilation-error-regexp-alist))

My compilation formatting example is taken directly from the following package: jde eclipse compiler server. The eclipse compiler server is also interesting, and I plan to try that out at some point; however, the projects that I work on are ant-driven, so the only benefit I would get from using the compiler server is if I got it working with jde-flymake to get continuous syntax checking … hmmm … maybe another day.