Having Problems?

This page details some steps you can take to try and resolve any problems you may be having with Ant. If you find you can't resolve the problem, then this page will help you collect some of the relevant information to provide in a bug report. This information will help the Ant developers understand and resolve the problem. Of course, not all the steps here will make sense for every problem you may encounter - these are just some suggestions to point you in the right direction.

Read the Manual

The first step to take when you have a problem with Ant is to read the manual entry for the task or concept that is giving you trouble. In particular, check the meaning of a task's attributes and nested elements. Perhaps an attribute is available that would provide the behavior you require. If you have problems with the manual itself, you can submit a documentation bug report (see below) to help us improve the Ant documentation.

Examine Debug Output

If you're still having a problem, the next step is to try and gather additional information about what Ant is doing. Try running Ant with the verbose flag:

ant -verbose

or

ant -v

This will produce output that starts like the following:

Ant version 1.4.1 compiled on October 11 2001
Buildfile: build.xml
Detected Java version: 1.3 in: D:\usr\local\java\jdk13\jre
Detected OS: Windows NT
parsing buildfile D:\ant\build.xml with URI = file:D:/ant/build.xml
Project base dir set to: D:\ant
[property] Loading Environment env.
[property] Loading D:\ant\conf.properties
Build sequence for target 'debug' is [debug]
Complete build sequence is [debug, gensrc, compile, jar, test]
. . .

You should be able to see from the trace more about what Ant is doing and why it's taking a particular course of action. If you need even more information, you can use the -debug flag rather than -verbose. This will generally produce so much output that you may want to save the output to a file and analyze it in an editor. You can save the output using the -logfile <filename> flag, or using redirection.

Once you have all this debug information, how can you use it to solve your problem? That will depend on the task in question and the nature of your problem. Each task logs different aspects of its operation, but it should give you an idea of what is going on. For example, the <javac> task logs the reasons why it chooses to compile particular class files and not others, along with which compiler it is using and the arguments it will pass to that compiler. The following partial trace shows why <javac> is adding one class file but skipping another. This is followed by which compiler it will be using, the arguments that will get passed to the compiler, and a list of all the class files to be compiled.

[javac] Test.java omitted as D:\classes\Test.class is up to date.
[javac] Unset.java added as D:\classes\Unset.class is outdated.
[javac] Compiling 1 source file to D:\classes
[javac] Using classic compiler
[javac] Compilation args: -d D:\classes -classpath D:\classes;
D:\jdk118\classes.zip; -sourcepath D:\src\java -g:none
[javac] File to be compiled:
D:\src\java\Unset.java

In many cases, Ant tasks are wrappers around OS commands or other Java classes. In debug mode, many of these tasks will print out the equivalent command line, as the <javac> task output does. If you are having a problem, it is often useful to run the command directly from the command line, in the same way Ant is running it, and see if the problem occurs from there as well. The problem may be in the command that is being run, or it may be in the way the Ant task is running the command. You can also see the effect of changing attribute values on the generated command line. This can help you to understand whether you are using the correct attributes and values.

Has It Been Fixed?

After examining the debug output, if you still believe that the problem you are having is caused by Ant, chances are that someone else may have already encountered this problem, and perhaps it has been fixed. The next step, therefore, may be to try a nightly build of Ant to see if the problem has been fixed. Nightly builds for Ant are available from the Ant web site. While Ant nightly builds are typically quite stable and are used by Gump to build many other Jakarta projects, these builds should nonetheless be treated as experimental. Note that nightly builds do not build many of the optional tasks the come with Ant. A snapshot of these optional tasks is occasionally uploaded to the nightly download area. However, even this snapshot does not contain every optional task.

Has It Been Reported?

If the current nightly build doesn't resolve your problem, it is possible that someone else has reported the issue. It is time to look at the Apache Bug Database. This system is easy to use, and it will let you search the currently open and resolved bugs to see if your problem has already been reported. If your problem has been reported, you can see whether any of the developers have commented, suggesting workarounds, or the reason for the bug, etc. Or you may have information to add (see about creating and modifying bug reports below), in which case, go right ahead and add the information. If you don't have any additional information, you may just want to vote for this bug, and perhaps add yourself to the CC list to follow the progress of this bug.

Filing a Bug Report

By this time, you may have decided that there is an unreported bug in Ant. You have a few choices at this point. You can send an email to the user mailing list to see if others have encountered your issue and find out how they may have worked around it. If after some discussion, you feel it is time to create a bug report, this is a simple operation in the bug database. Please try to provide as much information as possible in order to assist the developers in resolving the bug. Please try to enter correct values for the various inputs when creating the bug, such as which version of Ant you are running, and on which platform, etc. Once the bug is created, you can also add attachments to the bug report.

What information should you include in your bug report? The easiest bugs to fix are those that are most easily reproducible, so it is really helpful if you can produce a small test case that exhibits the problem. In this case, you would attach the build file and any other files necessary to reproduce the problem, probably packed together in an archive. If you can't produce a test case, you should try to include a snippet from your build file and the relevant sections from the verbose or debug output from Ant. Try to include the header information where Ant states the version, the OS and VM information, etc. As debug output is likely to be very large, it's best to remove any output that is not relevant. Once the bug is entered into the bug database, you will be kept informed by email about progress on the bug. If you receive email asking for further information, please try to respond, as it will aid in the resolution of your bug.

Asking for an Enhancement

Sometimes, you may find that Ant just doesn't do what you need it to. It isn't a bug, as such, since Ant is working the way it is supposed to work. Perhaps it is some additional functionality for a task that hasn't been thought of yet, or maybe a completely new task. For these situations, you will want to raise an enhancement request. Enhancement requests are managed using the same Apache Bug Database described above. These are just a different type of bug report. If you look in the bug database, you will see that one of the severity settings for a bug is "Enhancement". Just fill the bug report in, set the severity of the bug to "Enhancement", and state in the description how you would like to have Ant enhanced. Again, you should first check whether there are any existing enhancment requests that cover your needs. If so, just add your vote to these.

Fixing the Bug

If you aren't satisfied with just filing a bug report, you can try to find the cause of the problem and provide a fix yourself. The best way to do that is by working with the latest code from CVS. Alternatively, you can work with the source code available from the source distributions. If you are going to tackle the problem at this level, you may want to discuss some details first on the dev mailing list. Once you have a fix for the problem, you may submit the fix as a patch to either the dev mailing list, or enter the bug database as described above and attach the patch to the bug report. Using the bug database has the advantage of being able to track the progress of your patch.

If you have a patch to submit and are sending it to the dev mailing list, prefix "[PATCH]" to your message subject. Please include any relevant bug numbers. Patch files should be created with the -u option of the diff or cvs diff command. For example:

diff -u Javac.java.orig Javac.java > javac.diffs

or, if you have source from CVS:

cvs diff -u Javac.java > javac.diffs

Note: You should give your patch files meaningful names. This makes it easier for developers who need to apply a number of different patch files.