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From "Martin van den Bemt" <>
Subject RE: [PROPOSAL] Class dependency checking for optional tasks
Date Sun, 21 Jan 2001 15:27:04 GMT
Shouldn't there also be an option to download (maby embedded in the main
build.xml for ant to download all tasks that depend on external sources?
(like what they do in netbeans  modules)They also use the build.xml to do

- You have a default stable distribution
- You want e.g. the Junit tasks
- You run build Junit
- This target gets all the stuff that the junit task needs
- Rebuilds ant when necessary.

- You're using the Junit task in a build.xml
- If not present, throw a buildexception saying to get the junit optional
and how to accomplish that. (maby offer it right away for download).
- rebuild ant when necessary.

Martin van den Bemt

-----Original Message-----
From: Bill Burton []
Sent: Sunday, January 21, 2001 4:02 AM
To: Ant Developers Mailing List
Subject: [PROPOSAL] Class dependency checking for optional tasks


I've been thinking about ways to improve usability of Ant, particulary for
first time users.  Here's one idea in that direction.

One of the questions that comes up a lot on the ant-user list is, "Where
do a find the classes for ftp support, etc?"  As a result, it was good to
see Nico's patches to clarify the docs in this area.  I've been thinking
about this problem from a little different perspective.


Each task requiring external classes should provide a way the task
developer can declare the required jar file(s) by specifing a class within
each jar to check for the availability of the jar.  If the class isn't
available, the task will throw a BuildException with the name of the
missing jar and the URL where it can be obtained.

This feature is conceptually similar to the <available classname=... />
task but would force the build to stop if the specified class is not
available by throwing a BuildException.

Implementation Details would be modified by adding a method similar to the following

     * Tries to load the specified class ensuring any associated jar
     * file is available.  If the class is not available, a BuildException
     * is thrown with the specified comment.  The comment should concisely
     * provide information indicating what's missing and where it can be
     * obtained.
     * @param name name of class to check in the classpath
     * @param loader class loader or null for the default
     *        class loader
     * @param comment text describing the name of the class or
     *        associated jar file and the URL or location where it
     *        can be obtained
    public void checkForRequiredClass(String name, ClassLoader loader,
String comment)
        throws BuildExeception
        try {
            if (loader == null)
                loader = this.getClass().getClassLoader();
            Class.forName(name, true, loader);
        } catch (ClassNotFoundException cnfe) {
            // Maybe this should also output the location too?
            throw (new BuildException("Missing class " + name + ": " +
        // Need to catch other exceptions here?

The task developer could use it in either the init() or execute() methods
like this:
    checkForRequiredClass("", null
                          "Requires ORO NetComponents available at");

The <script> task could have many calls to this method, one for BSF and
one for each of the supported scripting languages.

If the consensus is that this is a good idea, I'll work on a patch for
this functionality.

-Bill Burton

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