How to load an optional task into ant without -lib

问题:

I want to use the FTP task in ant, and I have found the appropriate jar files and got everything working fine. I have put the jar files in a "libs" directory alongside the other files used in the build. The only problem is that the user must run "ant -lib commons-net-ftp-2.0.jar" to make a build; I would really prefer that it were possible to just run "ant" with no arguments.

Reading the ant optional tasks intallation page, I see that there are five ways one can load up extra libraries in ant, and none of them are really what I'm looking for. I do not want to force the user to make any modifications to their system to run this task; it should be possible to just load it from the "libs" directory inside of our product's source folder. So that means setting the global CLASSPATH is also out (which is a bad idea anyways).

The last option, as noted in the documentation, is the preferred approach... loading the jarfiles individually from the build script itself. I have done this in the past with the ant-contrib tasks and JUnit, and would like to do that here, but I don't see how I can accomplish this. The FTP task doesn't support a nested classpath element, and I don't know the XML resource I would need to load this library via a taskdef. How can I load the libraries from within ant?

Edit: In response to the answers and questions which have been posted here so far, I'm using ant 1.7.1. Making an ftp taskdef definitely does not work; that throws the following error:

BUILD FAILED /my/path/build.xml:13: taskdef class org.apache.tools.ant.taskdefs.optional.net.FTP cannot be found

Perhaps this is because the classname is wrong. How exactly do I find the classname I'm supposed to use if I only have a jarfile? It's not documented anywhere, and I couldn't find anything in the jar itself resembling that path.

回答1:

The problem you are having is due to the different class-loaders in use. The Commons Net classes must be loaded by the same class-loader that loads the FTP task. Because the FTP task is loaded by Ant on start-up, you need to add the Commons Net to Ant's classpath so that it is loaded by the same class-loader. That's why the documentation gives you 4 different ways to do this.

I agree that none of them are ideal (the CLASSPATH environment variable being the worst). One way around this is to supply a shell script with your project that invokes Ant and passes the apporpriate -lib argument. You then get people to use this rather than invoking Ant directly. In fact, you could deviously name it 'ant' so that it gets run instead of the existing 'ant' on the path (this only works if the current directory is on the path, ahead of other directories).

The fifth option in the documentation is great in theory. They finally fixed the class-loading problems in 1.7.0. Unfortunately, as you mention, nobody retro-fitted the FTP task to take a classpath. You could try submitting an enhancement request, but this won't help in the short term.

There is one other option, which isn't any better than the others. Instead of making sure that the Commons Net classes are loaded by the class-loader that loads the FTP task, you could make sure that the FTP task is loaded by the class-loader that loads the Commons Net classes. To do this you have to remove the ant-commons-lib.jar file from the 'lib' directory of the Ant installation. This means that the FTP task won't get loaded on start-up. This is actually why the optional tasks are broken up into so many separate JARs - so that they can be individually removed. Put this JAR file alongside the Commons Net JAR file so that it can be loaded at the same time. Then you can do something like this (I tried this and it works):

<taskdef name="ftp"
         classname="org.apache.tools.ant.taskdefs.optional.net.FTP">
  <classpath>
    <pathelement location="${basedir}/lib/ant-commons-net.jar"/>
    <pathelement location="${basedir}/lib/commons-net-2.0.jar"/>
  </classpath>
</taskdef>
<ftp server="yourserver.com"
     userid="anonymous"
     password="blah">
  <fileset dir="somedirectory"/>
</ftp>

But this is probably a worse option than just using the -lib switch (with or without a wrapper script). The only other thing I can think of is to try to find a third-party FTP task to use instead of the default one.

回答2:

I have a solution:

you can download a new "classloader" task from http://enitsys.sourceforge.net/ant-classloadertask/ and load it whith:

    <taskdef resource="net/jtools/classloadertask/antlib.xml"
            classpath="XXX/ant-classloadertask.jar"/>

Naw can do things like loading classes with the same classloader that ant use for his task:

    <classloader loader="system" classpath="XXX/commons-net-2.0.jar"/>

or "loader="project""

Then you definde your task:

    <taskdef name="ftp" classname="org.apache.tools.ant.taskdefs.optional.net.FTP"/>    

and go :-)

回答3:

So I succeeded in doing this for the ant-salesforce.jar that you get when trying to do salesforce work (fun...)

Check to see if the jar has an xml file in it that looks something like this:

<antlib>
  <typedef name="compileAndTest" classname="com.salesforce.ant.CompileAndTest"/>
  ....
</antlib>

Then in ant give it a taskdev that reads that file from inside the given jar, like this:

<taskdef resource="com/salesforce/antlib.xml" classpath="lib/ant-salesforce.jar" />

Hope that helps some.

回答4:

Ah, man, this is just so nasty. I run ant from eclipse. I don't want to reconfigure ant in eclipse for new workspaces, so here's what I decided to do, to decouple running the task and configuring ant. I extracted the ftp task to a separate build file. Next I added a native call to the command line to start a completely new ant process with the required libraries on the path:

<target name="deploy-ftp">
    <exec command="ant">
        <arg line="-buildfile ftp.xml deploy-ftp -lib lib/ant"/>
    </exec>
</target>

Now the master build file can be run without any special arguments and no modifications are required to the ant installation. It's nasty though, since the ftp task runs in a completely clean environment. None of the properties and paths from the master build file are available. Luckily I had all of these in a separate property file anyway, so I only needed a single import.

I would like to add a big thanks to Dan Dyer. Without your extensive explanation of what's going on behind the scenes, I wouldn't have found this solution.

回答5:

Will this work assuming libs is directly under you project's base directory

<taskdef name="ftp" classname="org.apache.tools.ant.taskdefs.optional.net.FTP">
  <classpath>
    <pathelement location="${basedir}\libs\commons-net-1.4.0.jar"/>
  </classpath>
</taskdef>

回答6:

Your users all have ant installed on their machines but you can't / don't want to make them add the FTP jar? Can you bundle ant with your project make tasks that call YOUR ant bundle, with the jars placed so it'll work as follows?

<taskdef name="ftp" classname="org.apache.tools.ant.taskdefs.optional.net.FTP">
  <classpath>
    <pathelement location="\lib\commons-net-1.4.0.jar"/>
  </classpath>
</taskdef>
<target name="testFtp">
  <ftp server="blah" userid="foo" password="bar">
    <fileset file="test.file" />
  </ftp>
</target>