Generating a classpath that dynamically chooses .jar files

Question

I have a project where we store a local copy of some client API jars. These jars may or may not be the same as the final run-time versions used by the client. When I build the project locally for testing, I want to use the local copies of the jars. However, when I'm on-site with the client, I want to look at an external location from my project and check if the client updated jars are available. If they are we use them, if not we fall back on our local copies.

I have found a way to conditionally build a file-set containing the given jars, but I can't figure out how to get the file-set into my classpath.

Below is the script I have generated so far. I do not have access to the ant-contrib IF statements, so this is the only way I've found to conditionally build the file-set.

<condition property="externalFileExists">
     <available file="[path to external file]"/>
</condition>

<target name="buildExternalFileset" if="externalFileExists">
     <fileset id="fileset" includes="[path to external library]"/>
</target>

<target name="buildInternalFileset" unless="externalFileExists">
     <fileset id="fileset" includes="[path to internal library]"/>
</target>

<target name="buildFileset depends="buildExternalFileset, buildInternalFileSet>
</target>

Once I have this file-set built, how do I include it in the classpath?

<path id="classpath">
     <!-- other filesets -->
     <!-- line that includes the conditional fileset by ID -->
</path>

According to the documentation for path-like structures you can include a path within another path, but I don't see an example for including an external file-set. Perhaps I've answered my question - - should I be building paths instead of file-sets? Additionally, file-set documentation doesn't actually include the option to add IDs, do they work?

If anyone has a better way to do this I'd be more than happy to hear about it!

Answer 1

Try something like this

<classpath>

      <fileset dir="[external-path1]">
        <include name="**/*.jar"/>
      </fileset>
      <fileset dir="[external-path2]">
        <include name="**/*.jar"/>
      </fileset>
      <fileset dir="[external-path3]">
        <include name="**/*.jar"/>
      </fileset>

    </classpath>

found here

https://ant.apache.org/manual/using.html#path

Answer 2

I would suggest using a dependency manager rather than try and building your own.

Apache ivy is able to download dependencies from configured locations. It also caches downloaded files removing the need to store them locally if they are universally available from Maven Central.

Example

This project has an ivy settings file that pulls dependencies from either the local "lib" directory or from Maven central.

├── build.xml
├── ivysettings.xml
├── ivy.xml
└── lib
    ├── hamcrest-core-1.3.jar
    ├── junit-4.11.jar
    ├── log4j-1.2.17.jar
    ├── slf4j-api-1.7.5.jar
    └── slf4j-log4j12-1.7.5.jar

build.xml

<project name="demo" default="resolve" xmlns:ivy="antlib:org.apache.ivy.ant">

  <property name="build.dir" location="target"/>

  <available classname="org.apache.ivy.Main" property="ivy.installed"/>

  <target name="install-ivy" unless="ivy.installed">
    <mkdir dir="${user.home}/.ant/lib"/>
    <get dest="${user.home}/.ant/lib/ivy.jar" src="http://search.maven.org/remotecontent?filepath=org/apache/ivy/ivy/2.4.0/ivy-2.4.0.jar"/>
    <fail message="Ivy installed  run build again"/>
  </target>

  <target name="resolve" depends="install-ivy" description="Use ivy to resolve classpaths">
    <ivy:resolve/>

    <ivy:report todir='${build.dir}/ivy-reports' graph='false' xml='false'/>

    <ivy:cachepath pathid="compile.path" conf="compile"/>
    <ivy:cachepath pathid="test.path"    conf="test"/>
  </target>


  <target name="clean">
    <delete dir="${build.dir}"/>
  </target>

  <target name="clean-all" depends="clean">
    <ivy:cleancache/>
  </target>

</project>

Notes:

• Ivy does not come bundled with ANT. The "install-ivy" task ensures it gets installed on the first ant run
• The "cachepath" tasks will create classpaths for use in your javac, junit and java tasks.
• The "report" and "cleancache" tasks are useful additional tasks.

ivy.xml

<ivy-module version="2.0">
    <info organisation="com.myspotontheweb" module="demo"/>

    <configurations>
        <conf name="compile" description="Required to compile application"/>
        <conf name="runtime" description="Additional run-time dependencies" extends="compile"/>
        <conf name="test"    description="Required for test only" extends="runtime"/>
    </configurations>

    <dependencies>
        <!-- compile dependencies -->
        <dependency org="org.slf4j" name="slf4j-api" rev="1.7.5" conf="compile->default"/>

        <!-- runtime dependencies -->
        <dependency org="org.slf4j" name="slf4j-log4j12" rev="1.7.5" conf="runtime->default"/>

        <!-- test dependencies -->
        <dependency org="junit" name="junit" rev="4.11" conf="test->default"/>
    </dependencies>

</ivy-module>

Notes:

• Uses configurations to keep dependencies separated. Note how this is used by the "cachepath" tasks to control dependency classpaths

ivysettings.xml

<ivysettings>
  <settings defaultResolver="my-resolvers"/>
  <resolvers>
    <chain name="my-resolvers" returnFirst="true">
      <filesystem name="local-lib">
        <artifact pattern="${ivy.settings.dir}/lib/[artifact]-[revision].[ext]"/> 
      </filesystem>
      <ibiblio name="central" m2compatible="true"/>
    </chain>
  </resolvers>
</ivysettings>

Notes:

• This file is optional. By default Ivy will retrieve from Maven Central
• The special chain resolver controls which source of dependencies is used. In this case the local "lib" directory is favoured over Maven Cental.

Answer 3

I'm not very familiar with ant, but how about a build configuration on ant ?

Try this site for a tutorial on how to do it: http://ant.apache.org/easyant/history/trunk/howto/BuildConfigurations.html