[GitHub] [ant] maartenc edited a comment on pull request #134: [WIP] Add the possibility to specify a custom filename mapper when creating an INDEX.LIST

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maartenc edited a comment on pull request #134:
URL: https://github.com/apache/ant/pull/134#issuecomment-671239026


   Hi @bodewig ,
   
   You are right, here is a bit more context of the problem.
   
   Our applications are installed like this:
   ```
   <some root dir>
       /Shared
           /org/apache/commons-io/commons-io-2.4.jar
           /org/apache/commons-lang/commons-lang-2.6.jar
           ...
       /ApplicationA
           main.jar
           lib1.jar
           lib2.jar
           ...
       /ApplicationB
           main.jar
           lib1.jar
           lib3.jar
       ...
   ```
   
   Our biggest application uses about 500 jars. To speed up classloading, we are adding an INDEX.LIST to main.jar.
   The INDEX.LIST spec says that the jar file paths in the INDEX.LIST should be relative to main.jar. So the INDEX.LIST should look like:
   
   ```
   JarIndex-Version: 1.0
   
   main.jar
   [...]
   
   lib1.jar
   [...]
   
   ../Shared/org/apache/commons-io/commons-io-2.4.jar
   [...]
   
   ../Shared/org/apache/commons-lang/commons-lang-2.6.jar
   [...]
   ```
   
   With the current Ant `<jar>` task, there are 2 possibilities to configure the jar file paths in the INDEX.LIST.
   1. if main.jar doesn't contain a `Class-Path` attribute (our use-case), all jar file paths are flattened.
   2. if main.jar does contain a `Class-Path` attribute, the jar file path is taken from that `Class-Path` attribute.
   
   Since we don't have a `Class-Path` attribute (which is intentionaly), we end up with a flatten path names in INDEX.LIST.
   
   A workaround could probably be to:
   1. add a `Class-Path` attribute to the MANIFEST.MF with the wanted mapping for INDEX.LIST
   2. generate the INDEX.LIST
   3. remove the `Class-Path` attribute from the MANIFEST.MF
   
   This is off course a suboptimal solution making the build script needlessly complex.
   
   The attached patch tries to address the issue by making it possible to specify a filename-mapper **inside** the `<indexjars>` element. If this mapper isn't specified, the default mapping (as specified above) is used. 
   
   ```
   <jar ...>
       <indexjars>
           <fileset dir="build/lib/**/*.jar"/>
           <firstmatchmapper>
               <globmapper from="${basedir}/build/lib/${application}/*" to="*" handledirsep="true" />
               <globmapper from="${basedir}/build/lib/Shared/*" to="../Shared/*" handledirsep="true"/>
           </firstmatchmapper>
       </indexjars>
   </jar>
   ```
   
   An alternative patch could be to add an extra mapper subelement to the `<jar>` task directly (and not inside the `<indexjars>` element), something like:
   
   ```
   <jar ...>
       <indexjars>
           <fileset dir="build/lib/**/*.jar"/>
       </indexjars>
       <indexjarsmapper>
           <firstmatchmapper>
               <globmapper from="${basedir}/build/lib/${application}/*" to="*" handledirsep="true" />
               <globmapper from="${basedir}/build/lib/Shared/*" to="../Shared/*" handledirsep="true"/>
           </firstmatchmapper>
       </indexjarsmapper>
   </jar>
   ```
   
   I think the first solutions results in a cleaner build.xml. But with perhaps a little bit more complex java code (and with a not 100% backwards compatible API change). But the second solution is also a possibility, I can create a new patch if you prefer that solution.
   
   Maarten


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