[MWAR-446] Add an option to put libs in STORED mode (instead of DEFLATED)

[jira-importer]

Gaël Lalire opened MWAR-446 and commented

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Issue Links:

• MEAR-306 Add an option to put libs in STORED mode (instead of DEFLATED)

[jira-importer]

Michael Osipov commented

What about https://maven.apache.org/plugins/maven-war-plugin/war-mojo.html#recompressZippedFiles?

[jira-importer]

Michael Osipov commented

I expect this to work: https://codehaus-plexus.github.io/plexus-archiver/xref/org/codehaus/plexus/archiver/zip/ConcurrentJarCreator.html#L264

[jira-importer]

Gaël Lalire commented

recompressZippedFiles does not seems to do anything (at least for Maven dependencies, I don't know if you put a zip in src/main/resources).

Tested with 3.3.2 at https://github.com/vestige-java-app/mywar/tree/testRecompressOption with false and true value, the dependencies are always deflated.

[jira-importer]

Michael Osipov commented

Thanks, I reproducer is always good. I will take a look.

[jira-importer]

Michael Osipov commented

I did a bit of analysis. The issue is not in Plexus Archiver because there is a test which guarantees that ZIP types aren't recompressed:

$ zipinfo dont-recompress-added-zips.zip
Archive:  dont-recompress-added-zips.zip
Zip file size: 3368 bytes, number of entries: 5
-rw-r--r--  2.0 unx      383 b- defN 21-Dec-19 15:02 test.tar.gz
-rw-r--r--  2.0 unx      157 b- stor 21-Dec-19 15:02 test.zip
-rw-r--r--  2.0 unx      167 b- stor 21-Dec-19 15:02 namelessrootfolder.jar
-rw-r--r--  2.0 unx     1070 b- stor 21-Dec-19 15:02 test.jar
-rwxr-xr-x  2.0 unx     1070 b- stor 21-Dec-19 15:02 test.rar
5 files, 2847 bytes uncompressed, 2852 bytes compressed:  -0.2%

So the bug must be either in MWAR or MARCHIVER.

[jira-importer]

Michael Osipov commented

Just debugged, the ConcurrentJarCreator is never used here. I assume that this class is only used for JARs...

[elharo]

Issue Overview & Context

This issue (originally MWAR-446, GitHub issue #526) requests an enhancement to allow library dependencies (.jar files in WEB-INF/lib) to be packaged into the WAR using the ZIP STORED method (0% compression) rather than the default DEFLATED method.

Because .jar files are already compressed archives, applying DEFLATED compression to them a second time during the WAR packaging phase yields negligible file size reduction and wastes CPU cycles. More importantly, when nested JARs are STORED rather than DEFLATED, specialized classloaders and execution environments can memory-map and read the nested archives directly from disk via byte offsets, eliminating the overhead of extracting them to a temporary file system directory at runtime.

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Is it still accurate?

Yes, the technical description is accurate.

The maven-war-plugin delegates archive creation to maven-archiver and plexus-archiver. By default, these components compress all files added to the archive unless instructed otherwise. Currently, the WAR plugin does not expose granular configuration to selectively apply the STORED method specifically to the WEB-INF/lib payload while retaining DEFLATED compression for text-based resources (such as HTML, CSS, JS, and XML files).

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Should it be fixed or closed?

It should be fixed.

Reasons to Implement:

1. Build Performance: Skipping the deflation phase for already-compressed binary files reduces CPU utilization and speeds up the packaging phase of the build, particularly for large applications with numerous dependencies.
2. Runtime Efficiency: STORED nested JARs enable zero-copy operations and direct classloading. This is a proven architectural optimization utilized extensively by modern frameworks (e.g., Spring Boot's fat JAR packaging requires nested libraries to be STORED to function efficiently).
3. Ecosystem Consistency: Similar optimizations have been requested or implemented in related Apache Maven plugins (such as maven-ear-plugin via MEAR-306). Providing this functionality in the WAR plugin brings it up to par with modern Java packaging requirements.

[elharo]

The underlying plexus-archiver already possesses a setRecompressAddedZips(boolean) method designed specifically to prevent the redundant compression of archive files.

The maven-war-plugin can expose this as a direct configuration parameter. By setting this to false, the plugin would instruct the archiver to use the STORED method for any file it identifies as a ZIP-based archive (including .jar files).

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-war-plugin</artifactId>
    <version>3.4.0</version>
    <configuration>
        <!-- Instructs the archiver to use STORED for nested archives -->
        <recompressZippedFiles>false</recompressZippedFiles>
    </configuration>
</plugin>

Backward compatibility is maintained by defaulting the parameter to true.