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Align Behavior and Documentation About Jlink Compression

The jlink tool guide states that you can set compression level using the --compress option or its short form -c.

jlink --module-path $JAVA_HOME/jmods/ \
    --add-modules java.base \
    --compress=zip-1 \
    --output runtime

Furthermore, while not documented, a command like the one below produces a runtime image compressed with the deprecated compression level 2.

jlink --module-path $JAVA_HOME/jmods/ \
    --add-modules java.base \
    -c \
    --output runtime

Yet, prior to JDK 26, utilizing jlink with -c followed by an argument would result in an error. This behavior has been corrected in JDK 26 and running jlink with either --compress or -c produces the same result:

jlink --module-path $JAVA_HOME/jmods/ \
    --add-modules java.base \
    -c zip-1 \
    --output runtime

Call to Action

By aligning the behavior of -c and --compress for jlink, both options now require an argument. If you use jlink -c without specifying an argument for compression level, it is recommended to either select a level or omit the option altogether. In the latter case, the resulting runtime image will be compressed using the default compression level (zip-6).

This fix has been incorporated into the 26-ea mainline build available here. For more details on this change, check JDK-8321139.