-executable ( rejar= STORE | DEFLATE ) ( ',' strip= matcher ( ',' matcher )* )

When an executable JAR is created by the Project Launcher the compression is controlled with the -compression instruction. However, this über JAR contains bundles and JARs for the run path. Since executable JARs are sometimes used in embedded environments it is important that they are small and the code can loaded quickly. It is difficult to have defaults for this since there are many aspects:

• Speed of memory for accessing. I.e. RAM is faster than FLASH
• Cost of memory, FLASH is cheaper
• Speed of the CPU
• Number of cores
• Compression of the inner JARs
• Compression of the outer über JAR

In such a complex trade off there are no singular answers. This -executable instruction allows therefore to set the different options and then benchmark the result.

Hints

Experience shows that the size can be minimized by rejarring the inner bundles and JARs with the STORE compression but using DEFLATE for the outer/über JAR. This decreases the size because the compression algorithm then works on all class files of all bundles. This is much more efficient for the DEFLATE algorithm then compressing each class file on its own. Gains seen are 20%-30%.

rejar = (DEFLATE|STORE)

The rejar option in the -executable instruction can take the values STORE or DEFLATE. This will open the embedded JARs and write them in the given compression in the über JAR.

For example:

-executable: rejar=STORE

The default is to not touch the bundle.

strip= matcher ( ‘,’ matcher )*

The strip option can be used to strip resources from JARs embedded in the execetable. Its parameter can define a list of two GLOBs. The first GLOB must match the file name of the resource and the second GLOB must match the resource name in the bundle. GLOBs are separated with a colon (‘:’). If no colon is present then the first GLOB is assumed to be the wildcard GLOB that matches anything.

Syntax:

strip   ::=  matcher ( ',' matcher )*
matcher ::=  ( GLOB ':' ) GLOB

Some examples:

• *.map – Match all resources ending in .map
• OSGI-OPT/* – Remove the optional resources in bundle
• com.example.some.bundle.*:readme.md – Remove the readme’s from bundles withe file name matching com.example.some.bundle.*.

Note hat if you combine multiple GLOBs then you must separate them with a comma (‘,’) and that implies the total must be quoted with single or double quotes. If it is a single GLOB (pair) then quoting is optional. For example:

-executable: rejar=STORE, strip='OSGI-OPT,*.map'

The default is to not strip anything.

Signed Bundles

Rejarring and stripping should work for unsigned bundles since the signatures should not be affected by the compression algorithms used.