Pack200
abstract class Pack200
kotlin.Any | |
↳ | java.util.jar.Pack200 |
Transforms a JAR file to or from a packed stream in Pack200 format. Please refer to Network Transfer Format JSR 200 Specification at http://jcp.org/aboutJava/communityprocess/review/jsr200/index.html
Typically the packer engine is used by application developers to deploy or host JAR files on a website. The unpacker engine is used by deployment applications to transform the byte-stream back to JAR format.
Here is an example using packer and unpacker:
<code>import java.util.jar.Pack200; import java.util.jar.Pack200.*; ... // Create the Packer object Packer packer = Pack200.newPacker(); // Initialize the state by setting the desired properties Map p = packer.properties(); // take more time choosing codings for better compression p.put(Packer.EFFORT, "7"); // default is "5" // use largest-possible archive segments (>10% better compression). p.put(Packer.SEGMENT_LIMIT, "-1"); // reorder files for better compression. p.put(Packer.KEEP_FILE_ORDER, Packer.FALSE); // smear modification times to a single value. p.put(Packer.MODIFICATION_TIME, Packer.LATEST); // ignore all JAR deflation requests, // transmitting a single request to use "store" mode. p.put(Packer.DEFLATE_HINT, Packer.FALSE); // discard debug attributes p.put(Packer.CODE_ATTRIBUTE_PFX+"LineNumberTable", Packer.STRIP); // throw an error if an attribute is unrecognized p.put(Packer.UNKNOWN_ATTRIBUTE, Packer.ERROR); // pass one class file uncompressed: p.put(Packer.PASS_FILE_PFX+0, "mutants/Rogue.class"); try { JarFile jarFile = new JarFile("/tmp/testref.jar"); FileOutputStream fos = new FileOutputStream("/tmp/test.pack"); // Call the packer packer.pack(jarFile, fos); jarFile.close(); fos.close(); File f = new File("/tmp/test.pack"); FileOutputStream fostream = new FileOutputStream("/tmp/test.jar"); JarOutputStream jostream = new JarOutputStream(fostream); Unpacker unpacker = Pack200.newUnpacker(); // Call the unpacker unpacker.unpack(f, jostream); // Must explicitly close the output. jostream.close(); } catch (IOException ioe) { ioe.printStackTrace(); } </code>
A Pack200 file compressed with gzip can be hosted on HTTP/1.1 web servers. The deployment applications can use "Accept-Encoding=pack200-gzip". This indicates to the server that the client application desires a version of the file encoded with Pack200 and further compressed with gzip. Please refer to Java Deployment Guide for more details and techniques.
Unless otherwise noted, passing a null argument to a constructor or method in this class will cause a NullPointerException
to be thrown.
Summary
Nested classes | |
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abstract |
The packer engine applies various transformations to the input JAR file, making the pack stream highly compressible by a compressor such as gzip or zip. |
abstract |
The unpacker engine converts the packed stream to a JAR file. |
Public methods | |
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open static Pack200.Packer! |
Obtain new instance of a class that implements Packer. |
open static Pack200.Unpacker! |
Obtain new instance of a class that implements Unpacker. |
Public methods
newPacker
open static fun newPacker(): Pack200.Packer!
Obtain new instance of a class that implements Packer.
- If the system property java.util.jar.Pack200.Packer is defined, then the value is taken to be the fully-qualified name of a concrete implementation class, which must implement Packer. This class is loaded and instantiated. If this process fails then an unspecified error is thrown.
- If an implementation has not been specified with the system property, then the system-default implementation class is instantiated, and the result is returned.
Note: The returned object is not guaranteed to operate correctly if multiple threads use it at the same time. A multi-threaded application should either allocate multiple packer engines, or else serialize use of one engine with a lock.
Return | |
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Pack200.Packer! |
A newly allocated Packer engine. |
newUnpacker
open static fun newUnpacker(): Pack200.Unpacker!
Obtain new instance of a class that implements Unpacker.
- If the system property java.util.jar.Pack200.Unpacker is defined, then the value is taken to be the fully-qualified name of a concrete implementation class, which must implement Unpacker. The class is loaded and instantiated. If this process fails then an unspecified error is thrown.
- If an implementation has not been specified with the system property, then the system-default implementation class is instantiated, and the result is returned.
Note: The returned object is not guaranteed to operate correctly if multiple threads use it at the same time. A multi-threaded application should either allocate multiple unpacker engines, or else serialize use of one engine with a lock.
Return | |
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Pack200.Unpacker! |
A newly allocated Unpacker engine. |