Pack200public abstract class Pack200 extends Object | Transforms a JAR file to or from a packed stream in Pack200 format.
Please refer to Network Trasfer 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:
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();
}
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 {@link NullPointerException} to be thrown. |
| Fields Summary |
|---|
| private static final String | PACK_PROVIDER | | private static final String | UNPACK_PROVIDER | | private static Class | packerImpl | | private static Class | unpackerImpl |
| Constructors Summary |
|---|
private Pack200()
|
| Methods Summary |
|---|
| private static synchronized java.lang.Object | newInstance(java.lang.String prop)
String implName = "(unknown)";
try {
Class impl = (prop == PACK_PROVIDER)? packerImpl: unpackerImpl;
if (impl == null) {
// The first time, we must decide which class to use.
implName = (String)
java.security.AccessController.doPrivileged
(new sun.security.action.GetPropertyAction(prop,""));
if (implName != null && !implName.equals(""))
impl = Class.forName(implName);
else if (prop == PACK_PROVIDER)
impl = com.sun.java.util.jar.pack.PackerImpl.class;
else
impl = com.sun.java.util.jar.pack.UnpackerImpl.class;
}
// We have a class. Now instantiate it.
return impl.newInstance();
} catch (ClassNotFoundException e) {
throw new Error("Class not found: " + implName +
":\ncheck property " + prop +
" in your properties file.", e);
} catch (InstantiationException e) {
throw new Error("Could not instantiate: " + implName +
":\ncheck property " + prop +
" in your properties file.", e);
} catch (IllegalAccessException e) {
throw new Error("Cannot access class: " + implName +
":\ncheck property " + prop +
" in your properties file.", e);
}
| | public static synchronized java.util.jar.Pack200$Packer | newPacker()Obtain new instance of a class that implements Packer.
If the system property java.util.jar.Pack200.Packer
is defined, then the value is taken to be the fully-qualified name
of a concrete implementation class, which must implement Packer.
This class is loaded and instantiated. If this process fails
then an unspecified error is thrown.
If an implementation has not been specified with the system
property, then the system-default implementation class is instantiated,
and the result is returned.
Note: The returned object is not guaranteed to operate
correctly if multiple threads use it at the same time.
A multi-threaded application should either allocate multiple
packer engines, or else serialize use of one engine with a lock.
return (Packer) newInstance(PACK_PROVIDER);
| | public static java.util.jar.Pack200$Unpacker | newUnpacker()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 (Unpacker) newInstance(UNPACK_PROVIDER);
|
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