/*
* Copyright (c) 2003, 2006, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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*/
package java.util.jar;
import java.util.SortedMap;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.File;
import java.io.IOException;
import java.beans.PropertyChangeListener;
import java.beans.PropertyChangeEvent;
import java.security.AccessController;
import java.security.PrivilegedAction;
/**
* Transforms a JAR file to or from a packed stream in Pack200 format.
* Please refer to Network Transfer Format JSR 200 Specification at
* <a href=http://jcp.org/aboutJava/communityprocess/review/jsr200/index.html>http://jcp.org/aboutJava/communityprocess/review/jsr200/index.html</a>
* <p>
* 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.
* <p>
* Here is an example using packer and unpacker:<p>
* <blockquote><pre>
* 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();
* }
* </pre></blockquote>
* <p>
* 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 <a href="{@docRoot}/../technotes/guides/deployment/deployment-guide/pack200.html">Java Deployment Guide</a> for more details and
* techniques.
* <p>
* Unless otherwise noted, passing a <tt>null</tt> argument to a constructor or
* method in this class will cause a {@link NullPointerException} to be thrown.
*
* @author John Rose
* @author Kumar Srinivasan
* @since 1.5
*/
public abstract class Pack200 {
private Pack200() {} //prevent instantiation
// Static methods of the Pack200 class.
/**
* Obtain new instance of a class that implements Packer.
*
* <li><p>If the system property <tt>java.util.jar.Pack200.Packer</tt>
* 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.</p></li>
*
* <li><p>If an implementation has not been specified with the system
* property, then the system-default implementation class is instantiated,
* and the result is returned.</p></li>
*
* <p>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 A newly allocated Packer engine.
*/
public synchronized static Packer newPacker() {
return (Packer) newInstance(PACK_PROVIDER);
}
/**
* Obtain new instance of a class that implements Unpacker.
*
* <li><p>If the system property <tt>java.util.jar.Pack200.Unpacker</tt>
* 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.</p></li>
*
* <li><p>If an implementation has not been specified with the
* system property, then the system-default implementation class
* is instantiated, and the result is returned.</p></li>
*
* <p>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 A newly allocated Unpacker engine.
*/
public static Unpacker newUnpacker() {
return (Unpacker) newInstance(UNPACK_PROVIDER);
}
// Interfaces
/**
* 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. An instance of the engine can be obtained
* using {@link #newPacker}.
* The high degree of compression is achieved
* by using a number of techniques described in the JSR 200 specification.
* Some of the techniques are sorting, re-ordering and co-location of the
* constant pool.
* <p>
* The pack engine is initialized to an initial state as described
* by their properties below.
* The initial state can be manipulated by getting the
* engine properties (using {@link #properties}) and storing
* the modified properties on the map.
* The resource files will be passed through with no changes at all.
* The class files will not contain identical bytes, since the unpacker
* is free to change minor class file features such as constant pool order.
* However, the class files will be semantically identical,
* as specified in the Java Virtual Machine Specification
* <a href="http://java.sun.com/docs/books/vmspec/html/ClassFile.doc.html">http://java.sun.com/docs/books/vmspec/html/ClassFile.doc.html</a>.
* <p>
* By default, the packer does not change the order of JAR elements.
* Also, the modification time and deflation hint of each
* JAR element is passed unchanged.
* (Any other ZIP-archive information, such as extra attributes
* giving Unix file permissions, are lost.)
* <p>
* Note that packing and unpacking a JAR will in general alter the
* bytewise contents of classfiles in the JAR. This means that packing
* and unpacking will in general invalidate any digital signatures
* which rely on bytewise images of JAR elements. In order both to sign
* and to pack a JAR, you must first pack and unpack the JAR to
* "normalize" it, then compute signatures on the unpacked JAR elements,
* and finally repack the signed JAR.
* Both packing steps should
* use precisely the same options, and the segment limit may also
* need to be set to "-1", to prevent accidental variation of segment
* boundaries as class file sizes change slightly.
* <p>
* (Here's why this works: Any reordering the packer does
* of any classfile structures is idempotent, so the second packing
* does not change the orderings produced by the first packing.
* Also, the unpacker is guaranteed by the JSR 200 specification
* to produce a specific bytewise image for any given transmission
* ordering of archive elements.)
* <p>
* In order to maintain backward compatibility, if the input JAR-files are
* solely comprised of 1.5 (or lesser) classfiles, a 1.5 compatible
* pack file is produced. Otherwise a 1.6 compatible pack200 file is
* produced.
* <p>
* @since 1.5
*/
public interface Packer {
/**
* This property is a numeral giving the estimated target size N
* (in bytes) of each archive segment.
* If a single input file requires more than N bytes,
* it will be given its own archive segment.
* <p>
* As a special case, a value of -1 will produce a single large
* segment with all input files, while a value of 0 will
* produce one segment for each class.
* Larger archive segments result in less fragmentation and
* better compression, but processing them requires more memory.
* <p>
* The size of each segment is estimated by counting the size of each
* input file to be transmitted in the segment, along with the size
* of its name and other transmitted properties.
* <p>
* The default is 1000000 (a million bytes). This allows input JAR files
* of moderate size to be transmitted in one segment. It also puts
* a limit on memory requirements for packers and unpackers.
* <p>
* A 10Mb JAR packed without this limit will
* typically pack about 10% smaller, but the packer may require
* a larger Java heap (about ten times the segment limit).
*/
String SEGMENT_LIMIT = "pack.segment.limit";
/**
* If this property is set to {@link #TRUE}, the packer will transmit
* all elements in their original order within the source archive.
* <p>
* If it is set to {@link #FALSE}, the packer may reorder elements,
* and also remove JAR directory entries, which carry no useful
* information for Java applications.
* (Typically this enables better compression.)
* <p>
* The default is {@link #TRUE}, which preserves the input information,
* but may cause the transmitted archive to be larger than necessary.
*/
String KEEP_FILE_ORDER = "pack.keep.file.order";
/**
* If this property is set to a single decimal digit, the packer will
* use the indicated amount of effort in compressing the archive.
* Level 1 may produce somewhat larger size and faster compression speed,
* while level 9 will take much longer but may produce better compression.
* <p>
* The special value 0 instructs the packer to copy through the
* original JAR file directly, with no compression. The JSR 200
* standard requires any unpacker to understand this special case
* as a pass-through of the entire archive.
* <p>
* The default is 5, investing a modest amount of time to
* produce reasonable compression.
*/
String EFFORT = "pack.effort";
/**
* If this property is set to {@link #TRUE} or {@link #FALSE}, the packer
* will set the deflation hint accordingly in the output archive, and
* will not transmit the individual deflation hints of archive elements.
* <p>
* If this property is set to the special string {@link #KEEP}, the packer
* will attempt to determine an independent deflation hint for each
* available element of the input archive, and transmit this hint separately.
* <p>
* The default is {@link #KEEP}, which preserves the input information,
* but may cause the transmitted archive to be larger than necessary.
* <p>
* It is up to the unpacker implementation
* to take action upon the hint to suitably compress the elements of
* the resulting unpacked jar.
* <p>
* The deflation hint of a ZIP or JAR element indicates
* whether the element was deflated or stored directly.
*/
String DEFLATE_HINT = "pack.deflate.hint";
/**
* If this property is set to the special string {@link #LATEST},
* the packer will attempt to determine the latest modification time,
* among all the available entries in the original archive or the latest
* modification time of all the available entries in each segment.
* This single value will be transmitted as part of the segment and applied
* to all the entries in each segment, {@link #SEGMENT_LIMIT}.
* <p>
* This can marginally decrease the transmitted size of the
* archive, at the expense of setting all installed files to a single
* date.
* <p>
* If this property is set to the special string {@link #KEEP},
* the packer transmits a separate modification time for each input
* element.
* <p>
* The default is {@link #KEEP}, which preserves the input information,
* but may cause the transmitted archive to be larger than necessary.
* <p>
* It is up to the unpacker implementation to take action to suitably
* set the modification time of each element of its output file.
* @see #SEGMENT_LIMIT
*/
String MODIFICATION_TIME = "pack.modification.time";
/**
* Indicates that a file should be passed through bytewise, with no
* compression. Multiple files may be specified by specifying
* additional properties with distinct strings appended, to
* make a family of properties with the common prefix.
* <p>
* There is no pathname transformation, except
* that the system file separator is replaced by the JAR file
* separator '/'.
* <p>
* The resulting file names must match exactly as strings with their
* occurrences in the JAR file.
* <p>
* If a property value is a directory name, all files under that
* directory will be passed also.
* <p>
* Examples:
* <pre><code>
* Map p = packer.properties();
* p.put(PASS_FILE_PFX+0, "mutants/Rogue.class");
* p.put(PASS_FILE_PFX+1, "mutants/Wolverine.class");
* p.put(PASS_FILE_PFX+2, "mutants/Storm.class");
* # Pass all files in an entire directory hierarchy:
* p.put(PASS_FILE_PFX+3, "police/");
* </pre></code>.
*/
String PASS_FILE_PFX = "pack.pass.file.";
/// Attribute control.
/**
* Indicates the action to take when a class-file containing an unknown
* attribute is encountered. Possible values are the strings {@link #ERROR},
* {@link #STRIP}, and {@link #PASS}.
* <p>
* The string {@link #ERROR} means that the pack operation
* as a whole will fail, with an exception of type <code>IOException</code>.
* The string
* {@link #STRIP} means that the attribute will be dropped.
* The string
* {@link #PASS} means that the whole class-file will be passed through
* (as if it were a resource file) without compression, with a suitable warning.
* This is the default value for this property.
* <p>
* Examples:
* <pre><code>
* Map p = pack200.getProperties();
* p.put(UNKNOWN_ATTRIBUTE, ERROR);
* p.put(UNKNOWN_ATTRIBUTE, STRIP);
* p.put(UNKNOWN_ATTRIBUTE, PASS);
* </pre></code>
*/
String UNKNOWN_ATTRIBUTE = "pack.unknown.attribute";
/**
* When concatenated with a class attribute name,
* indicates the format of that attribute,
* using the layout language specified in the JSR 200 specification.
* <p>
* For example, the effect of this option is built in:
* <code>pack.class.attribute.SourceFile=RUH</code>.
* <p>
* The special strings {@link #ERROR}, {@link #STRIP}, and {@link #PASS} are
* also allowed, with the same meaning as {@link #UNKNOWN_ATTRIBUTE}.
* This provides a way for users to request that specific attributes be
* refused, stripped, or passed bitwise (with no class compression).
* <p>
* Code like this might be used to support attributes for JCOV:
* <pre><code>
* Map p = packer.properties();
* p.put(CODE_ATTRIBUTE_PFX+"CoverageTable", "NH[PHHII]");
* p.put(CODE_ATTRIBUTE_PFX+"CharacterRangeTable", "NH[PHPOHIIH]");
* p.put(CLASS_ATTRIBUTE_PFX+"SourceID", "RUH");
* p.put(CLASS_ATTRIBUTE_PFX+"CompilationID", "RUH");
* </code></pre>
* <p>
* Code like this might be used to strip debugging attributes:
* <pre><code>
* Map p = packer.properties();
* p.put(CODE_ATTRIBUTE_PFX+"LineNumberTable", STRIP);
* p.put(CODE_ATTRIBUTE_PFX+"LocalVariableTable", STRIP);
* p.put(CLASS_ATTRIBUTE_PFX+"SourceFile", STRIP);
* </code></pre>
*/
String CLASS_ATTRIBUTE_PFX = "pack.class.attribute.";
/**
* When concatenated with a field attribute name,
* indicates the format of that attribute.
* For example, the effect of this option is built in:
* <code>pack.field.attribute.Deprecated=</code>.
* The special strings {@link #ERROR}, {@link #STRIP}, and
* {@link #PASS} are also allowed.
* @see #CLASS_ATTRIBUTE_PFX
*/
String FIELD_ATTRIBUTE_PFX = "pack.field.attribute.";
/**
* When concatenated with a method attribute name,
* indicates the format of that attribute.
* For example, the effect of this option is built in:
* <code>pack.method.attribute.Exceptions=NH[RCH]</code>.
* The special strings {@link #ERROR}, {@link #STRIP}, and {@link #PASS}
* are also allowed.
* @see #CLASS_ATTRIBUTE_PFX
*/
String METHOD_ATTRIBUTE_PFX = "pack.method.attribute.";
/**
* When concatenated with a code attribute name,
* indicates the format of that attribute.
* For example, the effect of this option is built in:
* <code>pack.code.attribute.LocalVariableTable=NH[PHOHRUHRSHH]</code>.
* The special strings {@link #ERROR}, {@link #STRIP}, and {@link #PASS}
* are also allowed.
* @see #CLASS_ATTRIBUTE_PFX
*/
String CODE_ATTRIBUTE_PFX = "pack.code.attribute.";
/**
* The unpacker's progress as a percentage, as periodically
* updated by the unpacker.
* Values of 0 - 100 are normal, and -1 indicates a stall.
* Observe this property with a {@link PropertyChangeListener}.
* <p>
* At a minimum, the unpacker must set progress to 0
* at the beginning of a packing operation, and to 100
* at the end.
* @see #addPropertyChangeListener
*/
String PROGRESS = "pack.progress";
/** The string "keep", a possible value for certain properties.
* @see #DEFLATE_HINT
* @see #MODIFICATION_TIME
*/
String KEEP = "keep";
/** The string "pass", a possible value for certain properties.
* @see #UNKNOWN_ATTRIBUTE
* @see #CLASS_ATTRIBUTE_PFX
* @see #FIELD_ATTRIBUTE_PFX
* @see #METHOD_ATTRIBUTE_PFX
* @see #CODE_ATTRIBUTE_PFX
*/
String PASS = "pass";
/** The string "strip", a possible value for certain properties.
* @see #UNKNOWN_ATTRIBUTE
* @see #CLASS_ATTRIBUTE_PFX
* @see #FIELD_ATTRIBUTE_PFX
* @see #METHOD_ATTRIBUTE_PFX
* @see #CODE_ATTRIBUTE_PFX
*/
String STRIP = "strip";
/** The string "error", a possible value for certain properties.
* @see #UNKNOWN_ATTRIBUTE
* @see #CLASS_ATTRIBUTE_PFX
* @see #FIELD_ATTRIBUTE_PFX
* @see #METHOD_ATTRIBUTE_PFX
* @see #CODE_ATTRIBUTE_PFX
*/
String ERROR = "error";
/** The string "true", a possible value for certain properties.
* @see #KEEP_FILE_ORDER
* @see #DEFLATE_HINT
*/
String TRUE = "true";
/** The string "false", a possible value for certain properties.
* @see #KEEP_FILE_ORDER
* @see #DEFLATE_HINT
*/
String FALSE = "false";
/** The string "latest", a possible value for certain properties.
* @see #MODIFICATION_TIME
*/
String LATEST = "latest";
/**
* Get the set of this engine's properties.
* This set is a "live view", so that changing its
* contents immediately affects the Packer engine, and
* changes from the engine (such as progress indications)
* are immediately visible in the map.
*
* <p>The property map may contain pre-defined implementation
* specific and default properties. Users are encouraged to
* read the information and fully understand the implications,
* before modifying pre-existing properties.
* <p>
* Implementation specific properties are prefixed with a
* package name associated with the implementor, beginning
* with <tt>com.</tt> or a similar prefix.
* All property names beginning with <tt>pack.</tt> and
* <tt>unpack.</tt> are reserved for use by this API.
* <p>
* Unknown properties may be ignored or rejected with an
* unspecified error, and invalid entries may cause an
* unspecified error to be thrown.
*
* <p>
* The returned map implements all optional {@link SortedMap} operations
* @return A sorted association of property key strings to property
* values.
*/
SortedMap<String,String> properties();
/**
* Takes a JarFile and converts it into a Pack200 archive.
* <p>
* Closes its input but not its output. (Pack200 archives are appendable.)
* @param in a JarFile
* @param out an OutputStream
* @exception IOException if an error is encountered.
*/
void pack(JarFile in, OutputStream out) throws IOException ;
/**
* Takes a JarInputStream and converts it into a Pack200 archive.
* <p>
* Closes its input but not its output. (Pack200 archives are appendable.)
* <p>
* The modification time and deflation hint attributes are not available,
* for the JAR manifest file and its containing directory.
*
* @see #MODIFICATION_TIME
* @see #DEFLATE_HINT
* @param in a JarInputStream
* @param out an OutputStream
* @exception IOException if an error is encountered.
*/
void pack(JarInputStream in, OutputStream out) throws IOException ;
/**
* Registers a listener for PropertyChange events on the properties map.
* This is typically used by applications to update a progress bar.
*
* @see #properties
* @see #PROGRESS
* @param listener An object to be invoked when a property is changed.
*/
void addPropertyChangeListener(PropertyChangeListener listener) ;
/**
* Remove a listener for PropertyChange events, added by
* the {@link #addPropertyChangeListener}.
*
* @see #addPropertyChangeListener
* @param listener The PropertyChange listener to be removed.
*/
void removePropertyChangeListener(PropertyChangeListener listener);
}
/**
* The unpacker engine converts the packed stream to a JAR file.
* An instance of the engine can be obtained
* using {@link #newUnpacker}.
* <p>
* Every JAR file produced by this engine will include the string
* "<tt>PACK200</tt>" as a zip file comment.
* This allows a deployer to detect if a JAR archive was packed and unpacked.
* <p>
* This version of the unpacker is compatible with all previous versions.
* @since 1.5
*/
public interface Unpacker {
/** The string "keep", a possible value for certain properties.
* @see #DEFLATE_HINT
*/
String KEEP = "keep";
/** The string "true", a possible value for certain properties.
* @see #DEFLATE_HINT
*/
String TRUE = "true";
/** The string "false", a possible value for certain properties.
* @see #DEFLATE_HINT
*/
String FALSE = "false";
/**
* Property indicating that the unpacker should
* ignore all transmitted values for DEFLATE_HINT,
* replacing them by the given value, {@link #TRUE} or {@link #FALSE}.
* The default value is the special string {@link #KEEP},
* which asks the unpacker to preserve all transmitted
* deflation hints.
*/
String DEFLATE_HINT = "unpack.deflate.hint";
/**
* The unpacker's progress as a percentage, as periodically
* updated by the unpacker.
* Values of 0 - 100 are normal, and -1 indicates a stall.
* Observe this property with a {@link PropertyChangeListener}.
* <p>
* At a minimum, the unpacker must set progress to 0
* at the beginning of a packing operation, and to 100
* at the end.
* @see #addPropertyChangeListener
*/
String PROGRESS = "unpack.progress";
/**
* Get the set of this engine's properties. This set is
* a "live view", so that changing its
* contents immediately affects the Packer engine, and
* changes from the engine (such as progress indications)
* are immediately visible in the map.
*
* <p>The property map may contain pre-defined implementation
* specific and default properties. Users are encouraged to
* read the information and fully understand the implications,
* before modifying pre-existing properties.
* <p>
* Implementation specific properties are prefixed with a
* package name associated with the implementor, beginning
* with <tt>com.</tt> or a similar prefix.
* All property names beginning with <tt>pack.</tt> and
* <tt>unpack.</tt> are reserved for use by this API.
* <p>
* Unknown properties may be ignored or rejected with an
* unspecified error, and invalid entries may cause an
* unspecified error to be thrown.
*
* @return A sorted association of option key strings to option values.
*/
SortedMap<String,String> properties();
/**
* Read a Pack200 archive, and write the encoded JAR to
* a JarOutputStream.
* The entire contents of the input stream will be read.
* It may be more efficient to read the Pack200 archive
* to a file and pass the File object, using the alternate
* method described below.
* <p>
* Closes its input but not its output. (The output can accumulate more elements.)
* @param in an InputStream.
* @param out a JarOutputStream.
* @exception IOException if an error is encountered.
*/
void unpack(InputStream in, JarOutputStream out) throws IOException;
/**
* Read a Pack200 archive, and write the encoded JAR to
* a JarOutputStream.
* <p>
* Does not close its output. (The output can accumulate more elements.)
* @param in a File.
* @param out a JarOutputStream.
* @exception IOException if an error is encountered.
*/
void unpack(File in, JarOutputStream out) throws IOException;
/**
* Registers a listener for PropertyChange events on the properties map.
* This is typically used by applications to update a progress bar.
*
* @see #properties
* @see #PROGRESS
* @param listener An object to be invoked when a property is changed.
*/
void addPropertyChangeListener(PropertyChangeListener listener) ;
/**
* Remove a listener for PropertyChange events, added by
* the {@link #addPropertyChangeListener}.
*
* @see #addPropertyChangeListener
* @param listener The PropertyChange listener to be removed.
*/
void removePropertyChangeListener(PropertyChangeListener listener);
}
// Private stuff....
private static final String PACK_PROVIDER = "java.util.jar.Pack200.Packer";
private static final String UNPACK_PROVIDER = "java.util.jar.Pack200.Unpacker";
private static Class packerImpl;
private static Class unpackerImpl;
private synchronized static Object newInstance(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 = 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);
}
}
}