/* * Copyright (c) 2003, 2013, 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 * or visit www.oracle.com if you need additional information or have any * questions. */ 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; /** * 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();
 *    }
 * }
*

* 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. * * @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. *

* *

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. *

* *

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. *

* 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. *

* 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.) *

* 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. *

* (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.) *

* In order to maintain backward compatibility, the pack file's version is * set to accommodate the class files present in the input JAR file. In * other words, the pack file version will be the latest, if the class files * are the latest and conversely the pack file version will be the oldest * if the class file versions are also the oldest. For intermediate class * file versions the corresponding pack file version will be used. * For example: * If the input JAR-files are solely comprised of 1.5 (or lesser) * class files, a 1.5 compatible pack file is produced. This will also be * the case for archives that have no class files. * If the input JAR-files contains a 1.6 class file, then the pack file * version will be set to 1.6. *

* Note: Unless otherwise noted, passing a null argument to a * constructor or method in this class will cause a {@link NullPointerException} * to be thrown. *

* @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. *

* 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. *

* 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. *

* The default is -1, which means the packer will always create a single * segment output file. In cases where extremely large output files are * generated, users are strongly encouraged to use segmenting or break * up the input file into smaller JARs. *

* 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. *

* 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.) *

* 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. *

* 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. *

* 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. *

* 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. *

* The default is {@link #KEEP}, which preserves the input information, * but may cause the transmitted archive to be larger than necessary. *

* It is up to the unpacker implementation * to take action upon the hint to suitably compress the elements of * the resulting unpacked jar. *

* 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}. *

* This can marginally decrease the transmitted size of the * archive, at the expense of setting all installed files to a single * date. *

* If this property is set to the special string {@link #KEEP}, * the packer transmits a separate modification time for each input * element. *

* The default is {@link #KEEP}, which preserves the input information, * but may cause the transmitted archive to be larger than necessary. *

* 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. *

* There is no pathname transformation, except * that the system file separator is replaced by the JAR file * separator '/'. *

* The resulting file names must match exactly as strings with their * occurrences in the JAR file. *

* If a property value is a directory name, all files under that * directory will be passed also. *

* Examples: *

{@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/");
         * }
*/ 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}. *

* The string {@link #ERROR} means that the pack operation * as a whole will fail, with an exception of type IOException. * 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. *

* Examples: *

{@code
         *     Map p = pack200.getProperties();
         *     p.put(UNKNOWN_ATTRIBUTE, ERROR);
         *     p.put(UNKNOWN_ATTRIBUTE, STRIP);
         *     p.put(UNKNOWN_ATTRIBUTE, PASS);
         * }
*/ 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. *

* For example, the effect of this option is built in: * pack.class.attribute.SourceFile=RUH. *

* 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). *

* Code like this might be used to support attributes for JCOV: *


         *     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 like this might be used to strip debugging attributes: *


         *     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);
         * 
*/ 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: * pack.field.attribute.Deprecated=. * 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: * pack.method.attribute.Exceptions=NH[RCH]. * 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: * pack.code.attribute.LocalVariableTable=NH[PHOHRUHRSHH]. * 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. * Progress can be monitored by polling the value of this * property. *

* At a minimum, the unpacker must set progress to 0 * at the beginning of a packing operation, and to 100 * at the end. */ 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. * *

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. *

* Implementation specific properties are prefixed with a * package name associated with the implementor, beginning * with com. or a similar prefix. * All property names beginning with pack. and * unpack. are reserved for use by this API. *

* Unknown properties may be ignored or rejected with an * unspecified error, and invalid entries may cause an * unspecified error to be thrown. * *

* The returned map implements all optional {@link SortedMap} operations * @return A sorted association of property key strings to property * values. */ SortedMap properties(); /** * Takes a JarFile and converts it into a Pack200 archive. *

* 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. *

* Closes its input but not its output. (Pack200 archives are appendable.) *

* 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. * *

The default implementation of this method does nothing and has * no side-effects.

* *

WARNING: This method is omitted from the interface * declaration in all subset Profiles of Java SE that do not include * the {@code java.beans} package.

* @see #properties * @see #PROGRESS * @param listener An object to be invoked when a property is changed. * @deprecated The dependency on {@code PropertyChangeListener} creates * a significant impediment to future modularization of the * Java platform. This method will be removed in a future * release. * Applications that need to monitor progress of the packer * can poll the value of the {@link #PROGRESS PROGRESS} * property instead. */ @Deprecated default void addPropertyChangeListener(PropertyChangeListener listener) { } /** * Remove a listener for PropertyChange events, added by * the {@link #addPropertyChangeListener}. * *

The default implementation of this method does nothing and has * no side-effects.

* *

WARNING: This method is omitted from the interface * declaration in all subset Profiles of Java SE that do not include * the {@code java.beans} package.

* * @see #addPropertyChangeListener * @param listener The PropertyChange listener to be removed. * @deprecated The dependency on {@code PropertyChangeListener} creates * a significant impediment to future modularization of the * Java platform. This method will be removed in a future * release. */ @Deprecated default 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}. *

* Every JAR file produced by this engine will include the string * "PACK200" as a zip file comment. * This allows a deployer to detect if a JAR archive was packed and unpacked. *

* Note: Unless otherwise noted, passing a null argument to a * constructor or method in this class will cause a {@link NullPointerException} * to be thrown. *

* 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. * Progress can be monitored by polling the value of this * property. *

* At a minimum, the unpacker must set progress to 0 * at the beginning of a packing operation, and to 100 * at the end. */ 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. * *

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. *

* Implementation specific properties are prefixed with a * package name associated with the implementor, beginning * with com. or a similar prefix. * All property names beginning with pack. and * unpack. are reserved for use by this API. *

* 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 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. *

* 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. *

* 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. * *

The default implementation of this method does nothing and has * no side-effects.

* *

WARNING: This method is omitted from the interface * declaration in all subset Profiles of Java SE that do not include * the {@code java.beans} package.

* * @see #properties * @see #PROGRESS * @param listener An object to be invoked when a property is changed. * @deprecated The dependency on {@code PropertyChangeListener} creates * a significant impediment to future modularization of the * Java platform. This method will be removed in a future * release. * Applications that need to monitor progress of the * unpacker can poll the value of the {@link #PROGRESS * PROGRESS} property instead. */ @Deprecated default void addPropertyChangeListener(PropertyChangeListener listener) { } /** * Remove a listener for PropertyChange events, added by * the {@link #addPropertyChangeListener}. * *

The default implementation of this method does nothing and has * no side-effects.

* *

WARNING: This method is omitted from the interface * declaration in all subset Profiles of Java SE that do not include * the {@code java.beans} package.

* * @see #addPropertyChangeListener * @param listener The PropertyChange listener to be removed. * @deprecated The dependency on {@code PropertyChangeListener} creates * a significant impediment to future modularization of the * Java platform. This method will be removed in a future * release. */ @Deprecated default 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 = (PACK_PROVIDER.equals(prop))? 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); // Android-changed: Remove default Packer Impl. // // else if (PACK_PROVIDER.equals(prop)) // 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); } } }