1 <?xml version="1.0"?> 2 <!-- 3 4 Licensed to the Apache Software Foundation (ASF) under one or more 5 contributor license agreements. See the NOTICE file distributed with 6 this work for additional information regarding copyright ownership. 7 The ASF licenses this file to You under the Apache License, Version 2.0 8 (the "License"); you may not use this file except in compliance with 9 the License. You may obtain a copy of the License at 10 11 http://www.apache.org/licenses/LICENSE-2.0 12 13 Unless required by applicable law or agreed to in writing, software 14 distributed under the License is distributed on an "AS IS" BASIS, 15 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 16 See the License for the specific language governing permissions and 17 limitations under the License. 18 19 --> 20 <document> 21 <properties> 22 <title>Commons Compress Pack200 Package</title> 23 <author email="dev (a] commons.apache.org">Commons Documentation Team</author> 24 </properties> 25 <body> 26 <section name="The Pack200 package"> 27 28 <p>The Pack200 algorithm is not a general purpose compression 29 algorithm but one specialized for compressing JAR archives. JAR 30 archives compressed with Pack200 will in general be different 31 from the original archive when decompressed again. More 32 information can be found in the Javadocs of the <a 33 href="https://docs.oracle.com/javase/7/docs/api/java/util/jar/Pack200.Packer.html">Pack200.Packer 34 class</a>.</p> 35 36 <p>While the <code>pack200</code> command line utility of the 37 JDK creates GZip compressed archives (<code>.pack.gz</code>) by 38 default, the streams provided by the Pack200 package only 39 perform the actual Pack200 operation. Wrap them in an 40 additional <code>GzipCompressor(In|Out)putStream</code> in order to deal 41 with deflated streams.</p> 42 43 <subsection name="Pack200Strategy"> 44 45 <p>The Pack200-API provided by the java class library is not 46 streaming friendly as it wants to consume its input completely 47 in a single operation. Because of this 48 <code>Pack200CompressorInputStream</code>'s constructor will immediately 49 unpack the stream, cache the results and provide an input 50 stream to the cache.</p> 51 52 <p><code>Pack200CompressorOutputStream</code> will cache all data that 53 is written to it and then pack it once the <code>finish</code> 54 or <code>close</code> method is called.</p> 55 56 <p>Two different caching modes are available - "in memory", 57 which is the default, and "temporary file". By default data 58 is cached in memory but you should switch to the temporary 59 file option if your archives are really big.</p> 60 61 <p>Given there always is an intermediate result 62 the <code>getBytesRead</code> and <code>getCount</code> 63 methods of <code>Pack200CompressorInputStream</code> are 64 meaningless (read from the real stream or from the 65 intermediate result?) and always return 0.</p> 66 67 </subsection> 68 69 <subsection name="Normalization"> 70 71 <p>As a pack/unpack cycle may create a JAR archive that is 72 different from the original, digital signatures created for 73 the initial JAR will be broken by the process. There is a way 74 to "normalize" JAR archives prior to packing them that ensures 75 signatures applied to the "normalized" JAR will still be valid 76 aftre a pack/unpack cycle - see <a 77 href="https://download.oracle.com/javase/7/docs/api/java/util/jar/Pack200.Packer.html">Pack200.Packer</a>'s 78 javadocs.</p> 79 80 <p>The <code>Pack200Utils</code> class in the 81 <code>pack200</code> package provides several overloads of a 82 <code>normalize</code> method that can be used to prepare a 83 JAR archive in place or to a separate file.</p> 84 85 </subsection> 86 87 </section> 88 </body> 89 </document> 90
