有时需要修改很多jar(假设这些jar都位于lib目录)中其中一个jar中的某一个类,而且又没有原始代码或ide,这时最简单的方式是:
1 进入lib目录
# cd lib # ls test.jar dependency1.jar dependency2.jar
2 查看待修改jar包内类结构
$ unzip -l test.jar or $ vim test.jar
3 解压待修改jar包
$ mkdir test_dir
$ unzip test.jar -d test_dir
4 查看class的jdk版本
$ vi -b test_dir/package/Class.class :%!xxd 0000000: cafe babe 0000 0032 0123 0700 0201 0023 .......2.#.....#
取第15-16位,上例即32,
5 将要修改的文件放到class同目录下(如果没有源代码可以尝试反编译),并修改
$ vi test_dir/package/Class.java
6 收集classpath
由于jar包可能非常多,所以使用命令来生成
$ ls *.jar|sed ':a;N;$!ba;s/ /:/g' test.jar:dependency1.jar:dependency2.jar
注linux下是:分隔,windows下是;分隔
7 编译
$ javac -help Usage: javac <options> <source files> where possible options include: -g Generate all debugging info -g:none Generate no debugging info -g:{lines,vars,source} Generate only some debugging info -nowarn Generate no warnings -verbose Output messages about what the compiler is doing -deprecation Output source locations where deprecated APIs are used -classpath <path> Specify where to find user class files and annotation processors -cp <path> Specify where to find user class files and annotation processors -sourcepath <path> Specify where to find input source files -bootclasspath <path> Override location of bootstrap class files -extdirs <dirs> Override location of installed extensions -endorseddirs <dirs> Override location of endorsed standards path -proc:{none,only} Control whether annotation processing and/or compilation is done. -processor <class1>[,<class2>,<class3>...] Names of the annotation processors to run; bypasses default discovery process -processorpath <path> Specify where to find annotation processors -parameters Generate metadata for reflection on method parameters -d <directory> Specify where to place generated class files -s <directory> Specify where to place generated source files -h <directory> Specify where to place generated native header files -implicit:{none,class} Specify whether or not to generate class files for implicitly referenced files -encoding <encoding> Specify character encoding used by source files -source <release> Provide source compatibility with specified release -target <release> Generate class files for specific VM version -profile <profile> Check that API used is available in the specified profile -version Version information -help Print a synopsis of standard options -Akey[=value] Options to pass to annotation processors -X Print a synopsis of nonstandard options -J<flag> Pass <flag> directly to the runtime system -Werror Terminate compilation if warnings occur @<filename> Read options and filenames from file
实际命令
$ javac -cp test.jar:dependency1.jar:dependency2.jar -source 1.6 -target 1.6 -sourcepath test_dir -d test_dir test_dir/package/Class.java
8 重新打jar包
$ cd test_dir
$ zip -r test.jar ./*
9 删除临时目录和原始jar
$ cd .. $ cp test_dir/test.jar test.jar $ /bin/rm -rf test_dir