【原创】Java基础之简单修改jar包中的class

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,

【原创】Java基础之简单修改jar包中的class

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/\n/:/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

10 测试修改生效

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