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# lstest.jar dependency1.jar dependency2.jar

2 查看待修改jar包内类结构

$ unzip -l test.jaror$ 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:%!xxd0000000: 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/\n/:/g'test.jar:dependency1.jar:dependency2.jar

注linux下是:分隔，windows下是;分隔

7 编译

$ javac -helpUsage: javac 
      
      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 
      
                 Specify where to find user class files and annotation processors  -cp 
       
                         Specify where to find user class files and annotation processors  -sourcepath 
        
                  Specify where to find input source files  -bootclasspath 
         
                Override location of bootstrap class files  -extdirs 
          
            Override location of installed extensions -endorseddirs 
           
             Override location of endorsed standards path -proc:{none,only} Control whether annotation processing and/or compilation is done. -processor 
            
             [,
             
              ,
              
               ...] Names of the annotation processors to run; bypasses default discovery process -processorpath 
               
                 Specify where to find annotation processors -parameters Generate metadata for reflection on method parameters -d 
                
                  Specify where to place generated class files -s 
                 
                   Specify where to place generated source files -h 
                  
                    Specify where to place generated native header files -implicit:{none,class} Specify whether or not to generate class files for implicitly referenced files -encoding 
                   
                     Specify character encoding used by source files -source 
                    
                      Provide source compatibility with specified release -target 
                     
                       Generate class files for specific VM version -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
                       
                         Pass 
                        
                          directly to the runtime system -Werror Terminate compilation if warnings occur @
                         
                           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