示例说明
①、 javassist.iedis.crack.IedisCrack1和javassist.iedis.crack.IedisCrack2为使用javassist破解iedis插件的代码.
最后将tmp目录下生成的class文件打包替换iedis-2.43.jar其操作命令如下:
jar -uvf iedis-2.43.jar com/②、javaagent.sample.App演示了javaagent结合javassist案例
javaagent.sample.transformer.IedisTransformer 演示了使用javaagent结合javassist破解iedis插件
javaagent.sample.transformer.InjectPrintTransformer 演示了使用javaagent结合javassist匹配返回值为String的方法，在其方法内插入代码，输出方法名、方法参数列表、方法返回值信息等。
使用javaagent的方式破解iedis插件须知:
确保src/main/resources/META-INF/MANIFEST.MF文件内容如下所示:
Manifest-Version: 1.0
Premain-Class: javaagent.sample.App
Can-Redefine-Classes: true
Can-Retransform-Classes: true
Can-Set-Native-Method-Prefix: true
最后执行mvn assembly:assembly打包，然后在idea.exe.vmoptions或idea64.exe.vmoptions中添加-javaagent:javaagent-samples-1.0.jar=iedis重启idea使其生效。
③、javaagent.samples.sample1.Agent演示了javaagent的基本用法，其内部声明了如下的两个方法:
public static void premain(String agentArgs, Instrumentation inst); // a
public static void premain(String agentArgs); // ba和b同时存在时，a会优先被执行，而b则会被忽略。具体参照 https://docs.oracle.com/javase/8/docs/api/java/lang/instrument/package-summary.html
javaagent.samples.sample1.AgentTest 运行启动类，在ide中运行时需添加jvm参数
add VM options:
-javaagent:javaagent-samples-1.0.jar=agent1,agent2
确保src/main/resources/META-INF/MANIFEST.MF文件内容如下所示:
Manifest-Version: 1.0
Premain-Class: javaagent.samples.sample1.Agent
Can-Redefine-Classes: true
Can-Retransform-Classes: true
Can-Set-Native-Method-Prefix: true
最后执行mvn assembly:assembly打包，在ide中运行javaagent.samples.sample1.AgentTest观察控制台输出，其输出大致如下所示：
---------public static void premain(String agentArgs, Instrumentation inst)--------->agent1,agent2
Hello,Agent!
④、javaagent.samples.sample2.Agent演示了使用javaagent结合javassist增强方法，在javaagent.samples.sample2包下的方法中插入计算方法执行耗时的代码
其中javaagent.samples.sample2.PerformMonitorTransformer为核心业务代码，请务必理解该部分代码.
javaagent.samples.sample2.AgentTest为运行启动类，在ide中运行时需添加jvm参数
add VM options:
-javaagent:javaagent-samples-1.0.jar
确保src/main/resources/META-INF/MANIFEST.MF文件内容如下所示:
Manifest-Version: 1.0
Premain-Class: javaagent.samples.sample2.Agent
Can-Redefine-Classes: true
Can-Retransform-Classes: true
Can-Set-Native-Method-Prefix: true
最后执行mvn assembly:assembly打包，在ide中运行javaagent.samples.sample2.AgentTest观察控制台输出，其输出大致如下所示：
this is an perform monitor agent.
now transform: [javaagent.samples.sample2.AgentTest]
this is fun 1.
method:[fun1] cost:[77399ns]
this is fun 2.
method:[fun2] cost:[18123ns]
------------------------------------
now transform: [javaagent.samples.sample2.Another]
this is fun 3.
method:[fun3] cost:[58521ns]
this is fun 4.
method:[fun4] cost:[18123ns]
⑤、javaagent.samples.sample3.Agent演示了使用javaagent结合bytebuddy增强方法，拦截javaagent.samples.sample3.example包下的方法，统计其运行所花费的时间
javaagent.samples.sample3.RunTimeInterceptor为自定义的bytebuddy拦截器，务必理解javaagent.samples.sample3.Agent和javaagent.samples.sample3.RunTimeInterceptor中的代码逻辑
javaagent.samples.sample3.example.AgentTest为运行启动类，在ide中运行时需添加jvm参数
add VM options:
-javaagent:javaagent-samples-1.0.jar
确保src/main/resources/META-INF/MANIFEST.MF文件内容如下所示:
Manifest-Version: 1.0
Premain-Class: javaagent.samples.sample3.Agent
Can-Redefine-Classes: true
Can-Retransform-Classes: true
Can-Set-Native-Method-Prefix: true
最后执行mvn assembly:assembly打包，在ide中运行javaagent.samples.sample3.example.AgentTest观察控制台输出，其输出大致如下所示：
this is an perform monitor agent.
this is fun 1.
private void javaagent.samples.sample3.example.AgentTest.fun1() throws java.lang.Exception: took 500ms
this is fun 2.
private void javaagent.samples.sample3.example.AgentTest.fun2() throws java.lang.Exception: took 1000ms
public static void javaagent.samples.sample3.example.AgentTest.main(java.lang.String[]) throws java.lang.Exception: took 1500ms
⑥、javaagent.samples.sample4.Agent演示了使用javaagent每隔5000毫秒输出一次程序内存和GC情况
javaagent.samples.sample4.Metric里面是程序运行期间jvm内存和gc的业务逻辑代码
javaagent.samples.sample4.AgentTest为运行启动类，在ide中运行时需添加jvm参数
add VM options:
-javaagent:javaagent-samples-1.0.jar
确保src/main/resources/META-INF/MANIFEST.MF文件内容如下所示:
Manifest-Version: 1.0
Premain-Class: javaagent.samples.sample4.Agent
Can-Redefine-Classes: true
Can-Retransform-Classes: true
Can-Set-Native-Method-Prefix: true
最后执行mvn assembly:assembly打包，在ide中运行javaagent.samples.sample4.AgentTest观察控制台输出，其输出大致如下所示：
this is an perform monitor agent.
init: 256MB max: 3621MB used: 6MB committed: 245MB use rate: 2%
init: 2MB max: 0MB used: 6MB committed: 8MB use rate: 82%
name: PS Scavenge count:0 took:0 pool name:[PS Eden Space, PS Survivor Space]
name: PS MarkSweep count:0 took:0 pool name:[PS Eden Space, PS Survivor Space, PS Old Gen]
init: 256MB max: 3621MB used: 148MB committed: 991MB use rate: 14%
init: 2MB max: 0MB used: 7MB committed: 8MB use rate: 83%
name: PS Scavenge count:10 took:96 pool name:[PS Eden Space, PS Survivor Space]
name: PS MarkSweep count:0 took:0 pool name:[PS Eden Space, PS Survivor Space, PS Old Gen]
init: 256MB max: 3621MB used: 837MB committed: 1483MB use rate: 56%
init: 2MB max: 0MB used: 7MB committed: 8MB use rate: 84%
name: PS Scavenge count:12 took:98 pool name:[PS Eden Space, PS Survivor Space]
name: PS MarkSweep count:0 took:0 pool name:[PS Eden Space, PS Survivor Space, PS Old Gen]
init: 256MB max: 3621MB used: 592MB committed: 1360MB use rate: 43%
init: 2MB max: 0MB used: 7MB committed: 8MB use rate: 84%
name: PS Scavenge count:14 took:99 pool name:[PS Eden Space, PS Survivor Space]
name: PS MarkSweep count:0 took:0 pool name:[PS Eden Space, PS Survivor Space, PS Old Gen]
- JavaAgent
https://docs.oracle.com/javase/8/docs/api/java/lang/instrument/package-summary.html
https://zeroturnaround.com/rebellabs/how-to-inspect-classes-in-your-jvm
- javassist
https://jboss-javassist.github.io/javassist/tutorial/tutorial.html
https://jboss-javassist.github.io/javassist/tutorial/tutorial2.html
http://zhxing.iteye.com/blog/1703305
- bytebuddy