java agent

1  -agentlib:<libname>[=<选项>]
2                加载本机代理库 <libname>, 例如 -agentlib:hprof
3                另请参阅 -agentlib:jdwp=help 和 -agentlib:hprof=help
4  -agentpath:<pathname>[=<选项>]
5                按完整路径名加载本机代理库
6  -javaagent:<jarpath>[=<选项>]
7                加载 Java 编程语言代理, 请参阅 java.lang.instrument

  1 // Dll.cpp : 定义 DLL 应用程序的导出函数。
  2 //
  3 /*
  4 * The VM starts each agent by invoking a start-up function. 
  5 * If the agent is started in the OnLoad phase the function Agent_OnLoad will be invoked. 
  6 * If the agent is started in the live phase the function Agent_OnAttach will be invoked. 
  7 * Exactly one call to a start-up function is made per agent.
  8 * 中文总结一下上面的含义：
  9 * java agent有2个启动函数分别为Agent_OnLoad和Agent_OnAttach
 10 * Agent_OnLoad在onload阶段被调用
 11 * Agent_OnAttach在live阶段被调用
 12 * 但是每个agent只有一个启动函数会被调用
 13 */
 14 #include "stdafx.h"
 15 #include "jvmti.h"
 16 #include <iostream>
 17 
 18 /*
 19 * 此阶段JVM还没有初始化，所以能做的操作比较受限制
 20 * JVM参数都无法获取
 21 * The return value from Agent_OnLoad is used to indicate an error. 
 22 * Any value other than zero indicates an error and causes termination of the VM.
 23 * 任何非零的返回值都会导致JVM终止。
 24 */
 25 
 26 
 27 JNIEXPORT jint JNICALL
 28 Agent_OnLoad(JavaVM *vm, char *options, void *reserved) {
 29     jvmtiEnv* jvmti;
 30     jvmtiCapabilities capabilities;
 31     options = options == nullptr ? "" : options;
 32     jint error = vm->GetEnv((void**)&jvmti, JVMTI_VERSION);
 33     if (error) {
 34         std::cout << "get jvmtiEnv error!\n";
 35     }
 36     else {
 37         jvmti->GetCapabilities(&capabilities);
 38         std::cout << "capabilities.can_access_local_variables : "
 39             << capabilities.can_access_local_variables
 40             << std::endl;
 41     }
 42 
 43     std::cout << "Agent_OnLoad\n" << "options ===== " << options << std::endl;
 44 
 45     
 46     
 47 
 48     return 0;
 49 }
 50 /*
 51 * Any value other than zero indicates an error. 
 52 * An error does not cause the VM to terminate. 
 53 * Instead the VM ignores the error, or takes some implementation specific action -- for example it might print an error to standard error, or record the error in a system log.
 54 *
 55 */
 56 JNIEXPORT jint JNICALL
 57 Agent_OnAttach(JavaVM* vm, char* options, void* reserved) {
 58     options = options == nullptr ? "" : options;
 59     std::cout << "Agent_OnAttach\n" << "options ===== " << options << std::endl;
 60 
 61     jvmtiEnv *jvmti;
 62     jint result = vm->GetEnv((void**)&jvmti, JVMTI_VERSION);//获取jvmti指针
 63     jint count;//用于保存加载类的数量
 64     jclass* klasses;//指向保存已加载的类的指针
 65     jvmtiError error = jvmti->GetLoadedClasses(&count, &klasses);//获取已加载的类和数量
 66     std::cout << "jvmtiError : " << error << std::endl;
 67     if (error)
 68         std::cout << "get loadedClasses error!\n";
 69     else {
 70         std::cout << "signatures : \n";
 71         for (int i = 0; i < count; i++) {//循环打印类的签名
 72             char* signature;
 73             jvmti->GetClassSignature(klasses[i], &signature, NULL);
 74             std::cout << signature << std::endl;
 75         }
 76         std::cout << "signatures end! ------------------\n";//已加载类签名打印结束标志
 77     }
 78     
 79 
 80 
 81     jint threadCount;//用于保存线程数量
 82     jthread* threads;//指向保存线程信息的指针
 83     error = jvmti->GetAllThreads(&threadCount, &threads);//获取到线程信息
 84     if (error)
 85         std::cout << "get all threads error!\n";
 86     else {
 87         jvmtiThreadInfo threadInfo;//保存每个线程的信息，它是一个结构体的指针
 88         for (size_t i = 0; i < threadCount; i++) {
 89             error = jvmti->GetThreadInfo(threads[i], &threadInfo);
 90             if (error)
 91                 std::cout << "第 " << i << " 线程获取出错！\n";
 92             else
 93                 std::cout << "thread name:" << threadInfo.name << std::endl;
 94         }
 95         std::cout << "thread info end! ---------------------\n";
 96     }
 97 
 98 
 99     return 0;
100 }
101 /*
102 * This function can be used to clean-up resources allocated by the agent.
103 */
104 JNIEXPORT void JNICALL
105 Agent_OnUnload(JavaVM *vm) {
106     std::cout << "*********Agent_OnUnload**********\n";
107 
108 }

 1 public class Test {
 2 
 3     
 4     public static void main(String[] args) throws AgentLoadException, AgentInitializationException, IOException, AttachNotSupportedException {
 5         attach();
 6     }
 7     
 8     public static void attach() throws AgentLoadException, AgentInitializationException, IOException, AttachNotSupportedException{
 9         String pid = "10748";//java进程号
10         String agentPath = "C:\\Users\\DanteJ\\source\\repos\\agent\\x64\\Debug\\agent.dll";//本地库路径
11         System.out.println("attaching....pid="+pid);
12         VirtualMachine virtualMachine = VirtualMachine.attach(pid);//attach JVM
13         virtualMachine.loadAgentPath(agentPath);//加载本地库
14         virtualMachine.detach();//断开
15     }
16 }

public static void premain(String agentArgs, Instrumentation ins)

public class Agent {
    
    public static void premain(String agentArgs, Instrumentation ins){
        System.out.println("--------------javaagent-----------------");
    }

}

Manifest-Version: 1.0
Premain-Class: com.ideal.javaagent.Agent

public static void main(String[] args) throws AgentLoadException, AgentInitializationException, IOException, AttachNotSupportedException {
        System.out.println("main");
    }