根据本教程，我尝试使Java代理正常工作。 https://www.baeldung.com/java-instrumentation#loading-a-java-agent
我确实得到了[Agent] Transforming class TestApplication
我没有错误，但是看不到转换类的任何效果。
最终，我想同时使静态负载和动态负载都能工作，但现在我只关注静态方式。
public class Static_Agent {
public static void premain(String agentArgs, Instrumentation inst) {
String[] tokens = agentArgs.split(";");
String className = tokens[0];
String methodName = tokens[1];
System.out.println(">> "+className);
System.out.println(">> "+methodName);
transformClass(className, methodName, inst);
}
public static void transformClass(String className, String methodName, Instrumentation instrumentation) {
Class<?> targetCls = null;
ClassLoader targetClassLoader = null;
// see if we can get the class using forName
try {
targetCls = Class.forName(className);
targetClassLoader = targetCls.getClassLoader();
transform(targetCls, methodName, targetClassLoader, instrumentation);
return;
} catch (Exception ex) {
ex.printStackTrace();
}
// otherwise iterate all loaded classes and find what we want
for(Class<?> clazz: instrumentation.getAllLoadedClasses()) {
if(clazz.getName().equals(className)) {
targetCls = clazz;
targetClassLoader = targetCls.getClassLoader();
transform(targetCls, methodName, targetClassLoader, instrumentation);
return;
}
}
throw new RuntimeException("Failed to find class [" + className + "]");
}
public static void transform(Class<?> clazz, String methodName, ClassLoader classLoader, Instrumentation instrumentation) {
Transformer dt = new Transformer(clazz.getName(), methodName, classLoader);
instrumentation.addTransformer(dt, true);
try {
instrumentation.retransformClasses(clazz);
} catch (Exception ex) {
throw new RuntimeException("Transform failed for class: [" + clazz.getName() + "]", ex);
}
}
}
public class Transformer implements ClassFileTransformer {
/** The internal form class name of the class to transform */
private String targetClassName;
/** The class loader of the class we want to transform */
private ClassLoader targetClassLoader;
private String targetMethodName;
public Transformer(String targetClassName, String targetMethodName, ClassLoader targetClassLoader) {
this.targetClassName = targetClassName;
this.targetClassLoader = targetClassLoader;
this.targetMethodName = targetMethodName;
}
@Override
public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined,
ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
byte[] byteCode = classfileBuffer;
String finalTargetClassName = this.targetClassName.replaceAll("\\.", "/");
if (!className.equals(finalTargetClassName)) {
return byteCode;
}
if (className.equals(finalTargetClassName) && loader.equals(targetClassLoader)) {
System.out.println("[Agent] Transforming class TestApplication");
try {
ClassPool cp = ClassPool.getDefault();
CtClass cc = cp.get(targetClassName);
CtMethod m = cc.getDeclaredMethod(targetMethodName);
m.addLocalVariable("startTime", CtClass.longType);
m.insertBefore("startTime = System.currentTimeMillis();");
StringBuilder endBlock = new StringBuilder();
m.addLocalVariable("endTime", CtClass.longType);
m.addLocalVariable("opTime", CtClass.longType);
endBlock.append("endTime = System.currentTimeMillis();");
endBlock.append("opTime = (endTime-startTime)/1000;");
endBlock.append("System.out.println(\"[Application] Withdrawal operation completed in:\" + opTime + \" seconds!\");");
m.insertAfter(endBlock.toString());
byteCode = cc.toBytecode();
cc.detach();
} catch (Exception e) {
System.out.println("Exception"+e);
}
}
return byteCode;
}
}
public class TestApplication {
public static void main(String[] args) {
try {
TestApplication.run();
} catch (Exception e) {
e.printStackTrace();
}
}
public static void run() throws Exception {
System.out.println("--- start ---");
while (true) {
test();
Thread.sleep(4_000);
}
}
static int count = 0;
public static void test() {
System.out.println(count++);
}
}
我以以下方式启动
： java -javaagent:static_agent.jar="doeke.application.TestApplication;test" -jar application.jar
在有帮助的情况下，该项目位于此处： https://github.com/clankill3r/java_agent
编辑：
在文件末尾附近的Transformer.java中，我现在使用e.printStackTrace();。
我收到以下错误：
[Agent]转换类TestApplication javassist.NotFoundException：doeke.application.TestApplication在 javassist.ClassPool.get（ClassPool.java:436）在 doeke.transformer.Transformer.transform（Transformer.java:48）在 java.instrument / java.lang.instrument.ClassFileTransformer.transform（ClassFileTransformer.java:246） 在 java.instrument / sun.instrument.TransformerManager.transform（TransformerManager.java:188） 在 java.instrument / sun.instrument.InstrumentationImpl.transform（InstrumentationImpl.java:563） 在 java.instrument / sun.instrument.InstrumentationImpl.retransformClasses0（本机 方法） java.instrument / sun.instrument.InstrumentationImpl.retransformClasses（InstrumentationImpl.java:167） 在doeke.static_agent.Static_Agent.transform（Static_Agent.java:56） 在 doeke.static_agent.Static_Agent.transformClass（Static_Agent.java:34） 在doeke.static_agent.Static_Agent.premain（Static_Agent.java:22）在 java.base / jdk.internal.reflect.NativeMethodAccessorImpl.invoke0（本机 方法） java.base / jdk.internal.reflect.NativeMethodAccessorImpl.invoke（NativeMethodAccessorImpl.java:62） 在 java.base / jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke（DelegatingMethodAccessorImpl.java:43） 在java.base / java.lang.reflect.Method.invoke（Method.java:566）在 java.instrument / sun.instrument.InstrumentationImpl.loadClassAndStartAgent（InstrumentationImpl.java:513） 在 java.instrument / sun.instrument.InstrumentationImpl.loadClassAndCallPremain（InstrumentationImpl.java:525）
---开始---
0
1
答案 0 :(得分：6)
感谢提出这个问题，让我有机会对Java Instrumentation有所了解。
花了一些时间来交叉检查示例代码和提供的教程。问题不在于编程代码，而在于如何启动程序。
如果在Transformer.java的transform（）方法中添加一些记录器，则会发现在运行后代码路径已损坏：
ClassPool cp = ClassPool.getDefault();
然后，用相同的方法从以下位置替换异常捕获代码：
} catch (Exception e) {
收件人：
} catch (NotFoundException | CannotCompileException | IOException e) {
它将为您提供更多提示，如下所示：
Exception in thread "main" java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at sun.instrument.InstrumentationImpl.loadClassAndStartAgent(Unknown Source)
at sun.instrument.InstrumentationImpl.loadClassAndCallPremain(Unknown Source)
Caused by: java.lang.NoClassDefFoundError: javassist/NotFoundException
at doeke.static_agent.Static_Agent.transform(Static_Agent.java:60)
at doeke.static_agent.Static_Agent.transformClass(Static_Agent.java:40)
at doeke.static_agent.Static_Agent.premain(Static_Agent.java:28)
... 6 more
Caused by: java.lang.ClassNotFoundException: javassist.NotFoundException
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
... 9 more
FATAL ERROR in native method: processing of -javaagent failed
到目前为止，根本原因更加明显。这是因为在启动程序时，那些与Javassist相关的类（例如ClassPool，CtClass，CtMethod等）在运行时无法引用其相应的库。
因此，解决方案是：
假定您已将static_agent.jar导出到与application.jar相同的“ build”文件夹中
所有其他文件夹结构与您提供的github中显示的相同
将“ cd”放入命令控制台中的内部版本文件夹
修改原始程序启动脚本，如下所示
Windows操作系统：
java -javaagent:static_agent.jar="doeke.application.TestApplication;test" -cp ../libs/javassist-3.12.1.GA.jar;application.jar doeke.application.TestApplication
Unix / Linux操作系统：
java -javaagent:static_agent.jar="doeke.application.TestApplication;test" -cp ../libs/javassist-3.12.1.GA.jar:application.jar doeke.application.TestApplication
您最终将获得预期的结果：
[Agent] In premain method.
>> doeke.application.TestApplication
>> test
[Agent] Transforming class
--- start ---
0
[Application] Withdrawal operation completed in:0 seconds!
1
[Application] Withdrawal operation completed in:0 seconds!
编辑
此外，让我粘贴一些有关如何通过javassist在方法中间插入代码的代码。
如果将TestApplication.java中的test（）方法更改为：
line 30 public static void test() {
line 31 System.out.println(count++);
line 32
line 33 System.out.println("Last line of test() method");
line 34 }
假设我们要在 count 和 ========== 之间添加一条线，假设“这是行分隔符”，结果如下：
1
-- This is line separator --
Last line of test() method
然后，在Transformer.java的transform（...）方法中，可以添加如下代码行：
m.insertAt(32,"System.out.println(\"-- This is line separator --\");");
这将变成：
@Override
public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined,
ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
byte[] byteCode = classfileBuffer;
String finalTargetClassName = this.targetClassName.replaceAll("\\.", "/");
if (!className.equals(finalTargetClassName)) {
return byteCode;
}
if (className.equals(finalTargetClassName) && loader.equals(targetClassLoader)) {
System.out.println("[Agent] Transforming class TestApplication");
try {
// Step 1 Preparation
ClassPool cp = ClassPool.getDefault();
CtClass cc = cp.get(targetClassName);
CtMethod m = cc.getDeclaredMethod(targetMethodName);
// Step 2 Declare variables
m.addLocalVariable("startTime", CtClass.longType);
m.addLocalVariable("endTime", CtClass.longType);
m.addLocalVariable("opTime", CtClass.longType);
// Step 3 Insertion of extra logics/implementation
m.insertBefore("startTime = System.currentTimeMillis();");
m.insertAt(32,"System.out.println(\"-- This is line separator --\");");
StringBuilder endBlock = new StringBuilder();
endBlock.append("endTime = System.currentTimeMillis();");
endBlock.append("opTime = (endTime-startTime)/1000;");
endBlock.append("System.out.println(\"[Application] Withdrawal operation completed in:\" + opTime + \" seconds!\");");
m.insertAfter(endBlock.toString());
// Step 4 Detach from ClassPool and clean up stuff
byteCode = cc.toBytecode();
cc.detach();
} catch (NotFoundException | CannotCompileException | IOException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
}
return byteCode;
}
最后，将得到如下结果，将结果打印在方法中间：
[Agent] In premain method.
className=doeke.application.TestApplication
methodName=test
>> doeke.application.TestApplication
>> test
[Agent] Transforming class TestApplication
--- start ---
0
-- This is line separator --
=========
[Application] Withdrawal operation completed in:0 seconds!
1
-- This is line separator --
=========
[Application] Withdrawal operation completed in:0 seconds!
2
-- This is line separator --
=========
[Application] Withdrawal operation completed in:0 seconds!