因此，我将 java 代理与 javassist 结合使用，目的是将一些与监控相关的小代码注入(inject)到不同类中的不同方法中。
我的java代理代码:
public class ConverterAgent implements ClassFileTransformer {
public static void premain(String args, Instrumentation instrumentation){
System.out.println(">>>>>>>>>> Intializing Java agent <<<<<<<<<<");
ConverterAgent transformer = new ConverterAgent();
instrumentation.addTransformer(transformer);
}
public static void agentmain(String args, Instrumentation instrumentation){
System.out.println(">>>>>>>>>> Intializing Java agent <<<<<<<<<<");
ConverterAgent transformer=new ConverterAgent();
instrumentation.addTransformer(transformer);
}
@Override
public byte[] transform(final ClassLoader loader,
String className,
Class<?> classBeingRedefined,
ProtectionDomain protectionDoman,
byte[] classFileBuffer)
throws IllegalClassFormatException {
//javassist code goes here
return classFileBuffer;
}
}
我的 javassist 注入(inject)看起来像这样:
if ("className1".equals(className)){
//code
}
if ("className2".equals(className)){
//same code as in first class
}
if ("className3".equals(className)){
//same code as in first and second class
}
所以我多次注入(inject)完全相同的代码，我想优化我的流程并为每次注入(inject)调用一个方法，这样我就不必一遍又一遍地复制相同的代码。但这就是我遇到问题的地方，我应该使用什么方法类型以及除了类和方法名称之外它还需要什么参数。
最佳答案
在您的转换方法中，您正在获取类字节码，然后返回经过修改的"new"类字节码。
这意味着您肯定要返回的是包含转换方法所需信息的字节[]。
所以你的方法应该是这样的:
public class DynamicTransformer implements ClassFileTransformer {
public byte[] transform(ClassLoader loader, String className, Class classBeingRedefined,
ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
byte[] byteCode = classfileBuffer;
// into the transformer will arrive every class loaded so you filter
// to match only what you need
if (className.equals("com/full/path/to/be/instrumented/className1") ||
className.equals("com/full/path/to/be/instrumented/className2") ||
className.equals("com/full/path/to/be/instrumented/className3") ) {
byteCode = myMethodThatTransform(className, byteCode);
}
return byteCode;
}
public byte[] myMethodThatTransform(String className, byte[] byteCode){\
try {
// retrive default Javassist class pool
ClassPool cp = ClassPool.getDefault();
// get from the class pool our class with this qualified name
CtClass cc = cp.get(className);
// get all the methods of the retrieved class
CtMethod[] methods = cc.getDeclaredMethods()
for(CtMethod meth : methods) {
// The instrumentation code to be returned and injected
final StringBuffer buffer = new StringBuffer();
String name = meth.getName();
// just print into the buffer a log for example
buffer.append("System.out.println(\"Method " + name + " executed\" );");
meth.insertBefore(buffer.toString())
}
// create the byteclode of the class
byteCode = cc.toBytecode();
// remove the CtClass from the ClassPool
cc.detach();
} catch (Exception ex) {
ex.printStackTrace();
}
return byteCode;
}
}
关于Java javassist 方法调用，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/42621130/