ClassFileTransformer Arayüzü - Instrumentation API

Giriş

Şu satırı dahil ederiz

import java.lang.instrumen.Instrumentation;

Açıklaması şöyle

The ClassFileTransformer interface is a critical component of the Instrumentation API. It provides a transform() method that is called when a class is being loaded by the JVM. The transform() method receives the original class bytecode and returns the modified bytecode.

Örnek

Şöyle yaparız

import java.lang.instrument.Instrumentation;

public class LoggingAgent {
  public static void premain(String agentArgs, Instrumentation inst) {
    inst.addTransformer(new LoggingTransformer());
  }
}

import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.IllegalClassFormatException;
import java.security.ProtectionDomain;

public class LoggingTransformer implements ClassFileTransformer {
  @Override
  public byte[] transform(
    ClassLoader loader, 
    String className, 
    Class<?> classBeingRedefined, 
    ProtectionDomain protectionDomain, 
    byte[] classfileBuffer) throws IllegalClassFormatException {
        
    // Check if the class should be instrumented for logging
    if (className.startsWith("com.example")) {
      System.out.println("Instrumenting class: " + className);
            
      // Inject logging code into the class bytecode
      // ...
    }
    return classfileBuffer;
  }
}

Örnek

Şöyle yaparız

import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.IllegalClassFormatException;
import java.security.ProtectionDomain;

public class MethodTransformer implements ClassFileTransformer {
  @Override
  public byte[] transform(
    ClassLoader loader, 
    String className, 
    Class<?> classBeingRedefined, 
    ProtectionDomain protectionDomain, 
    byte[] classfileBuffer) throws IllegalClassFormatException {
        
    if (className.equals("com.example.Calculator")) {
      System.out.println("Instrumenting class: " + className);
            
      // Modify the bytecode of the add() method
      return modifyAddMethod(classfileBuffer);
    }
        
    return classfileBuffer;
  }
    
  private byte[] modifyAddMethod(byte[] originalBytecode) {
    // ... Bytecode manipulation to modify the add() method ...
  }
}