每当分配对象但遇到问题时,我都会尝试调用静态方法。我已将代码缩减为小型工作示例。
MemorySnifferAgent.java
public class MemorySnifferAgent {
public static void premain(String agentArguments, Instrumentation instrumentation) {
Callback.main(); //Make sure the class is loaded ?
instrumentation.addTransformer(new MemoryAllocationTransformer());
}
}
MemoryAllocationTransformer.java
public class MemoryAllocationTransformer implements ClassFileTransformer {
public byte[] instrumentByteCode(byte[] bytecode) {
ClassReader reader = new ClassReader(bytecode);
ClassWriter writer = new ClassWriter(ClassWriter.COMPUTE_MAXS);
CustomClassReader customVisitor = new CustomClassReader(Opcodes.ASM4, writer);
reader.accept(customVisitor, 0);
return writer.toByteArray();
}
public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
byte[] bytes = instrumentByteCode(classfileBuffer);
return bytes;
}
}
CustomClassReader.java
public class CustomClassReader extends ClassVisitor {
public CustomClassReader(int api, ClassWriter classWriter) {
super(api, classWriter);
}
public MethodVisitor visitMethod(final int access, final String name,
final String desc, final String signature, final String[] exceptions) {
MethodVisitor methodWritter = super.visitMethod(access, name, desc, signature, exceptions);
return new CustomMethodWritter(api, name, methodWritter);
}
}
CustomMethodWritter.java
class CustomMethodWritter extends MethodVisitor {
String name;
public CustomMethodWritter(int i, String name, MethodVisitor methodWriter) {
super(i, methodWriter);
this.name = name;
}
@Override
public void visitTypeInsn(int opcode, String type) {
super.visitTypeInsn(opcode, type);
if (opcode == Opcodes.NEW) {
super.visitMethodInsn(Opcodes.INVOKESTATIC, "com/chasingnanos/Callback", "onAllocation", "()V", false);
}
}
}
注意:
- 我意识到利用所有分配需要利用所有新*操作码和反射 API
- super.visitMethodInsn(Opcodes.INVOKESTATIC, "com/chasingnanos/Callback", "onAllocation", "()V", false);似乎是问题所在。虽然我无法找到问题所在。
如果这是一个非常基本的问题,我们深表歉意。我是字节码操作的新手。
我得到的错误:
java.lang.NoClassDefFoundError - klass: 'java/lang/NoClassDefFoundError'
最佳答案
我认为这个问题与不同的ClassLoader
提供的隔离有关。特别是代理的代码和“主”代码由不同的类加载器加载,因此您无法从“主”代码调用您的回调。解决此问题的方法是将您的 Callback 类移动到不同的 jar 并使用 -Xbootclasspath/a
将其添加到引导类路径中选项。
另请参阅类似问题 Java NoClassDefFoundError when calling own class from instrumented method
更新(过滤)
如果您不想使用 Bootstrap ,而是想过滤掉无法访问您的Callback
的类,那么您可能应该这样做,而不是仅仅检查null
:
public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
// check if the class inside the loader can access Callback
// by analyzing its hierarchy of parent class loaders
for (ClassLoader curLoader = loader; ; curLoader = curLoader.getParent()) {
if (curLoader == null) {
System.out.println("Skip '" + className + "' for " + loader);
return null;
} else if (curLoader == Callback.class.getClassLoader())
break;
}
byte[] bytes = instrumentByteCode(classfileBuffer);
return bytes;
}
关于java - 通过检测字节码调用类的静态方法时出现 NoClassDefFoundError,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/42660451/