ByteBuddy报错：无法定位类中name字段，请求社区协助排查

我正在探索ByteBuddy库，尝试为方法创建Advice，但运行时抛出java.lang.IllegalStateException异常，提示无法找到org.purbarun.proxy.MyService$ByteBuddy$8XL9Iy3U类中的name字段。以下是异常信息和测试代码，请求帮忙排查错误。

异常信息 #

Exception in thread "main" java.lang.IllegalStateException: Cannot locate field named name for class org.purbarun.proxy.MyService$ByteBuddy$8XL9Iy3U
    at net.bytebuddy.asm.Advice$OffsetMapping$ForField$Unresolved.resolve(Advice.java:2534)
    at net.bytebuddy.asm.Advice$OffsetMapping$ForField.resolve(Advice.java:2459)
    at net.bytebuddy.asm.Advice$Dispatcher$Inlining$Resolved$ForMethodEnter.doApply(Advice.java:9979)
    at net.bytebuddy.asm.Advice$Dispatcher$Inlining$Resolved$ForMethodEnter$WithDiscardedEnterType.doApply(Advice.java:10081)
    at net.bytebuddy.asm.Advice$Dispatcher$Inlining$Resolved$ForMethodEnter.apply(Advice.java:9937)
    at net.bytebuddy.asm.Advice$Dispatcher$Inlining$Resolved$AdviceMethodInliner.visitMethod(Advice.java:9620)
    at net.bytebuddy.jar.asm.ClassReader.readMethod(ClassReader.java:1354)
    at net.bytebuddy.jar.asm.ClassReader.accept(ClassReader.java:745)
    at net.bytebuddy.utility.AsmClassReader$ForAsm.accept(AsmClassReader.java:225)
    at net.bytebuddy.asm.Advice$Dispatcher$Inlining$Resolved$AdviceMethodInliner.apply(Advice.java:9613)
    at net.bytebuddy.asm.Advice$AdviceVisitor.onAfterExceptionTable(Advice.java:11919)
    at net.bytebuddy.utility.visitor.ExceptionTableSensitiveMethodVisitor.considerEndOfExceptionTable(ExceptionTableSensitiveMethodVisitor.java:49)
    at net.bytebuddy.utility.visitor.ExceptionTableSensitiveMethodVisitor.visitVarInsn(ExceptionTableSensitiveMethodVisitor.java:113)
    at net.bytebuddy.implementation.bytecode.member.MethodVariableAccess$OffsetLoading.apply(MethodVariableAccess.java:354)
    at net.bytebuddy.implementation.bytecode.StackManipulation$Compound.apply(StackManipulation.java:243)
    at net.bytebuddy.implementation.SuperMethodCall$Appender.apply(SuperMethodCall.java:139)
    at net.bytebuddy.asm.Advice$Appender$EmulatingMethodVisitor.resolve(Advice.java:12525)
    at net.bytebuddy.asm.Advice$Appender.apply(Advice.java:12478)
    at net.bytebuddy.dynamic.scaffold.TypeWriter$MethodPool$Record$ForDefinedMethod$WithBody.applyCode(TypeWriter.java:732)
    at net.bytebuddy.dynamic.scaffold.TypeWriter$MethodPool$Record$ForDefinedMethod$WithBody.applyBody(TypeWriter.java:717)
    at net.bytebuddy.dynamic.scaffold.TypeWriter$MethodPool$Record$ForDefinedMethod.apply(TypeWriter.java:624)
    at net.bytebuddy.dynamic.scaffold.TypeWriter$Default$ForCreation.create(TypeWriter.java:6072)
    at net.bytebuddy.dynamic.scaffold.TypeWriter$Default.make(TypeWriter.java:2246)
    at net.bytebuddy.dynamic.DynamicType$Builder$AbstractBase$UsingTypeWriter.make(DynamicType.java:4085)
    at net.bytebuddy.dynamic.DynamicType$Builder$AbstractBase.make(DynamicType.java:3769)
    at net.bytebuddy.dynamic.DynamicType$Builder$AbstractBase$Delegator.make(DynamicType.java:4021)
    at org.purbarun.proxy.MainRunner.main(MainRunner.java:14)

测试代码 #

public class MyService {
    public void myMethod(String args) {
        System.out.println(args);
    }
}

public class MyServiceInterceptor {
    @OnMethodEnter
    static void enter(@This Object thisObject,
            @Origin String origin,
            @Origin("#t #m") String detaildOrigin,
            @AllArguments Object[] ary,
            @FieldValue(value = "name", readOnly = false) String nameField){
        System.out.println("test");
    }
}

public static void main(String[] args) throws IllegalAccessException, InvocationTargetException, NoSuchMethodException, SecurityException, InstantiationException, IllegalArgumentException {
        Class<? extends MyService> type=new ByteBuddy()
          .subclass(MyService.class)
          .method(ElementMatchers.isMethod()).intercept(Advice.to(MyServiceInterceptor.class))
          .make()
          .load(MyService.class.getClassLoader())
          .getLoaded();
        
        String returnVal = (String)type.getDeclaredMethod("myMethod", String.class).invoke(type.getDeclaredConstructor().newInstance(), "Method");
        System.out.println("return value: " + returnVal);
    }

问题原因和解决方案 #

核心问题 #

MyService类中不存在name字段，但拦截器方法enter中使用@FieldValue("name")尝试获取该字段，ByteBuddy在生成代理类时无法找到对应字段，因此抛出异常。

解决方案 #

方案1：添加需要的字段（如果确实需要操作name字段）

在MyService类中添加name字段：

public class MyService {
    private String name; // 添加name字段
    public void myMethod(String args) {
        System.out.println(args);
    }
}

方案2：移除无用的字段参数（如果不需要操作name字段）

删除拦截器中@FieldValue相关的参数：

public class MyServiceInterceptor {
    @OnMethodEnter
    static void enter(@This Object thisObject,
            @Origin String origin,
            @Origin("#t #m") String detaildOrigin,
            @AllArguments Object[] ary){
        System.out.println("test");
    }
}

额外修正点 #

myMethod是void返回类型，但main方法中强制将返回值转为String，会触发ClassCastException，需要修正main方法：

public static void main(String[] args) throws Exception {
    Class<? extends MyService> type = new ByteBuddy()
            .subclass(MyService.class)
            .method(ElementMatchers.isMethod()).intercept(Advice.to(MyServiceInterceptor.class))
            .make()
            .load(MyService.class.getClassLoader())
            .getLoaded();
    
    // void方法无需接收返回值
    type.getDeclaredMethod("myMethod", String.class)
        .invoke(type.getDeclaredConstructor().newInstance(), "Method");
}

内容的提问来源于stack exchange，提问作者purbarunc