java ASM异常：执行可能会从代码create（）V的末尾脱落

Question

我正在尝试向使用ASM框架的类添加一个新方法public void create(){}，但它会引发如下异常：

Exception in thread "main" java.lang.IllegalArgumentException: Execution can fall off the end of the code create()V

at org.objectweb.asm.util.CheckMethodAdapter$1.throwError(CheckMethodAdapter.java:474) at org.objectweb.asm.util.CheckMethodAdapter$1.visitEnd(CheckMethodAdapter.java:462) at org.objectweb.asm.MethodVisitor.visitEnd(MethodVisitor.java:783) at org.objectweb.asm.util.CheckMethodAdapter.visitEnd(CheckMethodAdapter.java:1036) at me.xx2bab.asmdemo.Weaver01AddRemoveFieldAndMethod$onProcess$classVisitor$1.visitEnd(Weaver01AddRemoveFieldAndMethod.kt:41) at org.objectweb.asm.ClassReader.accept(ClassReader.java:715) at org.objectweb.asm.ClassReader.accept(ClassReader.java:394)

以下是代码：

        val classReader = ClassReader(inputStream)
        val classWriter = ClassWriter(classReader, COMPUTE_FRAMES or COMPUTE_MAXS)
        val classVisitor = object : ClassVisitor(ASM9, CheckClassAdapter(classWriter, true)) {
            override fun visitEnd() {
//                visitField(
//                    Opcodes.ACC_PUBLIC,
//                    "newFieldName",
//                    "Ljava/lang/String;",
//                    null,
//                    null
//                ).visitEnd()
                visitMethod(
                    Opcodes.ACC_PUBLIC,
                    "create",
                    "()V",
                    null,
                    null
                )?.visitEnd() // This is where exception throws
                super.visitEnd()
            }

        }
        classReader.accept(classVisitor, 0)

我试过在visitMethod前面移动super.visitEnd()，它会抛出“调用visitEnd后无法访问成员”然而，类似的操作也适用于visitField，就像我注释掉的代码片段一样

不确定实现这一要求的真正方式是什么

Answer 1

根据@Holger来自comments的指示，我最终通过添加一个方法体解决了这个问题：

        // Add a new method
        val mv = classWriter.visitMethod(
            Opcodes.ACC_PUBLIC,
            "create",
            "()V",
            null,
            null
        )
        mv.visitFieldInsn(
            GETSTATIC,
            "java/lang/System",
            "out",
            "Ljava/io/PrintStream;"
        )
        mv.visitLdcInsn("this is add method print!")
        mv.visitMethodInsn(
            INVOKEVIRTUAL,
            "java/io/PrintStream",
            "println",
            "(Ljava/lang/String;)V",
            false
        )
        mv.visitInsn(RETURN)
        // this code uses a maximum of two stack elements and two local
        // variables
        mv.visitMaxs(0, 0)
        mv.visitEnd()

        return classWriter.toByteArray()