Java利用ASM读取变量值（Field value）问题研究

作者：网络转载发布时间：[ 2013/2/21 9:45:13 ] 推荐标签：

　　看似问题解决了一个，但是接下来的问题是，那些非final和非基本数据类型的变量的值该如何获取呢？这个问题着实困扰了许久，google了一大顿（ps：还是翻墙的google）也没找到答案，网上用ASM的多是用其生成字节码。不死心我的决定自己研究。在网上的一片博客中，我注意到一个样例，给出的是用MethodVisitor来改变一个变量的值。于是，我立即把目光从FieldNode转移到MethodNode之上。通过观察变异后class字节码，几番周折，有了如下代码：

    /**
         * @param args
         * @author lihzh
         * @date 2012-4-21 下午10:17:22
         */
        public static void main(String[] args) {
            try {
                ClassReader reader = new ClassReader(
                        "cn.home.practice.bean.ForReadClass");
                ClassNode cn = new ClassNode();
                reader.accept(cn， 0);
                List<MethodNode> methodList = cn.methods;
                for (MethodNode md : methodList) {
                    System.out.println(md.name);
                    System.out.println(md.access);
                    System.out.println(md.desc);
                    System.out.println(md.signature);
                    List<LocalVariableNode> lvNodeList = md.localVariables;
                    for (LocalVariableNode lvn : lvNodeList) {
                        System.out.println("Local name: " + lvn.name);
                        System.out.println("Local name: " + lvn.start.getLabel());
                        System.out.println("Local name: " + lvn.desc);
                        System.out.println("Local name: " + lvn.signature);
                    }
                    Iterator<AbstractInsnNode> instraIter = md.instructions.iterator();
                    while (instraIter.hasNext()) {
                        AbstractInsnNode abi = instraIter.next();
                        if (abi instanceof LdcInsnNode) {
                            LdcInsnNode ldcI = (LdcInsnNode) abi;
                            System.out.println("LDC node value: " + ldcI.cst);
                        }
                    }
                }
                MethodVisitor mv = cn.visitMethod(Opcodes.AALOAD， "<init>"， Type
                        .getType(String.class).toString()， null， null);
                mv.visitFieldInsn(Opcodes.GETFIELD， Type.getInternalName(String.class)， "str"， Type
                        .getType(String.class).toString());
                System.out.println(cn.name);
                List<FieldNode> fieldList = cn.fields;
                for (FieldNode fieldNode : fieldList) {
                    System.out.println("Field name: " + fieldNode.name);
                    System.out.println("Field desc: " + fieldNode.desc);
                    System.out.println("Filed value: " + fieldNode.value);
                    System.out.println("Filed access: " + fieldNode.access);
                    if (fieldNode.visibleAnnotations != null) {
                        for (AnnotationNode anNode : fieldNode.visibleAnnotations) {
                            System.out.println(anNode.desc);
                        }
                    }
                }
            } catch (IOException e) {
                e.printStackTrace();
            } catch (SecurityException e) {
                e.printStackTrace();
            } catch (IllegalArgumentException e) {
                e.printStackTrace();
            }
        }