Java 反射机制[Method反射]

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Java 反射机制[Method反射]

接着上一篇Java 反射机制[Field反射]，通过调用Person类的setName方法将obj的name字段的Value设置为"callPersonSetNameMethod"来了解什么是Method反射。示例代码很简单，很容易理解。

可以看到Method.invoke()实际上并不是自己实现的反射调用逻辑，而是委托给sun.reflect.MethodAccessor来处理。 真正的反射是调用MethodAccessor.invoke()真正完成反射调用。看源码可以发现MethodAccessor.invoke() 方法中出现了很多跟Cached有关的变量，说明method的反射十分消耗性能。

Java Code

/* * System Abbrev ： * system Name : * Component No ： * Component Name： * File name ：ReflectTestMain.java * Author ：Qiuzhenping * Date ：2014-10-25 * Description : */ /* Updation record 1： * Updation date : 2014-10-25 * Updator : Qiuzhenping * Trace No: * Updation No: * Updation Content: */ package com.qiuzhping.reflect.main; import java.lang.reflect.Constructor; import java.lang.reflect.Field; import java.lang.reflect.InvocationTargetException; import java.lang.reflect.Method; import java.lang.reflect.Modifier; /** * * 反射就是把Java类中的各种成分映射成相应的Java类。 * * * @author Qiuzhenping * @version [Version NO, 2014-10-25] * @see [Related classes/methods] * @since [product/module version] */ public class ReflectTestMain { /** */ public ReflectTestMain() { // TODO Auto-generated constructor stub } /** * 2014-10-25 * * @author Qiuzhenping * @param args [Parameters description] * @return void [Return type description] * @exception throws [Exception] [Exception description] * @see [Related classes#Related methods#Related properties] */ public static void main(String[] args) throws Exception{ // TODO Auto-generated method stub //Constructor[] contructor = Person.class.getConstructors(); //Method[] method = Person.class.getMethods(); Person p = new Person(24, "Qiuzhping", "100001", "Qiuzhping"); // Field [] field = p.getClass().getDeclaredFields(); // for(Field f:field){ // f.setAccessible(true); // System.out.println(f.getName()); // Object obj = f.get(p); // System.out.println(obj); // } changeStringValue(p); System.out.println(p.toString()); callPersonSetNameMethod(p); System.out.println(p.toString()); } /** * 通过调用Person类的setName方法将obj的name字段的Value设置为"callPersonSetNameMethod"来了解什么是Method反射 * 2014-10-26 * * @author Qiuzhenping * @param obj * @throws Exception [Parameters description] * @return void [Return type description] * @exception throws [Exception] [Exception description] * @see [Related classes#Related methods#Related properties] */ private static void callPersonSetNameMethod(Object obj) throws Exception { Method[] methods = Person.class.getMethods();//获取全部方法 for(Method m : methods){ m.setAccessible(true);//暴力反射 if(m.getName().equals("setName")){ m.invoke(obj, "callPersonSetNameMethod");//将obj的name字段的Value设置为"callPersonSetNameMethod" /** * 以下是Java method关于invoke方法的源码 * 可以看到Method.invoke()实际上并不是自己实现的反射调用逻辑，而是委托给sun.reflect.MethodAccessor来处理。 * 真正的反射是调用MethodAccessor.invoke()真正完成反射调用。 * 看源码可以发现MethodAccessor.invoke() 方法中出现了很多跟Cached有关的变量， * 说明method的反射十分消耗性能 * public Object invoke(Object obj, Object... args) throws IllegalAccessException, IllegalArgumentException, InvocationTargetException { if (!override) { if (!Reflection.quickCheckMemberAccess(clazz, modifiers)) { Class caller = Reflection.getCallerClass(1); Class targetClass = ((obj == null || !Modifier.isProtected(modifiers)) ? clazz : obj.getClass()); boolean cached; synchronized (this) { cached = (securityCheckCache == caller) && (securityCheckTargetClassCache == targetClass); } if (!cached) { Reflection.ensureMemberAccess(caller, clazz, obj, modifiers); synchronized (this) { securityCheckCache = caller; securityCheckTargetClassCache = targetClass; } } } } if (methodAccessor == null) acquireMethodAccessor(); return methodAccessor.invoke(obj, args); } * */ } } } /** * 将obj对象中的String类型的字段对应的Value中含有i的字符替换为abc * 2014-10-26 * * @author Qiuzhenping * @param obj [Parameters description] * @return void [Return type description] * @exception throws [Exception] [Exception description] * @see [Related classes#Related methods#Related properties] */ private static void changeStringValue(Object obj) throws Exception { Field[] fields = obj.getClass().getDeclaredFields(); for(Field f : fields){ f.setAccessible(true);//暴力反射 if(f.getType() == String.class){//字节码比较是用 == String oldValue = (String) f.get(obj); String newValue = oldValue.replaceAll("i", "abc");//将所有的i替换为abc f.set(obj, newValue); } } } static class Person { public Person(int age, String name, String id, String pwd) { super(); this.age = age; this.name = name; this.id = id; this.pwd = pwd; } @Override public String toString() { return "age = "+age +"\tname = "+name+"\tid = "+id+"\tpwd = "+pwd; } private int age; private String name; private String id; private String pwd; public int getAge() { return age; } public void setAge(int age) { this.age = age; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getId() { return id; } public void setId(String id) { this.id = id; } public String getPwd() { return pwd; } public void setPwd(String pwd) { this.pwd = pwd; } /** */ public Person() { // TODO Auto-generated constructor stub } } }