java 反射机制及动态代理

2018-07-17 本文已影响0人 nade_s

反射概述
Reflection（反射）是Java被视为动态语言的关键，反射机制允许程序在执行期借助于Reflection API取得任何类的內部信息，并能直接操作任意对象的内部属性及方法。

Java反射机制主要提供了以下功能：

在运行时构造任意一个类的对象
在运行时获取任意一个类所具有的成员变量和方法
在运行时调用任意一个对象的方法（属性）
生成动态代理

Class 是一个类; 一个描述类的类.
　　封装了描述方法的 Method,
描述字段的 Filed,
描述构造器的 Constructor 等属性.
下面我们以student为例一一介绍

先说获取Class对象的三种方式
1.通过类名获取类名.class
2.通过对象获取对象名.getClass()
3.通过全类名获取 Class.forName(全类名)

   //类名.class
    Class<ConStudent> conSC = ConStudent.class;
    System.out.print("---------类名.class---------"+"\n");
    //对象名.getClass()
    ConStudent conStudent = new ConStudent();
    Class<? extends ConStudent> conSC1 = conStudent.getClass();
    System.out.print("---------对象名.getClass()---------"+"\n");
    //Class.forName(全类名)
    Class<?> conSC2 = Class.forName("com.reflection.ConStudent");
    System.out.print("---------Class.forName(全类名)---------");

---------类名.class---------
静态代码：10
---------对象名.getClass()---------
静态代码：10
---------Class.forName(全类名)---------

public class ConStudent {

public static int number = 10;
static {
    System.out.print("静态代码："+number+"\n");
}

}

通过以上方式可以看出第二第三种方式是直接调用静态代码的从方便和效率来看第三中方式是最好的第一种也不错第二种是不推荐的个人建议仅供参考

现在说一下 Constructor

先看一下实体类

/**

Constructor
*/
public class ConStudent {

public ConStudent(){
System.out.print("ConStudent空参构造函数"+"\n");
}

public ConStudent(double score) {
System.out.print("ConStudent有参构造函数"+"\n");
}

private ConStudent(int age) {
System.out.print("ConStudent私有构造带参数"+age+"\n");
}
protected ConStudent(String name){
System.out.print("ConStudent受保护的构造参数"+name+"\n");
}

}
private static void constructor() throws ClassNotFoundException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {

    Class<?> conSC = Class.forName("com.reflection.ConStudent");
    Constructor<?>[] constructors = conSC.getConstructors();
    for (Constructor c :constructors){
        System.out.print("ReflectTest所有公有构造："+c+"\n");
    }
    System.out.print("ReflectTest----------分割线-------------"+"\n");

    Constructor<?>[] declaredConstructors = conSC.getDeclaredConstructors();
    for (Constructor c : declaredConstructors){

        System.out.print("ReflectTest所有构造方法："+c+"\n");
    }
    System.out.print("ReflectTest----------分割线-------------"+"\n");
    Constructor constructor = conSC.getConstructor();
    System.out.print("ReflectTest公有无参构造方法"+constructor+"\n");
    System.out.print("ReflectTest----------分割线-------------"+"\n");
    Constructor<?> declaredConstructor = conSC.getDeclaredConstructor(int.class);
    System.out.print("ReflectTest私有构造方法"+declaredConstructor+"\n");
    declaredConstructor.setAccessible(true);
    Object o = declaredConstructor.newInstance(11);
    System.out.print("ReflectTest调用私有构造"+o+"\n");
    System.out.print("ReflectTest----------分割线-------------"+"\n");
    Constructor<?> declaredConstructor1 = conSC.getDeclaredConstructor(String.class);
    declaredConstructor1.setAccessible(true);
    Object maoge = declaredConstructor1.newInstance("maoge");
    System.out.print("ReflectTest受保护的构造："+maoge);

}

输出内容

ReflectTest所有公有构造：public com.reflection.ConStudent(double)
ReflectTest所有公有构造：public com.reflection.ConStudent()
ReflectTest----------分割线-------------
ReflectTest所有构造方法：protected com.reflection.ConStudent(java.lang.String)
ReflectTest所有构造方法：private com.reflection.ConStudent(int)
ReflectTest所有构造方法：public com.reflection.ConStudent(double)
ReflectTest所有构造方法：public com.reflection.ConStudent()
ReflectTest----------分割线-------------
ReflectTest公有无参构造方法public com.reflection.ConStudent()
ReflectTest----------分割线-------------
ReflectTest私有构造方法private com.reflection.ConStudent(int)
ConStudent私有构造带参数11
ReflectTest调用私有构造com.reflection.ConStudent@14ae5a5
ReflectTest----------分割线-------------
ConStudent受保护的构造参数maoge
ReflectTest受保护的构造：com.reflection.ConStudent@7f31245a
Process finished with exit code 0

下面看一下 Filed
实体也是三个参数代表三种权限

/**

Filed
*/
public class FiledStudent {
public int age;
private String name;
protected double score;

@Override
public String toString() {
return "FiledStudent{" +
"age=" + age +
", name='" + name + ''' +
", score=" + score +
'}';
}

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 double getScore() {
return score;
}

public void setScore(double score) {
this.score = score;
}
}

private static void filedTest() throws ClassNotFoundException, NoSuchFieldException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
Class<?> filedSC = Class.forName("com.reflection.FiledStudent");
Field[] fields = filedSC.getFields();
for (Field f :fields){
System.out.print("ReflectTest所有公有的参数："+f+"\n");
}
System.out.print("ReflectTest----------分割线-------------"+"\n");
Field age = filedSC.getField("age");
Object o = filedSC.getConstructor().newInstance();
age.set(o,11);
FiledStudent student = (FiledStudent) o;
System.out.print("ReflectTest获取公有参数："+student.getAge()+"\n");
System.out.print("ReflectTest----------分割线-------------"+"\n");
Field[] declaredFields = filedSC.getDeclaredFields();
for (Field f :declaredFields){
System.out.print("ReflectTest获取所有参数："+f+"\n");
}
System.out.print("ReflectTest----------分割线-------------"+"\n");
Field name = filedSC.getDeclaredField("name");
name.setAccessible(true);
name.set(o,"Maoge");

    System.out.print("ReflectTest获取指定的私有参数："+student.getName()+"\n");
    System.out.print("ReflectTest----------分割线-------------"+"\n");
    Field score = filedSC.getDeclaredField("score");
    score.setAccessible(true);
    score.set(o,9.8);
    System.out.print("ReflectTest获取受保护的参数："+student.getScore());

}

下面看 mothed

/**

Method
*/
public class MethodStudent{
int age;
String name;
double score;

public void showName( ){
System.out.print("(公共)姓名：");
}
private void showAge(){
System.out.print("（私有）年龄：");
}
protected void showScore(){
System.out.print("(保护)分数：");
}

public String printName(String name){
System.out.print("(公共string)name:"+name);
return name;
}
private double printScore(double score){
System.out.print("(私有double)score:"+score);
return score;
}
protected int printAge(int age){
System.out.print("(保护age)age:"+age);
return age;
}

}

private static void methodTest() throws ClassNotFoundException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
Class<?> methodSC = Class.forName("com.reflection.MethodStudent");
Method[] declaredMethods = methodSC.getDeclaredMethods();
for (Method m : declaredMethods){
System.out.print("ReflectTest 获取所有的方法："+m+"\n");
}
System.out.print("ReflectTest----------分割线-------------"+"\n");
Method[] methods = methodSC.getMethods();
for (Method m : methods){
System.out.print("ReflectTest获取所有的公有方法"+m+"\n");
}
System.out.print("ReflectTest----------分割线-------------"+"\n");
Method score = methodSC.getDeclaredMethod("printScore", double.class);
Object o = methodSC.getConstructor().newInstance();
score.setAccessible(true);
Object invoke = score.invoke(o, 9.8);
System.out.print("ReflectTest调用制定的私有方法："+invoke+"\n");
System.out.print("ReflectTest----------分割线-------------"+"\n");

    Method printName = methodSC.getMethod("printName", String.class);
    Object maoge = printName.invoke(o, "Maoge");
    System.out.print("ReflectTest公有有参数方法："+maoge+"\n");
    System.out.print("ReflectTest----------分割线-------------"+"\n");
    Method showName = methodSC.getMethod("showName", null);
    System.out.print("ReflectTest公有无参方法："+showName+"\n");
    System.out.print("ReflectTest----------分割线-------------"+"\n");
    Method printAge = methodSC.getDeclaredMethod("printAge", int.class);
    printAge.setAccessible(true);
    Object invoke1 = printAge.invoke(o, 20);
    System.out.print("ReflectTest受保护的方法："+invoke1);
}

这是反射的一些基础使用

下面说一下动态代理（代理可以让我们的方法或者类进行功能扩展解耦等好处）

新建一个接口

public interface Person {
void work();
}

新建一个接口实现类（被角色代理）

public class PersonImpl implements Person{

@Override
public void work() {
    System.out.print("i am PersonImpl.calss");

}

}

新建一个代理角色

public class PersonHandler implements InvocationHandler {
public Object px;

public PersonHandler(Object px) {
    this.px = px;
}

@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    System.out.print("do work"+"\n");
    return method.invoke(px,args);
}

}

绑定代理

public class PersonProxyTest {
public static void main(String[] args) {
Person person = new PersonImpl();
Person o = (Person) Proxy.newProxyInstance(Person.class.getClassLoader(), new Class[]{Person.class}, new PersonHandler(person));
o.work();
}

}

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java 反射机制及动态代理

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