Java基础知识回顾第七篇 - 反射Reflect

什么是java反射？核心在于一个对动态二字的理解，即：在运行状态中，能动态获取类的属性和方法，以及动态调用对象的属性和方法。

 

反射的作用：一方面用于反编译(.class到.java文件)，另一方面用来动态访问对象的属性、方法等。

 

反射机制中主要的类：

java.lang.Class;                

java.lang.reflect.Constructor; 

java.lang.reflect.Field;        

java.lang.reflect.Method;

java.lang.reflect.Modifier;

 

下面贴出一些示例代码：

package com.tu.test.reflect;

 

import java.io.Serializable;

 

public class User implements Serializable{

private static final long serialVersionUID = 9016949872478554542L;

 

public User() {

 

}

public User(String name,int age,String phone){

this.name = name;

this.age = age;

this.phone = phone;

}

 

private String name;

private int age;

private String phone;

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public int getAge() {

return age;

}

public void setAge(int age) {

this.age = age;

}

public String getPhone() {

return phone;

}

public void setPhone(String phone) {

this.phone = phone;

}

 

}

 

package com.tu.test.reflect;

 

import java.lang.reflect.Constructor;

import java.lang.reflect.Field;

import java.lang.reflect.Method;

import java.lang.reflect.Modifier;

 

public class ReflectTest {

//获取User类型

public static void getUser() throws Exception{

/**1、获取类**/

//获取类的第一种方法

Class clz1 = Class.forName("com.tu.test.reflect.User");

//获取类的第二种方法(java中每个类型都有class属性)

Class clz2 = User.class;

//获取类的第三种方法(java中任何一个对象都有getClass()方法)

User user = new User();

Class clz3 = user.getClass();

 

/**2、创建对象**/

Object userObj = clz1.newInstance();

 

/**3、获取类的所有属性、方法等信息**/

Field[] fields = clz1.getDeclaredFields();

StringBuilder fieldSb = new StringBuilder();

for (Field field : fields) {

fieldSb.append(Modifier.toString(field.getModifiers())).append(" ");

fieldSb.append(field.getType().getName()).append(" ");

fieldSb.append(field.getName()).append(" ");

fieldSb.append("\n");

}

System.out.println("User类的所有属性信息：" + fieldSb.toString());

 

Method[] methods = clz1.getDeclaredMethods();

StringBuilder methodSb = new StringBuilder();

for (Method method : methods) {

methodSb.append(Modifier.toString(method.getModifiers())).append(" ");

methodSb.append(method.getReturnType().getName()).append(" ");

methodSb.append(method.getName()).append(" ");

 

Class<?>[] paramClzs = method.getParameterTypes();

methodSb.append("(");

for (Class<?> paramClz : paramClzs) {

methodSb.append(paramClz.getName());

}

methodSb.append(method.getParameterTypes()).append(")");

methodSb.append("\n");

}

System.out.println("User类的所有方法信息：" + methodSb.toString());

 

Constructor[] constructors = clz1.getConstructors();

for (Constructor constructor : constructors) {

System.out.println("构造方法：" + constructor.getName());

}

 

/**4、获取特定属性**/

Field name = clz1.getDeclaredField("name");

name.setAccessible(true);//反射机制可打破java封装

name.set(userObj, "wuhoujian");

System.out.println("My name is : " + name.get(userObj));

}

 

public static void main(String[] args) {

try {

getUser();

} catch (Exception e) {

e.printStackTrace();

}

}

}

 

输出结果：

User类的所有属性信息：private static final long serialVersionUID 

private java.lang.String name 

private int age 

private java.lang.String phone 

 

User类的所有方法信息：public int getAge ([Ljava.lang.Class;@19bb25a)

public void setAge (int[Ljava.lang.Class;@da6bf4)

public java.lang.String getPhone ([Ljava.lang.Class;@1e58cb8)

public void setPhone (java.lang.String[Ljava.lang.Class;@179935d)

public java.lang.String getName ([Ljava.lang.Class;@b9e45a)

public void setName (java.lang.String[Ljava.lang.Class;@3ef810)

 

构造方法：com.tu.test.reflect.User

构造方法：com.tu.test.reflect.User

My name is : wuhoujian

 

补充一个示例：

package com.ali.test;

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.Arrays;

/**
 * Created by hjwue on 2016/11/24.
 */
public class DumpMethods {
    public static void main(String[] args) {
        try {
            Class myClass = Class.forName("java.util.HashMap");

System.out.println("Show all constructors:");
Constructor[] constructors = myClass.getDeclaredConstructors();
System.out.println("The size of all constructors is:" + constructors.length);
Arrays.asList(constructors).forEach(constructor -> System.out.println(constructor.toString()));

System.out.println("Show all public constructors:");
Constructor[] publicConstructors = myClass.getConstructors();
System.out.println("The size of all constructors is:" + publicConstructors.length);
Arrays.asList(publicConstructors).forEach(publicConstructor -> System.out.println(publicConstructor.toString()));

System.out.println("Show all fields:");
Field[] fields = myClass.getDeclaredFields();
System.out.println("The size of all fields is : " + fields.length);
Arrays.asList(fields).forEach(field -> System.out.println(field.toString()));

System.out.println("Show all public fields:");
Field[] publicFields = myClass.getFields();
System.out.println("The size of all public fields is : " + publicFields.length);
Arrays.asList(publicFields).forEach(publicField -> System.out.println(publicField.toString()));

System.out.println("Show all methods:");
Method[] methods = myClass.getDeclaredMethods();
System.out.println("The size of all method is : " + methods.length);
Arrays.asList(methods).forEach((m -> System.out.println(m.toString())));

System.out.println("Show all public methods:");
Method[] publicMethods = myClass.getMethods();
System.out.println("The size of all public method is : " + publicMethods.length);
Arrays.asList(publicMethods).forEach(publicMethod -> System.out.println(publicMethod.toString()));
} catch(Exception e){
            e.printStackTrace();
}
    }
}

 

注：关于上面为提到的操作方法，参考URL：http://tool.oschina.net/apidocs/apidoc?api=jdk-zh

API文档是一个很好的老师，大家平时要多查阅一下。