Java反射常用API

Java反射概述

Java通过反射技术可以动态的创建类的实例并可以拿到类的定义、方法、属性等，从而可以实现非常灵活的功能。

Java反射常用API

直接上代码。

MyReflect.java

package com.mrbcy.bigdata.basic.reflect;

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

import org.junit.Before;
import org.junit.Test;


public class MyReflect {
    public String className = null;
    public Class personClass = null;

    @Before
    public void init() throws Exception {
        className = "com.mrbcy.bigdata.basic.reflect.Person";
        personClass = Class.forName(className);
    }

    @Test
    public void getClassName() throws Exception {
        System.out.println(personClass);
    }

    @Test
    public void getClassName2() throws Exception {
        System.out.println(Person.class);
    }

    @Test
    // 获得实例
    public void getNewInstance() throws Exception {
        System.out.println(personClass.newInstance());
    }

    // 获得非私有的构造函数
    @Test
    public void getPublicConstructors() throws Exception {
        Constructor constructor = personClass.getConstructor(Long.class,String.class);
        Person person = (Person) constructor.newInstance(100L,"你好");
        System.out.println(person); 
    }

    // 获得私有的构造函数
    @Test
    public void getPrivateConstructor() throws Exception {
        Constructor constructor = personClass.getDeclaredConstructor(String.class);
        constructor.setAccessible(true); // 强制取消Java的权限检测
        Person person = (Person) constructor.newInstance("啊哈哈哈");
        System.out.println(person);
    }

    // 获得非私有的成员变量
    @Test
    public void getNotPrivateField() throws Exception {
        Constructor constructor = personClass.getConstructor(Long.class,String.class);
        Object object = constructor.newInstance(100L,"张三");

        Field field = personClass.getField("name");
        field.set(object, "李四");
        System.out.println(object);
    }

    // 获得私有的成员变量
    @Test
    public void getPrivateField() throws Exception {
        Constructor constructor = personClass.getConstructor(Long.class);
        Object object = constructor.newInstance(10000L);
        Field field = personClass.getDeclaredField("id");
        field.setAccessible(true);
        field.set(object, 1L);
        System.out.println(object);
    }

    /**
     *获取非私有的成员函数
     */
    @Test
    public void getNotPrivateMethod() throws Exception {
        System.out.println(personClass.getMethod("toString"));

        Object obj = personClass.newInstance();//获取空参的构造函数
        Method toStringMethod = personClass.getMethod("toString");
        Object object = toStringMethod.invoke(obj);
        System.out.println(object);
    }
    /**
     *获取私有的成员函数
     */
    @Test
    public void getPrivateMethod() throws Exception {
        Object obj = personClass.newInstance();//获取空参的构造函数
        Method method = personClass.getDeclaredMethod("getSomeThing");
        method.setAccessible(true);
        Object value = method.invoke(obj);
        System.out.println(value);

    }

    // 其他方法
    @Test
    public void otherMethod() throws Exception {
        //当前加载这个class文件的那个类加载器对象
        System.out.println(personClass.getClassLoader());
        //获取某个类实现的所有接口
        Class[] interfaces = personClass.getInterfaces();
        for (Class class1 : interfaces) {
            System.out.println(class1);
        }
        //反射当前这个类的直接父类
        System.out.println(personClass.getGenericSuperclass());
        /**
         * getResourceAsStream这个方法可以获取到一个输入流，这个输入流会关联到name所表示的那个文件上。
         */
        //path 不以’/'开头时默认是从此类所在的包下取资源，以’/'开头则是从ClassPath根下获取。其只是通过path构造一个绝对路径，最终还是由ClassLoader获取资源。
        System.out.println(personClass.getResourceAsStream("/log4j.properties"));
        System.out.println(personClass.getResourceAsStream("log4j.properties"));

        //判断当前的Class对象表示是否是数组
        System.out.println(personClass.isArray());
        System.out.println(new String[3].getClass().isArray());

        //判断当前的Class对象表示是否是枚举类
        System.out.println(personClass.isEnum());
        System.out.println(Class.forName("com.mrbcy.bigdata.basic.reflect.City").isEnum());

        //判断当前的Class对象表示是否是接口
        System.out.println(personClass.isInterface());
        System.out.println(Class.forName("com.mrbcy.bigdata.basic.reflect.TestInterface").isInterface());


    }
}

Person.java

package com.mrbcy.bigdata.basic.reflect;

import java.io.Serializable;



public class Person implements Serializable,TestInterface{
    private Long id;
    public String name;

    public Person() {
        this.id = 100L;
        this.name = "afsdfasd";
    }

    public Person(Long id, String name) {
//      super();
        this.id = id;
        this.name = name;
    }


    public Person(Long id) {
        super();
        this.id = id;
    }
    @SuppressWarnings("unused")
    private Person(String name) {
        super();
        this.name = name+"=======";
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String toString() {
        return "Person [id=" + id + ", name=" + name + "]";
    }
    private String getSomeThing() {
        return "sdsadasdsasd";
    }

    private void testPrivate(){
        System.out.println("this is a private method");
    }
}

TestInterface.java

package com.mrbcy.bigdata.basic.reflect;

public interface TestInterface {

}

City.java

package com.mrbcy.bigdata.basic.reflect;

public enum City {

}