java进阶---反射

获取class对象

	@Test
    void reflect() throws Exception {
        Class userClass = User.class;
        System.out.println(userClass.getName()); // 全类名 com.zyw.proxydemo.pojo.User
        System.out.println(userClass.getSimpleName()); // 简名 User
        Class userClass1 = Class.forName("com.zyw.proxydemo.pojo.User");
        System.out.println(userClass == userClass1);
        User user = new User();
        Class userClass2 = user.getClass();
        System.out.println(userClass1 == userClass2);
    }

输出结果

User在内存中只存在一份class对象,所有三种方式拿到的是同一个class对象

获取类的构造器

	@Test
    void reflect() throws Exception {
        Class userClass = User.class;
        Constructor[] constructors = userClass.getConstructors();
        for (Constructor constructor : constructors) {
            System.out.println(constructor.getName() + "--->" + constructor.getParameterCount());
        }
        // 获取某个构造器
        // 有参构造  public User(String name, Integer age) 
        Constructor constructor = userClass.getConstructor(String.class, Integer.class);
        // 无参构造
        Constructor constructor1 = userClass.getConstructor();

    }

用构造器创建对象

	@Test
    void reflect() throws Exception {
        Class userClass = User.class;
        // 获取某个构造器
        // 有参构造  public User(String name, Integer age)
        Constructor constructor = userClass.getDeclaredConstructor(String.class, Integer.class);
        // 无参构造
        Constructor constructor1 = userClass.getDeclaredConstructor();

        User user = (User) constructor1.newInstance();
        user.setName("chenlin");
        user.setAge(18);

        constructor.setAccessible(true); // 禁止检查访问权限 
        User user1 = (User) constructor.newInstance("mahong", 18);
        System.out.println(user1.getName());
    }

获取类的成员变量

    @Test
    void reflect() throws Exception {
        Class userClass = User.class;
        Field[] fields = userClass.getDeclaredFields();
        for (Field field : fields) {
            System.out.println(field.getName() + ": " + field.getType());
        }
        // 某个成员变量
        Field age = userClass.getDeclaredField("age");
        age.setAccessible(true); // 暴力反射
        // 赋值
        User user = new User();
        age.set(user, 18);
        // 取值
        Integer age1 = (Integer) age.get(user);
        System.out.println(age1);
    }

获取类的成员方法

    @Test
    void reflect() throws Exception {
        Class userClass = User.class;
        // 获取所有的方法
        Method[] methods = userClass.getDeclaredMethods();
        // 获取某个方法
        Method method = userClass.getDeclaredMethod("say", String.class);
        method.setAccessible(true);
        User user = new User();
        String result = (String) method.invoke(user, "nihao");
        System.out.println(result);
    }

应用场景

• 反射在框架开发中广泛使用, 下面是一个简单使用的例子

import java.io.*;
import java.lang.reflect.Field;


/**
 * 将对象信息持久化到文件
 * @author zhou yu
 * @date 2024/4/9 8:29
 */
public class ObjectFrame {

    public static void savaObject(Object object) throws Exception {
        Class oClass = object.getClass();
        String simpleName = oClass.getSimpleName();
        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(new FileOutputStream("src\\save.txt", true)));
        bw.write("-------------" + simpleName + "-------------\n");
        Field[] fields = oClass.getDeclaredFields();
        for (Field field : fields) {
            field.setAccessible(true);
            String name = field.getName();
            String value = field.get(object) + "";
            bw.write(name + ": " + value + "\n");
        }
        bw.write("\n");
        bw.flush();
        bw.close();
    }
}