Java基础知识回顾11-反射基本操作

一、获取对象

创建一个测试的实体类

package day02;

/**
 * @author qx
 * @date 2023/10/11
 * @des
 */
public class Student {

    public Long id;

    public String name;

    public Student() {
    }

    public Student(Long id, String name) {
        this.id = id;
        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;
    }

    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
}

package day02;

import java.lang.reflect.Constructor;

/**
 * @author qx
 * @date 2023/10/27
 * @des
 */
public class ReflectTest {
    public static void main(String[] args) throws Exception {
        Class<?> aClass = Class.forName("day02.Student");
        // 1.通过无参构造器创建一个对象
        Student student = (Student) aClass.newInstance();
        System.out.println(student);

        // 2.通过构造器创建对象
        Constructor<?> declaredConstructor = aClass.getDeclaredConstructor(Long.class, String.class);
        Student student1 = (Student) declaredConstructor.newInstance(1L, "qx");
        System.out.println(student1);
    }
}

输出:

Student{id=null, name='null'}
Student{id=1, name='qx'}

二、调用普通方法

package day02;

import java.lang.reflect.Method;

/**
 * @author qx
 * @date 2023/10/27
 * @des
 */
public class ReflectTest {
    public static void main(String[] args) throws Exception {
        Class<?> aClass = Class.forName("day02.Student");
        Student student = (Student) aClass.newInstance();
        // 通过反射调用基本方法
        Method setNameMethod = aClass.getDeclaredMethod("setName", String.class);
        setNameMethod.invoke(student, "admin");
        System.out.println(student.getName());
    }
}

输出:

admin

三、通过反射获取属性

package day02;

import java.lang.reflect.Field;

/**
 * @author qx
 * @date 2023/10/27
 * @des
 */
public class ReflectTest {
    public static void main(String[] args) throws Exception {
        Class<?> aClass = Class.forName("day02.Student");
        Student student = (Student) aClass.newInstance();
        // 通过反射获取操作属性
        Field name = aClass.getDeclaredField("name");
        name.setAccessible(true);
        name.set(student,"lisi");
        System.out.println(student.getName());
    }
}

输出:

lisi

四、通过配置文件动态调用方法

1.创建一个配置文件

2.新建一个Person类

package day03;

/**
 * @author qx
 * @date 2023/10/27
 * @des
 */
public class Person {
    private Long id;
    private String name;

    public Person(){}

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

    public static void getPerson(){
        System.out.println("i am a person");
    }

}

3.通过反射获取配置文件中内容调用类中方法

package day03;

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.lang.reflect.Method;
import java.util.Properties;

/**
 * @author qx
 * @date 2023/10/27
 * @des
 */
public class ReflectTest {
    public static void main(String[] args) throws Exception {
        Properties properties = new Properties();
        properties.load(new FileReader("D:\\reflect.txt"));

        String classname = properties.getProperty("classname");
        String methodname = properties.getProperty("methodname");

        Class<?> aClass = Class.forName(classname);
        // 获取方法
        Method method = aClass.getMethod(methodname);
        // 通过反射执行方法
        method.invoke(aClass.newInstance());
    }
}

输出:

i am a person