Java反射——通过Java反射机制设置属性值

    本示例使用Java反射机制分别设置当前类的private、public属性以及其父类的private属性来说明如何通过Java反射机制设置属性值。（注：设置继承的父类属性时，无法通过当前类的Class对象直接获取其属性字段，须通过其父类Class对象得到Field对象操作）

首先，建立父类User

public class User {
	private String name;
	private int age;

	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;
	}
}

建立子类Student继承User

public class Student extends User {
	//学号
	private String stuNo;
	//专业
	public String major;

	public String getStuNo() {
		return stuNo;
	}

	public void setStuNo(String stuNo) {
		this.stuNo = stuNo;
	}

	public String getMajor() {
		return major;
	}

	public void setMajor(String major) {
		this.major = major;
	}
}

新建测试类

public class Test {
	public static void main(String[] args) throws Exception {
		Object stu = new Student();
		Class clazz = stu.getClass();
		System.out.println("-------设置当前类stuNo(private)属性---------------");
		System.out.println("Before stuNo:"+((Student)stu).getStuNo());
		Field stuNo = clazz.getDeclaredField("stuNo");//通过反射获取stuNo字段
		stuNo.setAccessible(true);//private属性必须设置
		stuNo.set(stu,"13201233");
		System.out.println("After stuNo:"+((Student)stu).getStuNo());
		
		System.out.println("-------设置当前类major(public)属性---------------");
		System.out.println("Before major:"+((Student)stu).getMajor());
		Field major = clazz.getDeclaredField("major");//通过反射获取stuNo字段
		major.set(stu,"软件工程");
		System.out.println("After major:"+((Student)stu).getMajor());

		System.out.println("-------设置继承的父类name属性------------");
		System.out.println("Before name:"+((Student)stu).getName());
		Field name = clazz.getSuperclass().getDeclaredField("name");//通过反射获取父类name字段
		name.setAccessible(true);//private属性必须设置
		name.set(stu,"Edward");
		System.out.println("After name:"+((Student)stu).getName());
	}
}

运行结果：

-------设置当前类stuNo(private)属性---------------
Before stuNo:null
After stuNo:13201233
-------设置当前类major(public)属性---------------
Before major:null
After major:软件工程
-------设置继承的父类name属性------------
Before name:null
After name:Edward

注意：设置private属性值时，必须设置setAccessible(true)，否则会抛出如下异常：

Exception in thread "main" java.lang.IllegalAccessException: Class cn.ll.test.Test can not access a member of class cn.ll.test.Student with modifiers "private"
	at sun.reflect.Reflection.ensureMemberAccess(Reflection.java:102)
	at java.lang.reflect.AccessibleObject.slowCheckMemberAccess(AccessibleObject.java:296)
	at java.lang.reflect.AccessibleObject.checkAccess(AccessibleObject.java:288)
	at java.lang.reflect.Field.set(Field.java:761)
	at cn.ll.test.Test.main(Test.java:17)