通過反射，如何操作私有成員變量（取/賦值），如何調用私有方法？

Java的反射工具很強大，有句著名的話：No reflection ,no frameworks.

工作中直到涉及到UT，才體會到它的重要性，現歸納整理一個小例子：

 

反射工具類:

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

public class ReflectionUtil {

    /***
     * 獲取私有成員變量的值
     * 
     */
    public static Object getValue(Object instance, String fieldName)
            throws IllegalAccessException, NoSuchFieldException {

        Field field = instance.getClass().getDeclaredField(fieldName);
        field.setAccessible(true); // 參數值為true，禁止訪問控制檢查

        return field.get(instance);
    }

    /***
     * 設置私有成員變量的值
     * 
     */
    public static void setValue(Object instance, String fileName, Object value)
            throws NoSuchFieldException, SecurityException, IllegalArgumentException, IllegalAccessException {

        Field field = instance.getClass().getDeclaredField(fileName);
        field.setAccessible(true);
        field.set(instance, value);
    }

    /***
     * 訪問私有方法
     * 
     */
    public static Object callMethod(Object instance, String methodName, Class[] classes, Object[] objects)
            throws NoSuchMethodException, SecurityException, IllegalAccessException, IllegalArgumentException,
            InvocationTargetException {

        Method method = instance.getClass().getDeclaredMethod(methodName, classes);
        method.setAccessible(true);
        return method.invoke(instance, objects);
    }
}

 

package com.test;

public class Person {

    private String name;
    private int age;

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    private String getInfo(String str, int num) {
        return str + num + " apples";
    }

}

 

import com.test.Person;

public class ReflectTest {

    public static void main(String[] args) throws Exception {

        Person person = new Person("jack", 25);

        // test get private value
        System.out.println("jack's name:" + ReflectionUtil.getValue(person, "name"));
        System.out.println("jack's age:" + ReflectionUtil.getValue(person, "age"));

        // test set private value
        ReflectionUtil.setValue(person, "name", "jason");
        ReflectionUtil.setValue(person, "age", 10);
        System.out.println("jack's name:" + ReflectionUtil.getValue(person, "name"));
        System.out.println("jack's age:" + ReflectionUtil.getValue(person, "age"));

        // test call private method
        String result = (String) ReflectionUtil.callMethod(person, "getInfo", new Class[] { String.class, int.class },
                new Object[] { "I hava ", 4 });
        System.out.println("result: " + result);
    }
}

 

結果：

jack's name:jack
jack's age:25
jack's name:jason
jack's age:10
result: I hava 4 apples