通过Java反射测试类私有成员

在Java开发阶段，因为追求架构规范和遵循设计原则，所以要用private和protected修饰符去定义类的成员方法、变量、常量，这使得代码具封装性、内聚性等，但在测试阶段会造成一定的不便。通过Java的反射机制，便能很好地解决该问题。

ReflectUtil.java

//......

/**
 * @author yumin
 * @since 2015-03-02 14:52
 */
public class ReflectUtil {

    private ReflectUtil() {
    }

    //部份代码略

    public static Object invokeMethod(Object object, String methodName, Class[] parameterTypes, Object[] args) {
        Object result = null;

        if (null != object) {
            try {
                Method method = getDeclaredMethod(object, methodName, parameterTypes);
                result = method.invoke(object, args);
            } catch (NoSuchMethodException e) {
                //......
            } catch (IllegalAccessException e) {
                //......
            } catch (InvocationTargetException e) {
                //......
            }

        }

        return result;
    }

    public static Method getDeclaredMethod(Object object, String methodName, Class[] parameterTypes) throws NoSuchMethodException {
        Method method = null;

        if (null != object) {
            method = object.getClass().getDeclaredMethod(methodName, parameterTypes);
            method.setAccessible(true);
        }

        return method;
    }
}

ReflectUtilTest.java

//......

/**
 * @author yumin
 * @since 2015-03-02 14:53
 */
public class ReflectUtilTest {

    //部份代码略

    @Test
    public void testInvokeMethod() throws Exception {
        String whatIsYourName = null;
        String howOldAreYou = null;
        String name = "yumin";
        int age = 18;
        Person person = new Person();

        whatIsYourName = (String) ReflectUtil.invokeMethod(person, "whatIsYourName", null, null);
        howOldAreYou = (String) ReflectUtil.invokeMethod(person, "howOldAreYou", new Class[]{int.class}, new Object[]{age});

        Assert.assertEquals(Person.whatIsYourName + name, whatIsYourName);
        Assert.assertEquals(Person.howOldAreYou + age, howOldAreYou);
    }

    public class Person {

        public static final String whatIsYourName = "My name is ";
        public static final String howOldAreYou = "I‘m ";
        private String name = "yumin"; // 姓名

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

        private String whatIsYourName() {
            return whatIsYourName + name;
        }

        private String howOldAreYou(int age) {
            return howOldAreYou + age;
        }
    }
}

可以看到通过Java反射机制，实现了对被private和protected所修饰方法和属性的调用、取值、传值等读写操作，未破坏原始代码也能完成对私有成员的单元测试。需要特别注意的是，建议仅运用在测试场景，切莫图方便在生产环境发行的代码逻辑中也通过反射调用类私有成员，这样便破坏原有的类设计，产生不可预料的结果及污染体系结构造成后续难以维护。

更详细代码请参见：https://github.com/wangym/java-common/