Java 基础 - Reflection: 访问私有的方法，成员变量

一. 访问自身的私有方法，成员变量

1 ) 比如我们有PrivateClassA.java

public class PrivateClassA {
	private Map<String, String> map = new HashMap<String, String>();
	
	public PrivateClassA(){		
		map.put("a", "a");
		map.put("b", "b");
	}	
	
	public void getPublic(){
		System.out.println("hi, I'm public method");
	}
	
	@SuppressWarnings("unused")
	private void getPrivate(){
		System.out.println("hi, I'm private method");
	}
}

2 ) 访问测试用例如下

public class PrivateClassATest {
	
	@Test
	public void testAccessPublic() throws Exception{
		Method med = PrivateClassA.class.getMethod("getPublic", new Class[]{});
		med.invoke(PrivateClassA.class.newInstance(), new Object[]{});
		
		Method med2 = PrivateClassA.class.getDeclaredMethod("getPublic", new Class[]{});
		med2.invoke(PrivateClassA.class.newInstance(), new Object[]{});
	}

	@Test
	public void testAccessPrivate() throws Exception{
		Method med = PrivateClassA.class.getDeclaredMethod("getPrivate", new Class[]{});
		
		med.setAccessible(true);
		med.invoke(PrivateClassA.class.newInstance(), new Object[]{});
	}
	
	// Access the private attribute
	@SuppressWarnings("unchecked")
	@Test
	public void testAccessPrivateAttribute()  throws Exception{
		// 如果访问的是私有变量，要用 getDeclaredField
		Field f = PrivateClassA.class.getDeclaredField("map");
		f.setAccessible( true );
		Map<String, String> map = (Map<String, String>) f.get( new PrivateClassA() );
		
		Assert.assertEquals( map.size(), 2 );
		Iterator<String> keyIter = map.keySet().iterator();
		Assert.assertEquals( keyIter.next(), "a" );
		Assert.assertEquals( keyIter.next(), "b" );
		
	}

}

二. 访问超类的私有方法，成员变量  

1 ) 比如我们有如下的子类和父类

// Super Class
public class PrivateFather {
	
	private void saidToChildren(){
		System.out.println("hi, child, I'm your private father");
	}
}

// Children
public class PrivateChildren extends PrivateFather{
	
}

2 ) 创建一个访问私有方法的工具类

public class ReflectionUtils {
	
	public static Method findMethod(Class srcClass, String name, Class[] parameters) throws NoSuchMethodException{
		Method method = null;
		try {
			method = srcClass.getDeclaredMethod(name, parameters);
		} catch (NoSuchMethodException e) {
			// TODO Auto-generated catch block
			if( srcClass.getSuperclass() == null ) 	throw e;
			else{
				return findMethod(srcClass.getSuperclass(), name, parameters);
			}
		}
		return method;
	}
}

 3 ) Junit Test cases

public class FatherPrivateMethodTest{
	
	@Test
	public void testGetPrivateFromFather() throws IllegalArgumentException, 
IllegalAccessException, InvocationTargetException, InstantiationException{
		Method superPrivateMed = null;
		try {
			superPrivateMed = ReflectionUtils.findMethod(PrivateChildren.class, "saidToChildren", null);
			superPrivateMed.setAccessible(true);
		} catch (NoSuchMethodException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		superPrivateMed.invoke(PrivateChildren.class.newInstance(), null);
		superPrivateMed.invoke(new PrivateChildren(), null);
	}
}

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