How to call a private method from outside a java class

问题

I have a Dummy class that has a private method called sayHello. I want to call sayHello from outside Dummy. I think it should be possible with reflection but I get an IllegalAccessException. Any ideas???

回答1:

use setAccessible(true) on your Method object before using its invoke method.

import java.lang.reflect.*;
class Dummy{
    private void foo(){
        System.out.println("hello foo()");
    }
}

class Test{
    public static void main(String[] args) throws Exception {
        Dummy d = new Dummy();
        Method m = Dummy.class.getDeclaredMethod("foo");
        //m.invoke(d);// throws java.lang.IllegalAccessException
        m.setAccessible(true);// Abracadabra 
        m.invoke(d);// now its OK
    }
}

回答2:

First you gotta get the class, which is pretty straight forward, then get the method by name using getDeclaredMethod then you need to set the method as accessible by setAccessible method on the Method object.

    Class<?> clazz = Class.forName("test.Dummy");

    Method m = clazz.getDeclaredMethod("sayHello");

    m.setAccessible(true);

    m.invoke(new Dummy());

回答3:

method = object.getClass().getDeclaredMethod(methodName);
method.setAccessible(true);
method.invoke(object);

回答4:

If you want to pass any parameter to private function you can pass it as second, third..... arguments of invoke function. Following is sample code.

Method meth = obj.getClass().getDeclaredMethod("getMyName", String.class);
meth.setAccessible(true);
String name = (String) meth.invoke(obj, "Green Goblin");

Full example you can see Here

回答5:

Example of accessing private method(with parameter) using java reflection as follows :

import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
class Test
{
    private void call(int n)  //private method
    {
        System.out.println("in call()  n: "+ n);
    }
}
public class Sample
{
    public static void main(String args[]) throws ClassNotFoundException,   NoSuchMethodException, SecurityException, InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException, NoSuchFieldException
    {
        Class c=Class.forName("Test");  //specify class name in quotes
        Object obj=c.newInstance();

        //----Accessing private Method
        Method m=c.getDeclaredMethod("call",new Class[]{int.class}); //getting method with parameters
        m.setAccessible(true);
        m.invoke(obj,7);
    }
}

来源：https://stackoverflow.com/questions/11282265/how-to-call-a-private-method-from-outside-a-java-class

标签

java

reflection

call

private