Any way to Invoke a private method?
If the method accepts non-primitive data type then the following method can be used to invoke a private method of any class:
public static Object genericInvokeMethod(Object obj, String methodName,
Object... params) {
int paramCount = params.length;
Method method;
Object requiredObj = null;
Class<?>[] classArray = new Class<?>[paramCount];
for (int i = 0; i < paramCount; i++) {
classArray[i] = params[i].getClass();
}
try {
method = obj.getClass().getDeclaredMethod(methodName, classArray);
method.setAccessible(true);
requiredObj = method.invoke(obj, params);
} catch (NoSuchMethodException e) {
e.printStackTrace();
} catch (IllegalArgumentException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
}
return requiredObj;
}
The Parameter accepted are obj, methodName and the parameters. For example
public class Test {
private String concatString(String a, String b) {
return (a+b);
}
}
Method concatString can be invoked as
Test t = new Test();
String str = (String) genericInvokeMethod(t, "concatString", "Hello", "Mr.x");
you can do this using ReflectionTestUtils of Spring (org.springframework.test.util.ReflectionTestUtils)
ReflectionTestUtils.invokeMethod(instantiatedObject,"methodName",argument);
Example : if you have a class with a private method square(int x)
Calculator calculator = new Calculator();
ReflectionTestUtils.invokeMethod(calculator,"square",10);
Use getDeclaredMethod()
to get a private Method object and then use method.setAccessible()
to allow to actually call it.
You can invoke private method with reflection. Modifying the last bit of the posted code:
Method method = object.getClass().getDeclaredMethod(methodName);
method.setAccessible(true);
Object r = method.invoke(object);
There are a couple of caveats. First, getDeclaredMethod
will only find method declared in the current Class
, not inherited from supertypes. So, traverse up the concrete class hierarchy if necessary. Second, a SecurityManager
can prevent use of the setAccessible
method. So, it may need to run as a PrivilegedAction
(using AccessController
or Subject
).