How to set Array using reflection

Question

I have a class in which there is setter and getter like this

private String[] message;

public String[] getMessage() {
    return message;
}

public void setMessage(String[] message) {
    this.message = message;
}

Now i am trying to call setter using reflection like

private static String[] getMessageArray(int traineeIndex) {
    ....
    String[] messageArray = new String[nodesLength];

    for (int i = 0; i < nodesLength; i++) {
        ...
        messageArray[i] = nodeValue;
    }
    return messageArray;
} //end of getMessageArray()

private static void doProcessedStuff() {
     ...
     for (int i=1; i<=count ; i++) {

        Object myClassInstance = dynamicClassLoading(packageName, className);
        ...
        String[] messageArray = getMessageArray(i);
        printXpathResult(myClassInstance, result, messageArray);    
    }
} //end of doProcessedStuff()

public static void printXpathResult(Object myClassInstance, Object result, String[] messageArray){
    ...
    String methodName = methodPrefix + nodeName;  //setMessage
    invokeMethodDynamically(myClass, myClassInstance, methodName, null, messageArray);
} //end of printXpathResult()

private static void invokeMethodDynamically(Class<?> myClass, Object myClassInstance, String methodName, 
        String methodParameter, String[] messageArray) {
    ...
    if (messageArray != null) { 
        myMethod = myClass.getMethod(methodName, new Class[] { Array.class });
        String returnValue = (String) myMethod.invoke(myClassInstance, messageArray);            

    } else { 
        myMethod = myClass.getMethod(methodName, new Class[] { String.class }); 
        String returnValue = (String) myMethod.invoke(myClassInstance, new String(methodParameter));
    }
} //end of invokeMethodDynamically().

But when i come to line

myMethod = myClass.getMethod(methodName, new Class[] { Array.class });

i get the following error

java.lang.NoSuchMethodException: 
pk.training.basitMahmood.ParsingXmlUsingXpath.ResponseTrainee.
setMessage(java.lang.reflect.Array)
at java.lang.Class.getMethod(Class.java:1607)
at pk.training.basitMahmood.ParsingXmlUsingXpath.TryXpath.
invokeMethodDynamically(TryXpath.java:498)
...

What i am doing wrong ?

Thanks

did you checked this? docs.oracle.com/javase/tutorial/reflect/special/… — gurvinder372
– gurvinder372, Commented Jul 15, 2013 at 10:29

morgano · Accepted Answer · 2013-07-15 10:28:25Z

1

Try this in the line you're getting the error:

myMethod = myClass.getMethod(methodName, new Class[] { String[].class });

answered Jul 15, 2013 at 10:28

morgano

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2 Comments

Basit Over a year ago

Thanks. But now when i come to line String returnValue = (String) myMethod.invoke(myClassInstance, messageArray); I get the java.lang.IllegalArgumentException: wrong number of arguments. Why i am getting this exception. I have message array with 2 length(messageArray). Thanks

morgano Over a year ago

now in the second line try String returnValue = (String) myMethod.invoke(myClassInstance, (Object)messageArray)

veritas · Accepted Answer · 2013-07-15 10:44:00Z

You Might Need to cast The Array reference to Object before calling the invoke method. see the below example

public class ReflectionTest {

    public static void main(String[] args) throws SecurityException, NoSuchMethodException, IllegalArgumentException, IllegalAccessException, InvocationTargetException {
        String []  data = {"mango", "apple"};
        Method method = Dummy.class.getMethod("setMessage", new Class[] { String[].class });
        Dummy dummy = new Dummy();
        method.invoke(dummy,(Object)data);
        for(String mesg : dummy.getMessage()){
            System.out.println(mesg);
        }

    }

    static class Dummy  {

        private String [] message;

        public String[] getMessage() {
            return message;
        }

        public void setMessage(String[] message) {
            this.message = message;
        }
    }
}

Its because invoke method takes varargs as parameter which is essentially an array. So now if you pass array as an reference it thinks that you are passing array.length number of arguments. And hence Wrong Argument exception. So therefore you might need to cast it before Object ref so that it consider it as a Single argument

M Abbas · Accepted Answer · 2013-07-15 10:31:48Z

0

You should replace:

myMethod = myClass.getMethod(methodName, new Class[] { Array.class });

By

 myMethod = myClass.getMethod(methodName, new Class[] { String[].class });

answered Jul 15, 2013 at 10:31

M Abbas

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