callback.java

source code for fishnet

import java.lang.reflect.Method;
import java.lang.reflect.InvocationTargetException;

/**
 * <pre>   
 * Generic class to facilate use of callbacks
 * Also provides a static helper function to get an object of Method that can be passed to the constructor of this class
 * Example:
 *         To get a Method object for the method public foo(String str) in class Test:
 *         String[] paramTypes = {"java.lang.String"};
 *         Method method = Callback.getMethod("foo", this, paramTypes);
 *         Callback cb = new Callback(method, this, "fooTest");
 *
 * The above code snippet assumes that it is written inside class Test, hence the use of this.
 * The method must have public visibility.
 * </pre>   
 */
public class Callback {
    private Method method;
    private Object obj;
    private Object[] params;

    /**
     * Initializes member variables
     * @param method The method to be invoked
     * @param obj The object on which the method is to be invoked
     * @param params An array of objects to be passed to the method as parameters when it is invoked. 
     *               Can be null if no parameters are to be passed
     */
    public Callback(Method method, Object obj, Object[] params) {
	this.method = method;
	this.obj = obj;
	this.params = params;
    }

    /**
     * Sets the params to be passed to the method when it is invoked
     * @param params The params to be passed to the method when it is invoked
     */
    public void setParams(Object[] params) {
	this.params = params;
    }

    /**
     * Invokes the callback
     * @throws IllegalAccessException Thrown by invoke method in class Method 
     * @throws InvocationTargetException Thrown by invoke method in class Method, if the underlying method throws an exception
     */
    public void invoke() throws IllegalAccessException, InvocationTargetException {
	this.method.invoke(this.obj, this.params);
    }

    /**
     * Helper function to get a Method object which is needed to pass to the constructor of this class
     * @param methodName The name of the method that we want a Method object for
     * @param obj The object that owns the method
     * @return A Method object which can be passed to the constructor of this class
     * @param parameterTypes Array of strings of parameter type names. Can be null if there are no parameter types
     * @throws ClassNotFoundException This exception is thrown by Class.forName if the given class name does not exist
     * @throws NoSuchMethodException Thrown by Class.getMethod if a matching method is not found
     * @throws SecurityException Thrown by Class.getMethod if access to the information is denied
     */
    public static Method getMethod(String methodName, Object obj, String[] parameterTypes) throws ClassNotFoundException, 
												  NoSuchMethodException, 
												  SecurityException 
    {
	return obj.getClass().getMethod(methodName, Callback.getParameterTypes(parameterTypes));
    }

    private static Class[] getParameterTypes(String[] parameterTypes) throws ClassNotFoundException {
	if ((parameterTypes == null) || (parameterTypes.length == 0)) {
	    return null;
	}

	Class[] paramTypes = new Class[parameterTypes.length];
	for(int i = 0; i < paramTypes.length; i++) {
	    paramTypes[i] = Class.forName(parameterTypes[i]);
	}
	return paramTypes;
    }
}