org.springframework.webflow.ViewSelection Maven / Gradle / Ivy
/*
* Copyright 2002-2006 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.webflow;
import java.io.ObjectStreamException;
import java.io.Serializable;
/**
* Abstract base class for value objects that provide SWF callers with
* information about a logical response to issue and the data necessary to issue
* it.
*
* This class is a generic marker returned from a request into an executing flow
* has completed processing, indicating a client response needs to be issued. An
* instance of a ViewSelection subclass represents the selection of a concrete
* response type. It is expected that callers introspect the returned view
* selection instance to handle the response types they support.
*
* View selections are returned as a result of entering a {@link ViewState} or
* {@link EndState}, typically created by those states delegating to a
* {@link ViewSelector} factory (a creational strategy). When a state of either
* of those types is entered and returns, the caller into the web flow system is
* handed a fully-configured ViewSelection instance and is
* expected to present some form inteface to the client that allows for
* interaction at that point within the flow.
*
* @see org.springframework.webflow.ViewSelector
*
* @author Keith Donald
* @author Erwin Vervaet
*/
public abstract class ViewSelection implements Serializable {
/**
* Constant for a null or empty view selection, indicating no
* response should be issued.
*/
public static final ViewSelection NULL_VIEW = new NullViewSelection();
/**
* The definition of the 'null' view selection type, indicating that no
* response should be issued.
* @author Keith Donald
*/
private static final class NullViewSelection extends ViewSelection {
// resolve the singleton instance
private Object readResolve() throws ObjectStreamException {
return NULL_VIEW;
}
}
}