org.springframework.webflow.execution.ViewSelection Maven / Gradle / Ivy
/*
* Copyright 2004-2007 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.execution;
import java.io.ObjectStreamException;
import java.io.Serializable;
/**
* Abstract base class for value objects that provide callers into a flow execution information about a logical response
* to issue and the data necessary to issue it.
*
* This class is a generic marker returned when 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.
*
* @see FlowExecution
*
* @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 NullView();
/**
* The definition of the 'null' view selection type, indicating that no response should be issued.
*/
private static final class NullView extends ViewSelection {
// resolve the singleton instance
private Object readResolve() throws ObjectStreamException {
return NULL_VIEW;
}
public String toString() {
return "null";
}
}
}