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XWork is an command-pattern framework that is used to power WebWork as well as other applications. XWork provides an Inversion of Control container, a powerful expression language, data type conversion, validation, and pluggable configuration.

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/*
 * Copyright (c) 2002-2006 by OpenSymphony
 * All rights reserved.
 */
package com.opensymphony.xwork2.interceptor;

import com.opensymphony.xwork2.ActionInvocation;
import com.opensymphony.xwork2.ModelDriven;
import com.opensymphony.xwork2.util.ValueStack;
import com.opensymphony.xwork2.util.CompoundRoot;


/**
 * 
 *
 * Watches for {@link ModelDriven} actions and adds the action's model on to the value stack.
 *
 *  Note:  The ModelDrivenInterceptor must come before the both {@link StaticParametersInterceptor} and
 * {@link ParametersInterceptor} if you want the parameters to be applied to the model.
 * 
 * 
 Note:  The ModelDrivenInterceptor will only push the model into the stack when the
 * model is not null, else it will be ignored.
 *
 * 
 *
 * 
 Interceptor parameters:
 *
 * 
 *
 * 

 *
 * refreshModelBeforeResult - set to true if you want the model to be refreshed on the value stack after action
 * execution and before result execution.  The setting is useful if you want to change the model instance during the
 * action execution phase, like when loading it from the data layer.  This will result in getModel() being called at
 * least twice.
 *
 * 
 *
 * 
 *
 *  Extending the interceptor:
 *
 * 

 *
 * 
 *
 * There are no known extension points to this interceptor.
 *
 * 
 *
 * 
 Example code:
 *
 * 
 * 
 * <action name="someAction" class="com.examples.SomeAction">
 *     <interceptor-ref name="modelDriven"/>
 *     <interceptor-ref name="basicStack"/>
 *     <result name="success">good_result.ftl</result>
 * </action>
 * 
 * 
 * 
 * @author tm_jee
 * @version $Date: 2007-11-07 08:21:46 +0100 (Wed, 07 Nov 2007) $ $Id: ModelDrivenInterceptor.java 1665 2007-11-07 07:21:46Z mrdon $
 */
public class ModelDrivenInterceptor extends AbstractInterceptor {

    protected boolean refreshModelBeforeResult = false;

    public void setRefreshModelBeforeResult(boolean val) {
        this.refreshModelBeforeResult = val;
    }

    public String intercept(ActionInvocation invocation) throws Exception {
        Object action = invocation.getAction();

        if (action instanceof ModelDriven) {
            ModelDriven modelDriven = (ModelDriven) action;
            ValueStack stack = invocation.getStack();
            Object model = modelDriven.getModel();
            if (model !=  null) {
            	stack.push(model);
            }
            if (refreshModelBeforeResult) {
                invocation.addPreResultListener(new RefreshModelBeforeResult(modelDriven, model));
            }
        }
        return invocation.invoke();
    }

    /**
     * Refreshes the model instance on the value stack, if it has changed
     */
    protected static class RefreshModelBeforeResult implements PreResultListener {
        private Object originalModel = null;
        protected ModelDriven action;


        public RefreshModelBeforeResult(ModelDriven action, Object model) {
            this.originalModel = model;
            this.action = action;
        }

        public void beforeResult(ActionInvocation invocation, String resultCode) {
            ValueStack stack = invocation.getStack();
            CompoundRoot root = stack.getRoot();

            boolean needsRefresh = true;
            Object newModel = action.getModel();

            // Check to see if the new model instance is already on the stack
            for (Object item : root) {
                if (item == newModel) {
                    needsRefresh = false;
                }
            }

            // Add the new model on the stack
            if (needsRefresh) {

                // Clear off the old model instance
                if (originalModel != null) {
                    root.remove(originalModel);
                }
                if (newModel != null) {
                    stack.push(newModel);
                }
            }
        }
    }
}