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spring framework 3.0.0 » org » springframework » web » servlet » ModelAndView.java
/*
 * Copyright 2002-2009 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.web.servlet;

import java.util.Map;

import org.springframework.ui.ModelMap;
import org.springframework.util.CollectionUtils;

/**
 * Holder for both Model and View in the web MVC framework.
 * Note that these are entirely distinct. This class merely holds
 * both to make it possible for a controller to return both model
 * and view in a single return value.
 *
 * <p>Represents a model and view returned by a handler, to be resolved
 * by a DispatcherServlet. The view can take the form of a String
 * view name which will need to be resolved by a ViewResolver object;
 * alternatively a View object can be specified directly. The model
 * is a Map, allowing the use of multiple objects keyed by name.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @author Rob Harrop
 * @see DispatcherServlet
 * @see ViewResolver
 * @see HandlerAdapter#handle
 * @see org.springframework.web.servlet.mvc.Controller#handleRequest
 */
public class ModelAndView {

  /** View instance or view name String */
  private Object view;

  /** Model Map */
  private ModelMap model;

  /**
   * Indicates whether or not this instance has been cleared with a call to {@link #clear()}.
   */
  private boolean cleared = false;


  /**
   * Default constructor for bean-style usage: populating bean
   * properties instead of passing in constructor arguments.
   * @see #setView(View)
   * @see #setViewName(String)
   */
  public ModelAndView() {
  }

  /**
   * Convenient constructor when there is no model data to expose.
   * Can also be used in conjunction with <code>addObject</code>.
   * @param viewName name of the View to render, to be resolved
   * by the DispatcherServlet's ViewResolver
   * @see #addObject
   */
  public ModelAndView(String viewName) {
    this.view = viewName;
  }

  /**
   * Convenient constructor when there is no model data to expose.
   * Can also be used in conjunction with <code>addObject</code>.
   * @param view View object to render
   * @see #addObject
   */
  public ModelAndView(View view) {
    this.view = view;
  }

  /**
   * Creates new ModelAndView given a view name and a model.
   * @param viewName name of the View to render, to be resolved
   * by the DispatcherServlet's ViewResolver
   * @param model Map of model names (Strings) to model objects
   * (Objects). Model entries may not be <code>null</code>, but the
   * model Map may be <code>null</code> if there is no model data.
   */
  public ModelAndView(String viewName, Map<String, ?> model) {
    this.view = viewName;
    if (model != null) {
      getModelMap().addAllAttributes(model);
    }
  }

  /**
   * Creates new ModelAndView given a View object and a model.
   * <emphasis>Note: the supplied model data is copied into the internal
   * storage of this class. You should not consider to modify the supplied
   * Map after supplying it to this class</emphasis>
   * @param view View object to render
   * @param model Map of model names (Strings) to model objects
   * (Objects). Model entries may not be <code>null</code>, but the
   * model Map may be <code>null</code> if there is no model data.
   */
  public ModelAndView(View view, Map<String, ?> model) {
    this.view = view;
    if (model != null) {
      getModelMap().addAllAttributes(model);
    }
  }

  /**
   * Convenient constructor to take a single model object.
   * @param viewName name of the View to render, to be resolved
   * by the DispatcherServlet's ViewResolver
   * @param modelName name of the single entry in the model
   * @param modelObject the single model object
   */
  public ModelAndView(String viewName, String modelName, Object modelObject) {
    this.view = viewName;
    addObject(modelName, modelObject);
  }

  /**
   * Convenient constructor to take a single model object.
   * @param view View object to render
   * @param modelName name of the single entry in the model
   * @param modelObject the single model object
   */
  public ModelAndView(View view, String modelName, Object modelObject) {
    this.view = view;
    addObject(modelName, modelObject);
  }


  /**
   * Set a view name for this ModelAndView, to be resolved by the
   * DispatcherServlet via a ViewResolver. Will override any
   * pre-existing view name or View.
   */
  public void setViewName(String viewName) {
    this.view = viewName;
  }

  /**
   * Return the view name to be resolved by the DispatcherServlet
   * via a ViewResolver, or <code>null</code> if we are using a View object.
   */
  public String getViewName() {
    return (this.view instanceof String ? (String) this.view : null);
  }

  /**
   * Set a View object for this ModelAndView. Will override any
   * pre-existing view name or View.
   */
  public void setView(View view) {
    this.view = view;
  }

  /**
   * Return the View object, or <code>null</code> if we are using a view name
   * to be resolved by the DispatcherServlet via a ViewResolver.
   */
  public View getView() {
    return (this.view instanceof View ? (View) this.view : null);
  }

  /**
   * Indicate whether or not this <code>ModelAndView</code> has a view, either
   * as a view name or as a direct {@link View} instance.
   */
  public boolean hasView() {
    return (this.view != null);
  }

  /**
   * Return whether we use a view reference, i.e. <code>true</code>
   * if the view has been specified via a name to be resolved by the
   * DispatcherServlet via a ViewResolver.
   */
  public boolean isReference() {
    return (this.view instanceof String);
  }

  /**
   * Return the model map. May return <code>null</code>.
   * Called by DispatcherServlet for evaluation of the model.
   */
  protected Map<String, Object> getModelInternal() {
    return this.model;
  }

  /**
   * Return the underlying <code>ModelMap</code> instance (never <code>null</code>).
   */
  public ModelMap getModelMap() {
    if (this.model == null) {
      this.model = new ModelMap();
    }
    return this.model;
  }

  /**
   * Return the model map. Never returns <code>null</code>.
   * To be called by application code for modifying the model.
   */
  public Map<String, Object> getModel() {
    return getModelMap();
  }


  /**
   * Add an attribute to the model.
   * @param attributeName name of the object to add to the model
   * @param attributeValue object to add to the model (never <code>null</code>)
   * @see ModelMap#addAttribute(String, Object)
   * @see #getModelMap()
   */
  public ModelAndView addObject(String attributeName, Object attributeValue) {
    getModelMap().addAttribute(attributeName, attributeValue);
    return this;
  }

  /**
   * Add an attribute to the model using parameter name generation.
   * @param attributeValue the object to add to the model (never <code>null</code>)
   * @see ModelMap#addAttribute(Object)
   * @see #getModelMap()
   */
  public ModelAndView addObject(Object attributeValue) {
    getModelMap().addAttribute(attributeValue);
    return this;
  }

  /**
   * Add all attributes contained in the provided Map to the model.
   * @param modelMap a Map of attributeName -> attributeValue pairs
   * @see ModelMap#addAllAttributes(Map)
   * @see #getModelMap()
   */
  public ModelAndView addAllObjects(Map<String, ?> modelMap) {
    getModelMap().addAllAttributes(modelMap);
    return this;
  }


  /**
   * Clear the state of this ModelAndView object.
   * The object will be empty afterwards.
   * <p>Can be used to suppress rendering of a given ModelAndView object
   * in the <code>postHandle</code> method of a HandlerInterceptor.
   * @see #isEmpty()
   * @see HandlerInterceptor#postHandle
   */
  public void clear() {
    this.view = null;
    this.model = null;
    this.cleared = true;
  }

  /**
   * Return whether this ModelAndView object is empty,
   * i.e. whether it does not hold any view and does not contain a model.
   */
  public boolean isEmpty() {
    return (this.view == null && CollectionUtils.isEmpty(this.model));
  }

  /**
   * Return whether this ModelAndView object is empty as a result of a call to {@link #clear}
   * i.e. whether it does not hold any view and does not contain a model.
   * <p>Returns <code>false</code> if any additional state was added to the instance
   * <strong>after</strong> the call to {@link #clear}.
   * @see #clear()
   */
  public boolean wasCleared() {
    return (this.cleared && isEmpty());
  }


  /**
   * Return diagnostic information about this model and view.
   */
  @Override
  public String toString() {
    StringBuilder sb = new StringBuilder("ModelAndView: ");
    if (isReference()) {
      sb.append("reference to view with name '").append(this.view).append("'");
    }
    else {
      sb.append("materialized View is [").append(this.view).append(']');
    }
    sb.append("; model is ").append(this.model);
    return sb.toString();
  }
}
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