Java tutorial
/* * Copyright 2002-2017 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 * * https://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.view; import java.util.Map; import javax.servlet.RequestDispatcher; import javax.servlet.ServletException; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import org.springframework.lang.Nullable; import org.springframework.util.Assert; import org.springframework.util.StringUtils; import org.springframework.web.util.WebUtils; /** * Wrapper for a JSP or other resource within the same web application. * Exposes model objects as request attributes and forwards the request to * the specified resource URL using a {@link javax.servlet.RequestDispatcher}. * * <p>A URL for this view is supposed to specify a resource within the web * application, suitable for RequestDispatcher's {@code forward} or * {@code include} method. * * <p>If operating within an already included request or within a response that * has already been committed, this view will fall back to an include instead of * a forward. This can be enforced by calling {@code response.flushBuffer()} * (which will commit the response) before rendering the view. * * <p>Typical usage with {@link InternalResourceViewResolver} looks as follows, * from the perspective of the DispatcherServlet context definition: * * <pre class="code"><bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver"> * <property name="prefix" value="/WEB-INF/jsp/"/> * <property name="suffix" value=".jsp"/> * </bean></pre> * * Every view name returned from a handler will be translated to a JSP * resource (for example: "myView" -> "/WEB-INF/jsp/myView.jsp"), using * this view class by default. * * @author Rod Johnson * @author Juergen Hoeller * @author Rob Harrop * @see javax.servlet.RequestDispatcher#forward * @see javax.servlet.RequestDispatcher#include * @see javax.servlet.ServletResponse#flushBuffer * @see InternalResourceViewResolver * @see JstlView */ public class InternalResourceView extends AbstractUrlBasedView { private boolean alwaysInclude = false; private boolean preventDispatchLoop = false; /** * Constructor for use as a bean. * @see #setUrl * @see #setAlwaysInclude */ public InternalResourceView() { } /** * Create a new InternalResourceView with the given URL. * @param url the URL to forward to * @see #setAlwaysInclude */ public InternalResourceView(String url) { super(url); } /** * Create a new InternalResourceView with the given URL. * @param url the URL to forward to * @param alwaysInclude whether to always include the view rather than forward to it */ public InternalResourceView(String url, boolean alwaysInclude) { super(url); this.alwaysInclude = alwaysInclude; } /** * Specify whether to always include the view rather than forward to it. * <p>Default is "false". Switch this flag on to enforce the use of a * Servlet include, even if a forward would be possible. * @see javax.servlet.RequestDispatcher#forward * @see javax.servlet.RequestDispatcher#include * @see #useInclude(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse) */ public void setAlwaysInclude(boolean alwaysInclude) { this.alwaysInclude = alwaysInclude; } /** * Set whether to explicitly prevent dispatching back to the * current handler path. * <p>Default is "false". Switch this to "true" for convention-based * views where a dispatch back to the current handler path is a * definitive error. */ public void setPreventDispatchLoop(boolean preventDispatchLoop) { this.preventDispatchLoop = preventDispatchLoop; } /** * An ApplicationContext is not strictly required for InternalResourceView. */ @Override protected boolean isContextRequired() { return false; } /** * Render the internal resource given the specified model. * This includes setting the model as request attributes. */ @Override protected void renderMergedOutputModel(Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws Exception { // Expose the model object as request attributes. exposeModelAsRequestAttributes(model, request); // Expose helpers as request attributes, if any. exposeHelpers(request); // Determine the path for the request dispatcher. String dispatcherPath = prepareForRendering(request, response); // Obtain a RequestDispatcher for the target resource (typically a JSP). RequestDispatcher rd = getRequestDispatcher(request, dispatcherPath); if (rd == null) { throw new ServletException("Could not get RequestDispatcher for [" + getUrl() + "]: Check that the corresponding file exists within your web application archive!"); } // If already included or response already committed, perform include, else forward. if (useInclude(request, response)) { response.setContentType(getContentType()); if (logger.isDebugEnabled()) { logger.debug("Including [" + getUrl() + "]"); } rd.include(request, response); } else { // Note: The forwarded resource is supposed to determine the content type itself. if (logger.isDebugEnabled()) { logger.debug("Forwarding to [" + getUrl() + "]"); } rd.forward(request, response); } } /** * Expose helpers unique to each rendering operation. This is necessary so that * different rendering operations can't overwrite each other's contexts etc. * <p>Called by {@link #renderMergedOutputModel(Map, HttpServletRequest, HttpServletResponse)}. * The default implementation is empty. This method can be overridden to add * custom helpers as request attributes. * @param request current HTTP request * @throws Exception if there's a fatal error while we're adding attributes * @see #renderMergedOutputModel * @see JstlView#exposeHelpers */ protected void exposeHelpers(HttpServletRequest request) throws Exception { } /** * Prepare for rendering, and determine the request dispatcher path * to forward to (or to include). * <p>This implementation simply returns the configured URL. * Subclasses can override this to determine a resource to render, * typically interpreting the URL in a different manner. * @param request current HTTP request * @param response current HTTP response * @return the request dispatcher path to use * @throws Exception if preparations failed * @see #getUrl() */ protected String prepareForRendering(HttpServletRequest request, HttpServletResponse response) throws Exception { String path = getUrl(); Assert.state(path != null, "'url' not set"); if (this.preventDispatchLoop) { String uri = request.getRequestURI(); if (path.startsWith("/") ? uri.equals(path) : uri.equals(StringUtils.applyRelativePath(uri, path))) { throw new ServletException("Circular view path [" + path + "]: would dispatch back " + "to the current handler URL [" + uri + "] again. Check your ViewResolver setup! " + "(Hint: This may be the result of an unspecified view, due to default view name generation.)"); } } return path; } /** * Obtain the RequestDispatcher to use for the forward/include. * <p>The default implementation simply calls * {@link HttpServletRequest#getRequestDispatcher(String)}. * Can be overridden in subclasses. * @param request current HTTP request * @param path the target URL (as returned from {@link #prepareForRendering}) * @return a corresponding RequestDispatcher */ @Nullable protected RequestDispatcher getRequestDispatcher(HttpServletRequest request, String path) { return request.getRequestDispatcher(path); } /** * Determine whether to use RequestDispatcher's {@code include} or * {@code forward} method. * <p>Performs a check whether an include URI attribute is found in the request, * indicating an include request, and whether the response has already been committed. * In both cases, an include will be performed, as a forward is not possible anymore. * @param request current HTTP request * @param response current HTTP response * @return {@code true} for include, {@code false} for forward * @see javax.servlet.RequestDispatcher#forward * @see javax.servlet.RequestDispatcher#include * @see javax.servlet.ServletResponse#isCommitted * @see org.springframework.web.util.WebUtils#isIncludeRequest */ protected boolean useInclude(HttpServletRequest request, HttpServletResponse response) { return (this.alwaysInclude || WebUtils.isIncludeRequest(request) || response.isCommitted()); } }