https://github.com/spring-projects/spring-framework: Spring Web MVC (Spring IO)
  • Juergen Hoeller 
/*
 * 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
 *
 *      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.mvc;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.beans.factory.BeanNameAware;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.util.WebUtils;


Spring Controller implementation that forwards to a named servlet,
i.e. the "servlet-name" in web.xml rather than a URL path mapping.
A target servlet doesn't even need a "servlet-mapping" in web.xml
in the first place: A "servlet" declaration is sufficient.

Useful to invoke an existing servlet via Spring's dispatching infrastructure,
for example to apply Spring HandlerInterceptors to its requests. This will work
even in a minimal Servlet container that does not support Servlet filters.

Example: web.xml, mapping all "/myservlet" requests to a Spring dispatcher.
Also defines a custom "myServlet", but without servlet mapping.

<servlet>
  <servlet-name>myServlet</servlet-name>
  <servlet-class>mypackage.TestServlet</servlet-class>
</servlet>
<servlet>
  <servlet-name>myDispatcher</servlet-name>
  <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
</servlet>
<servlet-mapping>
  <servlet-name>myDispatcher</servlet-name>
  <url-pattern>/myservlet</url-pattern>
</servlet-mapping>

Example: myDispatcher-servlet.xml, in turn forwarding "/myservlet" to your
servlet (identified by servlet name). All such requests will go through the
configured HandlerInterceptor chain (e.g. an OpenSessionInViewInterceptor).
From the servlet point of view, everything will work as usual.

<bean id="urlMapping" class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
  <property name="interceptors">
    <list>
      <ref bean="openSessionInViewInterceptor"/>
    </list>
  </property>
  <property name="mappings">
    <props>
      <prop key="/myservlet">myServletForwardingController</prop>
    </props>
  </property>
</bean>
<bean id="myServletForwardingController" class="org.springframework.web.servlet.mvc.ServletForwardingController">
  <property name="servletName"><value>myServlet</value></property>
</bean>


Author:Juergen Hoeller
See Also:
Since:1.1.1
/**
 * Spring Controller implementation that forwards to a named servlet,
 * i.e. the "servlet-name" in web.xml rather than a URL path mapping.
 * A target servlet doesn't even need a "servlet-mapping" in web.xml
 * in the first place: A "servlet" declaration is sufficient.
 *
 * <p>Useful to invoke an existing servlet via Spring's dispatching infrastructure,
 * for example to apply Spring HandlerInterceptors to its requests. This will work
 * even in a minimal Servlet container that does not support Servlet filters.
 *
 * <p><b>Example:</b> web.xml, mapping all "/myservlet" requests to a Spring dispatcher.
 * Also defines a custom "myServlet", but <i>without</i> servlet mapping.
 *
 * <pre class="code">
 * &lt;servlet&gt;
 *   &lt;servlet-name&gt;myServlet&lt;/servlet-name&gt;
 *   &lt;servlet-class&gt;mypackage.TestServlet&lt;/servlet-class&gt;
 * &lt;/servlet&gt;
 *
 * &lt;servlet&gt;
 *   &lt;servlet-name&gt;myDispatcher&lt;/servlet-name&gt;
 *   &lt;servlet-class&gt;org.springframework.web.servlet.DispatcherServlet&lt;/servlet-class&gt;
 * &lt;/servlet&gt;
 *
 * &lt;servlet-mapping&gt;
 *   &lt;servlet-name&gt;myDispatcher&lt;/servlet-name&gt;
 *   &lt;url-pattern&gt;/myservlet&lt;/url-pattern&gt;
 * &lt;/servlet-mapping&gt;</pre>
 *
 * <b>Example:</b> myDispatcher-servlet.xml, in turn forwarding "/myservlet" to your
 * servlet (identified by servlet name). All such requests will go through the
 * configured HandlerInterceptor chain (e.g. an OpenSessionInViewInterceptor).
 * From the servlet point of view, everything will work as usual.
 *
 * <pre class="code">
 * &lt;bean id="urlMapping" class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping"&gt;
 *   &lt;property name="interceptors"&gt;
 *     &lt;list&gt;
 *       &lt;ref bean="openSessionInViewInterceptor"/&gt;
 *     &lt;/list&gt;
 *   &lt;/property&gt;
 *   &lt;property name="mappings"&gt;
 *     &lt;props&gt;
 *       &lt;prop key="/myservlet"&gt;myServletForwardingController&lt;/prop&gt;
 *     &lt;/props&gt;
 *   &lt;/property&gt;
 * &lt;/bean&gt;
 *
 * &lt;bean id="myServletForwardingController" class="org.springframework.web.servlet.mvc.ServletForwardingController"&gt;
 *   &lt;property name="servletName"&gt;&lt;value&gt;myServlet&lt;/value&gt;&lt;/property&gt;
 * &lt;/bean&gt;</pre>
 *
 * @author Juergen Hoeller
 * @since 1.1.1
 * @see ServletWrappingController
 * @see org.springframework.orm.jpa.support.OpenEntityManagerInViewInterceptor
 * @see org.springframework.orm.jpa.support.OpenEntityManagerInViewFilter
 */
public class ServletForwardingController extends AbstractController implements BeanNameAware {

	@Nullable
	private String servletName;

	@Nullable
	private String beanName;


	public ServletForwardingController() {
		super(false);
	}


	
Set the name of the servlet to forward to,
i.e. the "servlet-name" of the target servlet in web.xml.

Default is the bean name of this controller.

/**
	 * Set the name of the servlet to forward to,
	 * i.e. the "servlet-name" of the target servlet in web.xml.
	 * <p>Default is the bean name of this controller.
	 */
	public void setServletName(String servletName) {
		this.servletName = servletName;
	}

	@Override
	public void setBeanName(String name) {
		this.beanName = name;
		if (this.servletName == null) {
			this.servletName = name;
		}
	}


	@Override
	protected ModelAndView handleRequestInternal(HttpServletRequest request, HttpServletResponse response)
			throws Exception {

		ServletContext servletContext = getServletContext();
		Assert.state(servletContext != null, "No ServletContext");
		RequestDispatcher rd = servletContext.getNamedDispatcher(this.servletName);
		if (rd == null) {
			throw new ServletException("No servlet with name '" + this.servletName + "' defined in web.xml");
		}

		// If already included, include again, else forward.
		if (useInclude(request, response)) {
			rd.include(request, response);
			if (logger.isTraceEnabled()) {
				logger.trace("Included servlet [" + this.servletName +
						"] in ServletForwardingController '" + this.beanName + "'");
			}
		}
		else {
			rd.forward(request, response);
			if (logger.isTraceEnabled()) {
				logger.trace("Forwarded to servlet [" + this.servletName +
						"] in ServletForwardingController '" + this.beanName + "'");
			}
		}

		return null;
	}

	
Determine whether to use RequestDispatcher's include or forward method. 
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.

Params:
  • request – current HTTP request
  • response – current HTTP response
See Also:
Returns:true for include, false for forward
/**
	 * 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 (WebUtils.isIncludeRequest(request) || response.isCommitted());
	}

}