SpringMVC 3：Controller接口及其实现类_spring interface 调用接口 controller

※. Controller接口及其实现类

    Controller是控制器接口,此处只有一个方法handleRequest,
用于进行请求的功能处理,处理完请求后返回ModelAndView(Model模型数据部分 和 View视图部分)。
    
    如果想直接在处理器/控制器里使用response向客户端写回数据,
    可以通过返回null来告诉DispatcherServlet我们已经写出响应了,
    不需要它进行视图解析

例：
 
package com.briup.web.controller;
 
import java.io.PrintWriter;
 
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.mvc.Controller;
 
public class SecondController 
	implements Controller{
 
	@Override
	public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception {
//		PrintWriter pw=
//					response.getWriter();
//		pw.println("test...ok");
//		pw.flush();
                //request.getSession(false);
                //false：有session返回session对象，没有session返回null
                //true：有session返回session对象，没有session对象创建session
		request.getSession();
                //可以服务器内部页面跳转，不能重定向
                //因为浏览器拿不到WEB-INF下的jsp文件
		request.getRequestDispatcher("/WEB-INF/jsp/hello.jsp")
			.forward(request, response);
		//返回null 前端控制器不会调用
	//视图解析器处理
		return null;
	}
 
}
 
 
 
2.spring.xml配置
 
<bean name="/second" 
	class="com.briup.web.controller.SecondController"></bean>

    Spring默认提供了一些Controller接口的实现类以方便我们使用,在Eclipse中选择Controller接口然后右
键open type Hierarchy即可查看改接口的实现类,每个实现类都有自己特殊的功能,这里以实现类AbstractController为例简单介绍下。
    查看AbstractController类中代码可知,我们写一个Controller的时候可以继承AbstractController然后实现handleRequestInternal方法即可。

AbstractController类中private boolean synchronizeOnSession = false;锁属性定义了会话串行。

WebContentGenerator类中private Set<String> supportedMethods;属性设置了请求方式。

WebContentGenerator类中private boolean requireSession = false;属性判断了是否有session对象，没有报错。

WebContentGenerator类中private int cacheSeconds = -1;属性设置了是否缓存上次内容。

（AbstractController类，WebContentGenerator类可在jar包查看源码：spring-webmvc-5.0.10.RELEASE-sources.jar）

（注：RELEASE测试jar包）

都可以通过继承利用见下例：ThirdController.java类的配置。

    提供了【可选】的会话的串行化访问功能,例如:
  

 //即同一会话,线程同步
    public class HelloWorldController extends AbstractController{
        @Override
        protected ModelAndView handleRequestInternal(HttpServletRequest request, HttpServletResponse response)
                throws Exception {
            
            String name = request.getParameter("name");
            
            //ModelAndView对象中包括了要返回的逻辑视图,以及数据模型
            ModelAndView mv = new ModelAndView();
            //设置视图名称,可以是字符串 也可以是视图对象
            mv.setViewName("hello");
            //设置数据模型
            mv.addObject("name", name);
            
            return mv;
        }
 
 
    }
    <!--synchronizeOnSession,统一浏览器访问串行-->
    <bean name="/hello" class="com.briup.web.controller.HelloWorldController">
        <property name="synchronizeOnSession" value="test"></property>
    </bean>
 
    
 
    直接通过response写响应,例如:
    public class HelloWorldController extends AbstractController{
        @Override
        protected ModelAndView handleRequestInternal(HttpServletRequest request, HttpServletResponse response)
                throws Exception {
            
            response.getWriter().write("Hello World!!");        
            //如果想直接在该处理器/控制器写响应 可以通过返回null告诉DispatcherServlet自己已经写出响应了,不需要它进行视图解析
 
            return null;
        }
 
    }

    
    强制请求方法类型,例如:
  

  //只支持post和get方法
    <bean name="/hello" class="com.briup.web.controller.HelloWorldController">
        <property name="supportedMethods" value="POST,GET"></property>
    </bean>
 
 
    当前请求的session前置条件检查,如果当前请求无session将抛出HttpSessionRequiredException异常,例如:
    //在进入该控制器时,一定要有session存在,否则抛出HttpSessionRequiredException异常。
 
    <bean name="/hello" class="com.briup.web.controller.HelloWorldController">
        <property name="requireSession" value="true"/>
    </bean>

 ThirdController类：

例：避免重复刷新造成线程不安全
 
package com.briup.web.controller;
 
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.mvc.AbstractController;
 
/*
 * 实现特定的功能用特定类
 * 
 *同一个个浏览器。发出多个请求
 *请求相同的资源的时候，会话级别的
 *对访问的资源加锁
 *注意：浏览器每次发出一个请求服务器
 *都会启动一个线程去处理（多次请求
 *用同一个线程，也可能多个请求用的
 *不同的线程）
 */
public class ThirdController 
		extends AbstractController{
	@Override
	protected ModelAndView handleRequestInternal(HttpServletRequest request, HttpServletResponse response)
			throws Exception {
		ModelAndView mv=
					new ModelAndView();
		mv.setViewName("hello");
		return mv;
	}
 
}
 
 
 
 
spring.xml配置：
 
<bean name="/third" 
	class="com.briup.web.controller.ThirdController">
		<!-- <property name="synchronizeOnSession" 
					value="true"></property> -->
				<!--本次请求支持提交的方式 WebControllerGenerator类中supportedMethods属性 -->
                                <!--value中没有请求提交的方式会报405错误-->
				<!-- <property name="supportedMethods" value="POST,GET">
				</property> -->
				<!-- 本次请求,服务器必须给当前浏览器
				构建过session 会话，没有session直接报错
				 -->
				<!-- <property name="requireSession" 
					value="true"></property> -->
				<!-- （-1）表示默认，缓存上次的内容
					0 表示直接不缓存
					正数，表示缓存，缓存时间的设置
				 -->
				<property name="cacheSeconds" value="0"></property>
	</bean>

注：Controller抽象类Spring给了很多，方法很多，扩展性很强。
 
AbstractController类
 
/*
 * Copyright 2002-2016 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.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
 
import org.springframework.http.HttpMethod;
import org.springframework.lang.Nullable;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.support.WebContentGenerator;
import org.springframework.web.util.WebUtils;
 
/**
 * Convenient superclass for controller implementations, using the Template Method
 * design pattern.
 *
 * <p><b><a name="workflow">Workflow
 * (<a href="Controller.html#workflow">and that defined by interface</a>):</b><br>
 * <ol>
 * <li>{@link #handleRequest(HttpServletRequest, HttpServletResponse) handleRequest()}
 * will be called by the DispatcherServlet</li>
 * <li>Inspection of supported methods (ServletException if request method
 * is not support)</li>
 * <li>If session is required, try to get it (ServletException if not found)</li>
 * <li>Set caching headers if needed according to the cacheSeconds property</li>
 * <li>Call abstract method
 * {@link #handleRequestInternal(HttpServletRequest, HttpServletResponse) handleRequestInternal()}
 * (optionally synchronizing around the call on the HttpSession),
 * which should be implemented by extending classes to provide actual
 * functionality to return {@link org.springframework.web.servlet.ModelAndView ModelAndView} objects.</li>
 * </ol>
 *
 * <p><b><a name="config">Exposed configuration properties</a>
 * (<a href="Controller.html#config">and those defined by interface</a>):</b><br>
 * <table border="1">
 * <tr>
 * <td><b>name</b></th>
 * <td><b>default</b></td>
 * <td><b>description</b></td>
 * </tr>
 * <tr>
 * <td>supportedMethods</td>
 * <td>GET,POST</td>
 * <td>comma-separated (CSV) list of methods supported by this controller,
 * such as GET, POST and PUT</td>
 * </tr>
 * <tr>
 * <td>requireSession</td>
 * <td>false</td>
 * <td>whether a session should be required for requests to be able to
 * be handled by this controller. This ensures that derived controller
 * can - without fear of null pointers - call request.getSession() to
 * retrieve a session. If no session can be found while processing
 * the request, a ServletException will be thrown</td>
 * </tr>
 * <tr>
 * <td>cacheSeconds</td>
 * <td>-1</td>
 * <td>indicates the amount of seconds to include in the cache header
 * for the response following on this request. 0 (zero) will include
 * headers for no caching at all, -1 (the default) will not generate
 * <i>any headers</i> and any positive number will generate headers
 * that state the amount indicated as seconds to cache the content</td>
 * </tr>
 * <tr>
 * <td>synchronizeOnSession</td>
 * <td>false</td>
 * <td>whether the call to {@code handleRequestInternal} should be
 * synchronized around the HttpSession, to serialize invocations
 * from the same client. No effect if there is no HttpSession.
 * </td>
 * </tr>
 * </table>
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @author Rossen Stoyanchev
 * @see WebContentInterceptor
 */
public abstract class AbstractController extends WebContentGenerator implements Controller {
 
	private boolean synchronizeOnSession = false;
 
 
	/**
	 * Create a new AbstractController which supports
	 * HTTP methods GET, HEAD and POST by default.
	 */
	public AbstractController() {
		this(true);
	}
 
	/**
	 * Create a new AbstractController.
	 * @param restrictDefaultSupportedMethods {@code true} if this
	 * controller should support HTTP methods GET, HEAD and POST by default,
	 * or {@code false} if it should be unrestricted
	 * @since 4.3
	 */
	public AbstractController(boolean restrictDefaultSupportedMethods) {
		super(restrictDefaultSupportedMethods);
	}
 
 
	/**
	 * Set if controller execution should be synchronized on the session,
	 * to serialize parallel invocations from the same client.
	 * <p>More specifically, the execution of the {@code handleRequestInternal}
	 * method will get synchronized if this flag is "true". The best available
	 * session mutex will be used for the synchronization; ideally, this will
	 * be a mutex exposed by HttpSessionMutexListener.
	 * <p>The session mutex is guaranteed to be the same object during
	 * the entire lifetime of the session, available under the key defined
	 * by the {@code SESSION_MUTEX_ATTRIBUTE} constant. It serves as a
	 * safe reference to synchronize on for locking on the current session.
	 * <p>In many cases, the HttpSession reference itself is a safe mutex
	 * as well, since it will always be the same object reference for the
	 * same active logical session. However, this is not guaranteed across
	 * different servlet containers; the only 100% safe way is a session mutex.
	 * @see AbstractController#handleRequestInternal
	 * @see org.springframework.web.util.HttpSessionMutexListener
	 * @see org.springframework.web.util.WebUtils#getSessionMutex(javax.servlet.http.HttpSession)
	 */
	public final void setSynchronizeOnSession(boolean synchronizeOnSession) {
		this.synchronizeOnSession = synchronizeOnSession;
	}
 
	/**
	 * Return whether controller execution should be synchronized on the session.
	 */
	public final boolean isSynchronizeOnSession() {
		return this.synchronizeOnSession;
	}
 
 
	@Override
	@Nullable
	public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response)
			throws Exception {
 
		if (HttpMethod.OPTIONS.matches(request.getMethod())) {
			response.setHeader("Allow", getAllowHeader());
			return null;
		}
 
		// Delegate to WebContentGenerator for checking and preparing.
		checkRequest(request);
		prepareResponse(response);
 
		// Execute handleRequestInternal in synchronized block if required.
		if (this.synchronizeOnSession) {
			HttpSession session = request.getSession(false);
			if (session != null) {
				Object mutex = WebUtils.getSessionMutex(session);
				synchronized (mutex) {
					return handleRequestInternal(request, response);
				}
			}
		}
 
		return handleRequestInternal(request, response);
	}
 
	/**
	 * Template method. Subclasses must implement this.
	 * The contract is the same as for {@code handleRequest}.
	 * @see #handleRequest
	 */
	@Nullable
	protected abstract ModelAndView handleRequestInternal(HttpServletRequest request, HttpServletResponse response)
			throws Exception;
 
}
 
 
 
WebContentGenerator类
 
/*
 * Copyright 2002-2018 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.support;
 
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.LinkedHashSet;
import java.util.Set;
import java.util.concurrent.TimeUnit;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
import org.springframework.http.CacheControl;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpMethod;
import org.springframework.lang.Nullable;
import org.springframework.util.ObjectUtils;
import org.springframework.util.StringUtils;
import org.springframework.web.HttpRequestMethodNotSupportedException;
import org.springframework.web.HttpSessionRequiredException;
import org.springframework.web.context.support.WebApplicationObjectSupport;
 
/**
 * Convenient superclass for any kind of web content generator,
 * like {@link org.springframework.web.servlet.mvc.AbstractController}
 * and {@link org.springframework.web.servlet.mvc.WebContentInterceptor}.
 * Can also be used for custom handlers that have their own
 * {@link org.springframework.web.servlet.HandlerAdapter}.
 *
 * <p>Supports HTTP cache control options. The usage of corresponding HTTP
 * headers can be controlled via the {@link #setCacheSeconds "cacheSeconds"}
 * and {@link #setCacheControl "cacheControl"} properties.
 *
 * <p><b>NOTE:</b> As of Spring 4.2, this generator's default behavior changed when
 * using only {@link #setCacheSeconds}, sending HTTP response headers that are in line
 * with current browsers and proxies implementations (i.e. no HTTP 1.0 headers anymore)
 * Reverting to the previous behavior can be easily done by using one of the newly
 * deprecated methods {@link #setUseExpiresHeader}, {@link #setUseCacheControlHeader},
 * {@link #setUseCacheControlNoStore} or {@link #setAlwaysMustRevalidate}.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @author Brian Clozel
 * @author Rossen Stoyanchev
 * @see #setCacheSeconds
 * @see #setCacheControl
 * @see #setRequireSession
 */
public abstract class WebContentGenerator extends WebApplicationObjectSupport {
 
	/** HTTP method "GET" */
	public static final String METHOD_GET = "GET";
 
	/** HTTP method "HEAD" */
	public static final String METHOD_HEAD = "HEAD";
 
	/** HTTP method "POST" */
	public static final String METHOD_POST = "POST";
 
	private static final String HEADER_PRAGMA = "Pragma";
 
	private static final String HEADER_EXPIRES = "Expires";
 
	protected static final String HEADER_CACHE_CONTROL = "Cache-Control";
 
 
	/** Set of supported HTTP methods */
	@Nullable
	private Set<String> supportedMethods;
 
	@Nullable
	private String allowHeader;
 
	private boolean requireSession = false;
 
	@Nullable
	private CacheControl cacheControl;
 
	private int cacheSeconds = -1;
 
	@Nullable
	private String[] varyByRequestHeaders;
 
 
	// deprecated fields
 
	/** Use HTTP 1.0 expires header? */
	private boolean useExpiresHeader = false;
 
	/** Use HTTP 1.1 cache-control header? */
	private boolean useCacheControlHeader = true;
 
	/** Use HTTP 1.1 cache-control header value "no-store"? */
	private boolean useCacheControlNoStore = true;
 
	private boolean alwaysMustRevalidate = false;
 
 
	/**
	 * Create a new WebContentGenerator which supports
	 * HTTP methods GET, HEAD and POST by default.
	 */
	public WebContentGenerator() {
		this(true);
	}
 
	/**
	 * Create a new WebContentGenerator.
	 * @param restrictDefaultSupportedMethods {@code true} if this
	 * generator should support HTTP methods GET, HEAD and POST by default,
	 * or {@code false} if it should be unrestricted
	 */
	public WebContentGenerator(boolean restrictDefaultSupportedMethods) {
		if (restrictDefaultSupportedMethods) {
			this.supportedMethods = new LinkedHashSet<>(4);
			this.supportedMethods.add(METHOD_GET);
			this.supportedMethods.add(METHOD_HEAD);
			this.supportedMethods.add(METHOD_POST);
		}
		initAllowHeader();
	}
 
	/**
	 * Create a new WebContentGenerator.
	 * @param supportedMethods the supported HTTP methods for this content generator
	 */
	public WebContentGenerator(String... supportedMethods) {
		setSupportedMethods(supportedMethods);
	}
 
 
	/**
	 * Set the HTTP methods that this content generator should support.
	 * <p>Default is GET, HEAD and POST for simple form controller types;
	 * unrestricted for general controllers and interceptors.
	 */
	public final void setSupportedMethods(@Nullable String... methods) {
		if (!ObjectUtils.isEmpty(methods)) {
			this.supportedMethods = new LinkedHashSet<>(Arrays.asList(methods));
		}
		else {
			this.supportedMethods = null;
		}
		initAllowHeader();
	}
 
	/**
	 * Return the HTTP methods that this content generator supports.
	 */
	@Nullable
	public final String[] getSupportedMethods() {
		return (this.supportedMethods != null ? StringUtils.toStringArray(this.supportedMethods) : null);
	}
 
	private void initAllowHeader() {
		Collection<String> allowedMethods;
		if (this.supportedMethods == null) {
			allowedMethods = new ArrayList<>(HttpMethod.values().length - 1);
			for (HttpMethod method : HttpMethod.values()) {
				if (method != HttpMethod.TRACE) {
					allowedMethods.add(method.name());
				}
			}
		}
		else if (this.supportedMethods.contains(HttpMethod.OPTIONS.name())) {
			allowedMethods = this.supportedMethods;
		}
		else {
			allowedMethods = new ArrayList<>(this.supportedMethods);
			allowedMethods.add(HttpMethod.OPTIONS.name());
 
		}
		this.allowHeader = StringUtils.collectionToCommaDelimitedString(allowedMethods);
	}
 
	/**
	 * Return the "Allow" header value to use in response to an HTTP OPTIONS request
	 * based on the configured {@link #setSupportedMethods supported methods} also
	 * automatically adding "OPTIONS" to the list even if not present as a supported
	 * method. This means subclasses don't have to explicitly list "OPTIONS" as a
	 * supported method as long as HTTP OPTIONS requests are handled before making a
	 * call to {@link #checkRequest(HttpServletRequest)}.
	 * @since 4.3
	 */
	@Nullable
	protected String getAllowHeader() {
		return this.allowHeader;
	}
 
	/**
	 * Set whether a session should be required to handle requests.
	 */
	public final void setRequireSession(boolean requireSession) {
		this.requireSession = requireSession;
	}
 
	/**
	 * Return whether a session is required to handle requests.
	 */
	public final boolean isRequireSession() {
		return this.requireSession;
	}
 
	/**
	 * Set the {@link org.springframework.http.CacheControl} instance to build
	 * the Cache-Control HTTP response header.
	 * @since 4.2
	 */
	public final void setCacheControl(@Nullable CacheControl cacheControl) {
		this.cacheControl = cacheControl;
	}
 
	/**
	 * Get the {@link org.springframework.http.CacheControl} instance
	 * that builds the Cache-Control HTTP response header.
	 * @since 4.2
	 */
	@Nullable
	public final CacheControl getCacheControl() {
		return this.cacheControl;
	}
 
	/**
	 * Cache content for the given number of seconds, by writing
	 * cache-related HTTP headers to the response:
	 * <ul>
	 * <li>seconds == -1 (default value): no generation cache-related headers</li>
	 * <li>seconds == 0: "Cache-Control: no-store" will prevent caching</li>
	 * <li>seconds > 0: "Cache-Control: max-age=seconds" will ask to cache content</li>
	 * </ul>
	 * <p>For more specific needs, a custom {@link org.springframework.http.CacheControl}
	 * should be used.
	 * @see #setCacheControl
	 */
	public final void setCacheSeconds(int seconds) {
		this.cacheSeconds = seconds;
	}
 
	/**
	 * Return the number of seconds that content is cached.
	 */
	public final int getCacheSeconds() {
		return this.cacheSeconds;
	}
 
	/**
	 * Configure one or more request header names (e.g. "Accept-Language") to
	 * add to the "Vary" response header to inform clients that the response is
	 * subject to content negotiation and variances based on the value of the
	 * given request headers. The configured request header names are added only
	 * if not already present in the response "Vary" header.
	 * @param varyByRequestHeaders one or more request header names
	 * @since 4.3
	 */
	public final void setVaryByRequestHeaders(@Nullable String... varyByRequestHeaders) {
		this.varyByRequestHeaders = varyByRequestHeaders;
	}
 
	/**
	 * Return the configured request header names for the "Vary" response header.
	 * @since 4.3
	 */
	@Nullable
	public final String[] getVaryByRequestHeaders() {
		return this.varyByRequestHeaders;
	}
 
	/**
	 * Set whether to use the HTTP 1.0 expires header. Default is "false",
	 * as of 4.2.
	 * <p>Note: Cache headers will only get applied if caching is enabled
	 * (or explicitly prevented) for the current request.
	 * @deprecated as of 4.2, since going forward, the HTTP 1.1 cache-control
	 * header will be required, with the HTTP 1.0 headers disappearing
	 */
	@Deprecated
	public final void setUseExpiresHeader(boolean useExpiresHeader) {
		this.useExpiresHeader = useExpiresHeader;
	}
 
	/**
	 * Return whether the HTTP 1.0 expires header is used.
	 * @deprecated as of 4.2, in favor of {@link #getCacheControl()}
	 */
	@Deprecated
	public final boolean isUseExpiresHeader() {
		return this.useExpiresHeader;
	}
 
	/**
	 * Set whether to use the HTTP 1.1 cache-control header. Default is "true".
	 * <p>Note: Cache headers will only get applied if caching is enabled
	 * (or explicitly prevented) for the current request.
	 * @deprecated as of 4.2, since going forward, the HTTP 1.1 cache-control
	 * header will be required, with the HTTP 1.0 headers disappearing
	 */
	@Deprecated
	public final void setUseCacheControlHeader(boolean useCacheControlHeader) {
		this.useCacheControlHeader = useCacheControlHeader;
	}
 
	/**
	 * Return whether the HTTP 1.1 cache-control header is used.
	 * @deprecated as of 4.2, in favor of {@link #getCacheControl()}
	 */
	@Deprecated
	public final boolean isUseCacheControlHeader() {
		return this.useCacheControlHeader;
	}
 
	/**
	 * Set whether to use the HTTP 1.1 cache-control header value "no-store"
	 * when preventing caching. Default is "true".
	 * @deprecated as of 4.2, in favor of {@link #setCacheControl}
	 */
	@Deprecated
	public final void setUseCacheControlNoStore(boolean useCacheControlNoStore) {
		this.useCacheControlNoStore = useCacheControlNoStore;
	}
 
	/**
	 * Return whether the HTTP 1.1 cache-control header value "no-store" is used.
	 * @deprecated as of 4.2, in favor of {@link #getCacheControl()}
	 */
	@Deprecated
	public final boolean isUseCacheControlNoStore() {
		return this.useCacheControlNoStore;
	}
 
	/**
	 * An option to add 'must-revalidate' to every Cache-Control header.
	 * This may be useful with annotated controller methods, which can
	 * programmatically do a last-modified calculation as described in
	 * {@link org.springframework.web.context.request.WebRequest#checkNotModified(long)}.
	 * <p>Default is "false".
	 * @deprecated as of 4.2, in favor of {@link #setCacheControl}
	 */
	@Deprecated
	public final void setAlwaysMustRevalidate(boolean mustRevalidate) {
		this.alwaysMustRevalidate = mustRevalidate;
	}
 
	/**
	 * Return whether 'must-revalidate' is added to every Cache-Control header.
	 * @deprecated as of 4.2, in favor of {@link #getCacheControl()}
	 */
	@Deprecated
	public final boolean isAlwaysMustRevalidate() {
		return this.alwaysMustRevalidate;
	}
 
 
	/**
	 * Check the given request for supported methods and a required session, if any.
	 * @param request current HTTP request
	 * @throws ServletException if the request cannot be handled because a check failed
	 * @since 4.2
	 */
	protected final void checkRequest(HttpServletRequest request) throws ServletException {
		// Check whether we should support the request method.
		String method = request.getMethod();
		if (this.supportedMethods != null && !this.supportedMethods.contains(method)) {
			throw new HttpRequestMethodNotSupportedException(method, this.supportedMethods);
		}
 
		// Check whether a session is required.
		if (this.requireSession && request.getSession(false) == null) {
			throw new HttpSessionRequiredException("Pre-existing session required but none found");
		}
	}
 
	/**
	 * Prepare the given response according to the settings of this generator.
	 * Applies the number of cache seconds specified for this generator.
	 * @param response current HTTP response
	 * @since 4.2
	 */
	protected final void prepareResponse(HttpServletResponse response) {
		if (this.cacheControl != null) {
			applyCacheControl(response, this.cacheControl);
		}
		else {
			applyCacheSeconds(response, this.cacheSeconds);
		}
		if (this.varyByRequestHeaders != null) {
			for (String value : getVaryRequestHeadersToAdd(response, this.varyByRequestHeaders)) {
				response.addHeader("Vary", value);
			}
		}
	}
 
	/**
	 * Set the HTTP Cache-Control header according to the given settings.
	 * @param response current HTTP response
	 * @param cacheControl the pre-configured cache control settings
	 * @since 4.2
	 */
	protected final void applyCacheControl(HttpServletResponse response, CacheControl cacheControl) {
		String ccValue = cacheControl.getHeaderValue();
		if (ccValue != null) {
			// Set computed HTTP 1.1 Cache-Control header
			response.setHeader(HEADER_CACHE_CONTROL, ccValue);
 
			if (response.containsHeader(HEADER_PRAGMA)) {
				// Reset HTTP 1.0 Pragma header if present
				response.setHeader(HEADER_PRAGMA, "");
			}
			if (response.containsHeader(HEADER_EXPIRES)) {
				// Reset HTTP 1.0 Expires header if present
				response.setHeader(HEADER_EXPIRES, "");
			}
		}
	}
 
	/**
	 * Apply the given cache seconds and generate corresponding HTTP headers,
	 * i.e. allow caching for the given number of seconds in case of a positive
	 * value, prevent caching if given a 0 value, do nothing else.
	 * Does not tell the browser to revalidate the resource.
	 * @param response current HTTP response
	 * @param cacheSeconds positive number of seconds into the future that the
	 * response should be cacheable for, 0 to prevent caching
	 */
	@SuppressWarnings("deprecation")
	protected final void applyCacheSeconds(HttpServletResponse response, int cacheSeconds) {
		if (this.useExpiresHeader || !this.useCacheControlHeader) {
			// Deprecated HTTP 1.0 cache behavior, as in previous Spring versions
			if (cacheSeconds > 0) {
				cacheForSeconds(response, cacheSeconds);
			}
			else if (cacheSeconds == 0) {
				preventCaching(response);
			}
		}
		else {
			CacheControl cControl;
			if (cacheSeconds > 0) {
				cControl = CacheControl.maxAge(cacheSeconds, TimeUnit.SECONDS);
				if (this.alwaysMustRevalidate) {
					cControl = cControl.mustRevalidate();
				}
			}
			else if (cacheSeconds == 0) {
				cControl = (this.useCacheControlNoStore ? CacheControl.noStore() : CacheControl.noCache());
			}
			else {
				cControl = CacheControl.empty();
			}
			applyCacheControl(response, cControl);
		}
	}
 
 
	/**
	 * @see #checkRequest(HttpServletRequest)
	 * @see #prepareResponse(HttpServletResponse)
	 * @deprecated as of 4.2, since the {@code lastModified} flag is effectively ignored,
	 * with a must-revalidate header only generated if explicitly configured
	 */
	@Deprecated
	protected final void checkAndPrepare(
			HttpServletRequest request, HttpServletResponse response, boolean lastModified) throws ServletException {
 
		checkRequest(request);
		prepareResponse(response);
	}
 
	/**
	 * @see #checkRequest(HttpServletRequest)
	 * @see #applyCacheSeconds(HttpServletResponse, int)
	 * @deprecated as of 4.2, since the {@code lastModified} flag is effectively ignored,
	 * with a must-revalidate header only generated if explicitly configured
	 */
	@Deprecated
	protected final void checkAndPrepare(
			HttpServletRequest request, HttpServletResponse response, int cacheSeconds, boolean lastModified)
			throws ServletException {
 
		checkRequest(request);
		applyCacheSeconds(response, cacheSeconds);
	}
 
	/**
	 * Apply the given cache seconds and generate respective HTTP headers.
	 * <p>That is, allow caching for the given number of seconds in the
	 * case of a positive value, prevent caching if given a 0 value, else
	 * do nothing (i.e. leave caching to the client).
	 * @param response the current HTTP response
	 * @param cacheSeconds the (positive) number of seconds into the future
	 * that the response should be cacheable for; 0 to prevent caching; and
	 * a negative value to leave caching to the client.
	 * @param mustRevalidate whether the client should revalidate the resource
	 * (typically only necessary for controllers with last-modified support)
	 * @deprecated as of 4.2, in favor of {@link #applyCacheControl}
	 */
	@Deprecated
	protected final void applyCacheSeconds(HttpServletResponse response, int cacheSeconds, boolean mustRevalidate) {
		if (cacheSeconds > 0) {
			cacheForSeconds(response, cacheSeconds, mustRevalidate);
		}
		else if (cacheSeconds == 0) {
			preventCaching(response);
		}
	}
 
	/**
	 * Set HTTP headers to allow caching for the given number of seconds.
	 * Does not tell the browser to revalidate the resource.
	 * @param response current HTTP response
	 * @param seconds number of seconds into the future that the response
	 * should be cacheable for
	 * @deprecated as of 4.2, in favor of {@link #applyCacheControl}
	 */
	@Deprecated
	protected final void cacheForSeconds(HttpServletResponse response, int seconds) {
		cacheForSeconds(response, seconds, false);
	}
 
	/**
	 * Set HTTP headers to allow caching for the given number of seconds.
	 * Tells the browser to revalidate the resource if mustRevalidate is
	 * {@code true}.
	 * @param response the current HTTP response
	 * @param seconds number of seconds into the future that the response
	 * should be cacheable for
	 * @param mustRevalidate whether the client should revalidate the resource
	 * (typically only necessary for controllers with last-modified support)
	 * @deprecated as of 4.2, in favor of {@link #applyCacheControl}
	 */
	@Deprecated
	protected final void cacheForSeconds(HttpServletResponse response, int seconds, boolean mustRevalidate) {
		if (this.useExpiresHeader) {
			// HTTP 1.0 header
			response.setDateHeader(HEADER_EXPIRES, System.currentTimeMillis() + seconds * 1000L);
		}
		else if (response.containsHeader(HEADER_EXPIRES)) {
			// Reset HTTP 1.0 Expires header if present
			response.setHeader(HEADER_EXPIRES, "");
		}
 
		if (this.useCacheControlHeader) {
			// HTTP 1.1 header
			String headerValue = "max-age=" + seconds;
			if (mustRevalidate || this.alwaysMustRevalidate) {
				headerValue += ", must-revalidate";
			}
			response.setHeader(HEADER_CACHE_CONTROL, headerValue);
		}
 
		if (response.containsHeader(HEADER_PRAGMA)) {
			// Reset HTTP 1.0 Pragma header if present
			response.setHeader(HEADER_PRAGMA, "");
		}
	}
 
	/**
	 * Prevent the response from being cached.
	 * Only called in HTTP 1.0 compatibility mode.
	 * <p>See {@code http://www.mnot.net/cache_docs}.
	 * @deprecated as of 4.2, in favor of {@link #applyCacheControl}
	 */
	@Deprecated
	protected final void preventCaching(HttpServletResponse response) {
		response.setHeader(HEADER_PRAGMA, "no-cache");
 
		if (this.useExpiresHeader) {
			// HTTP 1.0 Expires header
			response.setDateHeader(HEADER_EXPIRES, 1L);
		}
 
		if (this.useCacheControlHeader) {
			// HTTP 1.1 Cache-Control header: "no-cache" is the standard value,
			// "no-store" is necessary to prevent caching on Firefox.
			response.setHeader(HEADER_CACHE_CONTROL, "no-cache");
			if (this.useCacheControlNoStore) {
				response.addHeader(HEADER_CACHE_CONTROL, "no-store");
			}
		}
	}
 
 
	private Collection<String> getVaryRequestHeadersToAdd(HttpServletResponse response, String[] varyByRequestHeaders) {
		if (!response.containsHeader(HttpHeaders.VARY)) {
			return Arrays.asList(varyByRequestHeaders);
		}
		Collection<String> result = new ArrayList<>(varyByRequestHeaders.length);
		Collections.addAll(result, varyByRequestHeaders);
		for (String header : response.getHeaders(HttpHeaders.VARY)) {
			for (String existing : StringUtils.tokenizeToStringArray(header, ",")) {
				if ("*".equals(existing)) {
					return Collections.emptyList();
				}
				for (String value : varyByRequestHeaders) {
					if (value.equalsIgnoreCase(existing)) {
						result.remove(value);
					}
				}
			}
		}
		return result;
	}
 
}