利用spring session解决共享Session问题

1.共享Session问题HttpSession是通过Servlet容器创建和管理的，像Tomcat/Jetty都是保存在内存中的。而如果我们把web服务器搭建成分布式的集群，然后利用LVS或Nginx做负载均衡，那么来自同一用户的Http请求将有可能被分发到两个不同的web站点中去。那么问题就来了，如何保证不同的web站点能够共享同一份session数据呢？最简单的想法就是把session数据保存到内存以外的一个统一的地方，例如Memcached/Redis等数据库中。那么问题又来了，如何替换掉Servlet容器创建和管理HttpSession的实现呢？（1）设计一个Filter，利用HttpServletRequestWrapper，实现自己的 getSession()方法，接管创建和管理Session数据的工作。spring-session就是通过这样的思路实现的。（2）利用Servlet容器提供的插件功能，自定义HttpSession的创建和管理策略，并通过配置的方式替换掉默认的策略。不过这种方式有个缺点，就是需要耦合Tomcat/Jetty等Servlet容器的代码。这方面其实早就有开源项目了，例如memcached-session-manager，以及tomcat-redis-session-manager。暂时都只支持Tomcat6/Tomcat7。2.Spring Session介绍Spring Session是spring的项目之一，GitHub地址：https://github.com/spring-projects/spring-session。Spring Session提供了一套创建和管理Servlet HttpSession的方案。Spring Session提供了集群Session（Clustered Sessions）功能，默认采用外置的Redis来存储Session数据，以此来解决Session共享的问题。下面是来自官网的特性介绍：FeaturesSpring Session provides the following features:    API and implementations for managing a user's session    HttpSession - allows replacing the HttpSession in an application container (i.e. Tomcat) neutral way        Clustered Sessions - Spring Session makes it trivial to support clustered sessions without being tied to an application container specific solution.        Multiple Browser Sessions - Spring Session supports managing multiple users' sessions in a single browser instance (i.e. multiple authenticated accounts similar to Google).        RESTful APIs - Spring Session allows providing session ids in headers to work with RESTful APIs    WebSocket - provides the ability to keep the HttpSession alive when receiving WebSocket messages3.集成Spring Session的正确姿势下面是实际调试通过的例子，包含下面4个步骤：（1）第一步，添加Maven依赖根据官网Quick Start展示的依赖，在项目pom.xml中添加后各种找不到类引用。于是查看Spring Session项目的build.gradle文件，居然没有配置依赖的项目，难道还要我自己去找它的依赖，太不专业了吧？！！！[html] view plain copy    <dependencies>          <dependency>              <groupId>org.springframework.session</groupId>              <artifactId>spring-session</artifactId>              <version>1.0.1.RELEASE</version>          </dependency>      </dependencies>  终于在多番仔细研究Spring Session项目源码之后，看到了spring-session-data-redis项目：build.gradle文件里配置了Spring Session编译依赖的3个项目：[plain] view plain copy在CODE上查看代码片派生到我的代码片    apply from: JAVA_GRADLE      apply from: MAVEN_GRADLE            apply plugin: 'spring-io'            description = "Aggregator for Spring Session and Spring Data Redis"            dependencies {          compile project(':spring-session'),                  "org.springframework.data:spring-data-redis:$springDataRedisVersion",                  "redis.clients:jedis:$jedisVersion",                  "org.apache.commons:commons-pool2:$commonsPoolVersion"                springIoVersions "io.spring.platform:platform-versions:${springIoVersion}@properties"      }  于是，真正的Maven依赖改成spring-session-data-redis就OK了：[html] view plain copy在CODE上查看代码片派生到我的代码片    <dependency>          <groupId>org.springframework.session</groupId>          <artifactId>spring-session-data-redis</artifactId>          <version>1.0.1.RELEASE</version>      </dependency>  （2）第二步，编写一个配置类，用来启用RedisHttpSession功能，并向Spring容器中注册一个RedisConnectionFactory。[java] view plain copy在CODE上查看代码片派生到我的代码片    import org.springframework.context.annotation.Bean;      import org.springframework.data.redis.connection.RedisConnectionFactory;      import org.springframework.data.redis.connection.jedis.JedisConnectionFactory;      import org.springframework.session.data.redis.config.annotation.web.http.EnableRedisHttpSession;            @EnableRedisHttpSession(maxInactiveIntervalInSeconds = 7200)      public class RedisHttpSessionConfig {                @Bean          public RedisConnectionFactory connectionFactory() {              JedisConnectionFactory connectionFactory = new JedisConnectionFactory();              connectionFactory.setPort(6379);              connectionFactory.setHostName("10.18.15.190");              return connectionFactory;          }      }  （3）第三步，将RedisHttpSessionConfig加入到WebInitializer#getRootConfigClasses()中，让Spring容器加载RedisHttpSessionConfig类。WebInitializer是一个自定义的AbstractAnnotationConfigDispatcherServletInitializer实现类，该类会在Servlet启动时加载（当然也可以采用别的加载方法，比如采用扫描@Configuration注解类的方式等等）。[java] view plain copy在CODE上查看代码片派生到我的代码片    //该类采用Java Configuration，来代替web.xml         public class WebInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {                    @Override          protected Class<?>[] getRootConfigClasses() {              return new Class[]{Config1.class, Config2.class, RedisHttpSessionConfig.class};          }                    //......      }  （4）第四步，编写一个一个AbstractHttpSessionApplicationInitializer实现类，用于向Servlet容器中添加springSessionRepositoryFilter。[java] view plain copy在CODE上查看代码片派生到我的代码片    import org.springframework.session.web.context.AbstractHttpSessionApplicationInitializer;            public class SpringSessionInitializer extends AbstractHttpSessionApplicationInitializer {      }  4. Spring Session原理（1）前面集成spring-sesion的第二步中，编写了一个配置类RedisHttpSessionConfig，它包含注解@EnableRedisHttpSession，并通过@Bean注解注册了一个RedisConnectionFactory到Spring容器中。而@EnableRedisHttpSession注解通过Import，引入了RedisHttpSessionConfiguration配置类。该配置类通过@Bean注解，向Spring容器中注册了一个SessionRepositoryFilter（SessionRepositoryFilter的依赖关系：SessionRepositoryFilter --> SessionRepository --> RedisTemplate --> RedisConnectionFactory）。[java] view plain copy在CODE上查看代码片派生到我的代码片    package org.springframework.session.data.redis.config.annotation.web.http;            @Configuration      @EnableScheduling      public class RedisHttpSessionConfiguration implements ImportAware, BeanClassLoaderAware {          //......                    @Bean          public RedisTemplate<String,ExpiringSession> sessionRedisTemplate(RedisConnectionFactory connectionFactory) {              //......              return template;          }                    @Bean          public RedisOperationsSessionRepository sessionRepository(RedisTemplate<String, ExpiringSession> sessionRedisTemplate) {              //......              return sessionRepository;          }                    @Bean          public <S extends ExpiringSession> SessionRepositoryFilter<? extends ExpiringSession> springSessionRepositoryFilter(SessionRepository<S> sessionRepository, ServletContext servletContext) {              //......              return sessionRepositoryFilter;          }                    //......      }  （2）集成spring-sesion的第四步中，我们编写了一个SpringSessionInitializer 类，它继承自AbstractHttpSessionApplicationInitializer。该类不需要重载或实现任何方法，它的作用是在Servlet容器初始化时，从Spring容器中获取一个默认名叫sessionRepositoryFilter的过滤器类（之前没有注册的话这里找不到会报错），并添加到Servlet过滤器链中。[java] view plain copy在CODE上查看代码片派生到我的代码片    package org.springframework.session.web.context;            /**      * Registers the {@link DelegatingFilterProxy} to use the      * springSessionRepositoryFilter before any other registered {@link Filter}.       *      * ......      */      @Order(100)      public abstract class AbstractHttpSessionApplicationInitializer implements WebApplicationInitializer {                private static final String SERVLET_CONTEXT_PREFIX = "org.springframework.web.servlet.FrameworkServlet.CONTEXT.";                public static final String DEFAULT_FILTER_NAME = "springSessionRepositoryFilter";                //......                public void onStartup(ServletContext servletContext)                  throws ServletException {              beforeSessionRepositoryFilter(servletContext);              if(configurationClasses != null) {                  AnnotationConfigWebApplicationContext rootAppContext = new AnnotationConfigWebApplicationContext();                  rootAppContext.register(configurationClasses);                  servletContext.addListener(new ContextLoaderListener(rootAppContext));              }              insertSessionRepositoryFilter(servletContext);//注册一个SessionRepositoryFilter              afterSessionRepositoryFilter(servletContext);          }                /**          * Registers the springSessionRepositoryFilter          * @param servletContext the {@link ServletContext}          */          private void insertSessionRepositoryFilter(ServletContext servletContext) {              String filterName = DEFAULT_FILTER_NAME;//默认名字是springSessionRepositoryFilter              DelegatingFilterProxy springSessionRepositoryFilter = new DelegatingFilterProxy(filterName);//该Filter代理会在初始化时从Spring容器中查找springSessionRepositoryFilter，之后实际会使用SessionRepositoryFilter进行doFilter操作                     String contextAttribute = getWebApplicationContextAttribute();              if(contextAttribute != null) {                  springSessionRepositoryFilter.setContextAttribute(contextAttribute);              }              registerFilter(servletContext, true, filterName, springSessionRepositoryFilter);          }                    //......      }  SessionRepositoryFilter是一个优先级最高的javax.servlet.Filter，它使用了一个SessionRepositoryRequestWrapper类接管了Http Session的创建和管理工作。注意下面给出的是简化过的示例代码，与spring-session项目的源代码有所差异。[java] view plain copy在CODE上查看代码片派生到我的代码片    @Order(SessionRepositoryFilter.DEFAULT_ORDER)      public class SessionRepositoryFilter implements Filter {                    public doFilter(ServletRequest request, ServletResponse response, FilterChain chain) {                      HttpServletRequest httpRequest = (HttpServletRequest) request;                      SessionRepositoryRequestWrapper customRequest =                              new SessionRepositoryRequestWrapper(httpRequest);                            chain.doFilter(customRequest, response, chain);              }                    // ...      }  [java] view plain copy在CODE上查看代码片派生到我的代码片    public class SessionRepositoryRequestWrapper extends HttpServletRequestWrapper {                    public SessionRepositoryRequestWrapper(HttpServletRequest original) {                      super(original);              }                    public HttpSession getSession() {                      return getSession(true);              }                    public HttpSession getSession(boolean createNew) {                      // create an HttpSession implementation from Spring Session              }                    // ... other methods delegate to the original HttpServletRequest ...      }  （3）好了，剩下的问题就是，如何在Servlet容器启动时，加载下面两个类。幸运的是，这两个类由于都实现了WebApplicationInitializer接口，会被自动加载。    WebInitializer，负责加载配置类。它继承自AbstractAnnotationConfigDispatcherServletInitializer，实现了WebApplicationInitializer接口    SpringSessionInitializer，负责添加sessionRepositoryFilter的过滤器类。它继承自AbstractHttpSessionApplicationInitializer，实现了WebApplicationInitializer接口在Servlet3.0规范中，Servlet容器启动时会自动扫描javax.servlet.ServletContainerInitializer的实现类，在实现类中我们可以定制需要加载的类。在spring-web项目中，有一个ServletContainerInitializer实现类SpringServletContainerInitializer，它通过注解@HandlesTypes(WebApplicationInitializer.class)，让Servlet容器在启动该类时，会自动寻找所有的WebApplicationInitializer实现类。[java] view plain copy在CODE上查看代码片派生到我的代码片    package org.springframework.web;            @HandlesTypes(WebApplicationInitializer.class)      public class SpringServletContainerInitializer implements ServletContainerInitializer {                /**          * Delegate the {@code ServletContext} to any {@link WebApplicationInitializer}          * implementations present on the application classpath.          *          * <p>Because this class declares @{@code HandlesTypes(WebApplicationInitializer.class)},          * Servlet 3.0+ containers will automatically scan the classpath for implementations          * of Spring's {@code WebApplicationInitializer} interface and provide the set of all          * such types to the {@code webAppInitializerClasses} parameter of this method.          *          * <p>If no {@code WebApplicationInitializer} implementations are found on the          * classpath, this method is effectively a no-op. An INFO-level log message will be          * issued notifying the user that the {@code ServletContainerInitializer} has indeed          * been invoked but that no {@code WebApplicationInitializer} implementations were          * found.          *          * <p>Assuming that one or more {@code WebApplicationInitializer} types are detected,          * they will be instantiated (and <em>sorted</em> if the @{@link          * org.springframework.core.annotation.Order @Order} annotation is present or          * the {@link org.springframework.core.Ordered Ordered} interface has been          * implemented). Then the {@link WebApplicationInitializer#onStartup(ServletContext)}          * method will be invoked on each instance, delegating the {@code ServletContext} such          * that each instance may register and configure servlets such as Spring's          * {@code DispatcherServlet}, listeners such as Spring's {@code ContextLoaderListener},          * or any other Servlet API componentry such as filters.          *          * @param webAppInitializerClasses all implementations of          * {@link WebApplicationInitializer} found on the application classpath          * @param servletContext the servlet context to be initialized          * @see WebApplicationInitializer#onStartup(ServletContext)          * @see AnnotationAwareOrderComparator          */          @Override          public void onStartup(Set<Class<?>> webAppInitializerClasses, ServletContext servletContext)                  throws ServletException {              //......          }            }  5. 如何在Redis中查看Session数据？（1）Http Session数据在Redis中是以Hash结构存储的。（2）可以看到，还有一个key="spring:session:expirations:1431577740000"的数据，是以Set结构保存的。这个值记录了所有session数据应该被删除的时间（即最新的一个session数据过期的时间）。[plain] view plain copy在CODE上查看代码片派生到我的代码片    127.0.0.1:6379> keys *      1) "spring:session:expirations:1431577740000"      2) "spring:session:sessions:e2cef3ae-c8ea-4346-ba6b-9b3b26eee578"      127.0.0.1:6379> type spring:session:sessions:e2cef3ae-c8ea-4346-ba6b-9b3b26eee578      hash      127.0.0.1:6379> type spring:session:expirations:1431577740000      set  [plain] view plain copy在CODE上查看代码片派生到我的代码片    127.0.0.1:6379> keys *      1) "spring:session:expirations:1431527520000"      2) "spring:session:sessions:59f3987c-d1e4-44b3-a83a-32079942888b"      3) "spring:session:sessions:11a69da6-138b-42bc-9916-60ae78aa55aa"      4) "spring:session:sessions:0a51e2c2-4a3b-4986-a754-d886d8a5d42d"      5) "spring:session:expirations:1431527460000"            127.0.0.1:6379> hkeys spring:session:sessions:59f3987c-d1e4-44b3-a83a-32079942888b      1) "maxInactiveInterval"      2) "creationTime"      3) "lastAccessedTime"      4) "sessionAttr:attr1"            127.0.0.1:6379> hget spring:session:sessions:59f3987c-d1e4-44b3-a83a-32079942888b sessionAttr:attr1      "\xac\xed\x00\x05sr\x00\x11java.lang.Integer\x12\xe2\xa0\xa4\xf7\x81\x878\x02\x00\x01I\x00\x05valuexr\x00\x10java.lang.Number\x86\xac\x95\x1d\x0b\x94\xe0\x8b\x02\x00\x00xp\x00\x00\x00\x03"            127.0.0.1:6379> hget spring:session:sessions:59f3987c-d1e4-44b3-a83a-32079942888b creationTime      "\xac\xed\x00\x05sr\x00\x0ejava.lang.Long;\x8b\xe4\x90\xcc\x8f#\xdf\x02\x00\x01J\x00\x05valuexr\x00\x10java.lang.Number\x86\xac\x95\x1d\x0b\x94\xe0\x8b\x02\x00\x00xp\x00\x00\x01MM\x94(\xec"  6.参考文章Spring Session 1.01 Referencespring session入门集群session共享机制