利用spring session解决共享Session问题

刺骨的言语ヽ痛彻心扉 2022-08-08 09:13 153阅读 0赞

# 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：

## Features ##

Spring 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 messages

# 3.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？！！！

<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：

![20150513175643527][]

build.gradle文件里配置了Spring Session编译依赖的3个项目：

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：

<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。

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）。

//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。

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）。

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。

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。

@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);
            }
    
            // ...
    }

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。

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.
 	 *
 	 * 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.
 	 *
 	 * 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.
 	 *
 	 * Assuming that one or more {@code WebApplicationInitializer} types are detected,
 	 * they will be instantiated (and sorted 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）。

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

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 Reference][]

[spring session入门][spring session]

[集群session共享机制][session]

[memcached-session-manager]: https://github.com/magro/memcached-session-manager
[tomcat-redis-session-manager]: https://github.com/jcoleman/tomcat-redis-session-manager
[Spring Session]: http://projects.spring.io/spring-session/
[20150513175643527]: /images/20220805/7506681875e445d984d143396efba8d5.png
[Spring Session 1.01 Reference]: http://docs.spring.io/spring-data/data-redis/docs/current/reference/html/
[spring session]: http://blog.csdn.net/xiejx618/article/details/42919327
[session]: http://itindex.net/detail/53154-%E9%9B%86%E7%BE%A4-session-%E5%85%B1%E4%BA%AB