Spring Boot series 12 through Redis Tomcat cluster Session synchronization and source code analysis of its principle

In web containers such as Tomcat, sessions are stored in native memory. If we cluster Tomcat, session synchronization will inevitably be involved. We must ensure that tomcat sessions in the same cluster are shared. In order for the Tomcat cluster to work properly, there are usually the following methods:

A. Configure nginx on the front end of Tomcat to use the IP_hash load balancing algorithm to ensure that visitors from the same IP address access the same back-end server. In this way, session synchronization is avoided. This method also has a flaw. If the service is down, all user state is lost. Through tomcat's own cluster mode, multiple Tomcats share session information in real time. However, with the increase of the number of Tomcats and requests, the performance of this method will be severely degraded. Using the Filter method d. Using the Terracotta server to share sessions E. Use middleware such as Redis and memcached to store sessionsCopy the code

The following demonstrates session sharing using Redis in Spring Boot

Project name: Redis introduces dependency JARS

<! - spring is introduced into the session information is stored into the redis dependent packages - > < the dependency > < groupId > org. Springframework. Session < / groupId > <artifactId>spring-session-data-redis</artifactId> </dependency>Copy the code

Application-dev. properties Session-related configuration parameters

# # # session configuration start # # # # # # # # # # # # # session storage type configuration of spring. The session. The store - type = # redis spring. Session. Redis. Namespace = # Session duration server.session.timeout=300 ### End ############Copy the code

In sessionTestCtrl. Java, we will find that the redis shared session operation is no different from the default session operation. There are three methods of this class: login(): mock login, storing a value in the session

@RequestMapping("login") public Map<String,Object> login(HttpServletRequest request) { HttpSession httpSession = request.getSession(); // Set the value in session httpsession.setattribute ("username", "hry" + System.currentTimemillis ()); Map<String,Object> rtnMap = new HashMap<>(); Enumeration<String> attributeNames = request.getSession().getAttributeNames(); while(attributeNames.hasMoreElements()){ String name = attributeNames.nextElement(); rtnMap.put(name, httpSession.getAttribute(name)); } rtnMap.put("sessionId", httpSession.getId()); return rtnMap; }Copy the code

GetSession (): Gets the value from the session

@RequestMapping("get-session")
public Object getSession(HttpServletRequest request) {
    HttpSession httpSession = request.getSession();
    Map<String,Object> rtnMap = new HashMap<>();
    Enumeration<String> attributeNames = request.getSession().getAttributeNames();
    while(attributeNames.hasMoreElements()){
        String name = attributeNames.nextElement();
        rtnMap.put(name, httpSession.getAttribute(name));
    }
    int count;
    try {
        count = Integer.parseInt(String.valueOf(httpSession.getAttribute("count")));
        count++;
    }catch (NumberFormatException e){
        count = 1;
    }
    httpSession.setAttribute("count",count+"");

    rtnMap.put("sessionId", httpSession.getId());
    return rtnMap;
}Copy the code

Invalidate (): invalidates the sesion value

@RequestMapping("invalidate")
 public int invalidate(HttpServletRequest request) {
     HttpSession httpSession = request.getSession();
     httpSession.invalidate();
     return 1;
 }Copy the code

The full code for SessionTestCtrl is here

{"count":"7","sessionId":"a095bdf3-e907-4fac-bf5e-132f7d737000","username":"hry1517311682642"}Copy the code

Execute the URL using session invalidation: To perform HTTP: / / http://127.0.0.1:8080/get-session, http://127.0.0.1:8080/invalidate, and the session value has changed, and the count value, invalidate method for success

{"sessionId":"a54128d6-55c5-4233-aa97-54816b51c5cf"}  Copy the code

In the spring – the session – data – redis to define new HttpSession object instead of the default: ExpiringSessionHttpSession ExpiringSessionHttpSession: This class inherits HttpSession, which is actually the Session operation described above

The class ExpiringSessionHttpSession < S extends ExpiringSession > implements the HttpSession {... }Copy the code

In addition to redis, there are GemFire, Hazelcast, JDBC, Mongo,Map, etc

HttpSessionWrapper: to packaging when executed ExpiringSessionHttpSession ExpiringSessionHttpSession instance will be passed into the HttpSessionWrapper by constructing method

private final class HttpSessionWrapper extends ExpiringSessionHttpSession<S> { HttpSessionWrapper(S session, ServletContext servletContext) { super(session, servletContext); } @Override public void invalidate() { super.invalidate(); SessionRepositoryRequestWrapper.this.requestedSessionInvalidated = true; setCurrentSession(null); SessionRepositoryFilter.this.sessionRepository.delete(getId()); }}Copy the code

The SessionRepositoryFilter is a Fitler that intercepts all requests. Through the Filter will use our above SessionRepositoryRequestWrapper encapsulation it request

DoFilter OncePerRequestFilter Public final void doFilter(ServletRequest Request, ServletResponse Response, FilterChain FilterChain) throws ServletException, IOException {... doFilterInternal(httpRequest, httpResponse, filterChain); ... } Override protected void doFilterInternal(HttpServletRequest Request,  HttpServletResponse response, FilterChain filterChain) throws ServletException, IOException { request.setAttribute(SESSION_REPOSITORY_ATTR, this.sessionRepository); / / use our SessionRepositoryRequestWrapper to encapsulate request above, This involves the operation of the session is called above, we define SessionRepositoryRequestWrapper SessionRepositoryRequestWrapper wrappedRequest = new SessionRepositoryRequestWrapper( request, response, this.servletContext); SessionRepositoryResponseWrapper wrappedResponse = new SessionRepositoryResponseWrapper( wrappedRequest, response); HttpServletRequest strategyRequest = this.httpSessionStrategy .wrapRequest(wrappedRequest, wrappedResponse); HttpServletResponse strategyResponse = this.httpSessionStrategy .wrapResponse(wrappedRequest, wrappedResponse); Try {// Perform filterchain. doFilter(strategyRequest, strategyResponse); } finally { wrappedRequest.commitSession(); }}Copy the code

/ / introduce SpringHttpSessionConfiguration and initialize @ Import (SpringHttpSessionConfiguration. Class) @ Configuration public @ interface EnableSpringHttpSession { }Copy the code

Please use tag V0.13 instead of master as I can’t guarantee that the master code will always be the same