最近要在项目中做用户踢线的功能，由于项目使用spring session来管理用户session，因此特地翻了翻spring session的源码，看看spring session是如何管理的。我们使用redis来存储session，因此本文只对session在redis中的存储结构以及管理做解析。
1 spring session使用
Spring Session对HTTP的支持是通过标准的servlet filter来实现的，这个filter必须要配置为拦截所有的web应用请求，并且它最好是filter链中的第一个filter。Spring Session filter会确保随后调用javax.servlet.http.HttpServletRequest的getSession()方法时，都会返回Spring Session的HttpSession实例，而不是应用服务器默认的HttpSession。
spring session通过注解@EnableRedisHttpSession或者xml配置
<bean class="org.springframework.session.data.redis.config.annotation.web.http.RedisHttpSessionConfiguration"/>
来设置spring session的一些参数，比如session的最大活跃时间（maxInactiveIntervalInSeconds），redis命名空间（redisNamespace），session写入到redis的时机（FlushMode）以及如何序列化写到redis中的session value等等。
要想使用spring session，还需要创建名为springSessionRepositoryFilter的SessionRepositoryFilter类。该类实现了Sevlet Filter接口，当请求穿越sevlet filter链时应该首先经过springSessionRepositoryFilter，这样在后面获取session的时候，得到的将是spring session。为了springSessonRepositoryFilter作为filter链中的第一个，spring session提供了AbstractHttpSessionApplicationInitializer类， 它实现了WebApplicationInitializer类，在onStartup方法中将springSessionRepositoryFilter加入到其他fitler链前面。
public abstract class AbstractHttpSessionApplicationInitializer
implements WebApplicationInitializer {
/**
* The default name for Spring Session's repository filter.
*/
public static final String DEFAULT_FILTER_NAME = "springSessionRepositoryFilter";
public void onStartup(ServletContext servletContext) throws ServletException {
......
insertSessionRepositoryFilter(servletContext);
afterSessionRepositoryFilter(servletContext);
}
/**
* Registers the springSessionRepositoryFilter.
* @param servletContext the {@link ServletContext}
*/
private void insertSessionRepositoryFilter(ServletContext servletContext) {
String filterName = DEFAULT_FILTER_NAME;
DelegatingFilterProxy springSessionRepositoryFilter = new DelegatingFilterProxy(
filterName);
String contextAttribute = getWebApplicationContextAttribute();
if (contextAttribute != null) {
springSessionRepositoryFilter.setContextAttribute(contextAttribute);
}
registerFilter(servletContext, true, filterName, springSessionRepositoryFilter);
}
}
或者也可以在web.xml里面将springSessionRepositoryFilter加入到filter配置的第一个
该filter最终会把请求代理给具体的一个filter,通过入参的常量可看出它是委派给springSessionRepositoryFilter这样一个具体的filter(由spring容器管理)
DelegatingFilterProxy.png
查看其父类
public abstract class GenericFilterBean implements
Filter, BeanNameAware, EnvironmentAware, ServletContextAware, InitializingBean, DisposableBean {
/** Logger available to subclasses */
protected final Log logger = LogFactory.getLog(getClass());
/**
* Set of required properties (Strings) that must be supplied as
* config parameters to this filter.
*/
private final Set<String> requiredProperties = new HashSet<String>();
private FilterConfig filterConfig;
private String beanName;
private Environment environment = new StandardServletEnvironment();
private ServletContext servletContext;
/**
* Calls the {@code initFilterBean()} method that might
* contain custom initialization of a subclass.
* <p>Only relevant in case of initialization as bean, where the
* standard {@code init(FilterConfig)} method won't be called.
* @see #initFilterBean()
* @see #init(javax.servlet.FilterConfig)
*/
@Override
public void afterPropertiesSet() throws ServletException {
initFilterBean();
}
/**
* Subclasses can invoke this method to specify that this property
* (which must match a JavaBean property they expose) is mandatory,
* and must be supplied as a config parameter. This should be called
* from the constructor of a subclass.
* <p>This method is only relevant in case of traditional initialization
* driven by a FilterConfig instance.
* @param property name of the required property
*/
protected final void addRequiredProperty(String property) {
this.requiredProperties.add(property);
}
/**
* Standard way of initializing this filter.
* Map config parameters onto bean properties of this filter, and
* invoke subclass initialization.
* @param filterConfig the configuration for this filter
* @throws ServletException if bean properties are invalid (or required
* properties are missing), or if subclass initialization fails.
* @see #initFilterBean
*/
@Override
public final void init(FilterConfig filterConfig) throws ServletException {
Assert.notNull(filterConfig, "FilterConfig must not be null");
if (logger.isDebugEnabled()) {
logger.debug("Initializing filter '" + filterConfig.getFilterName() + "'");
}
this.filterConfig = filterConfig;
// Set bean properties from init parameters.
try {
PropertyValues pvs = new FilterConfigPropertyValues(filterConfig, this.requiredProperties);
BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
ResourceLoader resourceLoader = new ServletContextResourceLoader(filterConfig.getServletContext());
bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, this.environment));
initBeanWrapper(bw);
bw.setPropertyValues(pvs, true);
}
catch (BeansException ex) {
String msg = "Failed to set bean properties on filter '" +
filterConfig.getFilterName() + "': " + ex.getMessage();
logger.error(msg, ex);
throw new NestedServletException(msg, ex);
}
// Let subclasses do whatever initialization they like.
//初始化filter bean
initFilterBean();
if (logger.isDebugEnabled()) {
logger.debug("Filter '" + filterConfig.getFilterName() + "' configured successfully");
}
}
/**
* Initialize the BeanWrapper for this GenericFilterBean,
* possibly with custom editors.
* <p>This default implementation is empty.
* @param bw the BeanWrapper to initialize
* @throws BeansException if thrown by BeanWrapper methods
* @see org.springframework.beans.BeanWrapper#registerCustomEditor
*/
protected void initBeanWrapper(BeanWrapper bw) throws BeansException {
}
/**
* Make the FilterConfig of this filter available, if any.
* Analogous to GenericServlet's {@code getServletConfig()}.
* <p>Public to resemble the {@code getFilterConfig()} method
* of the Servlet Filter version that shipped with WebLogic 6.1.
* @return the FilterConfig instance, or {@code null} if none available
* @see javax.servlet.GenericServlet#getServletConfig()
*/
public final FilterConfig getFilterConfig() {
return this.filterConfig;
}
/**
* Make the name of this filter available to subclasses.
* Analogous to GenericServlet's {@code getServletName()}.
* <p>Takes the FilterConfig's filter name by default.
* If initialized as bean in a Spring application context,
* it falls back to the bean name as defined in the bean factory.
* @return the filter name, or {@code null} if none available
* @see javax.servlet.GenericServlet#getServletName()
* @see javax.servlet.FilterConfig#getFilterName()
* @see #setBeanName
*/
protected final String getFilterName() {
return (this.filterConfig != null ? this.filterConfig.getFilterName() : this.beanName);
}
/**
* Make the ServletContext of this filter available to subclasses.
* Analogous to GenericServlet's {@code getServletContext()}.
* <p>Takes the FilterConfig's ServletContext by default.
* If initialized as bean in a Spring application context,
* it falls back to the ServletContext that the bean factory runs in.
* @return the ServletContext instance, or {@code null} if none available
* @see javax.servlet.GenericServlet#getServletContext()
* @see javax.servlet.FilterConfig#getServletContext()
* @see #setServletContext
*/
protected final ServletContext getServletContext() {
return (this.filterConfig != null ? this.filterConfig.getServletContext() : this.servletContext);
}
/**
* Subclasses may override this to perform custom initialization.
* All bean properties of this filter will have been set before this
* method is invoked.
*/
protected void initFilterBean() throws ServletException {
}
/**
* Subclasses may override this to perform custom filter shutdown.
* <p>Note: This method will be called from standard filter destruction
* as well as filter bean destruction in a Spring application context.
* <p>This default implementation is empty.
*/
@Override
public void destroy() {
}
/**
* PropertyValues implementation created from FilterConfig init parameters.
*/
@SuppressWarnings("serial")
private static class FilterConfigPropertyValues extends MutablePropertyValues {
/**
* Create new FilterConfigPropertyValues.
*/
public FilterConfigPropertyValues(FilterConfig config, Set<String> requiredProperties)
throws ServletException {
Set<String> missingProps = (requiredProperties != null && !requiredProperties.isEmpty()) ?
new HashSet<String>(requiredProperties) : null;
Enumeration<?> en = config.getInitParameterNames();
while (en.hasMoreElements()) {
String property = (String) en.nextElement();
Object value = config.getInitParameter(property);
addPropertyValue(new PropertyValue(property, value));
if (missingProps != null) {
missingProps.remove(property);
}
}
// Fail if we are still missing properties.
if (missingProps != null && missingProps.size() > 0) {
throw new ServletException(
"Initialization from FilterConfig for filter '" + config.getFilterName() +
"' failed; the following required properties were missing: " +
StringUtils.collectionToDelimitedString(missingProps, ", "));
}
}
}
}
查看其真正实现方法的子类
public class DelegatingFilterProxy extends GenericFilterBean {
private String contextAttribute;
private WebApplicationContext webApplicationContext;
private String targetBeanName;
private boolean targetFilterLifecycle = false;
private volatile Filter delegate;
private final Object delegateMonitor = new Object();
public DelegatingFilterProxy() {
}
public DelegatingFilterProxy(Filter delegate) {
Assert.notNull(delegate, "delegate Filter object must not be null");
this.delegate = delegate;
}
public DelegatingFilterProxy(String targetBeanName) {
this(targetBeanName, null);
}
public DelegatingFilterProxy(String targetBeanName, WebApplicationContext wac) {
Assert.hasText(targetBeanName, "target Filter bean name must not be null or empty");
this.setTargetBeanName(targetBeanName);
this.webApplicationContext = wac;
if (wac != null) {
this.setEnvironment(wac.getEnvironment());
}
}
protected boolean isTargetFilterLifecycle() {
return this.targetFilterLifecycle;
}
@Override
protected void initFilterBean() throws ServletException {
//同步块,防止spring容器启动时委托的这些filter保证它们的执行顺序
synchronized (this.delegateMonitor) {
if (this.delegate == null) {
// If no target bean name specified, use filter name.
if (this.targetBeanName == null) {
this.targetBeanName = getFilterName();
}
// Fetch Spring root application context and initialize the delegate early,
// if possible. If the root application context will be started after this
// filter proxy, we'll have to resort to lazy initialization.
WebApplicationContext wac = findWebApplicationContext();
if (wac != null) {
this.delegate = initDelegate(wac);
}
}
}
}
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain)
throws ServletException, IOException {
// Lazily initialize the delegate if necessary.
Filter delegateToUse = this.delegate;
if (delegateToUse == null) {
synchronized (this.delegateMonitor) {
if (this.delegate == null) {
WebApplicationContext wac = findWebApplicationContext();
if (wac == null) {
throw new IllegalStateException("No WebApplicationContext found: no ContextLoaderListener registered?");
}
this.delegate = initDelegate(wac);
}
delegateToUse = this.delegate;
}
}
// Let the delegate perform the actual doFilter operation.
invokeDelegate(delegateToUse, request, response, filterChain);
}
@Override
public void destroy() {
Filter delegateToUse = this.delegate;
if (delegateToUse != null) {
destroyDelegate(delegateToUse);
}
}
protected WebApplicationContext findWebApplicationContext() {
if (this.webApplicationContext != null) {
// the user has injected a context at construction time -> use it
if (this.webApplicationContext instanceof ConfigurableApplicationContext) {
if (!((ConfigurableApplicationContext)this.webApplicationContext).isActive()) {
// the context has not yet been refreshed -> do so before returning it
((ConfigurableApplicationContext)this.webApplicationContext).refresh();
}
}
return this.webApplicationContext;
}
String attrName = getContextAttribute();
if (attrName != null) {
return WebApplicationContextUtils.getWebApplicationContext(getServletContext(), attrName);
}
else {
return WebApplicationContextUtils.getWebApplicationContext(getServletContext());
}
}
protected Filter initDelegate(WebApplicationContext wac) throws ServletException {
Filter delegate = wac.getBean(getTargetBeanName(), Filter.class);
if (isTargetFilterLifecycle()) {
delegate.init(getFilterConfig());
}
return delegate;
}
/**
* Actually invoke the delegate Filter with the given request and response.
* 调用了委托的doFilter方法
*/
protected void invokeDelegate(
Filter delegate, ServletRequest request, ServletResponse response, FilterChain filterChain)
throws ServletException, IOException {
delegate.doFilter(request, response, filterChain);
}
/**
* Destroy the Filter delegate.
* Default implementation simply calls {@code Filter.destroy} on it.
*/
protected void destroyDelegate(Filter delegate) {
if (isTargetFilterLifecycle()) {
delegate.destroy();
}
}
}
查看doFilter真正实现类(session包下)
每次只filter一次
abstract class OncePerRequestFilter implements Filter {
/**
* Suffix that gets appended to the filter name for the "already filtered" request
* attribute.
*/
public static final String ALREADY_FILTERED_SUFFIX = ".FILTERED";
private String alreadyFilteredAttributeName = getClass().getName()
.concat(ALREADY_FILTERED_SUFFIX);
/**
* This {@code doFilter} implementation stores a request attribute for
* "already filtered", proceeding without filtering again if the attribute is already
* there.
*/
public final void doFilter(ServletRequest request, ServletResponse response,
FilterChain filterChain) throws ServletException, IOException {
if (!(request instanceof HttpServletRequest)
|| !(response instanceof HttpServletResponse)) {
throw new ServletException(
"OncePerRequestFilter just supports HTTP requests");
}
HttpServletRequest httpRequest = (HttpServletRequest) request;
HttpServletResponse httpResponse = (HttpServletResponse) response;
//判断是否已经被Filter
boolean hasAlreadyFilteredAttribute = request
.getAttribute(this.alreadyFilteredAttributeName) != null;
if (hasAlreadyFilteredAttribute) {
// Proceed without invoking this filter...
filterChain.doFilter(request, response);
}
else {
// Do invoke this filter...
//确实调用此filter
request.setAttribute(this.alreadyFilteredAttributeName, Boolean.TRUE);
try {
//跳至下面的抽象方法
doFilterInternal(httpRequest, httpResponse, filterChain);
}
finally {
// Remove the "already filtered" request attribute for this request.
request.removeAttribute(this.alreadyFilteredAttributeName);
}
}
}
/**
* Same contract as for {@code doFilter}, but guaranteed to be just invoked once per
* request within a single request thread.
* <p>
* Provides HttpServletRequest and HttpServletResponse arguments instead of the
* default ServletRequest and ServletResponse ones.
*/
//唯一实现子类:SessionRepositoryFilter!!!
protected abstract void doFilterInternal(HttpServletRequest request,
HttpServletResponse response, FilterChain filterChain)
throws ServletException, IOException;
public void init(FilterConfig config) {
}
public void destroy() {
}
}
这个类应该是Spring-session里最关键的Bean了，他是一个Filter，他的作用就是封装HttpServietRequest，HttpServletResponse，改变其获取Session的行为，原始的获取Session方式是从服务器容器内获取，而SessionRepositoryFilter将其改变为从其他地方获取，比如从整合的Redis内，当不存在Session时，创建一个封装过的Session，设置到Redis中，同时将此Session关联的Cookie注入到返回结果中，可看其内部的Request和Session的包装类：
SessionRepositoryFilter.png
@Order(SessionRepositoryFilter.DEFAULT_ORDER)
public class SessionRepositoryFilter<S extends ExpiringSession>
extends OncePerRequestFilter {
private static final String SESSION_LOGGER_NAME = SessionRepositoryFilter.class
.getName().concat(".SESSION_LOGGER");
private static final Log SESSION_LOGGER = LogFactory.getLog(SESSION_LOGGER_NAME);
/**
* The session repository request attribute name.
*/
public static final String SESSION_REPOSITORY_ATTR = SessionRepository.class
.getName();
/**
* Invalid session id (not backed by the session repository) request attribute name.
*/
public static final String INVALID_SESSION_ID_ATTR = SESSION_REPOSITORY_ATTR
+ ".invalidSessionId";
/**
* The default filter order.
*/
public static final int DEFAULT_ORDER = Integer.MIN_VALUE + 50;
private final SessionRepository<S> sessionRepository;
private ServletContext servletContext;
private MultiHttpSessionStrategy httpSessionStrategy = new CookieHttpSessionStrategy();
/**
* Creates a new instance.
*/
public SessionRepositoryFilter(SessionRepository<S> sessionRepository) {
if (sessionRepository == null) {
throw new IllegalArgumentException("sessionRepository cannot be null");
}
this.sessionRepository = sessionRepository;
}
/**
* Sets the {@link HttpSessionStrategy} to be used.
*/
public void setHttpSessionStrategy(HttpSessionStrategy httpSessionStrategy) {
if (httpSessionStrategy == null) {
throw new IllegalArgumentException("httpSessionStrategy cannot be null");
}
this.httpSessionStrategy = new MultiHttpSessionStrategyAdapter(
httpSessionStrategy);
}
/**
* Sets the {@link MultiHttpSessionStrategy} to be used.
*/
public void setHttpSessionStrategy(MultiHttpSessionStrategy httpSessionStrategy) {
if (httpSessionStrategy == null) {
throw new IllegalArgumentException("httpSessionStrategy cannot be null");
}
this.httpSessionStrategy = httpSessionStrategy;
}
@Override
protected void doFilterInternal(HttpServletRequest request,
HttpServletResponse response, FilterChain filterChain)
throws ServletException, IOException {
request.setAttribute(SESSION_REPOSITORY_ATTR, this.sessionRepository);
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 {
filterChain.doFilter(strategyRequest, strategyResponse);
}
finally {
wrappedRequest.commitSession();
}
}
public void setServletContext(ServletContext servletContext) {
this.servletContext = servletContext;
}
/**
* Allows ensuring that the session is saved if the response is committed.
* 对现有Request的一个包装类
*/
private final class SessionRepositoryResponseWrapper
extends OnCommittedResponseWrapper {
private final SessionRepositoryRequestWrapper request;
SessionRepositoryResponseWrapper(SessionRepositoryRequestWrapper request,
HttpServletResponse response) {
super(response);
if (request == null) {
throw new IllegalArgumentException("request cannot be null");
}
this.request = request;
}
@Override
protected void onResponseCommitted() {
this.request.commitSession();
}
}
private final class SessionRepositoryRequestWrapper
extends HttpServletRequestWrapper {
private final String CURRENT_SESSION_ATTR = HttpServletRequestWrapper.class
.getName();
private Boolean requestedSessionIdValid;
private boolean requestedSessionInvalidated;
private final HttpServletResponse response;
private final ServletContext servletContext;
private SessionRepositoryRequestWrapper(HttpServletRequest request,
HttpServletResponse response, ServletContext servletContext) {
super(request);
this.response = response;
this.servletContext = servletContext;
}
/**
* 更新Session内的数据及最近访问时间到Redis中,若session过期，则清除浏览器cookie的sessionId值
* Uses the HttpSessionStrategy to write the session id to the response and
* persist the Session.
*/
private void commitSession() {
HttpSessionWrapper wrappedSession = getCurrentSession();
if (wrappedSession == null) {
if (isInvalidateClientSession()) {
SessionRepositoryFilter.this.httpSessionStrategy
.onInvalidateSession(this, this.response);
}
}
else {
S session = wrappedSession.getSession();
SessionRepositoryFilter.this.sessionRepository.save(session);
if (!isRequestedSessionIdValid()
|| !session.getId().equals(getRequestedSessionId())) {
SessionRepositoryFilter.this.httpSessionStrategy.onNewSession(session,
this, this.response);
}
}
}
@SuppressWarnings("unchecked")
private HttpSessionWrapper getCurrentSession() {
return (HttpSessionWrapper) getAttribute(this.CURRENT_SESSION_ATTR);
}
private void setCurrentSession(HttpSessionWrapper currentSession) {
if (currentSession == null) {
removeAttribute(this.CURRENT_SESSION_ATTR);
}
else {
setAttribute(this.CURRENT_SESSION_ATTR, currentSession);
}
}
@SuppressWarnings("unused")
public String changeSessionId() {
HttpSession session = getSession(false);
if (session == null) {
throw new IllegalStateException(
"Cannot change session ID. There is no session associated with this request.");
}
// eagerly get session attributes in case implementation lazily loads them
Map<String, Object> attrs = new HashMap<String, Object>();
Enumeration<String> iAttrNames = session.getAttributeNames();
while (iAttrNames.hasMoreElements()) {
String attrName = iAttrNames.nextElement();
Object value = session.getAttribute(attrName);
attrs.put(attrName, value);
}
SessionRepositoryFilter.this.sessionRepository.delete(session.getId());
HttpSessionWrapper original = getCurrentSession();
setCurrentSession(null);
HttpSessionWrapper newSession = getSession();
original.setSession(newSession.getSession());
newSession.setMaxInactiveInterval(session.getMaxInactiveInterval());
for (Map.Entry<String, Object> attr : attrs.entrySet()) {
String attrName = attr.getKey();
Object attrValue = attr.getValue();
newSession.setAttribute(attrName, attrValue);
}
return newSession.getId();
}
@Override
public boolean isRequestedSessionIdValid() {
if (this.requestedSessionIdValid == null) {
String sessionId = getRequestedSessionId();
S session = sessionId == null ? null : getSession(sessionId);
return isRequestedSessionIdValid(session);
}
return this.requestedSessionIdValid;
}
private boolean isRequestedSessionIdValid(S session) {
if (this.requestedSessionIdValid == null) {
this.requestedSessionIdValid = session != null;
}
return this.requestedSessionIdValid;
}
private boolean isInvalidateClientSession() {
return getCurrentSession() == null && this.requestedSessionInvalidated;
}
private S getSession(String sessionId) {
S session = SessionRepositoryFilter.this.sessionRepository
.getSession(sessionId);
if (session == null) {
return null;
}
session.setLastAccessedTime(System.currentTimeMillis());
return session;
}
//重写的getSession方法
//重写获取session的方法，服务区容器内不存在当前请求相关的session，但是请求内含有
//session=***形式的Cookie时,尝试通过此sessionId从Redis内获取相关的Session信息
//这就是实现SSO的关键之处
@Override
public HttpSessionWrapper getSession(boolean create) {
HttpSessionWrapper currentSession = getCurrentSession();
if (currentSession != null) {
return currentSession;
}
String requestedSessionId = getRequestedSessionId();
if (requestedSessionId != null
&& getAttribute(INVALID_SESSION_ID_ATTR) == null) {
S session = getSession(requestedSessionId);
if (session != null) {
this.requestedSessionIdValid = true;
currentSession = new HttpSessionWrapper(session, getServletContext());
currentSession.setNew(false);
setCurrentSession(currentSession);
return currentSession;
}
else {
// This is an invalid session id. No need to ask again if
// request.getSession is invoked for the duration of this request
if (SESSION_LOGGER.isDebugEnabled()) {
SESSION_LOGGER.debug(
"No session found by id: Caching result for getSession(false) for this HttpServletRequest.");
}
setAttribute(INVALID_SESSION_ID_ATTR, "true");
}
}
if (!create) {
return null;
}
if (SESSION_LOGGER.isDebugEnabled()) {
SESSION_LOGGER.debug(
"A new session was created. To help you troubleshoot where the session was created we provided a StackTrace (this is not an error). You can prevent this from appearing by disabling DEBUG logging for "
+ SESSION_LOGGER_NAME,
new RuntimeException(
"For debugging purposes only (not an error)"));
}
S session = SessionRepositoryFilter.this.sessionRepository.createSession();
//会存到redis中
session.setLastAccessedTime(System.currentTimeMillis());
//对session也进行了包装(和request的包装同理)
currentSession = new HttpSessionWrapper(session, getServletContext());
setCurrentSession(currentSession);
return currentSession;
}
@Override
public ServletContext getServletContext() {
if (this.servletContext != null) {
return this.servletContext;
}
// Servlet 3.0+
return super.getServletContext();
}
@Override
public HttpSessionWrapper getSession() {
return getSession(true);
}
@Override
public String getRequestedSessionId() {
return SessionRepositoryFilter.this.httpSessionStrategy
.getRequestedSessionId(this);
}
/**
* Allows creating an HttpSession from a Session instance.
*/
private final class HttpSessionWrapper extends ExpiringSessionHttpSession<S> {
HttpSessionWrapper(S session, ServletContext servletContext) {
super(session, servletContext);
}
//重写session失效方法,在设置Session失效的同时删除Redis数据库内Session信息
@Override
public void invalidate() {
super.invalidate();
SessionRepositoryRequestWrapper.this.requestedSessionInvalidated = true;
setCurrentSession(null);
SessionRepositoryFilter.this.sessionRepository.delete(getId());
}
}
}
/**
* A delegating implementation of {@link MultiHttpSessionStrategy}.
*/
static class MultiHttpSessionStrategyAdapter implements MultiHttpSessionStrategy {
private HttpSessionStrategy delegate;
/**
* Create a new {@link MultiHttpSessionStrategyAdapter} instance.
* @param delegate the delegate HTTP session strategy
*/
MultiHttpSessionStrategyAdapter(HttpSessionStrategy delegate) {
this.delegate = delegate;
}
public String getRequestedSessionId(HttpServletRequest request) {
return this.delegate.getRequestedSessionId(request);
}
public void onNewSession(Session session, HttpServletRequest request,
HttpServletResponse response) {
this.delegate.onNewSession(session, request, response);
}
public void onInvalidateSession(HttpServletRequest request,
HttpServletResponse response) {
this.delegate.onInvalidateSession(request, response);
}
public HttpServletRequest wrapRequest(HttpServletRequest request,
HttpServletResponse response) {
return request;
}
public HttpServletResponse wrapResponse(HttpServletRequest request,
HttpServletResponse response) {
return response;
}
}
}
对现有Request的一个包装类
SessionRepositoryRequestWrapper.png
2 创建spring session
RedisSession在创建时设置3个变量creationTime，maxInactiveInterval，lastAccessedTime。maxInactiveInterval默认值为1800，表示1800s之内该session没有被再次使用，则表明该session已过期。每次session被访问都会更新lastAccessedTime的值，session的过期计算公式：当前时间-lastAccessedTime > maxInactiveInterval.
/**
- Creates a new instance ensuring to mark all of the new attributes to be
- persisted in the next save operation.
**/
RedisSession() {
this(new MapSession());
this.delta.put(CREATION_TIME_ATTR, getCreationTime());
this.delta.put(MAX_INACTIVE_ATTR, getMaxInactiveIntervalInSeconds());
this.delta.put(LAST_ACCESSED_ATTR, getLastAccessedTime());
this.isNew = true;
this.flushImmediateIfNecessary();
}
public MapSession() {
this(UUID.randomUUID().toString());
}
flushImmediateIfNecessary判断session是否需要立即写入后端存储。
3 获取session
spring session在redis里面保存的数据包括：
SET类型的spring:session:expireations:[min]
min表示从1970年1月1日0点0分经过的分钟数，SET集合的member为expires:[sessionId],表示members会在在min分钟过期。
String类型的spring:session:sessions:expires:[sessionId]
该数据的TTL表示sessionId过期的剩余时间，即maxInactiveInterval。
Hash类型的spring:session:sessions:[sessionId]
session保存的数据，记录了creationTime，maxInactiveInterval，lastAccessedTime，attribute。前两个数据是用于session过期管理的辅助数据结构。
应用通过getSession(boolean create)方法来获取session数据，参数create表示session不存在时是否创建新的session。getSession方法首先从请求的“.CURRENT_SESSION”属性来获取currentSession，没有currentSession，则从request取出sessionId，然后读取spring:session:sessions:[sessionId]的值，同时根据lastAccessedTime和MaxInactiveIntervalInSeconds来判断这个session是否过期。如果request中没有sessionId，说明该用户是第一次访问，会根据不同的实现，如RedisSession，MongoExpiringSession，GemFireSession等来创建一个新的session。
另， 从request取sessionId依赖具体的HttpSessionStrategy的实现，spring session给了两个默认的实现CookieHttpSessionStrategy和HeaderHttpSessionStrategy，即从cookie和header中取出sessionId。
@Override
public HttpSessionWrapper getSession(boolean create) {
HttpSessionWrapper currentSession = getCurrentSession();
if (currentSession != null) {
return currentSession;
}
// 从request请求中得到sessionId
String requestedSessionId = getRequestedSessionId();
if (requestedSessionId != null
&& getAttribute(INVALID_SESSION_ID_ATTR) == null) {
S session = getSession(requestedSessionId);
if (session != null) {
this.requestedSessionIdValid = true;
currentSession = new HttpSessionWrapper(session, getServletContext());
currentSession.setNew(false);
setCurrentSession(currentSession);
return currentSession;
}
else {
// This is an invalid session id. No need to ask again if
// request.getSession is invoked for the duration of this request
setAttribute(INVALID_SESSION_ID_ATTR, "true");
}
}
if (!create) {
return null;
}
S session = SessionRepositoryFilter.this.sessionRepository.createSession();
session.setLastAccessedTime(System.currentTimeMillis());
currentSession = new HttpSessionWrapper(session, getServletContext());
setCurrentSession(currentSession);
return currentSession;
}
spring session为什么会使用3个key，而不是一个key？接下来回答。
4 session有效期与删除
spring session的有效期指的是访问有效期，每一次访问都会更新lastAccessedTime的值，过期时间为lastAccessedTime + maxInactiveInterval，也即在有效期内每访问一次，有效期就向后延长maxInactiveInterval。
对于过期数据，一般有三种删除策略：
1）定时删除，即在设置键的过期时间的同时，创建一个定时器， 当键的过期时间到来时，立即删除。
2）惰性删除，即在访问键的时候，判断键是否过期，过期则删除，否则返回该键值。
3）定期删除，即每隔一段时间，程序就对数据库进行一次检查，删除里面的过期键。至于要删除多少过期键，以及要检查多少个数据库，则由算法决定。
redis删除过期数据采用的是懒性删除+定期删除组合策略，也就是数据过期了并不会及时被删除。为了实现session过期的及时性，spring session采用了定时删除的策略，但它并不是如上描述在设置键的同时设置定时器，而是采用固定频率（1分钟）轮询删除过期值，这里的删除是惰性删除。
轮询操作并没有去扫描所有的spring:session:sessions:[sessionId]的过期时间，而是在当前分钟数检查前一分钟应该过期的数据，即spring:session:expirations:[min]的members，然后delete掉spring:session:expirations:[min]，惰性删除spring:session:sessions:expires:[sessionId]。
还有一点是，查看三个数据结构的TTL时间，spring:session:sessions:[sessionId]和spring:session:expirations:[min]比真正的有效期大5分钟，目的是确保当expire key数据过期后，监听事件还能获取到session保存的原始数据。
@Scheduled(cron = "${spring.session.cleanup.cron.expression:0 * * * * *}")
public void cleanupExpiredSessions() {
this.expirationPolicy.cleanExpiredSessions();
}
public void cleanExpiredSessions() {
long now = System.currentTimeMillis();
long prevMin = roundDownMinute(now);
// preMin时间到，将spring:session:expirations:[min], set集合中members包括了这一分钟之内需要过期的所有
// expire key删掉, member元素为expires:[sessionId]
String expirationKey = getExpirationKey(prevMin);
Set<Object> sessionsToExpire = this.redis.boundSetOps(expirationKey).members();
this.redis.delete(expirationKey);
for (Object session : sessionsToExpire) {
// sessionKey为spring:session:sessions:expires:[sessionId]
String sessionKey = getSessionKey((String) session);
//利用redis的惰性删除策略
touch(sessionKey);
}
}
spring session在redis中保存了三个key，为什么？ sessions key记录session本身的数据，expires key标记session的准确过期时间，expiration key保证session能够被及时删除，spring监听事件能够被及时处理。
上面的代码展示了session expires key如何被删除，那session每次都是怎样更新过期时间的呢？ 每一次http请求，在经过所有的filter处理过后，spring session都会通过onExpirationUpdated()方法来更新session的过期时间， 具体的操作看下面源码的注释。
public void onExpirationUpdated(Long originalExpirationTimeInMilli,
ExpiringSession session) {
String keyToExpire = "expires:" + session.getId();
long toExpire = roundUpToNextMinute(expiresInMillis(session));
if (originalExpirationTimeInMilli != null) {
long originalRoundedUp = roundUpToNextMinute(originalExpirationTimeInMilli);
// 更新expirations:[min],两个分钟数之内都有这个session，将前一个set中的成员删除
if (toExpire != originalRoundedUp) {
String expireKey = getExpirationKey(originalRoundedUp);
this.redis.boundSetOps(expireKey).remove(keyToExpire);
}
}
long sessionExpireInSeconds = session.getMaxInactiveIntervalInSeconds();
String sessionKey = getSessionKey(keyToExpire);
if (sessionExpireInSeconds < 0) {
this.redis.boundValueOps(sessionKey).append("");
this.redis.boundValueOps(sessionKey).persist();
this.redis.boundHashOps(getSessionKey(session.getId())).persist();
return;
}
String expireKey = getExpirationKey(toExpire);
BoundSetOperations<Object, Object> expireOperations = this.redis
.boundSetOps(expireKey);
expireOperations.add(keyToExpire);
long fiveMinutesAfterExpires = sessionExpireInSeconds
+ TimeUnit.MINUTES.toSeconds(5);
// expirations:[min] key的过期时间加5分钟
expireOperations.expire(fiveMinutesAfterExpires, TimeUnit.SECONDS);
if (sessionExpireInSeconds == 0) {
this.redis.delete(sessionKey);
}
else {
// expires:[sessionId] 值为“”，过期时间为MaxInactiveIntervalInSeconds
this.redis.boundValueOps(sessionKey).append("");
this.redis.boundValueOps(sessionKey).expire(sessionExpireInSeconds,
TimeUnit.SECONDS);
}
// sessions:[sessionId]的过期时间 加5分钟
this.redis.boundHashOps(getSessionKey(session.getId()))
.expire(fiveMinutesAfterExpires, TimeUnit.SECONDS);
}
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