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这篇文章主要介绍Tomcat9中如何管理session，文中介绍的非常详细，具有一定的参考价值，感兴趣的小伙伴们一定要看完！
session相关共有两个类：
StandardSession：默认的session的类，是对session的系统抽象
StandardManager：默认的session管理类，管理session的创建、加载、持久化等
protected synchronized void startInternal() throws LifecycleException {
...省略其他代码...
Manager contextManager = null;
Manager manager = getManager();
if (manager == null) {
if (log.isDebugEnabled()) {
log.debug(sm.getString("standardContext.cluster.noManager",
Boolean.valueOf((getCluster() != null)),
Boolean.valueOf(distributable)));
}
if ((getCluster() != null) && distributable) {
try {
contextManager = getCluster().createManager(getName());
} catch (Exception ex) {
log.error(sm.getString("standardContext.cluster.managerError"), ex);
ok = false;
}
} else {
contextManager = new StandardManager();
}
}
// Configure default manager if none was specified
if (contextManager != null) {
if (log.isDebugEnabled()) {
log.debug(sm.getString("standardContext.manager",
contextManager.getClass().getName()));
}
setManager(contextManager);
}
...省略其他代码...
public void setManager(Manager manager) {
Lock writeLock = managerLock.writeLock();
writeLock.lock();
Manager oldManager = null;
try {
// Change components if necessary
oldManager = this.manager;
if (oldManager == manager)
return;
this.manager = manager;
// Stop the old component if necessary
if (oldManager instanceof Lifecycle) {
try {
((Lifecycle) oldManager).stop();
((Lifecycle) oldManager).destroy();
} catch (LifecycleException e) {
log.error(sm.getString("standardContext.setManager.stop"), e);
}
}
// Start the new component if necessary
if (manager != null) {
manager.setContext(this);
}
if (getState().isAvailable() && manager instanceof Lifecycle) {
try {
((Lifecycle) manager).start();
} catch (LifecycleException e) {
log.error(sm.getString("standardContext.setManager.start"), e);
}
}
} finally {
writeLock.unlock();
}
// Report this property change to interested listeners
support.firePropertyChange("manager", oldManager, manager);
}
}在StandardContext的start方法中，会对sessionManager进行实例化，这里是支持Tomcat的集群session，本文以单机session管理为例，即StandardManager，在setManager中会调用StandardManager.start
protected synchronized void startInternal() throws LifecycleException {
super.startInternal();
// Load unloaded sessions, if any
try {
load();
} catch (Throwable t) {
ExceptionUtils.handleThrowable(t);
log.error(sm.getString("standardManager.managerLoad"), t);
}
setState(LifecycleState.STARTING);
}
protected String pathname = "SESSIONS.ser";
protected void doLoad() throws ClassNotFoundException, IOException {
if (log.isDebugEnabled()) {
log.debug("Start: Loading persisted sessions");
}
// Initialize our internal data structures
sessions.clear();
// Open an input stream to the specified pathname, if any
File file = file();
if (file == null) {
return;
}
if (log.isDebugEnabled()) {
log.debug(sm.getString("standardManager.loading", pathname));
}
Loader loader = null;
ClassLoader classLoader = null;
Log logger = null;
try (FileInputStream fis = new FileInputStream(file.getAbsolutePath());
BufferedInputStream bis = new BufferedInputStream(fis)) {
Context c = getContext();
loader = c.getLoader();
logger = c.getLogger();
if (loader != null) {
classLoader = loader.getClassLoader();
}
if (classLoader == null) {
classLoader = getClass().getClassLoader();
}
// Load the previously unloaded active sessions
synchronized (sessions) {
try (ObjectInputStream ois = new CustomObjectInputStream(bis, classLoader, logger,
getSessionAttributeValueClassNamePattern(),
getWarnOnSessionAttributeFilterFailure())) {
Integer count = (Integer) ois.readObject();
int n = count.intValue();
if (log.isDebugEnabled())
log.debug("Loading " + n + " persisted sessions");
for (int i = 0; i < n; i++) {
StandardSession session = getNewSession();
session.readObjectData(ois);
session.setManager(this);
sessions.put(session.getIdInternal(), session);
session.activate();
if (!session.isValidInternal()) {
// If session is already invalid,
// expire session to prevent memory leak.
session.setValid(true);
session.expire();
}
sessionCounter++;
}
} finally {
// Delete the persistent storage file
if (file.exists()) {
if (!file.delete()) {
log.warn(sm.getString("standardManager.deletePersistedFileFail", file));
}
}
}
}
} catch (FileNotFoundException e) {
if (log.isDebugEnabled()) {
log.debug("No persisted data file found");
}
return;
}
if (log.isDebugEnabled()) {
log.debug("Finish: Loading persisted sessions");
}
}
protected void doUnload() throws IOException {
if (log.isDebugEnabled())
log.debug(sm.getString("standardManager.unloading.debug"));
if (sessions.isEmpty()) {
log.debug(sm.getString("standardManager.unloading.nosessions"));
return; // nothing to do
}
// Open an output stream to the specified pathname, if any
File file = file();
if (file == null) {
return;
}
if (log.isDebugEnabled()) {
log.debug(sm.getString("standardManager.unloading", pathname));
}
// Keep a note of sessions that are expired
List list = new ArrayList<>();
try (FileOutputStream fos = new FileOutputStream(file.getAbsolutePath());
BufferedOutputStream bos = new BufferedOutputStream(fos);
ObjectOutputStream oos = new ObjectOutputStream(bos)) {
synchronized (sessions) {
if (log.isDebugEnabled()) {
log.debug("Unloading " + sessions.size() + " sessions");
}
// Write the number of active sessions, followed by the details
oos.writeObject(Integer.valueOf(sessions.size()));
for (Session s : sessions.values()) {
StandardSession session = (StandardSession) s;
list.add(session);
session.passivate();
session.writeObjectData(oos);
}
}
}
// Expire all the sessions we just wrote
if (log.isDebugEnabled()) {
log.debug("Expiring " + list.size() + " persisted sessions");
}
for (StandardSession session : list) {
try {
session.expire(false);
} catch (Throwable t) {
ExceptionUtils.handleThrowable(t);
} finally {
session.recycle();
}
}
if (log.isDebugEnabled()) {
log.debug("Unloading complete");
}
} 在start方法中，会调用load方法，load方法最终调用doLoad方法，会读取文件名为SESSIONS.ser的文件，该文件存储了Tomcat关闭时session的内容，具体存储逻辑在doUnload方法中
public HttpSession getSession() {
Session session = doGetSession(true);
if (session == null) {
return null;
}
return session.getSession();
}
protected Session doGetSession(boolean create) {
// There cannot be a session if no context has been assigned yet
Context context = getContext();
if (context == null) {
return null;
}
// Return the current session if it exists and is valid
if ((session != null) && !session.isValid()) {
session = null;
}
if (session != null) {
return session;
}
// Return the requested session if it exists and is valid
Manager manager = context.getManager();
if (manager == null) {
return null; // Sessions are not supported
}
if (requestedSessionId != null) {
try {
session = manager.findSession(requestedSessionId); //读取session
} catch (IOException e) {
session = null;
}
if ((session != null) && !session.isValid()) {
session = null;
}
if (session != null) {
session.access();
return session;
}
}
// Create a new session if requested and the response is not committed
if (!create) {
return null;
}
boolean trackModesIncludesCookie =
context.getServletContext().getEffectiveSessionTrackingModes().contains(SessionTrackingMode.COOKIE);
if (trackModesIncludesCookie && response.getResponse().isCommitted()) {
throw new IllegalStateException(sm.getString("coyoteRequest.sessionCreateCommitted"));
}
String sessionId = getRequestedSessionId();
if (requestedSessionSSL) {
// If the session ID has been obtained from the SSL handshake then
// use it.
} else if (("/".equals(context.getSessionCookiePath())
&& isRequestedSessionIdFromCookie())) {
if (context.getValidateClientProvidedNewSessionId()) {
boolean found = false;
for (Container container : getHost().findChildren()) {
Manager m = ((Context) container).getManager();
if (m != null) {
try {
if (m.findSession(sessionId) != null) {
found = true;
break;
}
} catch (IOException e) {
// Ignore. Problems with this manager will be
// handled elsewhere.
}
}
}
if (!found) {
sessionId = null;
}
}
} else {
sessionId = null;
}
session = manager.createSession(sessionId); //创建新的session
// Creating a new session cookie based on that session
if (session != null && trackModesIncludesCookie) {
Cookie cookie = ApplicationSessionCookieConfig.createSessionCookie(
context, session.getIdInternal(), isSecure());
response.addSessionCookieInternal(cookie);
}
if (session == null) {
return null;
}
session.access();
return session;
}在getSession方法中，会先根据sessionId在调用manager.findSession查找，如果查找不存在则会调用manager.createSession创建
public Session findSession(String id) throws IOException {
if (id == null) {
return null;
}
return sessions.get(id);
}
public Session createSession(String sessionId) {
if ((maxActiveSessions >= 0) &&
(getActiveSessions() >= maxActiveSessions)) {
rejectedSessions++;
throw new TooManyActiveSessionsException(
sm.getString("managerBase.createSession.ise"),
maxActiveSessions);
}
// Recycle or create a Session instance
Session session = createEmptySession();
// Initialize the properties of the new session and return it
session.setNew(true);
session.setValid(true);
session.setCreationTime(System.currentTimeMillis());
session.setMaxInactiveInterval(getContext().getSessionTimeout() * 60);
String id = sessionId;
if (id == null) {
id = generateSessionId();
}
session.setId(id);
sessionCounter++;
SessionTiming timing = new SessionTiming(session.getCreationTime(), 0);
synchronized (sessionCreationTiming) {
sessionCreationTiming.add(timing);
sessionCreationTiming.poll();
}
return session;
}所有的session为维护在一个HashMap中，在创建时会想Map中维护，读取是从Map中查找。
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