public void run() { //org.apache.catalina.session.PersistentManagerBase.run()while(!threadDone) {threadSleep();processExpires(); // 检查Session对象是否过期.processPersistenceChecks();}
}
public void processPersistenceChecks(){ // org.apache.catalina.session.PersistentManagerBase.processPersistenceChecks()processMaxIdleSwaps(); // highlight line.(下面我们只以processMaxIdleSwaps方法为例进行调用过程的分析，其他两个方法类似)processMaxActiveSwaps(); // highlight line.processMaxIdleBackups(); // highlight line.
}

/*** Swap idle sessions out to Store if they are idle too long.若session空闲太久则换出*/protected void processMaxIdleSwaps() {if (!isStarted() || maxIdleSwap < 0)return;Session sessions[] = findSessions();long timeNow = System.currentTimeMillis();// Swap out all sessions idle longer than maxIdleSwap// FIXME: What's preventing us from mangling a session during// a request?if (maxIdleSwap >= 0) {for (int i = 0; i < sessions.length; i++) {StandardSession session = (StandardSession) sessions[i];if (!session.isValid())continue;long lastAccessed = ((StandardSession)session).getLastUsedTime();int timeIdle = // Truncate, do not round up(int) ((timeNow - lastAccessed) / 1000L);if (timeIdle > maxIdleSwap && timeIdle > minIdleSwap) {if (debug > 1)log(sm.getString("persistentManager.swapMaxIdle",session.getId(), new Integer(timeIdle)));try {swapOut(session); // highlight line.} catch (IOException e) {;   // This is logged in writeSession()}}}}}

protected void swapOut(Session session) throws IOException { //换出操作if (store == null ||!session.isValid() ||isSessionStale(session, System.currentTimeMillis()))return;((StandardSession)session).passivate();writeSession(session); // highlight line.super.remove(session);session.recycle();}

protected void writeSession(Session session) throws IOException {if (store == null ||!session.isValid() ||isSessionStale(session, System.currentTimeMillis()))return;try {store.save(session); //highlight line.sessionSwapIgnore.remove(session.getId());} catch (IOException e) {log(sm.getString("persistentManager.serializeError", session.getId(), e));throw e;}}

public Session findSession(String id) throws IOException { //org.apache.catalina.session.PersistentManagerBase.findSession()Session session = super.findSession(id);if (session != null)return (session);// See if the Session is in the Storesession = swapIn(id); // highlight line.return (session);}

protected Session swapIn(String id) throws IOException { // the same as the above.if (store == null)return null;if (sessionSwapIgnore.contains(id)) {return null;}Session session = null;try {session = store.load(id); // highlight line.} catch (ClassNotFoundException e) {log(sm.getString("persistentManager.deserializeError", id, e));throw new IllegalStateException(sm.getString("persistentManager.deserializeError", id, e));}if (session == null) {sessionSwapIgnore.put(id,id);return (null);}if (!session.isValid()|| isSessionStale(session, System.currentTimeMillis())) {log("session swapped in is invalid or expired");session.expire(); // highlight line.store.remove(id); // highlight line.sessionSwapIgnore.put(id,id);return (null);}if(debug > 2)log(sm.getString("persistentManager.swapIn", id));session.setManager(this);// To make sure the listener knows about it.((StandardSession)session).tellNew();add(session);((StandardSession)session).activate();return (session);}

public final class PersistentManager extends PersistentManagerBase {  //org.apache.catalina.session.PersistentManager private static final String info = "PersistentManager/1.0";   protected static String name = "PersistentManager";  public String getInfo() {return (this.info);}  public String getName() {return (name);}}

 public Session createSession() {Session session = super.createSession(); // step1.ObjectOutputStream oos = null;ByteArrayOutputStream bos = null;ByteArrayInputStream bis = null;try {bos = new ByteArrayOutputStream();oos = new ObjectOutputStream(new BufferedOutputStream(bos));((StandardSession)session).writeObjectData(oos);oos.close();byte[] obs = bos.toByteArray();clusterSender.send(obs); // step2.if(debug > 0)log("Replicating Session: "+session.getId());} catch (IOException e) {log("An error occurred when replicating Session: "+session.getId());}return (session);}

public void run() { // org.apache.catalina.session.DistributedManager.run()// Loop until the termination semaphore is setwhile (!threadDone) {threadSleep();processClusterReceiver(); // 以该方法为例进行说明.processExpires();processPersistenceChecks();}}

/*** Called from our background thread to process new received Sessions**/public void processClusterReceiver() { //org.apache.catalina.session.DistributedManager.processClusterReceiver()Object[] objs = clusterReceiver.getObjects();StandardSession _session = null;ByteArrayInputStream bis = null;Loader loader = null;ClassLoader classLoader = null;ObjectInputStream ois = null;byte[] buf = new byte[5000];ReplicationWrapper repObj = null;for(int i=0; i < objs.length;i++) {try {bis = new ByteArrayInputStream(buf);repObj = (ReplicationWrapper)objs[i];buf = repObj.getDataStream();bis = new ByteArrayInputStream(buf, 0, buf.length);if (container != null)loader = container.getLoader();if (loader != null)classLoader = loader.getClassLoader();if (classLoader != null)ois = new CustomObjectInputStream(bis,classLoader);elseois = new ObjectInputStream(bis);_session = (StandardSession) super.createSession();_session.readObjectData(ois);_session.setManager(this);if (debug > 0)log("Loading replicated session: "+_session.getId());} catch (IOException e) {log("Error occurred when trying to read replicated session: "+e.toString());} catch (ClassNotFoundException e) {log("Error occurred when trying to read replicated session: "+e.toString());} finally {if (ois != null) {try {ois.close();bis = null;} catch (IOException e) {;}}}}}

public interface Store { // org.apache.catalina.Storepublic String getInfo(); public Manager getManager(); public void setManager(Manager manager); public int getSize() throws IOException; public void addPropertyChangeListener(PropertyChangeListener listener); public String[] keys() throws IOException; public Session load(String id) throws ClassNotFoundException, IOException;public void remove(String id) throws IOException; public void clear() throws IOException; public void removePropertyChangeListener(PropertyChangeListener listener); public void save(Session session) throws IOException;
} 

 public void run() { // org.apache.catalina.session.StoreBase.run()// Loop until the termination semaphore is setwhile (!threadDone) {threadSleep();processExpires();}}

public class SessionServlet extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {System.out.println("SessionServlet -- service");response.setContentType("text/html");PrintWriter out = response.getWriter();out.println("<html>");out.println("<head><title>SessionServlet</title></head>");out.println("<body>");String value = request.getParameter("value");HttpSession session = request.getSession(true);out.println("<br>the previous value is " +(String) session.getAttribute("value"));out.println("<br>the current value is " + value);session.setAttribute("value", value);out.println("<br><hr>");out.println("<form>");out.println("New Value: <input name=value>");out.println("<input type=submit>");out.println("</form>");out.println("</body>");out.println("</html>");}
} 

public static void main(String[] args) {//invoke: http://localhost:8080/myApp/SessionSystem.setProperty("catalina.base", System.getProperty("user.dir"));Connector connector = new HttpConnector();Wrapper wrapper1 = new SimpleWrapper();wrapper1.setName("Session");wrapper1.setServletClass("SessionServlet");Context context = new StandardContext();// StandardContext's start method adds a default mappercontext.setPath("/myApp");context.setDocBase("myApp");context.addChild(wrapper1);// context.addServletMapping(pattern, name);// note that we must use /myApp/Session, not just /Session// because the /myApp section must be the same as the path, so the cookie will// be sent back.context.addServletMapping("/myApp/Session", "Session");// add ContextConfig. This listener is important because it configures// StandardContext (sets configured to true), otherwise StandardContext// won't startLifecycleListener listener = new SimpleContextConfig();((Lifecycle) context).addLifecycleListener(listener);// here is our loaderLoader loader = new WebappLoader();// associate the loader with the Contextcontext.setLoader(loader);connector.setContainer(context);// add a ManagerManager manager = new StandardManager(); // highlight line.context.setManager(manager); // highlight line.try {connector.initialize();((Lifecycle) connector).start();((Lifecycle) context).start();// make the application wait until we press a key.System.in.read();((Lifecycle) context).stop();}catch (Exception e) {e.printStackTrace();}}
}

 public void invoke(Request request, Response response, ValveContext valveContext)throws IOException, ServletException {SimpleWrapper wrapper = (SimpleWrapper) getContainer();ServletRequest sreq = request.getRequest();ServletResponse sres = response.getResponse();Servlet servlet = null;HttpServletRequest hreq = null;if (sreq instanceof HttpServletRequest)hreq = (HttpServletRequest) sreq;HttpServletResponse hres = null;if (sres instanceof HttpServletResponse)hres = (HttpServletResponse) sres;//-- new addition -----------------------------------Context context = (Context) wrapper.getParent(); // highlight line.request.setContext(context); // highlight line.//-------------------------------------// Allocate a servlet instance to process this requesttry {servlet = wrapper.allocate();if (hres!=null && hreq!=null) {servlet.service(hreq, hres);}else {servlet.service(sreq, sres);}}catch (ServletException e) {}}

Manager manager = null;
if(contect != null)manager = context.getManager();