Tomcat - 如何使用 PersistentManager + FileStore 将会话立即保存到磁盘 [英] Tomcat - How to persist a session immediately to disk using PersistentManager + FileStore

问题描述

我想将 Tomcat 的 HttpSessions 持久化到磁盘，以便它可以在可扩展的云环境中使用.关键是将有许多 Tomcat 节点(在云 PaaS 中)并且客户端可以被定向到其中的任何一个.我们希望从共享磁盘机持久化和加载会话.

I want to persist Tomcat's HttpSessions to disk so that it can be used in a scalable cloud environment. The point is that there will be a number of Tomcat nodes up (in a cloud PaaS) and clients can be directed to any of them. We want to persist and load the sessions from a shared disk unit.

我以这种方式配置了 PersistentManager:

I have configured the PersistentManager this way:

context.xml

<Manager className="org.apache.catalina.session.PersistentManager">
   <Store className="org.apache.catalina.session.FileStore" directory="c:/somedir"/>
</Manager>

问题是会话显然从未刷新到磁盘.

The problem is that sessions are, apparently, never flushed to disk.

我更改了 配置，添加了 maxIdleBackup:

I changed the <Manager> config adding maxIdleBackup:

<Manager className="org.apache.catalina.session.PersistentManager maxIdleBackup="1">

这样我看到会话持续到磁盘需要将近一分钟的时间.奇怪的是，文档指出它应该需要大约一秒钟:

This way it takes almost a minute until I see the session persisted to disk. Oddly enough, the doc states that it should take around a second:

ma​​xIdleBackup:自上次访问以来的时间间隔(以秒为单位)在它有资格被持久化到会话之前的会话store 或 -1 禁用此功能.默认情况下，此功能是已禁用.

maxIdleBackup: The time interval (in seconds) since the last access to a session before it is eligible for being persisted to the session store, or -1 to disable this feature. By default, this feature is disabled.

其他配置:

按照 文档 我设置了系统属性

Following the documentation I set the system property

org.apache.catalina.session.StandardSession.ACTIVITY_CHECK -> true

有没有办法立即将会话刷新到磁盘?是否可以立即保留会话中的任何更改?

Is there a way to immediately flush the session to disk? Is is possible to make that any change in the session is also persisted right away?

更新:

我已尝试使用 maxIdleBackup="0" minIdleSwap="0" maxIdleSwap="1" 强制钝化会话并刷新到磁盘，但仍然需要将近一分钟.

I have tried to force the passivation of the session and flushing to disk with maxIdleBackup="0" minIdleSwap="0" maxIdleSwap="1", but it still takes almost a minute.

推荐答案

我终于设法解决了这个问题:

I finally managed to solve this:

1. 我扩展了 org.apache.catalina.session.ManagerBase 覆盖使用超类会话映射的每个方法，以便它直接攻击文件(或缓存).

1. I extended org.apache.catalina.session.ManagerBase overriding every method that used the superclass' sessions map, so that it attacked a file (or cache) directly.

示例:

@Override
public HashMap<String, String> getSession(String sessionId) {
    Session s = getSessionFromStore(sessionId);
    if (s == null) {
        if (log.isInfoEnabled()) {
            log.info("Session not found " + sessionId);
        }
        return null;
    }

    Enumeration<String> ee = s.getSession().getAttributeNames();
    if (ee == null || !ee.hasMoreElements()) {
        return null;
    }

    HashMap<String, String> map = new HashMap<>();
    while (ee.hasMoreElements()) {
        String attrName = ee.nextElement();
        map.put(attrName, getSessionAttribute(sessionId, attrName));
    }

    return map;

}

重要事项:

加载和卸载方法必须留空:

load and unload methods must be left empty:

    @Override
    public void load() throws ClassNotFoundException, IOException {
        // TODO Auto-generated method stub

    }

    @Override
    public void unload() throws IOException {
        // TODO Auto-generated method stub

    }

您必须覆盖 startInternal 和 stopInternal 以防止生命周期错误:

You have to override startInternal and stopInternal to prevent Lifecycle errors:

@Override
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);
}

@Override
protected synchronized void stopInternal() throws LifecycleException {

    if (log.isDebugEnabled()) {
        log.debug("Stopping");
    }

    setState(LifecycleState.STOPPING);

    // Write out sessions
    try {
        unload();
    } catch (Throwable t) {
        ExceptionUtils.handleThrowable(t);
        log.error(sm.getString("standardManager.managerUnload"), t);
    }

    // Expire all active sessions
    Session sessions[] = findSessions();
    for (int i = 0; i < sessions.length; i++) {
        Session session = sessions[i];
        try {
            if (session.isValid()) {
                session.expire();
            }
        } catch (Throwable t) {
            ExceptionUtils.handleThrowable(t);
        } finally {
            // Measure against memory leaking if references to the session
            // object are kept in a shared field somewhere
            session.recycle();
        }
    }

    // Require a new random number generator if we are restarted
    super.stopInternal();
} 

1. 上面允许始终从文件(或缓存)中读取，但是写操作呢?.为此，我扩展了 org.apache.catalina.session.StandardSession 覆盖了 public void setAttribute(String name, Object value, boolean notify) 和 public void removeAttribute(字符串名称，布尔通知).

1. The above allows to read always from the file (or cache) but what about the write operations?. For this, I extended org.apache.catalina.session.StandardSession overriding public void setAttribute(String name, Object value, boolean notify) and public void removeAttribute(String name, boolean notify).

示例:

@Override
public void setAttribute(String name, Object value, boolean notify) {
    super.setAttribute(name, value, notify);
    ((DataGridManager)this.getManager()).getCacheManager().getCache("sessions").put(this.getIdInternal(), this);
}

@Override
public void removeAttribute(String name, boolean notify) {
    super.removeAttribute(name, notify);
    ((DataGridManager)this.getManager()).getCacheManager().getCache("sessions").put(this.getIdInternal(), this);
}

重要提示:

在我们的例子中，真正的会话备份最终是一个缓存(而不是文件)，当我们从中读取扩展的 Tomcat 会话(在我们的 ManagerBase impl 类中)时，我们不得不以一种丑陋的方式调整它，以便一切正常:

In our case the real session backup ended up being a cache (not a file) and when we read the extended Tomcat session from it (in our ManagerBase impl class) we had to tweak it in an kind of ugly way so that everything worked:

    private Session getSessionFromStore(String sessionId){
        DataGridSession s = (DataGridSession)cacheManager.getCache("sessions").get(sessionId);
        if(s!=null){
            try {
                Field notesField;
                notesField = StandardSession.class.getDeclaredField("notes");
                notesField.setAccessible(true);
                notesField.set(s, new HashMap<String, Object>());
                s.setManager(this);
            } catch (IllegalArgumentException | IllegalAccessException | NoSuchFieldException | SecurityException e) {
                throw new RuntimeException(e);
            }
        }
        return s;
    }

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