[FIXED] Is RequestContextHolder thread-safe?

Issue

In my Spring JDBC project I have a class called DBStuff which i use to connect to DB and make simple DB operations. It's a web project and there are users, so naturally i use session mechanism. When i need to retrieve request data in DBStuff class, I use this line of code below:

HttpServletRequest request = ((ServletRequestAttributes) RequestContextHolder.getRequestAttributes()).getRequest();

But, there is no explanation that if the RequestContextHolder is thread-safe or not. Even the spring's official forum doesn't have an answer for that. Because of using servlet, I need to provide a thread-safe nature for the users.

By definition RequestContextHolder is defined as "Holder class to expose the web request in the form of a thread-bound RequestAttributes object." But I am not sure if "thread-bound" stands for thread-safe.

Solution

"thread-bound" means that every thread has own copy of the data, so it is thread-safe.

It uses ThreadLocal for that

private static final ThreadLocal<RequestAttributes> requestAttributesHolder = 
      new NamedThreadLocal<RequestAttributes>("Request attributes");

public static RequestAttributes getRequestAttributes() {
    RequestAttributes attributes = requestAttributesHolder.get();
    if (attributes == null) {
        attributes = inheritableRequestAttributesHolder.get();
    }
    return attributes;
}

requestAttributesHolder.get() returns RequestAttributes for the current thread, it is a thread that process an HTTP request. Every request has an own thread.

Method get() of ThreadLocal uses a map to bound the data to the Thread.currentThread()

public T get() {
    Thread t = Thread.currentThread();
    ThreadLocalMap map = getMap(t);
    if (map != null) {
        ThreadLocalMap.Entry e = map.getEntry(this);
        if (e != null)
            return (T)e.value;
    }
    return setInitialValue();
}

When and how should I use a ThreadLocal variable?

Answered By - v.ladynev
Answer Checked By - Dawn Plyler (JavaFixing Volunteer)