getSession()与getSession(boolean create)区别

getSession()与getSession(boolean create)区别

1. 通过HttpServletRequest的部分源码观察到

public interface HttpServletRequest extends ServletRequest {
    /**
     * Returns the current <code>HttpSession</code> associated with this request
     * or, if there is no current session and <code>create</code> is true,
     * returns a new session.
     * <p>
     * If <code>create</code> is <code>false</code> and the request has no valid
     * <code>HttpSession</code>, this method returns <code>null</code>.
     * <p>
     * To make sure the session is properly maintained, you must call this
     * method before the response is committed. If the container is using
     * cookies to maintain session integrity and is asked to create a new
     * session when the response is committed, an IllegalStateException is
     * thrown.
     *
     * @param create
     *            <code>true</code> to create a new session for this request if
     *            necessary; <code>false</code> to return <code>null</code> if
     *            there's no current session
     * @return the <code>HttpSession</code> associated with this request or
     *         <code>null</code> if <code>create</code> is <code>false</code>
     *         and the request has no valid session
     * @see #getSession()
     */
    public HttpSession getSession(boolean create);

    /**
     * Returns the current session associated with this request, or if the
     * request does not have a session, creates one.
     *
     * @return the <code>HttpSession</code> associated with this request
     * @see #getSession(boolean)
     */
    public HttpSession getSession();
}

2. getSession(boolean create)

注解大致意思是返回一个和request相关联的session，如果没有则判断create参数，如果create为true则创建一个返回，如果create为false，则返回null；

3. getSession()

上的注解大致是返回和request相关联的session，如果不存在就创建一个；
也就是 getSession() 相当于 getSession(true);

4. 使用注意

• 存数据一般使用 getSession() 就可以。
• 取数据一般使用 getSession(false) 还要做数据的判空处理；