ServletContext, Session, Request的attribute

ServletContext 不是thread safe的，因为它里面的信息是整个web app所有servlet和jsp共享的。所以访问是要进行并发控制。

public void doGet(HttpServletRequest request, 
    HttpServletResponse response) throws IOException, ServletException {
    response.setContentType(“text/html”);
    PrintWriter out = response.getWriter();
    out.println(“test context attributes”);
    synchronized(getServletContext()) {
        getServletContext().setAttribute(“foo”, “22”);
        getServletContext().setAttribute(“bar”, “42”);
        out.println(getServletContext().getAttribute(“foo”));
        out.println(getServletContext().getAttribute(“bar”));
    }
}

 

session也不是thread safe的。因为一个客户端可以开多个浏览器窗口，但是它们都属于一个session。

public void doGet(HttpServletRequest request, 
    HttpServletResponse response)
throws IOException, ServletException {
    response.setContentType(“text/html”);
    PrintWriter out = response.getWriter();
    out.println(“test session attributes<br>”);
    HttpSession session = request.getSession();
    synchronized(session) {
        session.setAttribute(“foo”, “22”);
        session.setAttribute(“bar”, “42”);
        out.println(session.getAttribute(“foo”));
        out.println(session.getAttribute(“bar”));
    }
}