容器初始化一個servlet時會建一個唯一的servletConfig,並只對這個servlet可用
<servlet>
<servlet-name>xxx</servlet-name>
<servlet-value>xxxxx</servlet-value>
<init-param>
<param-name>myinitparam</param-name>
<param-value>dddddddddd</param-value>
</init-param>
</servlet>
在servlet中取得
getServletConfig().getInitParameter("myinitparam ");
上下文參數servletContext對整個web應用可用(且只有一個,如果是分佈式應用,那麼每個jvm有一個servletContext),而不只是針對一個servlet
<context-param>
<param-name>myinitparam</param-name>
<param-value>test</param-value>
</context-param>
在servlet中使用
getServletContext().getInitParameter("myinitparam ");
另一種使用方法(有,不用,因爲只要繼承了httpServlet或者GenericServlet就有getServletContext())
getServletConfig().getServletContext().getInitParameter("myinitparam ");
但是上下文是非線程安全的,所以對屬性操作需要加鎖
synchronized(getServletContext()) {
getServletContext().setAttribute("ddd","ddd");
}
關於listener
在DD文件中配置
<listener>
<listener-class>
xxx.xxx.xxx.myListener
</listener-class>
</listener>
對session加鎖保證線程安全
HttpSession session = request.getSession();
synchronized(session) {
session.setAttribute("ddd", "ddd");
}
請求分派
RequestDispatcher dispatcher = request.getRequestDispatcher("view.jsp");
dispatcher.forward(request, response);
RequestDispatcher可以從servletRequest和servletContext中取得,
但是servletRequest需要設置相對路徑,而servletContext需要絕對路徑。
即:
servletRequest:
RequestDispatcher dispatcher = request.getRequestDispatcher("view.jsp");
servletContext:
RequestDispatcher dispatcher = getServletContext().getRequestDispatcher("/view.jsp");