1.context級別，整個應用共享：

在web.xml裡定義：

    <context-param>
        <param-name>dbname</param-name>
        <param-value>mysql</param-value>
    </context-param>

2.servlet級別，單個servlet使用：

在servlet標籤裡配置：

    <servlet>
        <servlet-name>HelloWorld</servlet-name>
        <servlet-class>controller.MainServlet</servlet-class>
        <init-param>
            <param-name>url</param-name>
            <param-value>jdbc:mysql://localhost:3306/mysql</param-value>
        </init-param>
    </servlet>
 

程式碼中分別使用servletContext和httpServlet的getInitParameter方法獲取：

    public void doGet(HttpServletRequest request,
                      HttpServletResponse response)
            throws ServletException, IOException
    {
        response.setContentType("text/html");

        PrintWriter out = response.getWriter();
        ServletContext context = getServletContext();
        out.println("context params:" + context.getInitParameter("dbname"));

        out.println("servlet params:" + this.getInitParameter("url"));

    }