servlet初始化参数

使用<context-param>标签初始化的参数是被应用程序中所有的servlet所共享。但是有时候我们需要为某一个特定的servlet配置参数，这个时候我们就需要使用servlet初始化参数。

1、servlet初始化参数，在web.xml中配置

1.1、配置web.xml文件

<servlet>
    <servlet-name>HelloServlet</servlet-name>
    <servlet-class>webDemo01.HelloServlet</servlet-class>
    <init-param>
        <param-name>data</param-name>
        <param-value>ServletConfig</param-value>
    </init-param>
    <init-param>
        <param-name>server</param-name>
        <param-value>1.1.1</param-value>
    </init-param>
  </servlet>
  <servlet-mapping>
    <servlet-name>HelloServlet</servlet-name>
    <url-pattern>/HelloServlet</url-pattern>
  </servlet-mapping>

1.2、在指定的servlet中获取参数

public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        //获取ServletConfig对象
        ServletConfig config = this.getServletConfig();
        //根据参数名获取参数值
        String initParameter1 = config.getInitParameter("data");
        String initParameter2 = config.getInitParameter("server");
        PrintWriter writer = response.getWriter();
        writer.append(initParameter1).append(initParameter2);
    }

2、使用注解完成servlet初始化参数。

 @WebServlet(
 2         name="HelloServlet02",
 3         urlPatterns={"/HelloServlet02"},
 4         initParams={
 5                 @WebInitParam(name="data",value="config"),
 6                 @WebInitParam(name="server",value="2.2.2")
 7         })
 public class HelloServlet02 extends HttpServlet {
     private static final long serialVersionUID = 1L;

     public void doGet(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
         this.doPost(request, response);
     }

     public void doPost(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
         ServletConfig config = this.getServletConfig();
         String initParameter = config.getInitParameter("data");
         String initParameter2 = config.getInitParameter("server");
         response.getWriter().append(initParameter).append(initParameter2);
     }

区别：

　　1、使用注解完成servlet初始化参数，如果修改了初始化参数，必须重新编译应用程序才能生效

　  2、将servlet参数添加到部署描述符，修改xml代码并重启应用程序即可使配置生效