Servlet Analysis

 @WebServlet("/cdiservlet")      //url映射
 public class NewServlet extends HttpServlet {
     private Message message;

     @Override             //重写doGet方法
     public void init() {
         message = new MessageB();    //对message初始化
     }

     @Override
     public void doGet(HttpServletRequest request, HttpServletResponse response)
                   throws IOException {              //抛出可能出现IO异常
         response.getWriter().write(message.get());   //捕获可能发生的异常
     }
 }

 public interface Message {         //servlet实现Message接口的一个对象实例
     public String get();
 }
 public class MessageB implements Message {          //servlet创建以下对象的实例
     public MessageB() { }

     @Override
     public String get() {
         return "message B";
     }
 }
 @WebServlet("/cdiservlet")              //使用CDI，servlet声明它对Message实例的依赖性，并让它由CDI运行时自动注入
 public class NewServlet extends HttpServlet {
     @Inject private Message message;

     @Override
     public void doGet(HttpServletRequest request, HttpServletResponse response)
                   throws IOException {       //抛出可能出现IO异常
           response.getWriter().write(message.get());  //捕获可能发生的异常
  }
 }