servlet injection 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
 }
}