注解配置

注解配置

一.注解配置使用
　　配置 servlvet 的映射路径, 全都在 web.xml 文件中, 非常不方便维护.
　　注解就是在每个 servlet 之上进行路径的配置

总结:
　　使用注解配置 servlet的映射路径: @WebServlet
　　使用注解配置过滤器: @WebFilter
　　使用注解配置监听器: @WebListener

注解配置映射路径
Demo: 注解配置 servlet

 1 @WebServlet(urlPatterns= {"/emp/*","/dept/*"})
 2 public class EmpServlet extends HttpServlet{
 3     @Override
 4     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
 5         System.out.println("使用注解配置的 servlet");
 6     }
 7     @Override
 8     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
 9         this.doGet(req, resp);
10     }
11 }

Demo: 注解配置过滤器

 1 @WebFilter(urlPatterns= {"/*"})
 2 public class MyFilter implements Filter {
 3     @Override
 4     public void init(FilterConfig filterConfig) throws ServletException {
 5         System.out.println("过滤器初始化");
 6     }
 7     @Override
 8     public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
 9             throws IOException, ServletException {
10         System.out.println("对拦截的请求进行处理,之后放行");
11         //向下转型
12         HttpServletRequest req = (HttpServletRequest)request;
13         HttpServletResponse resp = (HttpServletResponse)response;
14         //处理字符编码
15         req.setCharacterEncoding("utf-8");
16         resp.setContentType("text/html;charset=utf-8");
17         chain.doFilter(req, resp);
18     }
19     @Override
20     public void destroy() {
21         System.out.println("过滤器销毁");
22     }
23 }

Demo: 注解配置过滤器 (登录验证)

@WebFilter(urlPatterns= {"/emp/delete","/emp/updat","/emp/list","/emp_list.jsp","/dept/list"})
public class LoginFilter implements Filter{
}

如果有几百个资源(比如 jsp)需要登录验证, 可以将要进行登录验证的资源统一保存到一个文件夹 (如:pages)
然后过滤器只要对该文件夹进行验证即可.
Demo: 统一要验证的资源
@WebFilter(urlPatterns= {"/emp/delete","/emp/updat","/pages/*"})

Demo: 注解配置监听器

 1 @WebListener
 2 public class RequestAttributeListener implements ServletRequestAttributeListener{
 3     @Override
 4     public void attributeAdded(ServletRequestAttributeEvent event) {
 5         System.out.println("增加属性时候触发: " + event.getName() + ":" + event.getValue());
 6     }
 7     @Override
 8     public void attributeRemoved(ServletRequestAttributeEvent event) {
 9         System.out.println("删除属性时候触发: " + event.getName() + ":" + event.getValue());
10     }
11     @Override
12     public void attributeReplaced(ServletRequestAttributeEvent event) {
13         System.out.println("替换属性时候触发: " + event.getName() + ":" + event.getValue());
14     }
15 }

原文地址：https://www.cnblogs.com/yslf/p/10755423.html