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

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

Demo: 注解配置过滤器

@WebFilter(urlPatterns= {"/*"})
public class MyFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("过滤器初始化");
    }
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        System.out.println("对拦截的请求进行处理,之后放行");
        //向下转型
        HttpServletRequest req = (HttpServletRequest)request;
        HttpServletResponse resp = (HttpServletResponse)response;
        //处理字符编码
        req.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");
        chain.doFilter(req, resp);
    }
    @Override
    public void destroy() {
        System.out.println("过滤器销毁");
    }
}

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

@WebListener
public class RequestAttributeListener implements ServletRequestAttributeListener{
    @Override
    public void attributeAdded(ServletRequestAttributeEvent event) {
        System.out.println("增加属性时候触发: " + event.getName() + ":" + event.getValue());
    }
    @Override
    public void attributeRemoved(ServletRequestAttributeEvent event) {
        System.out.println("删除属性时候触发: " + event.getName() + ":" + event.getValue());
    }
    @Override
    public void attributeReplaced(ServletRequestAttributeEvent event) {
        System.out.println("替换属性时候触发: " + event.getName() + ":" + event.getValue());
    }
}