过滤器Filter
Filter使用:
javax.servlet.Filter
// init--> 初始化方法 default public void init(FilterConfig filterConfig) throws ServletException {} // doFilter--> 过滤器实体方法 public void doFilter(ServletRequest request, ServletResponse response,FilterChain chain)throws IOException, ServletException; // destroy --> 销毁过滤器的方法 default public void destroy() {}
init:在Web工程启动时就会调用进行初始化
doFilter:三个参数: request请求和response响应 chain链
FilterChain:过滤器链,当前过滤器过滤通过后会将请求或响应交给下一个过滤器执行,可以理解为当前过滤器允许该请求或响应通过
// 过滤器放行的固定写法 chain.doFilter(request, response);
destory:销毁该过滤器
配置Filter:
// 注解 @WebFilter(urlPatterns = {"/doFilter"}) // Web.xml配置 与配置Servlet方法相同 <filter> <filter-name>filterTest</filter-name> <filter-class>com.filter.TestFilter</filter-class> </filter> <filter-mapping> <filter-name>filterTest</filter-name> <url-pattern>/*</url-pattern> </filter-mapping>
使用实例:
向web界面输出文字,通过过滤器进行编码,不通过过滤器将会打印乱码
// 过滤器 @WebFilter(urlPatterns = {"/doFilter"}) public class Filter01 implements Filter { // 初始化方法 public void init(FilterConfig filterConfig) throws ServletException { System.out.println("Filter初始化完成"); } // 过滤器主体 public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { request.setCharacterEncoding("UTF-8"); response.setCharacterEncoding("UTF-8"); response.setContentType("text/html;charset:utf-8"); // 允许通过过滤器 chain.doFilter(request, response); } // 销毁方法 public void destroy() { System.out.println("Filter被销毁"); } } // Servlet @WebServlet(urlPatterns = {"/doFilter","/doNotFilter"}) public class Demo01 extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { resp.getWriter().write("<h1>你好,郑州</h1>"); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doGet(req, resp); } }
上述代码所示:当通过映射路径/doNotFilter将会打印出中文乱码,反之通过/doFilter则会设置好响应的中文编码正常输出