过滤器
把我们不需要的东西去除,其实就是给定一个规范把那个请求的一些条件筛选
注意一定要转发,不然会卡死arg2.doFilter(req, resp);通过该方法把req请求和resp请求分开
写一个类实现implements Filter,最重要的就是doFileter方法
需要在xml配置然后就可以使用了
xml中的配置
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
<?xml version="1.0" encoding="UTF-8"?> <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0" metadata-complete="false"> <display-name>2019_08_23_comprehensiveconnection</display-name> <welcome-file-list> <welcome-file>index.html</welcome-file> <welcome-file>index.htm</welcome-file> <welcome-file>index.jsp</welcome-file> <welcome-file>default.html</welcome-file> <welcome-file>default.htm</welcome-file> <welcome-file>default.jsp</welcome-file> </welcome-file-list> <filter> <filter-name>test</filter-name> <filter-class>cn.jiedada.filter.FilterTest</filter-class> <init-param> <param-name>encoding</param-name> <param-value>UTF-8</param-value><!-- 在init中通过encoding获得UTF-8 --> </init-param> </filter> <filter-mapping> <filter-name>test</filter-name> <url-pattern>/*</url-pattern> </filter-mapping> <filter> <filter-name>test1</filter-name> <filter-class>cn.jiedada.filter.LoginFilterTest</filter-class><!-- 通过该权限明获得过滤器 --> </filter> <filter-mapping> <filter-name>test1</filter-name> <url-pattern>/system/*</url-pattern><!-- 拦截范围为什么 --> </filter-mapping> <filter> <filter-name>test2</filter-name> <filter-class>cn.jiedada.filter.AddNullFilter</filter-class> </filter> <filter-mapping> <filter-name>test2</filter-name> <url-pattern>/add.user</url-pattern> </filter-mapping> </web-app>
空值判断过滤
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
package cn.jiedada.filter; import java.io.IOException; import javax.servlet.Filter; import javax.servlet.FilterChain; import javax.servlet.FilterConfig; import javax.servlet.ServletException; import javax.servlet.ServletRequest; import javax.servlet.ServletResponse; public class AddNullFilter implements Filter{ @Override public void destroy() { // TODO Auto-generated method stub } @Override public void doFilter(ServletRequest req, ServletResponse resp, FilterChain arg2) throws IOException, ServletException { String name = req.getParameter("name"); String pwd = req.getParameter("pwd"); if(name==null || name.trim().equals("")){ req.setAttribute("errorTrim", "用户名不能为空"); req.getRequestDispatcher("/system/user_add.jsp").forward(req, resp); return; }else if(pwd==null || pwd.trim().equals("")){ req.setAttribute("errorTrim", "密码不能为空"); req.setAttribute("username", name.trim()); req.getRequestDispatcher("/system/user_add.jsp").forward(req, resp); return; } //定一要转发 arg2.doFilter(req, resp); } @Override public void init(FilterConfig arg0) throws ServletException { // TODO Auto-generated method stub } }
编码设置过滤器
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
package cn.jiedada.filter; import java.io.IOException; import javax.servlet.Filter; import javax.servlet.FilterChain; import javax.servlet.FilterConfig; import javax.servlet.ServletException; import javax.servlet.ServletRequest; import javax.servlet.ServletResponse; public class FilterTest implements Filter{ FilterConfig config; @Override public void destroy() { } @Override public void doFilter(ServletRequest req, ServletResponse resp, FilterChain arg2) throws IOException, ServletException { String encoding = config.getInitParameter("encoding"); req.setCharacterEncoding(encoding); resp.setContentType("text/html;charset="+encoding); arg2.doFilter(req, resp); } @Override public void init(FilterConfig config) throws ServletException { // TODO Auto-generated method stub this.config=config; } }