过滤器

 

 

 

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

<?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

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

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;
    }

}