Javaweb之过滤器的简单使用

过滤器：

web服务器有一些垃圾请求，我后台不应该处理或者应该报错。
处理乱码问题。

filter开发步骤

1.导包
2.编写过滤器
代码如下：

//CharacterEncodingGilter 类
    package com.kuang.filter;

import javax.servlet.*;
import java.io.IOException;

//重写 Filter接口，实现过滤器
public class CharacterEncodingGilter implements Filter {

    //初始化   ：web服务器启动了，就开始初始化了
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("已经初始化了");
    }

    //chain:
    /*
    * 过滤器中的所有代码，在过滤特定请求的时候都会执行
    * 必须要让过滤器继续通行
    *   chain.doFilter(request,response);
    *
    * */
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        response.setCharacterEncoding("utf-8");
        request.setCharacterEncoding("utf-8");
        response.setContentType("text/html;charset=UTF-8");
        System.out.println("chain.doFilter(request,response); 执行前");
        chain.doFilter(request,response);  //让我们的请求继续走，如果不写，程序到这里就被拦截停止！
        System.out.println("chain.doFilter(request,response); 执行后");
    }
    //销毁
    public void destroy() {
        System.out.println("已经销毁了");
        //服务器关闭的时候，过滤器就销毁。
    }
}



//ShowServlet类
package com.kuang.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class ShowServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.getWriter().write("你好呀，世界！！！");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}


//web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">

    <servlet>
        <servlet-name>ShowServlet</servlet-name>
        <servlet-class>com.kuang.servlet.ShowServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>ShowServlet</servlet-name>
        <url-pattern>/s</url-pattern>
    </servlet-mapping>

    <servlet>
        <servlet-name>ShowServlet1</servlet-name>
        <servlet-class>com.kuang.servlet.ShowServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>ShowServlet1</servlet-name>
        <url-pattern>/s1</url-pattern>
    </servlet-mapping>


    <!--这里写过滤路径 注册过滤的处理类  跟servlet差不多-->
    <filter>
        <filter-name>CharacterEncodingGilter</filter-name>
        <filter-class>com.kuang.filter.CharacterEncodingGilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>CharacterEncodingGilter</filter-name>
        <!--填写要过滤的路径 -->
        <url-pattern>/*</url-pattern>
    </filter-mapping>
</web-app>