过滤器总结

凤临

已于 2022-06-06 20:51:38 修改

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文章标签： java webview eclipse idea

于 2022-06-06 20:20:19 首次发布

本文链接：https://blog.youkuaiyun.com/qq_52470307/article/details/125153341

本文详细介绍了如何在Java中使用过滤器进行字符编码过滤和登录验证，包括EncodingFilter实现UTF-8编码转换，以及LoginFilter的白名单访问控制机制。理解过滤器的执行流程和生命周期对于Web开发至关重要。

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Java过滤器能够对目标资源的请求和响应进行过滤和拦截

过滤器实现的过程

1、实现Filter接口

2、重写doFilter方法，

通过filterChain.doFilter(request,response);放行方法，将请求传递下去，如果没有使用该方法则请求停留在过滤器中，不会继续向后请求。

3、配置访问拦截的路径--确定哪些请求需要进行过滤，那些不需要

一、字符过滤--通过在web.xml中配置

public class EncodingFilter implements Filter {
    String encoding = null;
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        encoding = filterConfig.getInitParameter("encoding");
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        System.out.println("encoding:"+encoding);
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        HttpServletResponse response = (HttpServletResponse) servletResponse;
        request.setCharacterEncoding(encoding);
        response.setContentType("text/html;charset="+encoding);
        //请求向后传递
        filterChain.doFilter(request,response);
    }
}

    <filter>
        <filter-name>EncodingFilter</filter-name>
        <filter-class>com.filter.EncodingFilter</filter-class>
        <init-param>
            <param-name>encoding</param-name>
            <param-value>utf-8</param-value>
        </init-param>
    </filter>
    <filter-mapping>
        <filter-name>EncodingFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

二、登录过滤--通过注解进行过滤

import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebFilter("/*")
public class LoginFilter implements Filter {

    //设置白名单--对部分请求直接放行
    String[] whiteNames = {"/","/index.jsp","/login.jsp","/loginShow","/loginSubmit"};
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        HttpServletResponse response = (HttpServletResponse) servletResponse;

        String uri = request.getRequestURI();
        uri = uri.substring(uri.lastIndexOf("/"));
        boolean inWhiteNames = false;
        for (String name : whiteNames){
            if(name.equals(uri)){
                inWhiteNames = true;
                break;
            }
        }

        if(inWhiteNames){
            filterChain.doFilter(request,response);
        }else{
            if(request.getSession().getAttribute("username")==null){
                request.getRequestDispatcher("/login.jsp").forward(request,response);
            }else{
                filterChain.doFilter(request,response);
            }
        }
    }
}

三、过滤器的执行流程

客户端发出请求-->过滤器-->放行-->请求的资源-->响应-->过滤器-->客户端

过滤器1-->过滤器2-->执行请求-->过滤器2-->过滤器1

四、过滤器的生命周期

init():初始化-->doFilter():放行方法-->destroy():销毁方法