Filter 过滤器是web开发中很重要的一个组件，下面以一个session登陆的例子介绍下spring boot中如何使用Filter

首先要准备一个实现了Filter的接口的类 SessionFilter：

import org.slf4j.LoggerFactory;import javax.servlet.*;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;import java.io.IOException;import java.util.ArrayList;import java.util.List;import java.util.regex.Matcher;import java.util.regex.Pattern;/** * Created by mazhenhua on 2016/12/27. * * 过滤器 */public class SessionFilter implements Filter { private static final org.slf4j.Logger logger = LoggerFactory.getLogger(SessionFilter.class); /** * 封装，不需要过滤的list列表 */ protected static List<Pattern> patterns = new ArrayList<Pattern>(); @Override public void init(FilterConfig filterConfig) throws ServletException { } @Override public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain chain) throws IOException, ServletException { HttpServletRequest httpRequest = (HttpServletRequest) servletRequest; HttpServletResponse httpResponse = (HttpServletResponse) servletResponse; logger.info("aaaaaaaaaa"); String url = httpRequest.getRequestURI().substring(httpRequest.getContextPath().length()); if (url.startsWith("/") && url.length() > 1) { url = url.substring(1); } if (isInclude(url)){ chain.doFilter(httpRequest, httpResponse); return; } else { HttpSession session = httpRequest.getSession(); if (session.getAttribute("") != null){ // session存在 chain.doFilter(httpRequest, httpResponse); return; } else { // session不存在 准备跳转失败 chain.doFilter(httpRequest, httpResponse); return; } } } @Override public void destroy() { } /** * 是否需要过滤 * @param url * @return */ private boolean isInclude(String url) { for (Pattern pattern : patterns) { Matcher matcher = pattern.matcher(url); if (matcher.matches()) { return true; } } return false; }}

实际开发中往往有很多请求要直接请求进来，不需要鉴权登陆的，所以代码中过滤掉这种请求的代码，装进list就好了。

/** * 配置过滤器 * @return */ @Bean public FilterRegistrationBean someFilterRegistration() { FilterRegistrationBean registration = new FilterRegistrationBean(); registration.setFilter(sessionFilter()); registration.addUrlPatterns("/*"); registration.addInitParameter("paramName", "paramValue"); registration.setName("sessionFilter"); return registration; } /** * 创建一个bean * @return */ @Bean(name = "sessionFilter") public Filter sessionFilter() { return new SessionFilter(); }

经过上面这俩步的配置，过滤器基本上就可以了。

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