一、什么是CORS？

CORS是一個W3C標準，全稱是”跨域資源共享”（Cross-origin resource sharing），允許瀏覽器向跨源服務器，發出XMLHttpRequest請求，從而克服了AJAX只能同源使用的限制。

它通過服務器增加一個特殊的Header[Access-Control-Allow-Origin]來告訴客戶端跨域的限制，如果瀏覽器支持CORS、并且判斷Origin通過的話，就會允許XMLHttpRequest發起跨域請求。
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CORS Header?

• Access-Control-Allow-Origin: http://www.xxx.com
• Access-Control-Max-Age：86400
• Access-Control-Allow-Methods：GET, POST, OPTIONS, PUT, DELETE
• Access-Control-Allow-Headers: content-type
• Access-Control-Allow-Credentials: true

含義解釋：

filter過濾器的作用？

?二、SpringBoot跨域請求處理方式

方式一、直接采用SpringBoot的注解@CrossOrigin（也支持SpringMVC）

Controller層在需要跨域的類或者方法上加上該注解即可

實戰：

?備注說明:Spring 版本必須大于等于4.2

方法二、處理跨域請求的Configuration

servlet filter listener順序？增加一個配置類CrossOriginConfig.java。繼承WebMvcConfigurerAdapter或者實現WebMvcConfigurer接口

實戰:

import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.CorsRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;/*** AJAX請求跨域*/
@Configuration
public class CorsConfig extends WebMvcConfigurerAdapter {static final String ORIGINS[] = new String[] { "GET", "POST", "PUT", "DELETE" };@Overridepublic void addCorsMappings(CorsRegistry registry) {registry.addMapping("/**").allowedOrigins("*").allowCredentials(true).allowedMethods(ORIGINS).maxAge(3600);}

方法三、采用過濾器（filter）的方式(推薦)

增加一個CORSFilter 類，并實現Filter接口即可

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;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.annotation.Configuration;
import org.springframework.stereotype.Component;/*** * @ClassName:  CorsFilter   * @Description: SpringBoot 跨域處理攔截器*/@Component
public class CROSFilter implements Filter {public static final Logger logger = LoggerFactory.getLogger(CROSFilter.class);@Overridepublic void init(FilterConfig filterConfig) throws ServletException {// TODO Auto-generated method stub}@Overridepublic void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)throws IOException, ServletException {HttpServletResponse response = (HttpServletResponse) res;  HttpServletRequest reqs = (HttpServletRequest) req;  /** 跨域設置允所有請求跨域 * 如果允許指定的客戶端跨域設置: http://127.0.0.1:8020*/response.setHeader("Access-Control-Allow-Origin","*");  response.setHeader("Access-Control-Allow-Credentials", "true");  response.setHeader("Access-Control-Allow-Methods", "POST, GET, OPTIONS, DELETE");  response.setHeader("Access-Control-Max-Age", "3600");  response.setHeader("Access-Control-Allow-Headers", "Content-Type");  if (((HttpServletRequest) req).getMethod().equals("OPTIONS")) {response.getWriter().println("ok");return;}chain.doFilter(req, res);  }@Overridepublic void destroy() {// TODO Auto-generated method stub}}

解決遇到的錯誤

1、Request header field content-type is not allowed by Access-Control-Allow-Headers in preflight response.

怎么解決cors跨域、解決辦法:

  response.setHeader("Access-Control-Allow-Headers", "Content-Type");  

2、Response to preflight request doesn't pass access control check: It does not have HTTP ok status.

解決辦法:

if (((HttpServletRequest) req).getMethod().equals("OPTIONS")) {response.getWriter().println("ok");return;}