如今的这个生态圈百花齐放，前后分离开始热门起来了，前端也要MVC了，那么你最常碰到的问题是什么？跨域请求会不会在你的问题名单中？

这里有有张摘自网络的图片

简述跨域问题

SpringBoot跨域请求

1、直接采用SpringBoot的注解@CrossOrigin

Controller层在需要跨域的类或者方法上加上该注解即可。

2、处理跨域请求的Configuration

CrossOriginConfig.java
继承WebMvcConfigurerAdapter或者实现WebMvcConfigurer接口

import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.CorsRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;

/**
 * AJAX请求跨域
 * @author Mr.W
 * @time 2018-08-13
 */
@Configuration
public class CorsConfig extends WebMvcConfigurerAdapter {
    static final String ORIGINS[] = new String[] { "GET", "POST", "PUT", "DELETE" };
    @Override
    public void addCorsMappings(CorsRegistry registry) {
        registry.addMapping("/**").allowedOrigins("*").allowCredentials(true).allowedMethods(ORIGINS)
                .maxAge(3600);
    }
}

3、采用过滤器的方式

 @Component
public class CORSFilter implements Filter {

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        HttpServletResponse res = (HttpServletResponse) response;
        res.addHeader("Access-Control-Allow-Credentials", "true");
        res.addHeader("Access-Control-Allow-Origin", "*");
        res.addHeader("Access-Control-Allow-Methods", "GET, POST, DELETE, PUT");
        res.addHeader("Access-Control-Allow-Headers", "Content-Type,X-CAF-Authorization-Token,sessionToken,X-TOKEN");
        if (((HttpServletRequest) request).getMethod().equals("OPTIONS")) {
            response.getWriter().println("ok");
            return;
        }
        chain.doFilter(request, response);
    }
    @Override
    public void destroy() {
    }
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
    }
}

• 方式二

引入maven依赖：

 <dependency>
    <groupId>io.projectreactor</groupId>
    <artifactId>reactor-core</artifactId>
    <version>RELEASE</version>
</dependency>

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpMethod;
import org.springframework.http.HttpStatus;
import org.springframework.http.server.reactive.ServerHttpRequest;
import org.springframework.http.server.reactive.ServerHttpResponse;
import org.springframework.web.cors.reactive.CorsUtils;
import org.springframework.web.server.ServerWebExchange;
import org.springframework.web.server.WebFilter;
import org.springframework.web.server.WebFilterChain;
import reactor.core.publisher.Mono;


/**
 * @author JiaweiWu
 * @create 2018/3/22.
 */
@Configuration
public class RouteConfiguration {
    //这里为支持的请求头，如果有自定义的header字段请自己添加（不知道为什么不能使用*）
    private static final String ALLOWED_HEADERS = "x-requested-with, authorization, Content-Type, Authorization, credential, X-XSRF-TOKEN,token,username,client";
    private static final String ALLOWED_METHODS = "*";
    private static final String ALLOWED_ORIGIN = "*";
    private static final String ALLOWED_Expose = "*";
    private static final String MAX_AGE = "18000L";

    @Bean
    public WebFilter corsFilter() {
        return (ServerWebExchange ctx, WebFilterChain chain) -> {
            ServerHttpRequest request = ctx.getRequest();
            if (CorsUtils.isCorsRequest(request)) {
                ServerHttpResponse response = ctx.getResponse();
                HttpHeaders headers = response.getHeaders();
                headers.add("Access-Control-Allow-Origin", ALLOWED_ORIGIN);
                headers.add("Access-Control-Allow-Methods", ALLOWED_METHODS);
                headers.add("Access-Control-Max-Age", MAX_AGE);
                headers.add("Access-Control-Allow-Headers", ALLOWED_HEADERS);
                headers.add("Access-Control-Expose-Headers", ALLOWED_Expose);
                headers.add("Access-Control-Allow-Credentials", "true");
                if (request.getMethod() == HttpMethod.OPTIONS) {
                    response.setStatusCode(HttpStatus.OK);
                    return Mono.empty();
                }
            }
            return chain.filter(ctx);
        };
    }
}

前后分离的跨域问题其他解决方案

Nginx服务器反向代理

通过反向代理服务器监听同端口，同域名的访问，不同路径映射到不同的地址，比如，在nginx服务器中，监听同一个域名和端口，不同路径转发到客户端和服务器，把不同端口和域名的限制通过反向代理，来解决跨域的问题。

server {
        listen       80;
        server_name  abc.com;
        #charset koi8-r;
        #access_log  logs/host.access.log  main;

        location /client { #访问客户端路径
            proxy_pass http://localhost:81;
            proxy_redirect default;
        }
        location /apis { #访问服务器路径
            rewrite  ^/apis/(.*)$ /$1 break;
            proxy_pass   http://localhost:82;
       }
}

或者直接在Nginx中进行配置

location / {
   add_header Access-Control-Allow-Origin *;
   add_header Access-Control-Allow-Headers X-Requested-With;
   add_header Access-Control-Allow-Methods GET,POST,PUT,DELETE,OPTIONS;

   if ($request_method = 'OPTIONS') {
     return 204;
   }
}