摘要：而前端跨域請求的需求不減，于是乎。跨域也比較簡單，只需添加以下配置即可。參考文檔，阿里云中文檔描述到也可通過配置文件跨域，不過筆者并未采用這種方式。瀏覽器設置跨域本身是可以通過配置支持跨域請求的。跨域參考文檔跨域參考文檔

我們的后端使用Spring Boot。Spring Boot跨域非常簡單，只需書寫以下代碼即可。

@Configuration
public class CustomCORSConfiguration {
  private CorsConfiguration buildConfig() {
    CorsConfiguration corsConfiguration = new CorsConfiguration();
    corsConfiguration.addAllowedOrigin("*");
    corsConfiguration.addAllowedHeader("*");
    corsConfiguration.addAllowedMethod("*");
    return corsConfiguration;
  }
  @Bean
  public CorsFilter corsFilter() {
    UrlBasedCorsConfigurationSource source = new UrlBasedCorsConfigurationSource();
    source.registerCorsConfiguration("/**", buildConfig());
    return new CorsFilter(source);
  }
}

某天，我們將Spring Boot應用用Nginx反向代理。而前端跨域請求的需求不減，于是乎。

Nginx跨域也比較簡單，只需添加以下配置即可。

location / {
    proxy_pass http://localhost:8080;
    if ($request_method = "OPTIONS") {
        add_header "Access-Control-Allow-Origin" "*";
        add_header "Access-Control-Allow-Methods" "GET, POST, OPTIONS";
        add_header "Access-Control-Allow-Headers" "DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Content-Range,Range,Token";
        add_header "Access-Control-Max-Age" 1728000;
        add_header "Content-Type" "text/plain; charset=utf-8";
        add_header "Content-Length" 0;
        return 204;
    }
    if ($request_method = "POST") {
        add_header "Access-Control-Allow-Origin" "*";
        add_header "Access-Control-Allow-Methods" "GET, POST, OPTIONS";
        add_header "Access-Control-Allow-Headers" "DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Content-Range,Range,Token";
        add_header "Access-Control-Expose-Headers" "DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Content-Range,Range,Token";
    }
    if ($request_method = "GET") {
        add_header "Access-Control-Allow-Origin" "*";
        add_header "Access-Control-Allow-Methods" "GET, POST, OPTIONS";
        add_header "Access-Control-Allow-Headers" "DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Content-Range,Range,Token";
        add_header "Access-Control-Expose-Headers" "DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Content-Range,Range,Token";
    }
}

其中： add_header "Access-Control-Expose-Headers" 務必加上你請求時所帶的header。例如本例中的“Token”，其實是前端傳給后端過來的。如果記不得也沒有關系，瀏覽器的調試器會有詳細說明。

參考文檔：https://enable-cors.org/serve...

B.T.W，阿里云中文檔描述到Nginx也可通過crossdomain.xml配置文件跨域：https://helpcdn.aliyun.com/kn... ，不過筆者并未采用這種方式。

The following Nginx configuration enables CORS, with support for preflight requests.

#
# Wide-open CORS config for nginx
#
location / {
     if ($request_method = "OPTIONS") {
        add_header "Access-Control-Allow-Origin" "*";
        add_header "Access-Control-Allow-Methods" "GET, POST, OPTIONS";
        #
        # Custom headers and headers various browsers *should* be OK with but aren"t
        #
        add_header "Access-Control-Allow-Headers" "DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Content-Range,Range";
        #
        # Tell client that this pre-flight info is valid for 20 days
        #
        add_header "Access-Control-Max-Age" 1728000;
        add_header "Content-Type" "text/plain; charset=utf-8";
        add_header "Content-Length" 0;
        return 204;
     }
     if ($request_method = "POST") {
        add_header "Access-Control-Allow-Origin" "*";
        add_header "Access-Control-Allow-Methods" "GET, POST, OPTIONS";
        add_header "Access-Control-Allow-Headers" "DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Content-Range,Range";
        add_header "Access-Control-Expose-Headers" "DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Content-Range,Range";
     }
     if ($request_method = "GET") {
        add_header "Access-Control-Allow-Origin" "*";
        add_header "Access-Control-Allow-Methods" "GET, POST, OPTIONS";
        add_header "Access-Control-Allow-Headers" "DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Content-Range,Range";
        add_header "Access-Control-Expose-Headers" "DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Content-Range,Range";
     }
}

Chrome、Firefox本身是可以通過配置支持跨域請求的。

Chrome跨域：參考文檔：http://www.cnblogs.com/laden6...

Firefox跨域：參考文檔：https://segmentfault.com/q/10...