说明

• 资源请求的发起方与请求的资源不在同一个域中的；
• 一般的，只要网站的【协议名protocol】、【主机host】、【端口号port】这三个中的任意一个不同，网站间的数据请求与传输便构成了跨域调用；
• 跨域请求能够达到服务端，但是返回结果会被浏览器拦截；

方法一、@CrossOrigin

spring boot中只用在Controller类上添加一个“@CrossOrigin“注解就可以实现对当前controller 的跨域 访问了，当然这个标签也可以加到方法上。
其他controller类继承以上这个类就可以解决跨域问题。
注意：“@CrossOrigin“注解要求jdk1.8以上版本

@CrossOrigin
public class CommonController {

}

方法二、采用添加拦截器的方法

package com.autonavi.acis.system.conf;

import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.config.annotation.CorsRegistry;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.ResourceHandlerRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@Configuration
public class WebConfig extends WebMvcConfigurerAdapter {

    @Override
    public void addResourceHandlers(ResourceHandlerRegistry registry) {
        //添加静态资源
        registry.addResourceHandler("/js/**").addResourceLocations("classpath:/public/js/");
        registry.addResourceHandler("/css/**").addResourceLocations("classpath:/public/css/");
        registry.addResourceHandler("/fonts/**").addResourceLocations("classpath:/public/fonts/");
        registry.addResourceHandler("/favicon.ico").addResourceLocations("classpath:/static/favicon.ico");
    }

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new HandlerInterceptor() {
            @Override
            public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
                    throws Exception {
                    //允许所有请求
                response.addHeader("Access-Control-Allow-Origin", "*");
                response.addHeader("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, OPTIONS");
                response.addHeader("Access-Control-Allow-Headers",
                        "Content-Type,X-Requested-With,accept,Origin,Access-Control-Request-Method,Access-Control-Request-Headers,token");
                return true;
            }

            @Override
            public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
                                   ModelAndView modelAndView) throws Exception {

            }

            @Override
            public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler,
                                        Exception ex) throws Exception {
            }
        });
    }
    
    @Override
    public void addCorsMappings(CorsRegistry registry) {
    	//显式配置路径
        registry.addMapping("/public/api/ajxSelf/project/appVersions/*");
    }
}

新版替换类

Spring 5.0后，WebMvcConfigurerAdapter被废弃，取代的方法有两种：

①implements WebMvcConfigurer（官方推荐）

②extends WebMvcConfigurationSupport

使用第一种方法是实现了一个接口，可以任意实现里面的方法，不会影响到Spring Boot自身的@EnableAutoConfiguration，而使用第二种方法相当于覆盖了@EnableAutoConfiguration里的所有方法，每个方法都需要重写，比如，若不实现方法addResourceHandlers()，则会导致静态资源无法访问，实现的方法如下：

@Override
protected void addResourceHandlers(ResourceHandlerRegistry registry) {
    registry.addResourceHandler("/**")
            .addResourceLocations("classpath:/META-INF/resources/")
            .addResourceLocations("classpath:/resources/")
            .addResourceLocations("classpath:/static/")
            .addResourceLocations("classpath:/public/");
    super.addResourceHandlers(registry);
}

@Override
public void addCorsMappings(CorsRegistry registry) {
	   registry.addMapping("/public/api/ajxSelf/project/appVersions/*");
 }

方法三、filter处理器

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.HttpServletResponse;
import javax.servlet.annotation.WebFilter;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
 
@WebFilter(filterName = "OriginFilter", urlPatterns = "*")
public class OriginFilter implements Filter {
 
 	private final Logger logger= LoggerFactory.getLogger(this.getClass());
 
    @Override
    public void destroy() {
         
    }
 
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        HttpServletResponse  httpServletResponse = (HttpServletResponse) response;
        // * 表示允许所有请求
        httpServletResponse.setHeader("Access-Control-Allow-Origin", "*");
        httpServletResponse.setHeader("Access-Control-Allow-Methods", "OPTIONS,GET,POST,DELETE,PUT");
        httpServletResponse.setHeader("Access-Control-Allow-Credentials", "true");
        //httpServletResponse.setHeader("Access-Control-Allow-Headers", "Origin, X-Requested-With, content-Type, Accept,X-Requested-With, WG-App-Version, WG-Device-Id, WG-Network-Type, WG-Vendor, WG-OS-Type, WG-OS-Version, WG-Device-Model, WG-CPU, WG-Sid, WG-App-Id, WG-Token");
        httpServletResponse.setHeader("Access-Control-Allow-Headers", "X-Requested-With,content-type");
        chain.doFilter(request, httpServletResponse);
    }
 
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        logger.info("----------------过滤器正在启动-----------------");
    }
 
}

其他文档介绍：https://zhuanlan.zhihu.com/p/31016194

跨域是开发中经常会遇到的问题，当协议（http/https），主机(www.baidu.com/www.360.com||http://137.220.35.89/ /http://137.220.35.90/),端口（localhost:80/localhost:81）有一者不同时，即为跨域请求，详见跨源资源共享（CORS） - HTTP | MDN跨源资源共享 (CORS)（或通俗地译为跨域资源共享）是一种基于 HTTP 头的机制，该机制通过允许服务器标示除了它自己以外的其它origin（域，协议和端口），这样浏览器可以访问加载这些资源。跨源资源共享还通过一种机制来检查服务器是否会允许要发送的真实请求，该机制通过浏览器发起一个到服务器托管的跨源资源的"预检"请求。在预检中，浏览器发送的头中标示有HTTP方法和真实请求中会用到的头。https://developer.mozilla.org/zh-CN/docs/Web/HTTP/CORS

 在前后端分离项目中，经常会遇到跨域问题，Java中常用的三种解决方案如下：

1. 使用注解 `@CrossOrigin`,标注在controller类的方法上或者controller类上
2. crosFIlter

    @Bean
    public CorsWebFilter corsWebFilter(){

        // cors跨域配置对象
        CorsConfiguration configuration = new CorsConfiguration();
        configuration.addAllowedOrigin("*"); //设置允许访问的网络
        configuration.setAllowCredentials(true); // 设置是否从服务器获取cookie
        configuration.addAllowedMethod("*"); // 设置请求方法 * 表示任意
        configuration.addAllowedHeader("*"); // 所有请求头信息 * 表示任意

        // 配置源对象
        UrlBasedCorsConfigurationSource configurationSource = new UrlBasedCorsConfigurationSource();
        configurationSource.registerCorsConfiguration("/**", configuration);
        // cors过滤器对象
        return new CorsWebFilter(configurationSource);
    }



//或者



@Configuration
public class CorsConfig {

    private CorsConfiguration buildConfig() {
        CorsConfiguration corsConfiguration = new CorsConfiguration();
        corsConfiguration.setAllowCredentials(true);  //sessionid 多次访问一致

        // 允许访问的客户端域名
        List<String> allowedOriginPatterns = new ArrayList<>();
        allowedOriginPatterns.add("*");
        corsConfiguration.setAllowedOriginPatterns(allowedOriginPatterns);
//        corsConfiguration.addAllowedOrigin("*"); // 允许任何域名使用
        corsConfiguration.addAllowedHeader("*"); // 允许任何头
        corsConfiguration.addAllowedMethod("*"); // 允许任何方法（post、get等）
        return corsConfiguration;
    }

    @Bean
    public CorsFilter corsFilter() {
        UrlBasedCorsConfigurationSource source = new UrlBasedCorsConfigurationSource();
        source.registerCorsConfiguration("/**", buildConfig()); // 对接口配置跨域设置
        return new CorsFilter(source);
    }
}

 3. 

WebMvcConfigurer

//标注这个类是一个配置类
@Configuration
//实现 WebMvcConfigurer 接口
public class CorsConfig implements WebMvcConfigurer {
    @Override
    public void addCorsMappings(CorsRegistry registry) {

        registry.addMapping("/**")  //设置允许跨域访问的路径
                .allowedOriginPatterns("*")  //设置允许跨域访问的源
                .allowedMethods("*")  //允许跨域请求的方法
                .maxAge(168000)  //预检间隔时间
                .allowedHeaders("*")  //允许头部设置
                .allowCredentials(true);  //是否发送 cookie
    }
}

1.后台Controller注解方式

@CrossOrigin("*")

2.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.WebMvcConfigurer;

@Configuration
public class CorsConfig implements WebMvcConfigurer {

    @Override
    public void addCorsMappings(CorsRegistry registry) {
        registry.addMapping("/**")
            .allowedOrigins("*")
            .allowCredentials(true)
            .allowedMethods("GET", "POST", "PUT", "DELETE", "OPTIONS")
            .maxAge(3600);
    }
}

3.配置CorsWebFilter实现跨域，适用于分布式网关

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.cors.CorsConfiguration;
import org.springframework.web.cors.reactive.CorsWebFilter;
import org.springframework.web.cors.reactive.UrlBasedCorsConfigurationSource;

import java.util.Arrays;


@Configuration
public class GulimallCorsConfiguration{

    @Bean
    public CorsWebFilter corsWebFilter(){
        UrlBasedCorsConfigurationSource source = new UrlBasedCorsConfigurationSource();
        CorsConfiguration corsConfiguration = new CorsConfiguration();
        corsConfiguration.setAllowedHeaders(Arrays.asList(new String("*")));
        corsConfiguration.setAllowedMethods(Arrays.asList(new String("*")));
        corsConfiguration.addAllowedOrigin("*");
        corsConfiguration.setAllowCredentials(true);

        source.registerCorsConfiguration("/**",corsConfiguration);
        return new CorsWebFilter(source);
    }
}

4.使用nginx配置反向代理，适用于开发测试

  server {
        listen       8500;
        server_name  127.0.0.1;

        
        location / {
            root   html;
            proxy_pass http://127.0.0.1:8555/test;
        }
  }