[Java] Java 如何解决跨域问题

• 同一协议， 如http或https
  
• 同一IP地址, 如127.0.0.1
  
• 同一端口, 如8080
  

• 使用JSONP方式实现跨域调用；
  
• 使用NodeJS服务器做为服务代理，前端发起请求到NodeJS服务器， NodeJS服务器代理转发请求到后端服务器；
  

• nginx反向代理解决跨域
  
• 服务端设置Response Header(响应头部)的Access-Control-Allow-Origin
  
• 在需要跨域访问的类和方法中设置允许跨域访问（如Spring中使用@CrossOrigin注解）；
  
• 继承使用Spring Web的CorsFilter（适用于Spring MVC、Spring Boot）
  
• 实现WebMvcConfigurer接口（适用于Spring Boot）
  

@WebFilter
public class CorsFilter implements Filter { 
 
  @Override
  public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException { 
  HttpServletResponse response = (HttpServletResponse) res; 
  response.setHeader("Access-Control-Allow-Origin", "*"); 
  response.setHeader("Access-Control-Allow-Methods", "*"); 
  response.setHeader("Access-Control-Max-Age", "3600"); 
  response.setHeader("Access-Control-Allow-Headers", "*");
  response.setHeader("Access-Control-Allow-Credentials", "true");
  chain.doFilter(req, res); 
  } 
}

@Component
public class CrossInterceptor extends HandlerInterceptorAdapter {
 
  @Override
  public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
  response.setHeader("Access-Control-Allow-Origin", "*");
  response.setHeader("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, OPTIONS");
  response.setHeader("Access-Control-Max-Age", "3600");
  response.setHeader("Access-Control-Allow-Headers", "*");
  response.setHeader("Access-Control-Allow-Credentials", "true");
  return true;
  }
}

@Configuration
@SuppressWarnings("SpringJavaAutowiredFieldsWarningInspection")
public class AppConfig implements WebMvcConfigurer {
 
  @Override
  public void addCorsMappings(CorsRegistry registry) {
  registry.addMapping("/**") // 拦截所有的请求
    .allowedOrigins("http://www.abc.com") // 可跨域的域名，可以为 *
    .allowCredentials(true)
    .allowedMethods("*")  // 允许跨域的方法，可以单独配置
    .allowedHeaders("*"); // 允许跨域的请求头，可以单独配置
  }
}

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;
  }
}

@CrossOrigin
@RestController
@RequestMapping("/user")
public class UserController {
 
  @GetMapping("/{id}")
  public User get(@PathVariable Long id) {
    
  }
 
  @DeleteMapping("/{id}")
  public void remove(@PathVariable Long id) {
 
  }
}

@RestController
@RequestMapping("/user")
public class UserController {
 
  @CrossOrigin
  @GetMapping("/{id}")
  public User get(@PathVariable Long id) {
    
  }
 
  @DeleteMapping("/{id}")
  public void remove(@PathVariable Long id) {
 
  }
}

spring: 
 cloud:
  gateway:
   globalcors:
  cors-configurations:
   '[/**]':
    # 允许跨域的源(网站域名/ip)，设置*为全部
    # 允许跨域请求里的head字段，设置*为全部
    # 允许跨域的method， 默认为GET和OPTIONS，设置*为全部
    allow-credentials: true
    allowed-origins:
     - "http://xb.abc.com"
     - "http://sf.xx.com"
    allowed-headers: "*"
    allowed-methods:
     - OPTIONS
     - GET
     - POST
     - DELETE
     - PUT
     - PATCH
    max-age: 3600

import java.util.ArrayList;
import org.springframework.cloud.gateway.filter.GatewayFilterChain;
import org.springframework.cloud.gateway.filter.GlobalFilter;
import org.springframework.cloud.gateway.filter.NettyWriteResponseFilter;
import org.springframework.core.Ordered;
import org.springframework.http.HttpHeaders;
import org.springframework.stereotype.Component;
import org.springframework.web.server.ServerWebExchange;
import reactor.core.publisher.Mono;
 
@Component("corsResponseHeaderFilter")
public class CorsResponseHeaderFilter implements GlobalFilter, Ordered {
 
 @Override
 public int getOrder() {
  // 指定此过滤器位于NettyWriteResponseFilter之后
  // 即待处理完响应体后接着处理响应头
  return NettyWriteResponseFilter.WRITE_RESPONSE_FILTER_ORDER + 1;
 }
 
 @Override
 public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
  return chain.filter(exchange).then(Mono.defer(() -> {
   exchange.getResponse().getHeaders().entrySet().stream()
   .filter(kv -> (kv.getValue() != null && kv.getValue().size() > 1))
   .filter(kv -> (
     kv.getKey().equals(HttpHeaders.ACCESS_CONTROL_ALLOW_ORIGIN)
     || kv.getKey().equals(HttpHeaders.ACCESS_CONTROL_ALLOW_CREDENTIALS)
     || kv.getKey().equals(HttpHeaders.ACCESS_CONTROL_ALLOW_METHODS)
     || kv.getKey().equals(HttpHeaders.ACCESS_CONTROL_ALLOW_HEADERS)
     || kv.getKey().equals(HttpHeaders.ACCESS_CONTROL_MAX_AGE)))
   .forEach(kv -> {
    kv.setValue(new ArrayList<String>() {{
     add(kv.getValue().get(0));
    }});
   });
   return chain.filter(exchange);
  }));
 }
}