SpringBoot设置跨域的几种方式

什么是跨域？

　　浏览器从一个域名的网页去请求另一个域名的资源时，域名、端口、协议任一不同，都是跨域 

原因:

　　由于浏览器的同源策略, 即a网站只能访问a网站的内容,不能访问b网站的内容.

注意:

　　跨域问题只存在于浏览器,也就是说当你的前端页面访问后端简单请求的接口时,返回值是有的,只是服务器没有在请求头指定跨域的信息,所以浏览器自动把返回值给"屏蔽了".

　　经过上面的了解,可以得出几个解决跨域的方法(不考虑前端实现):

　　1.服务端指定跨域信息

　　2.在web页面与服务器之间加一层服务指定跨域信息,比如nginx
 

使用springboot提供了跨域的方法:

　　1.5版本为继承WebMvcConfigurerAdapter 类实现抽象方法,

//springboot 1.5方式
@Configuration
public class WebMvcConfig extends WebMvcConfigurerAdapter {
 
  @Override
  public void addCorsMappings(CorsRegistry registry) {
    registry.addMapping("/**").allowedHeaders("*")
      .allowedMethods("*")
      .allowedOrigins("*")
      .allowCredentials(true);
  }
}

2.0以后为实现WebMvcConfigurer 接口重写方法

//springboot 2.0以上的方式
@Configuration
public class WebMvcConfig implements WebMvcConfigurer {
 
    @Override
    public void addCorsMappings(CorsRegistry registry) {
        registry.addMapping("/**")
                .allowedHeaders("Content-Type","X-Requested-With","accept,Origin","Access-Control-Request-Method","Access-Control-Request-Headers","token")
                .allowedMethods("*")
                .allowedOrigins("*")
                .allowCredentials(true);
    }
}

使用拦截器实现跨域:

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.WebMvcConfigurer;
 
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
@Configuration
public class WebMvcConfig implements WebMvcConfigurer {
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new HandlerInterceptor() {
            @Override
            public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
                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 {
 
            }
        });
    }
 
}

注意:

请求头中自定义的字段是不允许跨域的,所以要指定

response.addHeader("Access-Control-Allow-Headers", "Content-Type,X-Requested-With,accept,Origin,Access-Control-Request-Method,Access-Control-Request-Headers,token");

或者

response.addHeader("Access-Control-Allow-Headers", "*");

还可以使用servlet提供的过滤器进行跨域配置:

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

/**
 * 请求的基本过滤器 预处理请求头
 */
@Component
@WebFilter(urlPatterns = {"/*"}, filterName = "tokenAuthorFilter")
public class TokenAuthorFilter implements Filter {

    private static Logger LOG = LoggerFactory.getLogger(TokenAuthorFilter.class);

    @Override
    public void destroy() {

    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
                         FilterChain chain) throws IOException, ServletException {
        HttpServletRequest req = (HttpServletRequest) request;
        HttpServletResponse rep = (HttpServletResponse) response;

        HttpSession session = req.getSession();
        LOG.info("sessionId:{}", session.getId());
        //LOG.info("Origin:{}", req.getHeader("Origin"));

        //设置允许跨域的配置
        // 这里填写你允许进行跨域的主机ip（正式上线时可以动态配置具体允许的域名和IP）
        rep.setHeader("Access-Control-Allow-Origin", "*");
        //rep.setHeader("Access-Control-Allow-Origin", "*");
        rep.setHeader("Access-Control-Expose-Headers", jwtProperties.getHeader());
        // 允许的访问方法
        rep.setHeader("Access-Control-Allow-Methods", "POST, GET, PUT, OPTIONS, DELETE, PATCH");
        // Access-Control-Max-Age 用于 CORS 相关配置的缓存
        rep.setHeader("Access-Control-Max-Age", "3600");
        rep.setHeader("Access-Control-Allow-Headers", "token, Origin, X-Requested-With, Content-Type, Accept");
        //若要返回cookie、携带seesion等信息则将此项设置我true
        rep.setHeader("Access-Control-Allow-Credentials", "true");
        // 把获取的Session返回个前端Cookie
        //rep.addCookie(new Cookie("JSSESIONID", session.getId()));
        chain.doFilter(req, rep);

    }

    @Override
    public void init(FilterConfig arg0) throws ServletException {

    }

}

灵活的跨域方式:

　　如果我们只想提供一个方法可以跨域,那么可以使用注解的形式:

@CrossOrigin
@RestController
public class TestController {

}