Java 里，解决跨域问题有多种办法

import javax.servlet.*;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

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", "*"); // 允许所有域名进行跨域调用
        response.setHeader("Access-Control-Allow-Methods", "GET,POST,PUT,DELETE,OPTIONS"); // 允许的请求方法
        response.setHeader("Access-Control-Allow-Headers", "Content-Type, Authorization"); // 允许的请求头
        response.setHeader("Access-Control-Max-Age", "3600"); // 预检请求的有效期，单位为秒
        chain.doFilter(req, res);
    }
}

<filter>
    <filter-name>CorsFilter</filter-name>
    <filter-class>com.example.CorsFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>CorsFilter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

import org.springframework.web.bind.annotation.CrossOrigin;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@CrossOrigin(origins = "*", maxAge = 3600) // 对所有方法都有效
public class MyController {

    @GetMapping("/api/data")
    public String getData() {
        return "这是跨域数据";
    }

    @GetMapping("/api/specific")
    @CrossOrigin(origins = "https://specific-domain.com") // 针对特定方法的细粒度控制
    public String getSpecificData() {
        return "特定域名的跨域数据";
    }
}

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.cors.CorsConfiguration;
import org.springframework.web.cors.UrlBasedCorsConfigurationSource;
import org.springframework.web.filter.CorsFilter;

@Configuration
public class CorsConfig {
    @Bean
    public CorsFilter corsFilter() {
        CorsConfiguration config = new CorsConfiguration();
        config.addAllowedOriginPattern("*"); // 允许所有域名进行跨域调用
        config.addAllowedHeader("*"); // 允许任何请求头
        config.addAllowedMethod("*"); // 允许任何方法（POST、GET等）
        config.setAllowCredentials(true); // 允许携带凭证

        UrlBasedCorsConfigurationSource source = new UrlBasedCorsConfigurationSource();
        source.registerCorsConfiguration("/**", config); // 对所有接口都有效

        return new CorsFilter(source);
    }
}

import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet("/api/custom")
@CrossOrigin(origins = "*", methods = {GET, POST}, allowedHeaders = "*")
public class CustomServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
        resp.getWriter().write("通过Servlet实现的跨域响应");
    }
}

import org.springframework.http.HttpEntity;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpMethod;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;

@RestController
public class ProxyController {
    private final RestTemplate restTemplate = new RestTemplate();

    @GetMapping("/proxy/data")
    public ResponseEntity<String> proxyData() {
        String targetUrl = "https://third-party-api.com/data";
        HttpHeaders headers = new HttpHeaders();
        // 设置必要的请求头
        HttpEntity<String> entity = new HttpEntity<>(headers);
        return restTemplate.exchange(targetUrl, HttpMethod.GET, entity, String.class);
    }
}

import javax.ws.rs.container.ContainerRequestContext;
import javax.ws.rs.container.ContainerResponseContext;
import javax.ws.rs.container.ContainerResponseFilter;
import javax.ws.rs.ext.Provider;
import java.io.IOException;

@Provider
public class CorsResponseFilter implements ContainerResponseFilter {
    @Override
    public void filter(ContainerRequestContext requestContext,
                       ContainerResponseContext responseContext) throws IOException {
        responseContext.getHeaders().add("Access-Control-Allow-Origin", "*");
        responseContext.getHeaders().add("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, OPTIONS");
        responseContext.getHeaders().add("Access-Control-Allow-Headers", "Content-Type, Authorization");
    }
}