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import org.springframework.http.MediaType;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.servlet.mvc.method.annotation.SseEmitter;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

@RestController
public class StreamController {

    private final ExecutorService executor = Executors.newCachedThreadPool();

    @GetMapping(value = "/stream-to-frontend", produces = MediaType.TEXT_EVENT_STREAM_VALUE)
    public SseEmitter streamToFrontend() {
        SseEmitter emitter = new SseEmitter(0L); // 超时时间设为0（永不超时）

        executor.execute(() -> {
            try {
                // 调用后端流式接口
                URL url = new URL("http://backend-service/stream");
                HttpURLConnection connection = (HttpURLConnection) url.openConnection();
                connection.setRequestMethod("GET");
                connection.setRequestProperty("Accept", "text/event-stream");

                try (BufferedReader reader = new BufferedReader(
                        new InputStreamReader(connection.getInputStream()))) {
                    String line;
                    while ((line = reader.readLine()) != null) {
                        if (line.startsWith("data:")) {
                            String eventData = line.substring(5).trim();
                            // 将数据通过 SSE 发送到前端
                            emitter.send(SseEmitter.event().data(eventData));
                        }
                    }
                    emitter.complete(); // 流结束时通知前端
                } catch (IOException e) {
                    emitter.completeWithError(e); // 异常时通知前端
                } finally {
                    connection.disconnect();
                }
            } catch (Exception e) {
                emitter.completeWithError(e);
            }
        });

        return emitter;
    }
}```