如何用RestTemplate像WebClient一样处理application/stream+json流式JSON？

Short answer: RestTemplate doesn't support streaming application/stream+json natively—and your current approach with Flux.just() won't work for the exact reason you've observed. Let's break this down:

Why your current attempt fails #

RestTemplate is a synchronous, blocking client designed to load the entire HTTP response into memory before returning it. When you wrap its getForEntity() result with Flux.just(), you're just taking a single, fully loaded response object and packaging it into a reactive stream. There's no actual streaming happening here—so it stops after the first (and only) "element" because that's all RestTemplate has fetched.

WebClient, by contrast, is built from the ground up for reactive, non-blocking streaming. It processes the response chunk-by-chunk as data arrives over the wire, which is why it handles application/stream+json seamlessly.

A workaround with RestTemplate (using InputStream) #

If you can't use WebClient right now, your hunch about InputStream is actually the right path. You can have RestTemplate return the raw input stream of the response, then manually parse the streaming JSON with a library like Jackson.

Here's a practical example:

RestTemplate restTemplate = new RestTemplate();
ResponseEntity<InputStream> response = restTemplate.exchange(
    "https://your-streaming-api-endpoint",
    HttpMethod.GET,
    null,
    InputStream.class
);

// Use Jackson to parse the streaming JSON incrementally
JsonFactory jsonFactory = new JsonFactory();
try (JsonParser jsonParser = jsonFactory.createParser(response.getBody())) {
    // Assuming the stream is an array of JSON objects
    while (jsonParser.nextToken() != JsonToken.END_ARRAY) {
        if (jsonParser.currentToken() == JsonToken.START_OBJECT) {
            // Deserialize each object as it arrives from the stream
            YourDataDto dto = jsonParser.readValueAs(YourDataDto.class);
            // Process the DTO here (e.g., send to a queue, log, etc.)
            System.out.println("Received streamed DTO: " + dto);
        }
    }
} catch (IOException e) {
    // Handle parsing or stream errors
    e.printStackTrace();
}

Caveats of this approach #

• This is still blocking: The thread will wait for data to arrive, unlike WebClient's non-blocking, event-driven model.
• You have to handle JSON parsing manually—there's no out-of-the-box reactive stream integration. You could wrap this logic in Flux.create() if you need to bridge to reactive code, but that adds extra complexity.
• It's less clean than WebClient, but it's a functional stopgap while you wait for the Spring Security fix.

Final note #

Since you're holding off on WebClient due to an unresolved Spring Security issue, this InputStream workaround is a reasonable temporary solution. Once the official support lands, switching back to WebClient will give you the clean, reactive streaming experience you're looking for.

内容的提问来源于stack exchange，提问作者Dmitry Korchemkin