Streaming HttpOutputMessage Examples

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Some examples of using Spring's `Streaming HttpOutputMessage` interface. 

Example 1: Streaming a File

import org.springframework.http.HttpHeaders;

import org.springframework.http.HttpStatus;

import org.springframework.http.MediaType;

import org.springframework.http.server.ServletServerHttpResponse;

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

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

import org.springframework.web.servlet.mvc.method.annotation.StreamingResponseBody;

import javax.servlet.http.HttpServletResponse;

import java.io.File;

import java.io.FileInputStream;

import java.io.IOException;

import java.io.OutputStream;

@RestController

public class FileStreamingController {

    @GetMapping("/download")

    public StreamingResponseBody downloadFile(HttpServletResponse response) throws IOException {

        response.setContentType(MediaType.APPLICATION_OCTET_STREAM_VALUE);

        response.setHeader(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\"example.txt\"");

        File file = new File("path/to/example.txt");

        FileInputStream inputStream = new FileInputStream(file);

        return outputStream -> {

            int nRead;

            byte[] data = new byte[1024];

            while ((nRead = inputStream.read(data, 0, data.length)) != -1) {

                outputStream.write(data, 0, nRead);

            }

            inputStream.close();

        };

    }

}

Example 2: Streaming JSON Response

import org.springframework.http.HttpHeaders;

import org.springframework.http.HttpStatus;

import org.springframework.http.MediaType;

import org.springframework.http.server.ServletServerHttpResponse;

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

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

import org.springframework.web.servlet.mvc.method.annotation.StreamingResponseBody;

import javax.servlet.http.HttpServletResponse;

import java.io.IOException;

import java.io.OutputStream;

import java.util.stream.IntStream;

@RestController

public class JsonStreamingController {

    @GetMapping("/stream")

    public StreamingResponseBody streamJson(HttpServletResponse response) throws IOException {

        response.setContentType(MediaType.APPLICATION_JSON_VALUE);

        return outputStream -> {

            for (int i = 1; i <= 10; i++) {

                String json = "{\"id\": " + i + ", \"name\": \"Item " + i + "\"}\n";

                outputStream.write(json.getBytes());

                outputStream.flush();

                Thread.sleep(1000); // Simulate delay between each item

            }

        };

    }

}

These examples demonstrate how to use `Streaming HttpOutputMessage` to stream a file or a JSON response. In the first example, a file is streamed as a response, while in the second example, a JSON stream is generated and sent as a response.

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