Detailed explanation of how to use SpringBoot to download JSON files

Overview

Implement the file download function in Spring Boot, which can be returned to the client by returning a JSON string as file content. Here are the implementation steps and code examples:

Implementation steps

Define the interface: Create a REST controller that handles file download requests.

Set response header: Set response header through HttpServletResponse, specify the file type and download file name.

Returns file content: Writes a JSON string to the response output stream.

Code implementation

1. Create Spring Boot Controller

import ;
import ;
import ;
 
import ;
import ;
import ;
 
@RestController
@RequestMapping("/api")
public class FileDownloadController {
 
    @GetMapping("/download-json")
    public void downloadJsonFile(HttpServletResponse response) throws IOException {
        // 1. Prepare the JSON string        String jsonContent = "{\"name\":\"John\", \"age\":30, \"city\":\"New York\"}";
 
        // 2. Set the response header        ("application/json"); // File type is JSON        ("Content-Disposition", "attachment; filename=\"\""); // Set the download file name 
        // 3. Write JSON string to the response output stream        ().write((StandardCharsets.UTF_8));
        ().flush();
    }
}

2. Run and test

Launch the Spring Boot app.

Access the interface address in the browser, for example: http://localhost:8080/api/download-json.

The browser will automatically download a file named , with the file contents as:

{"name":"John", "age":30, "city":"New York"}

Key points description

：

Used to set the response header and output stream.
setContentType("application/json"): Specify the file type to JSON.
setHeader("Content-Disposition", "attachment; filename=\"\""): Specify the file name and tell the browser to download it in attachment form.

2. Write file content:

Use ().write() to write a JSON string to the response output stream.
Make sure to use StandardCharsets.UTF_8 to specify character encoding to avoid garbled problems.

3. File name:

File names can be generated dynamically as needed, for example:

String fileName = "data_" + () + ".json";
("Content-Disposition", "attachment; filename=\"" + fileName + "\"");

Extended features

Dynamically generate JSON content: You can obtain data from a database or other services and dynamically generate JSON strings.

Download compressed file: If you need to download compressed files (such as .zip), you can use ZipOutputStream to package multiple files and return them.

Large file download: For large files, you can use Transfer-Encoding: chunked to optimize performance.

Example: Dynamically generate JSON content

@GetMapping("/download-dynamic-json")
public void downloadDynamicJsonFile(HttpServletResponse response) throws IOException {
    // Dynamically generate JSON data    Map&lt;String, Object&gt; data = new HashMap&lt;&gt;();
    ("timestamp", ());
    ("message", "Hello, this is a dynamic JSON file!");
 
    // Convert Map to JSON string    String jsonContent = new ObjectMapper().writeValueAsString(data);
 
    // Set response header    ("application/json");
    ("Content-Disposition", "attachment; filename=\"dynamic_data.json\"");
 
    // Write response output stream    ().write((StandardCharsets.UTF_8));
    ().flush();
}

Visit http://localhost:8080/api/download-dynamic-json and a JSON file containing dynamically generated content will be downloaded.

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