前言

众所周知，上传大文件是一件很麻烦的事情，假如一条路走到黑，直接一次性把文件上传上去，对于小文件是可以这样做，但是对于大文件可能会出现网络问题，请求响应时长等等导致文件上传失败，那么这次来教大家如何用vue+srpingboot项目上传大文件

逻辑

需要做大文件上传应该考虑到如下逻辑:

大文件上传一般需要将文件切片（chunk）上传，然后再将所有切片合并为完整的文件。可以按以下逻辑进行实现：

前端在页面中选择要上传的文件，并使用Blob.slice方法对文件进行切片，一般每个切片大小为固定值（比如5MB），并记录总共有多少个切片。

将切片分别上传到后端服务，可以使用XMLHttpRequest或Axios等库发送Ajax请求。对于每个切片，需要包含三个参数：当前切片索引（从0开始）、切片总数、切片文件数据。

后端服务接收到切片后，保存到指定路径下的临时文件中，并记录已上传的切片索引和上传状态。如果某个切片上传失败，则通知前端重传该切片。

当所有切片都上传成功后，后端服务读取所有切片内容并将其合并为完整的文件。可以使用java.io.SequenceInputStream和BufferedOutputStream来实现文件合并。

最后返回文件上传成功的响应结果给前端即可。

前端

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>File Upload</title>
</head>
<body>
    <input type="file" id="fileInput">
    <button onclick="upload()">Upload</button>
    <script>
        function upload() {
            let file = document.getElementById("fileInput").files[0];
            let chunkSize = 5 * 1024 * 1024; // 切片大小为5MB
            let totalChunks = Math.ceil(file.size / chunkSize); // 计算切片总数
            let index = 0;
            while (index < totalChunks) {
                let chunk = file.slice(index * chunkSize, (index + 1) * chunkSize);
                let formData = new FormData();
                formData.append("file", chunk);
                formData.append("index", index);
                formData.append("totalChunks", totalChunks);
                // 发送Ajax请求上传切片
                $.ajax({
                    url: "/uploadChunk",
                    type: "POST",
                    data: formData,
                    processData: false,
                    contentType: false,
                    success: function () {
                        if (++index >= totalChunks) {
                            // 所有切片上传完成，通知服务端合并文件
                            $.post("/mergeFile", {fileName: file.name}, function () {
                                alert("Upload complete!");
                            })
                        }
                    }
                });
            }
        }
    </script>
</body>
</html>

后端

controller层:

@RestController
public class FileController {

    @Value("${file.upload-path}")
    private String uploadPath;

    @PostMapping("/uploadChunk")
    public void uploadChunk(@RequestParam("file") MultipartFile file,
                            @RequestParam("index") int index,
                            @RequestParam("totalChunks") int totalChunks) throws IOException {
        // 以文件名+切片索引号为文件名保存切片文件
        String fileName = file.getOriginalFilename() + "." + index;
        Path tempFile = Paths.get(uploadPath, fileName);
        Files.write(tempFile, file.getBytes());
        // 记录上传状态
        String uploadFlag = UUID.randomUUID().toString();
        redisTemplate.opsForList().set("upload:" + fileName, index, uploadFlag);
        // 如果所有切片已上传，则通知合并文件
        if (isAllChunksUploaded(fileName, totalChunks)) {
            sendMergeRequest(fileName, totalChunks);
        }
    }

    @PostMapping("/mergeFile")
    public void mergeFile(String fileName) throws IOException {
        // 所有切片均已成功上传，进行文件合并
        List<File> chunkFiles = new ArrayList<>();
        for (int i = 0; i < getTotalChunks(fileName); i++) {
            String chunkFileName = fileName + "." + i;
            Path tempFile = Paths.get(uploadPath, chunkFileName);
            chunkFiles.add(tempFile.toFile());
        }
        Path destFile = Paths.get(uploadPath, fileName);
        try (OutputStream out = Files.newOutputStream(destFile);
             SequenceInputStream seqIn = new SequenceInputStream(Collections.enumeration(chunkFiles));
             BufferedInputStream bufIn = new BufferedInputStream(seqIn)) {
            byte[] buffer = new byte[1024];
            int len;
            while ((len = bufIn.read(buffer)) > 0) {
                out.write(buffer, 0, len);
            }
        }
        // 清理临时文件和上传状态记录
        for (int i = 0; i < getTotalChunks(fileName); i++) {
            String chunkFileName = fileName + "." + i;
            Path tempFile = Paths.get(uploadPath, chunkFileName);
            Files.deleteIfExists(tempFile);
            redisTemplate.delete("upload:" + chunkFileName);
        }
    }

    private int getTotalChunks(String fileName) {
        // 根据文件名获取总切片数
        return Objects.requireNonNull(Paths.get(uploadPath, fileName).toFile().listFiles()).length;
    }

    private boolean isAllChunksUploaded(String fileName, int totalChunks) {
        // 判断所有切片是否已都上传完成
        List<String> uploadFlags = redisTemplate.opsForList().range("upload:" + fileName, 0, -1);
        return uploadFlags != null && uploadFlags.size() == totalChunks;
    }

    private void sendMergeRequest(String fileName, int totalChunks) {
        // 发送合并文件请求
        new Thread(() -> {
            try {
                URL url = new URL("http://localhost:8080/mergeFile");
                HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                conn.setRequestMethod("POST");
                conn.setDoOutput(true);
                conn.setDoInput(true);
                conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded;charset=utf-8");
                OutputStream out = conn.getOutputStream();
                String query = "fileName=" + fileName;
                out.write(query.getBytes());
                out.flush();
                out.close();
                BufferedReader br = new BufferedReader(new InputStreamReader(conn.getInputStream(), StandardCharsets.UTF_8));
                while (br.readLine() != null) ;
                br.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }).start();
    }

    @Autowired
    private RedisTemplate<String, Object> redisTemplate;
}

其中，file.upload-path为文件上传的保存路径，可以在application.properties或application.yml中进行配置。同时需要添加RedisTemplate的Bean以便记录上传状态。

RedisTemplate配置

如果需要使用RedisTemplate，需要引入下方的包

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-redis</artifactId>
</dependency>

同时在yml配置redis的信息

spring.redis.host=localhost
spring.redis.port=6379
spring.redis.database=0

然后在自己的类中这样使用

@Component
public class myClass {

    @Autowired
    private RedisTemplate<String, Object> redisTemplate;

    public void set(String key, Object value) {
        redisTemplate.opsForValue().set(key, value);
    }

    public Object get(String key) {
        return redisTemplate.opsForValue().get(key);
    }
}