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java如何上传图片

2026-02-04 19:45:53Java

上传图片的基本方法

在Java中上传图片通常涉及文件读取、网络传输或数据库存储。以下是几种常见场景的实现方式。

通过HTTP上传图片

使用HttpURLConnection或第三方库（如Apache HttpClient、OkHttp）可以实现HTTP文件上传。以下是一个基于HttpURLConnection的示例：

String boundary = "----WebKitFormBoundary7MA4YWxkTrZu0gW";
String crlf = "\r\n";
String twoHyphens = "--";

URL url = new URL("http://example.com/upload");
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setDoOutput(true);
connection.setRequestMethod("POST");
connection.setRequestProperty("Content-Type", "multipart/form-data; boundary=" + boundary);

try (OutputStream output = connection.getOutputStream();
     PrintWriter writer = new PrintWriter(new OutputStreamWriter(output, StandardCharsets.UTF_8), true)) {

    // 添加文件部分
    writer.append(twoHyphens).append(boundary).append(crlf);
    writer.append("Content-Disposition: form-data; name=\"file\"; filename=\"image.jpg\"").append(crlf);
    writer.append("Content-Type: image/jpeg").append(crlf);
    writer.append(crlf).flush();
    Files.copy(Paths.get("path/to/image.jpg"), output);
    output.flush();
    writer.append(crlf);

    // 结束标记
    writer.append(twoHyphens).append(boundary).append(twoHyphens).append(crlf);
}

int responseCode = connection.getResponseCode();

使用Spring Boot上传图片

在Spring Boot中可以通过MultipartFile接收上传的文件：

@PostMapping("/upload")
public ResponseEntity<String> uploadImage(@RequestParam("file") MultipartFile file) {
    if (file.isEmpty()) {
        return ResponseEntity.badRequest().body("Empty file");
    }

    try {
        byte[] bytes = file.getBytes();
        Path path = Paths.get("uploads/" + file.getOriginalFilename());
        Files.write(path, bytes);
        return ResponseEntity.ok("Upload success");
    } catch (IOException e) {
        return ResponseEntity.internalServerError().body("Upload failed");
    }
}

存储到数据库

将图片以BLOB形式存储到数据库（以MySQL为例）：

String sql = "INSERT INTO images (name, data) VALUES (?, ?)";
try (Connection conn = DriverManager.getConnection(DB_URL, USER, PASS);
     PreparedStatement pstmt = conn.prepareStatement(sql)) {

    File imageFile = new File("path/to/image.jpg");
    try (FileInputStream fis = new FileInputStream(imageFile)) {
        pstmt.setString(1, imageFile.getName());
        pstmt.setBinaryStream(2, fis, (int) imageFile.length());
        pstmt.executeUpdate();
    }
}

使用Base64编码传输

将图片转换为Base64字符串：

String encodeImage(File file) throws IOException {
    byte[] fileContent = Files.readAllBytes(file.toPath());
    return Base64.getEncoder().encodeToString(fileContent);
}

解码Base64字符串还原为图片：

void decodeImage(String base64Image, String outputPath) throws IOException {
    byte[] imageBytes = Base64.getDecoder().decode(base64Image);
    Files.write(Paths.get(outputPath), imageBytes);
}