当前位置：首页 > Java

java 如何上传文件

2026-04-09 00:28:49Java

使用 HttpURLConnection 上传文件

通过 HttpURLConnection 可以实现基本的文件上传功能。需要设置请求头为 multipart/form-data，并手动构建请求体。

String boundary = "----WebKitFormBoundary7MA4YWxkTrZu0gW";
String lineEnd = "\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);

DataOutputStream outputStream = new DataOutputStream(connection.getOutputStream());

// 写入文件部分
outputStream.writeBytes(twoHyphens + boundary + lineEnd);
outputStream.writeBytes("Content-Disposition: form-data; name=\"file\"; filename=\"test.txt\"" + lineEnd);
outputStream.writeBytes("Content-Type: text/plain" + lineEnd + lineEnd);

FileInputStream fileInputStream = new FileInputStream("path/to/test.txt");
int bytesAvailable = fileInputStream.available();
byte[] buffer = new byte[bytesAvailable];
fileInputStream.read(buffer);
outputStream.write(buffer);
outputStream.writeBytes(lineEnd);

// 结束标记
outputStream.writeBytes(twoHyphens + boundary + twoHyphens + lineEnd);

fileInputStream.close();
outputStream.flush();
outputStream.close();

int responseCode = connection.getResponseCode();

使用 Apache HttpClient 上传文件

Apache HttpClient 提供了更简洁的 API 来处理文件上传，简化了 multipart 请求的构建过程。

CloseableHttpClient httpClient = HttpClients.createDefault();
HttpPost httpPost = new HttpPost("http://example.com/upload");

FileBody fileBody = new FileBody(new File("path/to/test.txt"));
MultipartEntityBuilder builder = MultipartEntityBuilder.create();
builder.setMode(HttpMultipartMode.BROWSER_COMPATIBLE);
builder.addPart("file", fileBody);
HttpEntity multipart = builder.build();

httpPost.setEntity(multipart);
CloseableHttpResponse response = httpClient.execute(httpPost);

int statusCode = response.getStatusLine().getStatusCode();
response.close();
httpClient.close();

使用 Spring 的 RestTemplate 上传文件

在 Spring 应用中，可以使用 RestTemplate 简化文件上传操作，特别适合与其他 Spring 组件集成。

RestTemplate restTemplate = new RestTemplate();
String url = "http://example.com/upload";

MultiValueMap<String, Object> body = new LinkedMultiValueMap<>();
body.add("file", new FileSystemResource("path/to/test.txt"));

HttpHeaders headers = new HttpHeaders();
headers.setContentType(MediaType.MULTIPART_FORM_DATA);

HttpEntity<MultiValueMap<String, Object>> requestEntity = new HttpEntity<>(body, headers);
ResponseEntity<String> response = restTemplate.postForEntity(url, requestEntity, String.class);

int statusCode = response.getStatusCodeValue();

使用 OkHttp 上传文件

OkHttp 是一个高效的 HTTP 客户端，特别适合移动端或需要高性能的场景。

OkHttpClient client = new OkHttpClient();

RequestBody requestBody = new MultipartBody.Builder()
        .setType(MultipartBody.FORM)
        .addFormDataPart("file", "test.txt",
            RequestBody.create(MediaType.parse("text/plain"), 
            new File("path/to/test.txt")))
        .build();

Request request = new Request.Builder()
        .url("http://example.com/upload")
        .post(requestBody)
        .build();

Response response = client.newCall(request).execute();
int statusCode = response.code();
response.close();