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java 如何上传

2026-03-20 02:17:01Java

使用 HttpURLConnection 上传文件

在 Java 中可以使用 HttpURLConnection 类实现文件上传功能。需要设置正确的请求头和输出流。

URL url = new URL("http://example.com/upload");
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("POST");
connection.setDoOutput(true);

String boundary = "===" + System.currentTimeMillis() + "===";
connection.setRequestProperty("Content-Type", "multipart/form-data; boundary=" + boundary);

OutputStream outputStream = connection.getOutputStream();
PrintWriter writer = new PrintWriter(new OutputStreamWriter(outputStream, "UTF-8"), true);

// 添加文件部分
writer.append("--" + boundary).append("\r\n");
writer.append("Content-Disposition: form-data; name=\"file\"; filename=\"file.txt\"").append("\r\n");
writer.append("Content-Type: text/plain").append("\r\n");
writer.append("\r\n").flush();
Files.copy(Paths.get("file.txt"), outputStream);
outputStream.flush();
writer.append("\r\n").flush();

// 结束请求
writer.append("--" + boundary + "--").append("\r\n");
writer.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。

java 如何上传

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

MultipartEntityBuilder builder = MultipartEntityBuilder.create();
builder.addPart("file", new FileBody(new File("file.txt")));
HttpEntity multipart = builder.build();

uploadFile.setEntity(multipart);
CloseableHttpResponse response = httpClient.execute(uploadFile);
HttpEntity responseEntity = response.getEntity();

使用 Spring RestTemplate 上传文件

在 Spring 应用中可以使用 RestTemplate 简化文件上传操作。

java 如何上传

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

MultiValueMap<String, Object> body = new LinkedMultiValueMap<>();
body.add("file", new FileSystemResource("file.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);

使用 Java 11 HttpClient 上传文件

Java 11 引入的新 HttpClient 也支持文件上传功能。

HttpClient client = HttpClient.newHttpClient();
HttpRequest request = HttpRequest.newBuilder()
    .uri(URI.create("http://example.com/upload"))
    .header("Content-Type", "multipart/form-data;boundary=boundary")
    .POST(ofInputStream(() -> Files.newInputStream(Paths.get("file.txt"))))
    .build();

HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());

处理大文件上传

对于大文件上传，应该考虑使用分块上传或流式处理，避免内存溢出。

File file = new File("largefile.zip");
FileInputStream inputStream = new FileInputStream(file);

HttpURLConnection connection = (HttpURLConnection) new URL("http://example.com/upload").openConnection();
connection.setDoOutput(true);
connection.setRequestMethod("POST");
connection.setRequestProperty("Content-Type", "application/octet-stream");
connection.setRequestProperty("Content-Length", String.valueOf(file.length()));

OutputStream outputStream = connection.getOutputStream();
byte[] buffer = new byte[4096];
int bytesRead;
while ((bytesRead = inputStream.read(buffer)) != -1) {
    outputStream.write(buffer, 0, bytesRead);
}

inputStream.close();
outputStream.close();
int responseCode = connection.getResponseCode();