java HTTP如何上传文件

在 Java 中通过 HTTP 上传文件，常见做法有几种，取决于你使用的是客户端还是服务端，以及使用的技术栈。下面按常见场景说明。

一、Java 作为客户端上传文件（HttpClient）

1️⃣ 使用 Java 11+ 原生 HttpClient（推荐）

import java.net.http.*;
import java.net.URI;
import java.nio.file.Path;
import java.time.Duration;

public class FileUpload {
    public static void main(String[] args) throws Exception {
        var file = Path.of("test.txt");

        var request = HttpRequest.newBuilder()
                .uri(URI.create("http://localhost:8080/upload"))
                .timeout(Duration.ofMinutes(1))
                .header("Content-Type", "multipart/form-data")
                .POST(HttpRequest.BodyPublishers.ofFile(file))
                .build();

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

        System.out.println(response.statusCode());
        System.out.println(response.body());
    }
}

⚠️ 注意：
原生 HttpClient 不直接支持 multipart/form-data 封装，如需表单上传，需要自己构造 body（较复杂），或使用下面方式。

2️⃣ 使用 Apache HttpClient（最常用）

Maven 依赖

<dependency>
  <groupId>org.apache.httpcomponents</groupId>
  <artifactId>httpclient</artifactId>
  <version>4.5.14</version>
</dependency>

上传示例

import org.apache.http.*;
import org.apache.http.client.methods.*;
import org.apache.http.entity.mime.MultipartEntityBuilder;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;

import java.io.File;

public class UploadClient {
    public static void main(String[] args) throws Exception {
        CloseableHttpClient client = HttpClients.createDefault();
        HttpPost post = new HttpPost("http://localhost:8080/upload");

        MultipartEntityBuilder builder = MultipartEntityBuilder.create();
        builder.addBinaryBody(
                "file",
                new File("test.txt"),
                ContentType.APPLICATION_OCTET_STREAM,
                "test.txt"
        );
        post.setEntity(builder.build());

        CloseableHttpResponse response = client.execute(post);
        System.out.println(response.getStatusLine());
        client.close();
    }
}

3️⃣ 使用 OkHttp（简洁）

OkHttpClient client = new OkHttpClient();

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

Request request = new Request.Builder()
        .url("http://localhost:8080/upload")
        .post(body)
        .build();

client.newCall(request).execute();

二、Java 作为服务端接收文件

1️⃣ Spring Boot（最常用）

Controller

@RestController
public class UploadController {

    @PostMapping("/upload")
    public String upload(@RequestParam("file") MultipartFile file) throws Exception {
        file.transferTo(new File("upload/" + file.getOriginalFilename()));
        return "上传成功";
    }
}

配置文件（application.yml）

spring:
  servlet:
    multipart:
      max-file-size: 10MB
      max-request-size: 10MB

2️⃣ 原生 Servlet

@WebServlet("/upload")
@MultipartConfig
public class UploadServlet extends HttpServlet {
    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        Part part = req.getPart("file");
        part.write("upload/" + part.getSubmittedFileName());
    }
}

三、常见 Content-Type

四、选择建议

✅ 客户端

• 简单文件流 → HttpClient
• 表单上传 → Apache HttpClient / OkHttp

✅ 服务端

• 企业项目 → Spring Boot
• 轻量 → Servlet

如果你有具体场景（如：Spring Boot 上传、大文件、断点续传、前后端分离），可以告诉我，我给你更针对性的代码。