以 QAnthing 上传文件（POST）接口为例，展示Java如何调用上传文件接口。
接口文档如下：

QAnthign接口文档地址

编码

RestTemplate 版

/**  * * @param url 接口地址  * @param filePath 文件本地路径  */  
public void uploadFile(String url, String filePath) {  // 使用RestTemplate上传文件  RestTemplate restTemplate = new RestTemplate();  // 设置请求头  HttpHeaders headers = new HttpHeaders();  headers.setContentType(org.springframework.http.MediaType.MULTIPART_FORM_DATA);  // 准备MultiValueMap来保存文件和其他表单字段  MultiValueMap<String, Object> body = new LinkedMultiValueMap<>();  body.add("files", new FileSystemResource(filePath));  body.add("user_id", "zzp");  body.add("kb_id", "KBb1dd58e8485443ce81166d24f6febda7");  body.add("mode", "soft");  // 创建HttpEntity  org.springframework.http.HttpEntity<MultiValueMap<String, Object>> requestEntity = new org.springframework.http.HttpEntity<>(body, headers);  // 发送请求  ResponseEntity<String> response = restTemplate.postForEntity(url, requestEntity,  String.class);  // 输出响应  System.out.println("Response: " + response.getBody());  
}private File downloadFile(String fileUrl) throws IOException {  try (InputStream in = new URL(fileUrl).openStream()) {  File tempFile = Files.createTempFile("uploaded-", ".tmp").toFile();  try (FileOutputStream out = new FileOutputStream(tempFile)) {  byte[] buffer = new byte[4096];  int bytesRead;  while ((bytesRead = in.read(buffer)) != -1) {  out.write(buffer, 0, bytesRead);  }  }  System.out.println("File downloaded to: " + tempFile.getAbsolutePath());  return tempFile;  }  
}

OkHttp 版

private void uploadFile(File file, String fileName, String fileSuffix, String url) throws IOException {  OkHttpClient client = new OkHttpClient().newBuilder()  .build();  MediaType mediaType = MediaType.parse("text/plain");  //MultipartBody.Builder builder = new MultipartBody.Builder().setType(MultipartBody.FORM)  //        .addFormDataPart("user_id", "zzp")    //        .addFormDataPart("kb_id", "KB3e7062d6d6c54b10af79164009e736d8_240625")    //        .addFormDataPart("mode", "soft");    //for (File file : fileList) {    //    builder.addFormDataPart("files", file.getName(),    //            RequestBody.create(MediaType.parse("application/octet-stream"),    //                    file));    //}    //RequestBody body = builder.build();    RequestBody body = new MultipartBody.Builder().setType(MultipartBody.FORM)  .addFormDataPart("files", fileName + "." + fileSuffix,  RequestBody.create(MediaType.parse("application/octet-stream"),  file))  .addFormDataPart("user_id", "zzp")  .addFormDataPart("kb_id", "KBb1dd58e8485443ce81166d24f6febda7")  .addFormDataPart("mode", "soft")  .build();  Request request = new Request.Builder()  .url(url)  .method("POST", body)  .build();  Response response = client.newCall(request).execute();  System.out.println(response);  
}

如果文件是互联网资源文件可以使用如下代码进行下载：

/**  * 下载文件  *  * @param fileUrl  * @return  * @throws IOException  */  
private File downloadFile(String fileUrl) throws IOException {  try (InputStream in = new URL(fileUrl).openStream()) {  File tempFile = Files.createTempFile("uploaded-", ".tmp").toFile();  try (FileOutputStream out = new FileOutputStream(tempFile)) {  byte[] buffer = new byte[4096];  int bytesRead;  while ((bytesRead = in.read(buffer)) != -1) {  out.write(buffer, 0, bytesRead);  }  }  System.out.println("File downloaded to: " + tempFile.getAbsolutePath());  return tempFile;  }  
}  /**  * 删除临时文件  *  * @param file  * @throws IOException  */  
private void delFile(File file) throws IOException {  // 删除临时文件  if (file.delete()) {  System.out.println("Temporary file deleted: " + file.getAbsolutePath());  } else {  System.out.println("Failed to delete temporary file: " + file.getAbsolutePath());  }  
}