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

上代码：
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());  
    }  
}