Java调用post 上传文件带参详解

在Java中调用post上传文件带参，可以使用Java自带的HttpURLConnection或者第三方库如Apache HttpClient。以下是使用HttpURLConnection的示例代码：

public static void uploadFileWithParams(String urlString, Map<String, String> params, String filePath) throws IOException {
    URL url = new URL(urlString);
    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);
    for (Map.Entry<String, String> entry : params.entrySet()) {
        writer.append("--" + boundary).append("\r\n");
        writer.append("Content-Disposition: form-data; name=\"" + entry.getKey() + "\"").append("\r\n");
        writer.append("Content-Type: text/plain; charset=UTF-8").append("\r\n");
        writer.append("\r\n");
        writer.append(entry.getValue()).append("\r\n");
    }
    writer.append("--" + boundary).append("\r\n");
    writer.append("Content-Disposition: form-data; name=\"file\"; filename=\"" + new File(filePath).getName() + "\"").append("\r\n");
    writer.append("Content-Type: " + URLConnection.guessContentTypeFromName(filePath)).append("\r\n");
    writer.append("\r\n");
    writer.flush();
    Files.copy(Paths.get(filePath), outputStream);
    outputStream.flush();
    writer.append("\r\n");
    writer.append("--" + boundary + "--").append("\r\n");
    writer.close();
    int responseCode = connection.getResponseCode();
    if (responseCode == HttpURLConnection.HTTP_OK) {
        // Handle success response
    } else {
        // Handle error response
    }
    connection.disconnect();
}

这段代码中，我们首先创建一个URL对象，然后使用它创建一个HttpURLConnection对象。我们设置请求方式为POST，开启输出流，设置Content-Type为multipart/form-data，指定boundary值。然后我们依次写入参数和文件信息，其中参数使用Content-Disposition设置name属性，文件使用Content-Disposition设置name和filename属性，使用URLConnection.guessContentTypeFromName获取文件类型。最后我们将文件内容拷贝到输出流中，关闭输出流，等待服务器响应。在响应中，我们可以根据responseCode判断上传是否成功。