java发送post请求body form-data传参

在Java中，发送POST请求并使用`form-data`传参通常可以使用`HttpURLConnection`或第三方库如Apache HttpClient来实现。以下是使用`HttpURLConnection`的示例代码：

import java.io.*;
import java.net.*;

public class HttpPostWithFormData {
    public static void main(String[] args) {
        try {
            URL url = new URL("http://example.com/api");
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setRequestMethod("POST");
            conn.setDoOutput(true);
            conn.setRequestProperty("Content-Type", "multipart/form-data; boundary=----WebKitFormBoundary7MA4YWxkTrZu0gW");

            String boundary = "----WebKitFormBoundary7MA4YWxkTrZu0gW";
            String LINE = "\r\n";

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

            // 添加表单字段
            writer.append("--" + boundary).append(LINE);
            writer.append("Content-Disposition: form-data; name=\"field1\"").append(LINE);
            writer.append("Content-Type: text/plain; charset=UTF-8").append(LINE);
            writer.append(LINE);
            writer.append("value1").append(LINE);

            writer.append("--" + boundary).append(LINE);
            writer.append("Content-Disposition: form-data; name=\"field2\"").append(LINE);
            writer.append("Content-Type: text/plain; charset=UTF-8").append(LINE);
            writer.append(LINE);
            writer.append("value2").append(LINE);

            // 结束边界
            writer.append("--" + boundary + "--").append(LINE);
            writer.close();

            int responseCode = conn.getResponseCode();
            System.out.println("Response Code: " + responseCode);

            BufferedReader in = new BufferedReader(new InputStreamReader(conn.getInputStream()));
            String inputLine;
            StringBuffer response = new StringBuffer();

            while ((inputLine = in.readLine()) != null) {
                response.append(inputLine);
            }
            in.close();

            // 输出响应结果
            System.out.println(response.toString());

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

在这个示例中，我们使用`HttpURLConnection`发送一个POST请求，并在请求体中以`form-data`格式传递参数。以下是一些关键步骤：

1. 设置请求的URL和请求方法。
2. 设置请求头`Content-Type`为`multipart/form-data`，并指定一个边界字符串。
3. 使用`PrintWriter`将表单字段写入请求体。
4. 结束边界并关闭`PrintWriter`。
5. 获取响应代码和响应内容。