如何设置SOAPMessage边界？

import javax.xml.soap.*;

public class SOAPMessageBoundaryExample {
    public static void main(String[] args) throws Exception {
        // 创建SOAPMessage对象
        SOAPMessage soapMessage = MessageFactory.newInstance().createMessage();

        // 创建SOAPPart对象，并将SOAPMessage对象的内容添加到SOAPPart中
        SOAPPart soapPart = soapMessage.getSOAPPart();
        SOAPEnvelope soapEnvelope = soapPart.getEnvelope();
        SOAPBody soapBody = soapEnvelope.getBody();
        soapBody.addBodyElement(soapEnvelope.createName("HelloWorld"));

        // 创建MimeHeaders对象，并设置Content-Type字段为multipart/related，并指定边界值
        MimeHeaders headers = soapMessage.getMimeHeaders();
        String boundary = "----SOAPBoundary";
        headers.addHeader("Content-Type", "multipart/related; boundary=" + boundary);

        // 将MimeHeaders对象添加到SOAPMessage对象中
        soapMessage.saveChanges();

        // 将SOAPMessage对象转换为字节数组
        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
        soapMessage.writeTo(outputStream);
        byte[] soapBytes = outputStream.toByteArray();

        // 创建HTTP请求，并设置请求方法、URL等参数
        HttpURLConnection connection = (HttpURLConnection) new URL("http://example.com/soap-endpoint").openConnection();
        connection.setRequestMethod("POST");
        connection.setDoOutput(true);

        // 设置HTTP请求的Content-Type字段为multipart/related，并指定边界值
        connection.setRequestProperty("Content-Type", "multipart/related; boundary=" + boundary);

        // 将SOAPMessage的字节数组作为请求体发送
        OutputStream requestStream = connection.getOutputStream();
        requestStream.write(soapBytes);
        requestStream.close();

        // 处理HTTP响应
        int responseCode = connection.getResponseCode();
        if (responseCode == HttpURLConnection.HTTP_OK) {
            // 读取响应内容
            InputStream responseStream = connection.getInputStream();
            // 处理响应数据
        } else {
            // 处理错误情况
        }
    }
}