LINE Notify Java

package chemp.notes.linenotify;
import java.io.*;
import java.net.*;
import java.util.regex.Pattern;

public class LineNotify {
	private static final String strEndpoint = "https://notify-api.line.me/api/notify";

	public boolean callEvent(String token, String message) {
		boolean result = false;
   		try {
			message = replaceProcess(message);
			message = URLEncoder.encode(message, "UTF-8");
			String strUrl = strEndpoint;
			URL url = new URL( strUrl );
			HttpURLConnection connection = (HttpURLConnection)url.openConnection();
			connection.addRequestProperty("Authorization",  "Bearer " + token);
			connection.setRequestMethod( "POST" );
			connection.addRequestProperty( "Content-Type", "application/x-www-form-urlencoded" );
			connection.setDoOutput( true );
			String parameterString = new String("message=" + message);
			PrintWriter printWriter = new PrintWriter(connection.getOutputStream());
			printWriter.print(parameterString);
			printWriter.close();
			connection.connect();
            
			int statusCode = connection.getResponseCode();
		        if ( statusCode == 200 ) {
		        	result = true;
		        } else {
		        	throw new Exception( "Error:(StatusCode)" + statusCode + ", " + connection.getResponseMessage() );
		        }
		        connection.disconnect();
		} catch (Exception e) {
			e.printStackTrace();
		}

		return result;
	}
	private String replaceProcess(String txt){
    		txt = replaceAllRegex(txt, "\\\\", "￥");		// \
		return txt;
	}
	private String replaceAllRegex(String value, String regex, String replacement) {
		if ( value == null || value.length() == 0 || regex == null || regex.length() == 0 || replacement == null )
			return "";
		return Pattern.compile(regex).matcher(value).replaceAll(replacement);
	}
}

hi, i just try the code but the error message shows :
stop at : throw new Exception( "Error:(StatusCode)" + statusCode + ", " + connection.getResponseMessage() );
error : java.lang.Exception: Error:(StatusCode)400, null
at com.egroup.util.LineUtil.callEvent(LineUtil.java:37)
at com.egroup.util.LineUtil.main(LineUtil.java:12)

i just write a main in same class and use the function like
LineNotify lineNotify = new LineNotify ();
lineNotify .callEvent("myToken","myMessage");
what may cause this error~