关于StreamConnection的有关问题

public class SocketConn {    public StreamConnection conn;    public DataOutputStream outputStream;    public DataInputStream inputStream;    public SocketConn() {    try {        if (null == conn) {        conn = (StreamConnection) Connector.open("socket://222.90.231.60:22616", Connector.READ_WRITE);        }    } catch (Exception e) {        e.printStackTrace();    }    }}public class RequestDataImpl extends SocketConn implements IRequestData{  //requestKeys（）这个方法是没问题的，能正常发送、接收数据  public void requestKeys() {     try {         outputStream = conn.openDataOutputStream();        outputStream.write(getConvert().hexStringToBytes(REQKEYSTR));        outputStream.flush();        inputStream = conn.openDataInputStream();       // ...    } catch (IOException e) {    }    }    public void loginSer() {     try {      [color=#FF0000]       //[b]问题：[/b]在conn.openDataOutputStream()的时候抛空指针（nullProintException）异常[/color]        outputStream = conn.openDataOutputStream();        outputStream.write("login");        outputStream.flush();        inputStream = conn.openDataInputStream();             //...    } catch (IOException e) {    }    }}

IRequestData reqData = new RequestDtaImpl();reqData.requestKey();reqData.loginSer();