请帮我看以下APPLET和SERVLET通讯的代码？？？？

applet-----------

import java.io.*;
import java.applet.Applet;
import java.awt.*;

public class SerAndApp extends Applet{
String response;
public void init()
{
try
{
java.net.URL url=
new java.net.URL(getDocumentBase(),"/servlet/SerAndApp");
java.net.URLConnection con=
url.openConnection();

con.setUseCaches(true);
con.setDoOutput(true);
con.setDoInput(true);
ByteArrayOutputStream byteout=new ByteArrayOutputStream();
DataOutputStream out=new DataOutputStream(byteout);
out.writeUTF("Hello world!");
out.flush();
byte buf[]=byteout.toByteArray();
con.setRequestProperty("Content-type","application/octest-stream");
con.setRequestProperty("Content-length",""+buf.length);
DataOutputStream dataout=new DataOutputStream(con.getOutputStream());
dataout.write(buf);
dataout.flush();
dataout.close();
DataInputStream in=new DataInputStream(con.getInputStream());
this.response=in.readUTF();
//System.out.println("read from server:"+response);
in.close();
}
catch(java.net.MalformedURLException e){}
catch(java.io.IOException e){}


}

public void paint(Graphics g)
{
g.drawString("read from server:"+this.response,10,20);
}
}




servlet--------------
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;

public class SerAndApp extends HttpServlet{
public void service(HttpServletRequest req,HttpServletResponse resp)
{
try
{
DataInputStream in=new DataInputStream(req.getInputStream());
resp.setContentType("application/octest-stream");
ByteArrayOutputStream byteout=new ByteArrayOutputStream();
DataOutputStream out=new DataOutputStream(byteout);
String response=in.readUTF();
out.writeUTF(response);
out.flush();
byte buf[]=byteout.toByteArray();
resp.setContentLength(buf.length);
ServletOutputStream servletout=resp.getOutputStream();
servletout.write(buf);
servletout.close();
}catch(java.io.IOException e){}
}
}

运行后APPLET中显示：read from server: null