How can I use URLConnection to use applet communication with servlet?

Question

I want to send a String to a servlet in applet.I now use URLConnection to communicat between applet and servlet.
====================the applet code below=========================
import java.io.*;
import java.applet.Applet;
import java.awt.*;
import java.net.*;
//I have tested that in applet get data from servlet is OK!
//Still I will change to test in applet post data to a servlet.
public class TestDataStreamApplet extends Applet
String response;
String baseurl;
double percentUsed;
String total;
public void init()
try
java.net.URL url = new java.net.URL(getDocumentBase(),"/servlet/dataStreamEcho");
//String currenturl=new String("http://lib.nju.edu.cn");
java.net.URLConnection con = url.openConnection();
//URL currentPage=getCodeBase();
// String protocol=currentPage.getProtocol();
// String host=currentPage.getHost();
//int port=currentPage.getPort();
// String urlSuffix="/servlet/dataStreamEcho";
// URL url=new URL(protocol,host,port,urlSuffix);
// URLConnection con=url.openConnection();
con.setUseCaches(false);
con.setDoOutput(true);
con.setDoInput(true);
ByteArrayOutputStream byteout = new ByteArrayOutputStream();
PrintWriter out=new PrintWriter(byteout,true);
String currenturl=new String("http://lib.nju.edu.cn");
String var1=this.encodedValue(currenturl); //encode the data
String data="currenturl="+var1;
out.print(data);
out.flush();
con.setRequestProperty("Content-Length",String.valueOf(byteout.size()));
con.setRequestProperty("Content-Type","application/x-www-form-urlencoded");
byteout.writeTo(con.getOutputStream());
BufferedReader in=new BufferedReader(new InputStreamReader(con.getInputStream()));
String line;
while((line=in.readLine())!=null)
     System.out.println(line);
catch (Exception e)
e.printStackTrace();
private String encodedValue(String rawValue)
     return(URLEncoder.encode(rawValue));
=========================The servlet code below=====================
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
public class DataStreamEcho extends HttpServlet
{public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
      res.setContentType("text/plain");
      PrintWriter out = res.getWriter();
      Runtime rt = Runtime.getRuntime();
      out.println(rt.freeMemory());
      out.println(rt.totalMemory());
      response.setContentType("text/html; charset=GBK");     
      request.setCharacterEncoding("GBK");
      PrintWriter out = response.getWriter();
      HttpSession session=request.getSession();
      ServletContext application=this.getServletContext();
      String currenturl=(String)session.getAttribute("currenturl");
      out.print(currenturl);
=============================================================
I have done up,but I found the program don't run as I have thought.
Can you help me to find where is wrong?Very thank!

Answer 1

You are trying to pass the current URL to the servlet
from the applet, right?
Well, what I put was correct. Your servlet code is
trying to read some information from session data.
request.getInputStream() is not the IP address of
anything...see
http://java.sun.com/products/servlet/2.2/javadoc/javax
servlet/ServletRequest.html#getInputStream()
Please read
http://www.j-nine.com/pubs/applet2servlet/Applet2Servle
.htmlNo,you all don't understand I.
I want to send an Object to the server from a applet on a client.not url only.I maybe want to send a JPEG file instead.
All I want is how to communicate with a servlet from an applet,send message to servlet from client's applet.
for example,Now I have a method get the desktop picture of my client .and I want to send it to a server with a servlet to done it.How can I write the applet and servlet program?
Now my program is down,But can only do string,can't not done Object yet.Can anyone help me?
=======================applet=============================
public void init()
try
java.net.URL url = new java.net.URL(getDocumentBase(),"/servlet/dataStreamEcho");
//String currenturl=new String("http://lib.nju.edu.cn");
java.net.URLConnection con = url.openConnection();
//URL currentPage=getCodeBase();
// String protocol=currentPage.getProtocol();
// String host=currentPage.getHost();
//int port=currentPage.getPort();
// String urlSuffix="/servlet/dataStreamEcho";
// URL url=new URL(protocol,host,port,urlSuffix);
// URLConnection con=url.openConnection();
con.setUseCaches(false);
con.setDoOutput(true);
con.setDoInput(true);
ByteArrayOutputStream byteout = new ByteArrayOutputStream();
PrintWriter out=new PrintWriter(byteout,true);
String currenturl=new String("http://lib.nju.edu.cn");
String var1=this.encodedValue(currenturl); //encode the data
String data="currenturl="+var1;
out.print(data);
out.flush();
con.setRequestProperty("Content-Length",String.valueOf(byteout.size()));
con.setRequestProperty("Content-Type","application/x-www-form-urlencoded");
byteout.writeTo(con.getOutputStream());
con.connect();
BufferedReader in=new BufferedReader(new InputStreamReader(con.getInputStream()));
String line;
while((line=in.readLine())!=null)
     System.out.println(line);
catch (Exception e)
e.printStackTrace();
=======================servlet=============================
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
     response.setContentType("text/html; charset=GBK");
//request.setCharacterEncoding("GBK");
PrintWriter out = response.getWriter();
HttpSession session=request.getSession();
ServletContext application=this.getServletContext();
//String currenturl=(String)session.getAttribute("currenturl");
String currenturl=(String)request.getParameter("currenturl");
out.print(currenturl);
File fileName=new File("c:\\noname.txt");
fileName.createNewFile();
FileOutputStream f=new FileOutputStream(fileName); //I just write the String data get from
//applet to a file for a test.
byte[] b=currenturl.getBytes();
f.write(b);
f.close();
}