Socket communication problem

Question

hello all,
i have written a small program to send a message to echo server and get back the response from the server.
it gives a error as
COULD NOT GET I/O FOR CONNECTION TO <ip address>
i am working on win nt version 4 service pack 4 installed on a home computer.
the code is as below:
import java.io.*;
import java.net.*;
public class net4a {
public static void main(String[] args) throws IOException{
Socket echoSocket = null;
DataOutputStream os = null;
DataInputStream is = null;
     DataInputStream stdIn = new DataInputStream(System.in);
     InetAddress host = InetAddress.getLocalHost();
try {
echoSocket = new Socket(host, 7);
os = new DataOutputStream(echoSocket.getOutputStream());
is = new DataInputStream(echoSocket.getInputStream());
} catch (UnknownHostException e) {
System.err.println("Don't know about host: " + host);
} catch (IOException e) {
System.err.println("Couldn't get I/O for the connection to: " + host);
if (echoSocket != null && os != null && is != null) {
try {
String userInput;
while ((userInput = stdIn.readLine()) != null) {
os.writeBytes(userInput);
os.writeByte('\n');
System.out.println("echo: " + is.readLine());
os.close();
is.close();
echoSocket.close();
} catch (IOException e) {
System.err.println("I/O failed on the connection to: " + host);
look forward to ur valuable tips on the same.

Answer 1

Hello,
Long time java programmer, first time forum user.
Looks like you looking to looking to get a java applet/program communicating with a web server. This is not an extremely difficult task and I have successfully got apache communicating CGI transactions to and from an applet with no drama�s.
This is very useful as it is restrictive to have to open up extra sockets across a network as many networks today restrict socket communication often for security or business/organization policies.
An alternative is to use HTTP request using the POST command to talk to a web server with the web server replying to the request. For example, you may need to ask a database to pull out all customer names from a server-side database. The applet need only send a URLEncoded request to the server, the webserver invokes the CGI process (I use Java to handle the CGI requests but other methods/languages can be used) which returns the result of the transaction.
I have listed some code that included the a �ping-pong� request to a server. It included the applet function that calls the webserver, the CGI batch script (for win NT/XP) to invoke the java program, the cgi-lib to simply parse the URL request (many thanks to the author) and the server-side java program that responds to the request.
I hope you find this useful. The download for apache, the webserver, is available at
http://www.apache.org/
and is a pretty simple install. Make sure you fix up the httpd.conf file to suit your system.
Good luck.
Dale Miller
CLIENT-SIDE (Java Applet Snippit)
public class Comm {
     private String server;
     private URL toServer;
     private URLConnection uRLConnection;
     private DataOutputStream dataOutputStream;
     private StringBuffer output;
     private BufferedReader dataInputStream;
     private String result;
     private int resultsLast;
     private String results[] = new String[100];
     private int firstTU;
     //this function starts in its own thread and takes care
     //of logins and there re-tries, the messaging.
     //Please see the actual function for better details
     //private LoginWatcher loginWatcher;
     public Comm(String serverAddress) throws UnsupportedEncodingException{
          System.out.println("loaded Comm class!");
          //First thing we need to do is set up the login watcher
          //loginWatcher = new LoginWatcher();
          this.output = new StringBuffer();
          this.server = serverAddress;
          try {
               this.toServer = new URL(server + "ping.cgi");
          } catch (MalformedURLException e) {
               System.out.println("ERROR : in contacting the server");
               System.out.println("Server : " + server);
               System.out.println("NOT FOUND!!");
          try {
               this.uRLConnection = toServer.openConnection();
          } catch (IOException e) {
               System.out.println("ERROR : Connection to server refused");
          this.uRLConnection.setUseCaches(false);
          this.uRLConnection.setDoInput(true);
          this.uRLConnection.setDoOutput(true);
          this.uRLConnection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
          try {
               this.dataOutputStream = new DataOutputStream(uRLConnection.getOutputStream());
          } catch (IOException e) {
               System.out.println("ERROR : opening dataoutputstream");
          this.output.setLength(0);
          output.append("first=" + URLEncoder.encode("I am", "UTF-8"));
          output.append("&last=" + URLEncoder.encode("number 1", "UTF-8"));
          try {
               dataOutputStream.writeBytes(new String(output));
          } catch (IOException e) {
               System.out.println("ERROR : Sending string to cgi ping.cgi");
          try {
               this.dataInputStream = new BufferedReader(new InputStreamReader(uRLConnection.getInputStream()));
          } catch (IOException e) {
               System.out.println("ERROR : Setting up input stream");
          String grab = new String();
          System.out.print("Searching for server..");
          try {
               grab = dataInputStream.readLine();
               grab = dataInputStream.readLine();
          } catch (IOException e) {
               System.out.println("ERROR : Reciving ping data from server");
          if (grab.equals("pass")) {
               System.out.println("OK");
          } else {
               System.out.println("ERROR\n\nSERVER NOT FOUND!!!");
               System.exit(-1);
          //loginWatcher.loginWatcherTh.start();
CGI BATCH TO INVOKE CGI PROGRAM
#!java -cp c:\ss\ middle
CGI-LIB TO PARSE HTTP REQUESTS
import java.util.*;
import java.io.*;
* cgi_lib.java<p>
* <p>
* Usage: This library of java functions, which I have encapsulated inside
* a class called cgi_lib as class (static) member functions,
* attempts to duplicate the standard PERL CGI library (cgi-lib.pl).
* You must invoke any Java program that uses this library from
* within a UNIX script, Windows batch file or equivalent. As you
* will see in the following example, all of the CGI environment
* variables must be passed from the script into the Java application
* using the -D option of the Java interpreter. This example
* UNIX script uses the "main" routine of this class as a
* CGI script:
* <pre>
* (testcgi.sh)
* #!/bin/sh
* java \
* -Dcgi.content_type=$CONTENT_TYPE \
* -Dcgi.content_length=$CONTENT_LENGTH \
* -Dcgi.request_method=$REQUEST_METHOD \
* -Dcgi.query_string=$QUERY_STRING \
* -Dcgi.server_name=$SERVER_NAME \
* -Dcgi.server_port=$SERVER_PORT \
* -Dcgi.script_name=$SCRIPT_NAME \
* -Dcgi.path_info=$PATH_INFO \
* cgi_lib
* </pre>
* Question and comments can be sent to [email protected].<p>
* @version 1.0
* @author Pat L. Durante
class cgi_lib
* Parse the form data passed from the browser into
* a Hashtable. The names of the input fields on the HTML form will
* be used as the keys to the Hashtable returned. If you have a form
* that contains an input field such as this,<p>
* <pre>
* &ltINPUT SIZE=40 TYPE="text" NAME="email" VALUE="[email protected]"&gt
* </pre>
* then after calling this method like this,<p>
* <pre>
* Hashtable form_data = cgi_lib.ReadParse(System.in);
* </pre>
* you can access that email field as follows:<p>
* <pre>
* String email_addr = (String)form_data.get("email");
* </pre>
* @param inStream The input stream from which the form data can be read.
* (Only used if the form data was posted using the POST method. Usually,
* you will want to simply pass in System.in for this parameter.)
* @return The form data is parsed and returned in a Hashtable
* in which the keys represent the names of the input fields.
public static Hashtable ReadParse(InputStream inStream)
Hashtable form_data = new Hashtable();
String inBuffer = "";
if (MethGet())
inBuffer = System.getProperty("cgi.query_string");
else
// TODO: I should probably use the cgi.content_length property when
// reading the input stream and read only that number of
// bytes. The code below does not use the content length
// passed in through the CGI API.
DataInput d = new DataInputStream(inStream);
String line;
try
while((line = d.readLine()) != null)
inBuffer = inBuffer + line;
catch (IOException ignored) { }
// Split the name value pairs at the ampersand (&)
StringTokenizer pair_tokenizer = new StringTokenizer(inBuffer,"&");
while (pair_tokenizer.hasMoreTokens())
String pair = urlDecode(pair_tokenizer.nextToken());
// Split into key and value
StringTokenizer keyval_tokenizer = new StringTokenizer(pair,"=");
String key = new String();
String value = new String();
if (keyval_tokenizer.hasMoreTokens())
key = keyval_tokenizer.nextToken();
else ; // ERROR - shouldn't ever occur
if (keyval_tokenizer.hasMoreTokens())
value = keyval_tokenizer.nextToken();
else ; // ERROR - shouldn't ever occur
// Add key and associated value into the form_data Hashtable
form_data.put(key,value);
return form_data;
* URL decode a string.<p>
* Data passed through the CGI API is URL encoded by the browser.
* All spaces are turned into plus characters (+) and all "special"
* characters are hex escaped into a %dd format (where dd is the hex
* ASCII value that represents the original character). You probably
* won't ever need to call this routine directly; it is used by the
* ReadParse method to decode the form data.
* @param in The string you wish to decode.
* @return The decoded string.
public static String urlDecode(String in)
StringBuffer out = new StringBuffer(in.length());
int i = 0;
int j = 0;
while (i < in.length())
char ch = in.charAt(i);
i++;
if (ch == '+') ch = ' ';
else if (ch == '%')
ch = (char)Integer.parseInt(in.substring(i,i+2), 16);
i+=2;
out.append(ch);
j++;
return new String(out);
* Generate a standard HTTP HTML header.
* @return A String containing the standard HTTP HTML header.
public static String Header()
return "Content-type: text/html\n\n";
* Generate some vanilla HTML that you usually
* want to include at the top of any HTML page you generate.
* @param Title The title you want to put on the page.
* @return A String containing the top portion of an HTML file.
public static String HtmlTop(String Title)
String Top = new String();
Top = "<html>\n";
Top+= "<head>\n";
Top+= "<title>\n";
Top+= Title;
Top+= "\n";
Top+= "</title>\n";
Top+= "</head>\n";
Top+= "<body>\n";
return Top;
* Generate some vanilla HTML that you usually
* want to include at the bottom of any HTML page you generate.
* @return A String containing the bottom portion of an HTML file.
public static String HtmlBot()
return "</body>\n</html>\n";
* Determine if the REQUEST_METHOD used to
* send the data from the browser was the GET method.
* @return true, if the REQUEST_METHOD was GET. false, otherwise.
public static boolean MethGet()
String RequestMethod = System.getProperty("cgi.request_method");
boolean returnVal = false;
if (RequestMethod != null)
if (RequestMethod.equals("GET") ||
RequestMethod.equals("get"))
returnVal=true;
return returnVal;
* Determine if the REQUEST_METHOD used to
* send the data from the browser was the POST method.
* @return true, if the REQUEST_METHOD was POST. false, otherwise.
public static boolean MethPost()
String RequestMethod = System.getProperty("cgi.request_method");
boolean returnVal = false;
if (RequestMethod != null)
if (RequestMethod.equals("POST") ||
RequestMethod.equals("post"))
returnVal=true;
return returnVal;
* Determine the Base URL of this script.
* (Does not include the QUERY_STRING (if any) or PATH_INFO (if any).
* @return The Base URL of this script as a String.
public static String MyBaseURL()
String returnString = new String();
returnString = "http://" +
System.getProperty("cgi.server_name");
if (!(System.getProperty("cgi.server_port").equals("80")))
returnString += ":" + System.getProperty("cgi.server_port");
returnString += System.getProperty("cgi.script_name");
return returnString;
* Determine the Full URL of this script.
* (Includes the QUERY_STRING (if any) or PATH_INFO (if any).
* @return The Full URL of this script as a String.
public static String MyFullURL()
String returnString;
returnString = MyBaseURL();
returnString += System.getProperty("cgi.path_info");
String queryString = System.getProperty("cgi.query_string");
if (queryString.length() > 0)
returnString += "?" + queryString;
return returnString;
* Neatly format all of the CGI environment variables
* and the associated values using HTML.
* @return A String containing an HTML representation of the CGI environment
* variables and the associated values.
public static String Environment()
String returnString;
returnString = "<dl compact>\n";
returnString += "<dt><b>CONTENT_TYPE</b> <dd>:<i>" +
System.getProperty("cgi.content_type") +
"</i>:<br>\n";
returnString += "<dt><b>CONTENT_LENGTH</b> <dd>:<i>" +
System.getProperty("cgi.content_length") +
"</i>:<br>\n";
returnString += "<dt><b>REQUEST_METHOD</b> <dd>:<i>" +
System.getProperty("cgi.request_method") +
"</i>:<br>\n";
returnString += "<dt><b>QUERY_STRING</b> <dd>:<i>" +
System.getProperty("cgi.query_string") +
"</i>:<br>\n";
returnString += "<dt><b>SERVER_NAME</b> <dd>:<i>" +
System.getProperty("cgi.server_name") +
"</i>:<br>\n";
returnString += "<dt><b>SERVER_PORT</b> <dd>:<i>" +
System.getProperty("cgi.server_port") +
"</i>:<br>\n";
returnString += "<dt><b>SCRIPT_NAME</b> <dd>:<i>" +
System.getProperty("cgi.script_name") +
"</i>:<br>\n";
returnString += "<dt><b>PATH_INFO</b> <dd>:<i>" +
System.getProperty("cgi.path_info") +
"</i>:<br>\n";
returnString += "</dl>\n";
return returnString;
* Neatly format all of the form data using HTML.
* @param form_data The Hashtable containing the form data which was
* parsed using the ReadParse method.
* @return A String containing an HTML representation of all of the
* form variables and the associated values.
public static String Variables(Hashtable form_data)
String returnString;
returnString = "<dl compact>\n";
for (Enumeration e = form_data.keys() ; e.hasMoreElements() ;)
String key = (String)e.nextElement();
String value = (String)form_data.get(key);
returnString += "<dt><b>" + key + "</b> <dd>:<i>" +
value +
"</i>:<br>\n";
returnString += "</dl>\n";
return returnString;
* The main routine is included here as a test CGI script to
* demonstrate the use of all of the methods provided above.
* You can use it to test your ability to execute a CGI script written
* in Java. See the sample UNIX script file included above to see
* how you would invoke this routine.<p>
* Please note that this routine references the member functions directly
* (since they are in the same class), but you would have to
* reference the member functions using the class name prefix to
* use them in your own CGI application:<p>
* <pre>
* System.out.println(cgi_lib.HtmlTop());
* </pre>
* @param args An array of Strings containing any command line
* parameters supplied when this program in invoked. Any
* command line parameters supplied are ignored by this routine.
public static void main( String args[] )
// This main program is simply used to test the functions in the
// cgi_lib class.
// That said, you can use this main program as a test cgi script. All
// it does is echo back the form inputs and enviroment information to
// the browser. Use the testcgi UNIX script file to invoke it. You'll
// notice that the script you use to invoke any Java application that
// uses the cgi_lib functions MUST pass all the CGI enviroment variables
// into it using the -D parameter. See testcgi for more details.
// Print the required CGI header.
System.out.println(Header());
// Create the Top of the returned HTML
// page (the parameter becomes the title).
System.out.println(HtmlTop("Hello World"));
System.out.println("<hr>");
// Determine the request method used by the browser.
if (MethGet())
System.out.println("REQUEST_METHOD=GET");
if (MethPost())
System.out.println("REQUEST_METHOD=POST");
System.out.println("<hr>");
// Determine the Base URL of this script.
System.out.println("Base URL: " + MyBaseURL());
System.out.println("<hr>");
// Determine the Full URL used to invoke this script.
System.out.println("Full URL: " + MyFullURL());
System.out.println("<hr>");
// Print all the CGI environment variables
// (usually only used while testing CGI scripts).
System.out.println(Environment());
System.out.println("<hr>");
// Parse the form data into a Hashtable.
Hashtable form_data = ReadParse(System.in);
// Print out each of the name/value pairs
// from sent from the browser.
System.out.println(Variables(form_data));
System.out.println("<hr>");
// Access a particular form value.
// (This assumes the form contains a "name" input field.)
String name = (String)form_data.get("name");
System.out.println("Name=" + name);
System.out.println("<hr>");
// Create the Bottom of the returned HTML page - which closes it cleanly.
System.out.println(HtmlBot());
SERVER-SIDE PROGRAM TO RETURN PING
import java.util.*;
import java.io.*;
class ping
     public static void main(String args[]) {
          System.out.println(cgi_lib.Header());
          Hashtable form_data = cgi_lib.ReadParse(System.in);
          String one = (String)form_data.get("first");
          String two = (String)form_data.get("last");
          boolean test;
          test = false;
          if (one.equals("I am")) {
               if (two.equals("number 1")) {
                    test = true;
          if (test == true) {
               System.out.println("pass");
          } else {
               System.out.println("fail");
     //Datavasee
ENJOY :)