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Socket connection not workin in flutter release apk

I am new to working with sockets, and I am working on this project where a connection between my android flutter app and a java server is needed, to do this I am trying socket programming.
The server code is fairly simple, I create a new thread for every client connected and I give them a bunch of URLs, later on, this should be replaced by a query result. here is the java code:
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
public class CrawlitServer {
// The port number on which the server will listen for incoming connections.
public static final int PORT = 6666;
//main method
public static void main(String[] args) {
System.out.println("The server started .. ");
// Create a new server socket
ServerSocket serverSocket = null;
try {
serverSocket = new ServerSocket(PORT);
} catch (Exception e) {
System.out.println("Error: " + e.getMessage());
}
// Listen for incoming connections and create a new thread for each one
while (true) {
try {
new CrawlitServerThread(serverSocket.accept()).start();
}
catch (Exception e) {
System.out.println("Error: " + e.getMessage());
}
}
}
public static class CrawlitServerThread extends Thread {
private final Socket socket;
public CrawlitServerThread(Socket socket) {
this.socket = socket;
}
public void run() {
List<String> list = new ArrayList<>();
//assign a value to list
list.add("http://www.google.com");
list.add("http://www.yahoo.com");
list.add("http://www.bing.com");
list.add("http://www.facebook.com");
list.add("http://www.twitter.com");
list.add("http://www.linkedin.com");
list.add("http://www.youtube.com");
list.add("http://www.wikipedia.com");
list.add("http://www.amazon.com");
list.add("http://www.ebay.com");
list.add("http://stackoverflow.com");
list.add("http://github.com");
list.add("http://quora.com");
list.add("http://reddit.com");
list.add("http://wikipedia.org");
try {
// Get the input stream from the socket
DataInputStream inputStream = new DataInputStream(socket.getInputStream());
Scanner scanner = new Scanner(inputStream);
DataOutputStream outputStream = new DataOutputStream(socket.getOutputStream());
PrintWriter writer = new PrintWriter(outputStream, true);
while (scanner.hasNextLine()) {
String line = scanner.nextLine();
System.out.println("Received Message from client: " + line);
writer.println(list + "\n");
}
}
catch (Exception e) {
System.out.println("Error: " + e.getMessage());
}
}
}
}
Now I run this server and connect to it using sockets in Flutter, I give it the IP address I get from the ipconfig command, and here is the dart code:
import 'dart:async';
import 'dart:io';
//Utilities that manage connections with server sockets.
//ServerUtil Class
class ServerUtil {
static const port = 6666;
static const host = MY_IP_GOES_HERE;
static late Socket socket;
static bool connected = false;
//a list of urls returned by the server
static List<String> urls = [];
//Constructor
ServerUtil() {
//Initialize the socket.
Socket.connect(host, port).then((Socket sock) {
socket = sock;
connected = true;
socket.listen(dataHandler,
onError: errorHandler, onDone: doneHandler, cancelOnError: false);
//send a message to the server.
}).catchError((e) {
print("Unable to connect: $e");
});
}
//Query method that sends a message to the server. The server will return a list of urls.
//The urls will be added to the urls list.
//The urls list will be returned.
static Future<List<String>> query(String userQuery) async {
urls.clear();
//check if socket is connected.
if (connected) {
//send the query to the server.
socket.writeln(userQuery);
await Future.delayed(const Duration(milliseconds: 200));
print(urls);
return urls;
}
//if socket is not connected, wait for 5 seconds and try again.
await Future.delayed(const Duration(milliseconds: 50));
return query(userQuery);
}
//Handles data from the server.
void dataHandler(data) {
//String of received data.
String dataString = String.fromCharCodes(data).trim();
//remove first and last character from the string.
dataString = dataString.substring(1, dataString.length - 1);
//remove all the whitespace characters from the string.
dataString = dataString.replaceAll(RegExp(r'\s+'), '');
urls = dataString.split(',');
}
//Handles errors from the server.
void errorHandler(error, StackTrace trace) {
print(error);
}
//Handles when the connection is done.
void doneHandler() {
socket.destroy();
}
}
This works perfectly fine while using a debug apk running it on my real Note 9 device. The problem however is that when I build a release apk and try it out, nothing happens.
The way I set it up is that I wait for the query method in an async and then I send the result to a new screen and push that screen into the navigator.
But in the release apk nothing happens, the new screen doesn't load.
So this leads me to my first question:
Is there a way to debug a release apk? see what exceptions it throws or print some stuff to console?
I have the server running on my Laptop, and the app runs on my phone which is on the same WIFI network.
My second question is:
Do I need to enable some sort of option with my router or my laptop to allow my phone to connect? it does connect in debug mode without any modifications
I tried some random things, like using 'localhost' instead of my IP, as I would normally connect say with a java client for example, but it didn't work.
My last question is:
Does the release apk or like android OS prevent connections to local hosts, maybe because it thinks it is not secure? but then it still connects in debug mode.
Thank you for your time.

I dont understand the scope of try catches when it comes to java sockets

I am in year 13 and have decided for my computer science coursework to make a small chat program using java. I have had to learn the networking aspect from scratch and my teachers are unfamiliar with it so they struggle to answer my questions. I have a client program and a server program and they communicate via a socket I creat, my issue is I dont understand the effect the try catches are having on my code. I am really fascinated with networking and thats why I chose it knowing full well it would be a challange, Ill leave my code below and the error I am having. If you could give me any tips on how I can solve my problem and also make my code 'better' that would be absolutely fantastic. Also please take into account I have only known java for around a year now and am still a novice futher more this is my first question on stack overflow!. Many thanks!
Client Code:
/*
* To change this license header, choose License Headers in Project Properties.
* To change this template file, choose Tools | Templates
* and open the template in the editor.
*/
package oclient;
import java.net.*;
import java.io.*;
import com.dosse.upnp.UPnP;
import java.util.Scanner;
/**
*
* #author sgmud
*/
public class CClient {
public Socket CSocket;
public PrintWriter out;
public BufferedReader in;
public int GetPort(){
Scanner scan = new Scanner(System.in);
System.out.println("please enter the port number");
int PortNum = scan.nextInt();
return PortNum;
}
public String GetAddress(){
Scanner scan = new Scanner(System.in);
System.out.println("Please enter the IP address of the host");
String Address = scan.nextLine();
return Address;
}
public void StartConnection(String ip, int port){
try{
CSocket = new Socket(ip, port);
out = new PrintWriter(CSocket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(CSocket.getInputStream()));
}catch(IOException e){
System.out.println("ERROR");
}
}
public void sendMessage(String msg){
//String Response;
out.println(msg); // outputs message
//try{
// Response = in.readLine();
//}catch(IOException e){
// System.out.println("ERROR");
//}
//System.out.println(Response);
//return Response;
}
public String receveMessage(){
String Response = "IfYouReadThisThetryCatchIsNotWorkingHowYouIntendItTo";
try{
Response = in.readLine();
}catch(IOException e){
System.out.println("Error");
}finally{
System.out.println(Response);
return Response;
}
}
public void convosation(){ // method will keep letting you send a message untill you stop
CClient client = new CClient();
while (true){
Scanner scan = new Scanner(System.in);
System.out.println("Type QUIT to end the convosation or press any key to send a message");
String qit = scan.nextLine();
if("QUIT".equals(qit)){
client.STOP();
}
else{
client.sendMessage(client.Message()); // Runs the send message method with the output from the Message method
client.receveMessage();
}
}
}
public String Message(){
Scanner scan = new Scanner(System.in);
System.out.println("please enter a mesasge to be sent");
String message = scan.nextLine();
return message;
}
public void STOP(){
try{
in.close();
out.close();
CSocket.close();
}catch(IOException e){
System.out.println("ERROR");
}
}
/**
*
*/
public static void main(String[] args){
CClient client = new CClient(); // Making a new client class
client.StartConnection(client.GetAddress(), client.GetPort()); // runs the startConnection method but runs the Get address and Get port method first so the Start connection method has the IP and Port number
client.convosation();
// client.STOP(); // runs the stop method which will terminate the server
}
}
Server Code:
/*
* To change this license header, choose License Headers in Project Properties.
* To change this template file, choose Tools | Templates
* and open the template in the editor.
*/
package oserver;
import java.net.*;
import java.io.*;
import com.dosse.upnp.UPnP;
import java.util.Scanner;
/**
*
* #author sgmud
*/
public class SServer { // Server Class
public ServerSocket SSocket;
public Socket CSocket;
public PrintWriter out;
public BufferedReader in;
public int GetPort(){ // Gets port number for socket to be set listening to
Scanner scan = new Scanner(System.in);
System.out.println("please enter the port number");
int PortNum = scan.nextInt();
return PortNum;
}
public void start(int port) { // Starts the server with the collected port
try{
System.out.println("Server Started");
UPnP.openPortTCP(port);
SSocket = new ServerSocket(port);
CSocket = SSocket.accept();
System.out.println("Server Connected");
out = new PrintWriter(CSocket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(CSocket.getInputStream()));
String input;
while ((input = in.readLine()) != null){
if(".".equals(input)){
out.println("goodbye");
break;
}
else{
out.println(input);
}
}
}catch(IOException e){
System.out.println("ERROR");
}
}
public void stop(){ // Will close all connections
try{
//in.close();
out.close();
CSocket.close();
SSocket.close();
}catch(IOException e){
System.out.println("ERROR");
}
}
public static void main(String[] args){
SServer server = new SServer(); // Creat new server class
server.start(server.GetPort()); // Starts the server with the port number
}
}
Error (This is on client side):
run:
Please enter the IP address of the host
0.0.0.0
please enter the port number
6666
Type QUIT to end the convosation or press any key to send a message
h
please enter a mesasge to be sent
hello
Exception in thread "main" java.lang.NullPointerException: Cannot invoke "java.io.PrintWriter.println(String)" because "this.out" is null
at oclient.CClient.sendMessage(CClient.java:54)
at oclient.CClient.convosation(CClient.java:94)
at oclient.CClient.main(CClient.java:125)

Your problem seems to not be try-catch but lack of error handling.
If we assume the commented-out code in sendMessage to be actually operational:
try{
Response = in.readLine();
}catch(IOException e){
System.out.println("ERROR");
}
System.out.println(Response);
return Response;
then what happens if there is an exception from code executing inside the 'try' is that you print out ERROR, and that is all you do.
Execution then carries on 'down the page' and you attempt to print out, and return, the value of Response. But Response was never assigned; the assignment inside the try-block never completed. So Response still has the value it had on entry to sendMessage, which may be null.
If you're going to catch the error-exception inside sendMessage, then (a) you need to write code to handle the error, and (b) sendMessage needs a way to indicate failure. Maybe you make the function return the response for success, null for failure. The caller then has to be aware that a null return is possible.
try{
Response = in.readLine();
}catch(IOException e){
System.out.println("ERROR");
return null;
}
System.out.println(Response);
return Response;
Alternatively, you could not catch the error there, but allow it to propagate out. That is, the caller of sendMessage has to be aware that sendMessage can throw an exception, and either handle it, or let it propagate out. The decision of where it is appropriate to handle the exception is something that needs to be considered on a wider basis than just one method.
Incidentally, many postings on Stack Overflow show the same pattern of exception handling by 'print and continue'. It's rarely a good way.

Stuck in write operation when reading from Socket

I'm sending a file and its name through Socket to a ServerSocket.
It works "partially" -- the server gets the file and saves it to disk but
it does not exit the loop in the copy() method in the ClientSession class.
public class Client{
DataOutputStream dos =null;
DataInputStream dis=null;
File f =new File("c:/users/supernatural.mp4");
public static void main(String[]ar) throws Exception{
try {
System.out.println("File upload started");
Socket socc = new Socket("localhost",8117);
dos = new DataOutputStream(socc.getOutputStream());
//send file name
dos.writeUTF(f.getName());
//send the file
write(f,dos);
//Files.copy(f.toPath(),dos);
//this prints
System.out.println("Data has been sent...waiting for server to respond ");
dis = new DataInputStream(socc.getInputStream());
//this never reads; stuck here
String RESPONSE = dis.readUTF();
//this never prints prints
System.out.println("Server sent: "+RESPONSE);
} catch(Exception ex) {
ex.printStackTrace();
} finally {
//close the exceptions
clean();
}
}
private static void write(File f,DataOutputStream d) throws Exception{
int count;
DataInputStream din = new DataInputStream(new BufferedInputStream(new FileInputStream(f)));
byte array[] = new byte[1024*4];
while((count =din.read(array)) >0){
d.write(array,0,count);
}
d.flush();
//this prints
System.out.println(" done sending...");
din.close();
}
}
//Server
public class MySocket implements Runnable{
int worker_thread=2;
volatile boolean shouldRun =false;
ServerSocket server;
String port = "8117";
//ExecutorService services;
static ExecutorService services;
public MySocket() {
this.server = new ServerSocket(Integer.valueOf(port));
services = Executors.newFixedThreadPool(this.worker_thread);
}
//A METHOD TO RUN SERVER THREAD
#Override
public void run(){
while(this.shouldRun){
Socket client =null;
try{
client = server.accept();
}catch(Exception ex){
ex.printStackTrace();
}
//hand it over to be processed
this.services.execute(new ClientSessions(client));
}
}
public static void main(String[]ar) throws Exception{
Thread t = new Thread(new MySocket());
t.start();
}
}
//the ClientSession
public class ClientSessions implements Runnable{
Socket s;
public ClientSessions(Socket s){
this.s = s;
}
DataInputStream dis=null;
DataOutputStream dos=null;
boolean success =true;
#Override
public void run(){
//get the data
try{
//get inside channels
dis = new DataInputStream(this.s.getInputStream());
//get outside channels
dos = new DataOutputStream(this.s.getOutputStream());
//read the name
//this works
String name=dis.readUTF();
String PATH_TO_SAVE ="c://folder//"+name;
//now copy file to disk
File f = new File(PATH_TO_SAVE);
copy(f,dis);
//Files.copy(dis,f.toPath());
//this doesnt print, stuck in the copy(f,dis) method
System.out.println("I am done");
success =true;
}catch(Exception ex){
ex.printStackTrace();
}finally{
//clean resources...
clean();
}
}
//copy from the stream to the disk
private void copy(File f,DataInputStream d)throws Exception{
f.getParentFile().mkdirs();
f.createNewFile();
int count =-1;
DataOutputStream out = new DataOutputStream(new BufferedOutputStream(new FileOutputStream(f)));
byte array[] = new byte[1024*8];
count =d.read(array);
while(count >0){
out.write(array,0,count);
count =d.read(array);
System.out.println("byte out: "+count);
}
//this never prints
System.out.println("last read: "+count);
out.flush();
out.close();
if(success)dos.writeUTF("Succesful");
else dos.writeUTF("error");
}
}
//for the clean method i simply have
void clean(){
if(dis!=null)dis.close();
if(dos!=null)dos.close();
}
I commented this //Files.copy(dis,f.toPath()); from server
because it does not go to next line after writing file to disk, sometimes even stuck there.
Could some pls point me in the right path, I believe i am doing something very wrong here
dont know if this is helpful but the client runs in eclipse and server in netbeans

Think about your procotol:
The Client sends the file name, then sends the binary file, then waits for the server response.
The Server reads the file name, then the binary file until the stream is closed, then sends the success message.
But the stream is never closed since the client is waiting for the response, hence you have a deadlock in your protocol.
This is usually solved by sending the file size first and having the server read exactly that many bytes.
Alternatively you can use the TCP's one-way shutdown feature to send a signal to the server that the output stream of the socket is closed. That can be done with socc.shutdownOutput();
And please use try-with-resources to avoid resource leaks (you must close the Socket, too).
Fixed Client:
try {
System.out.println("File upload started");
try (Socket socc = new Socket("localhost", 8117);
DataOutputStream dos = new DataOutputStream(socc.getOutputStream());
DataInputStream dis = new DataInputStream(socc.getInputStream())) {
// send file name
dos.writeUTF(f.getName());
// send the file
Files.copy(f.toPath(), dos);
dos.flush();
System.out.println("Data has been sent...waiting for server to respond ");
// signal to server that sending is finished
socc.shutdownOutput();
String RESPONSE = dis.readUTF();
// this never prints prints
System.out.println("Server sent: " + RESPONSE);
}
} catch (Exception ex) {
ex.printStackTrace();
}
Server:
public class MySocket implements Runnable {
int worker_thread = 2;
volatile boolean shouldRun = true;
ServerSocket server;
int port = 8117;
ExecutorService services;
public MySocket() throws IOException {
this.server = new ServerSocket(port);
services = Executors.newFixedThreadPool(this.worker_thread);
}
// A METHOD TO RUN SERVER THREAD
#Override
public void run() {
while (this.shouldRun) {
Socket client = null;
try {
client = server.accept();
} catch (Exception ex) {
ex.printStackTrace();
}
// hand it over to be processed
this.services.execute(new ClientSessions(client));
}
}
public static void main(String[] ar) throws Exception {
new MySocket().run();
}
}
class ClientSessions implements Runnable {
Socket s;
public ClientSessions(Socket s) {
this.s = s;
}
#Override
public void run() {
// get the data
try (DataInputStream dis = new DataInputStream(this.s.getInputStream());
DataOutputStream dos = new DataOutputStream(this.s.getOutputStream())) {
// read the name
// this works
String name = dis.readUTF();
String PATH_TO_SAVE = name;
// now copy file to disk
File f = new File("c://folder", PATH_TO_SAVE);
Files.copy(dis, f.toPath());
dos.writeUTF("Succesful");
System.out.println("I am done");
} catch (Exception ex) {
ex.printStackTrace();
} finally {
try {
s.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}

The issue with your code is, that you read from an input stream of a socket, that is never closed.
DataOutputStream out = new DataOutputStream(new BufferedOutputStream(new FileOutputStream(f)));
byte array[] = new byte[1024*8];
count =d.read(array);
while(count >0){
out.write(array,0,count);
count =d.read(array);
System.out.println("byte out: "+count);
}
//this never prints
System.out.println("last read: "+count);
d.read(array) is actively trying to read from the socket, blocking until it receives something. Since the InputStream is actively blocking, it never returns a value less than or equal to 0. This is because the stream awaits the next package from the other end of the Socket.
Closing the Socket after sending the File should help you. In that case, the end of the Stream is reached and the InputStream returns.
Note: The InputStream you are reading from will (if the socket is closed) return a -1, as you can see within the JavaDoc.
In your case, this however might not be viable!
You want to answer the Client with "okay", or "error". If you close the socket, you cannot answer through the same Socket. The solution to this can be complex.
This situation is a bit tricky. Most frameworks out there have a Thread that reads from the SocketInputStream and passes the return value to some sort of handler (in blocking IO). Your while loop basically is this main reading loop inside the Thread. This loop will only exit, if the connection is lost and therefor the System.out.println("last read: "+count); could be changed to System.out.println("disconnected");
To keep it simple: You could give an estimation on how big the file will be and (just for testing purposes) write something like this:
DataOutputStream out = new DataOutputStream(new
BufferedOutputStream(new FileOutputStream(f)));
byte array[] = new byte[/* Big enough */ 1024 * 1024 * 8];
d.read(array); // Read the file content
out.write(array); // Write to the file
//this never prints
System.out.println("last read: "+count);
I have left out every error check here! This means that you only read one package from the server, which has to be the File.

simple multi-threaded server chat using java

I'm creating a java chat server that handles multi clients I use this simple code for server
public class Server extends Thread {
ServerSocket serverSocket = null;
Socket socket = null;
private int unique_id;
ArrayList<Clients> cl;
public Server(int port) {
try {
serverSocket = new ServerSocket(port);
cl = new ArrayList<>();
this.start();
} catch (Exception e){
System.out.println("Error 5");
e.printStackTrace();
}
}
#Override
public void run(){
System.out.println("Server Start");
while (true){
try {
socket = serverSocket.accept();
Clients t = new Clients(socket); // add it to thread
cl.add(t);
t.start();
System.out.println("Connected " + String.valueOf(cl.size())); // printed ok
}catch (Exception e){
System.out.println("Error 4");
e.printStackTrace();
}
}
}
public synchronized void SendToAll(String s){ // this function used by client when one of client socket send a message then server send it to all
System.out.println("Sended is excuted"); // excuted normal each time i send a message from client but not send to all
for (int i = 0; i < cl.size(); i++){
cl.get(i).WriteToSocket(s);
}
}
public static void main(String args[]){
int port = 5002;
Server server = new Server(port); // start server
//server.run(); // start connections wait for it
}
class Clients extends Thread { // class extends thread
public Socket socket = null;
DataInputStream input = null; // read input
DataOutputStream output = null; // read output
public int myid = 0; // unique id for each client
public Clients(Socket soc) {
socket = soc;
try {
input = new DataInputStream(socket.getInputStream());
output = new DataOutputStream(socket.getOutputStream());
myid = ++unique_id;
System.out.println("Client Start Thread"); // printed ok !
} catch (IOException e){
System.out.println("Error 1");
e.printStackTrace();
}
}
public void WriteToSocket(String s) { // used to write a message to this socket
try {
output.write(s.getBytes());
}catch (IOException e){
System.out.println("Error 2");
e.printStackTrace();
}
}
#Override
public void run() { // run thread function wait for messages from clients
while (true){
try {
String s = input.readLine();
if (s.contains("quite")) {
socket.close();
input.close();
output.close();
cl.remove(this);
this.stop();
}
if (!s.isEmpty()) {
SendToAll(s);// when message come and not empty it use server function to send them to all clients
}
}catch (IOException e){
System.out.println("Error 3");
e.printStackTrace();
}
}
}
}
}
everything works fine when clients connect the server accept the connection and the client thread started
but the problem when I sent a message from the client it didn't received by the server I try my client application in java too with Qt c++ server and it works ?
so what did I do wrong here make the server can't receive the message ?
this my first time in network programming using java
Edit
I solve the NullPointerException the problem was that when client log out I didn't remove his socket from the ArrayList solved by making client before close send message contains quite so when I see it i remove his socket from array list Another Quetiosn Here i don't know how this message sentthe System.out.println() that is in the SendToAll function printed to the screen each time client send a message but why the message not send again to all clients ? actually the main problem is that server can't send the message to all clients in the array list after message comes from one client the problem not solved stell found
Client Code class
public class ClientSocket extends Thread {
public Socket socket = null;
public DataInputStream input = null;
public DataOutputStream output = null;
MainChat chat = null;
public ClientSocket(String ip, int port,MainChat ch) {
try {
socket = new Socket(ip,port);
input = new DataInputStream(socket.getInputStream());
output = new DataOutputStream(socket.getOutputStream());
chat = ch;
this.start();
}catch (IOException e){
}
}
#Override
public void run() {
while (true){
try {
String s = input.readLine();
if (!s.isEmpty()){
chat.WriteToScreen(s.trim());
}
}catch (IOException e){
}
}
}
public void WriteToSocket(String s) throws IOException{
output.write(s.getBytes());
}
}
Edit
when i use this code in main the SendToAll function send the message to all clients !! why when i use it from clients class using Thread it not sended to all ?
public static void main(String args[]){
int port = 5002;
Server server = new Server(port); // start server
//server.run(); // start connections wait for it
while (true) {
String s = in.next();
server.SendToAll(s + "\n"); // message sended to all client !!
}
}

The problem is that readLine reads until it finds a line terminator of end of file. This is why it works with other server in QT C++ but not with the Java server.
Please see here:
https://docs.oracle.com/javase/7/docs/api/java/io/DataInput.html#readLine()
https://docs.oracle.com/javase/7/docs/api/java/io/DataInputStream.html#readLine()
Please note that readLine in DataInputStream is deprecated. You should use BufferedReader to read a line (with readLine) as indicated in the DataInputStream link.
So, add '\n' to the end of the string sent and it will work.

I solve the problem, I am sorry for that it was my fault I forget to add \n in sendToAll function so this what cause the problem so no \n the clients can't read the line because I use readLine in DataInputStream
anyway I try another method to read bytes instead of readLine it's I think it's better especially when you receive UTF-8 char and after that changes from bytes to String

Java, Telnet, check for String in an InputStream

I am fairly raw. I am trying to write a Java class to interact with Telnet. I saw that Apache Commons and Jsacpe had APIs. I am using Jscape's Sinetfactory. The Telnet I am connecting to sends a prompt to enter 'User name?:' as soon as telnet.connect() occurs. I am required to verify that this prompt is actually happening so I do not just write the answer when something else may happen. I am inexperienced with this and am sure there is a simple answer, just wondering if anyone might be able to help.
Here is what I have, its a bit sloppy because I've been playing around for awhile not sure how to actually read the last characters from the stream.
import com.jscape.inet.telnet.*;
public class TelnetTest extends TelnetAdapter {
private final static String USER = "xxx\r";
private final static String PWORD = "yyy\r";
private final static String COMMAND = "zzz\r";
private final static byte[] USER_BYTE = USER.getBytes();
private final static byte[] PWORD_BYTE = PWORD.getBytes();
private final static byte[] COMMAND_BYTE = COMMAND.getBytes();
private Telnet telnet = null;
private OutputStream output = null;
private static BufferedReader reader = null;
private boolean connected = false;
private String hostname = "qqq";
//TelnetInputStream tis = null; NOT IN USE AS OF NOW
public TelnetTest() throws IOException, TelnetException {
// create new Telnet instance
telnet = new Telnet(hostname);
// register this class as TelnetListener
telnet.addTelnetListener(this);
// establish Telnet connection
telnet.connect();
connected = true;
output = telnet.getOutputStream();
// HERE IS WHERE I NEED HELP, NOT SURE HOW TO CHECK STREAM
String str = null;
if ((str = reader.readline()).equals("User name?:")) {
telnet.getOutputStream().write(USER_BYTE);
}
// SAME CHECK WOULD HAPPEN HERE FOR "Password"
telnet.getOutputStream().write(PWORD_BYTE);
// ANOTHER SIMILAR CHECK HERE
telnet.getOutputStream().write(COMMAND_BYTE);
// sends all data entered at console to Telnet server
String input = null;
while ((input = reader.readLine()) != null) {
if (connected) {
((TelnetOutputStream) output).println(input);
} else {
break;
}
}
}
public boolean streamContainsString(Reader reader, String searchString)
throws IOException {
Scanner streamScanner = new Scanner(reader);
if (streamScanner.findWithinHorizon(searchString, 0) != null) {
return true;
} else {
return false;
}
}
// Invoked when Telnet socked is connected.
public void connected(TelnetConnectedEvent event) {
System.out.println("Connected");
}
// Invoked when Telnet socket is disconnected. Disconnect can
public void disconnected(TelnetDisconnectedEvent event) {
connected = false;
System.out.print("Disconnected. Press enter key to quit.");
}
// Invoked when Telnet server requests that the Telnet client begin performing specified TelnetOption.
public void doOption(DoOptionEvent event) {
// refuse any options requested by Telnet server
telnet.sendWontOption(event.getOption());
}
// Invoked when Telnet server offers to begin performing specified TelnetOption.
public void willOption(WillOptionEvent event) {
// refuse any options offered by Telnet server
telnet.sendDontOption(event.getOption());
}
// Invoked when data is received from Telnet server.
public void dataReceived(TelnetDataReceivedEvent event) {
// print data recevied from Telnet server to console
System.out.print(event.getData());
}
public Telnet getTelnet() {
return telnet;
}
// starts console program
public static void main(String[] args) {
try {
// create BufferedReader to read data from console
reader = new BufferedReader(new InputStreamReader(System.in));
// create new TelnetExample instance
TelnetTest example = new TelnetTest();
} catch (Exception e) {
e.printStackTrace(System.out);
}
}
}

If you are reading/writing Strings then you should always use Reader and Writer. BufferedReader allows you to do line operations. So a BufferedReader wrapped around an Reader (around a InputStreamReader) will allow you to do a readLine() call to get the line of input from the connection:
BufferedReader reader =
new BufferedReader(new InputStreamReader(telnet.getInputStream()));
To write to the connection you would use a Writer around a OutputStreamWriter:
Writer writer = new OutputStreamWriter(telnet.getOutputStream()));
I'm not sure if that works with the stream from Telnet but it works with a raw Socket. You then could do something like the following pseudo code:
while (true) {
read a line from the server
some sort of if/then/else to test for the output
write your username/password or whatever is appropriate for the connection
repeat until some logout or IOException...
}
The Apache Telnet class has a number of interesting listeners and other handlers which you could use if you wanted to but the learning curve may be more. Here's a good sample application using TelnetClient:
http://www.java2s.com/Code/Java/Network-Protocol/ExampleofuseofTelnetClient.htm