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Call a class whose name is in a string

I'm trying to call a class whose part of the name is included in a string obtained by reading console input.
static void menu() {
System.out.println("Choose a menu:");
System.out.print("\n");
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
String nome = null;
try {
nome = reader.readLine();
} catch (IOException e) {
e.printStackTrace();
}
System.out.print("\n");
System.out.println("Opening: " + nome);
System.out.print("\n");
String funzione = nome + ".funzione();";
try {
Runtime.getRuntime().exec(funzione);
} catch (IOException e) {
System.out.println(funzione);
e.printStackTrace();
}
Basically, if I write "print", I'd like to execute print.function(); which is called later in the program. The code works but it also outputs an error java.io.IOException: Cannot run program "print.function();": error=2, No such file or directory, yet print.function(); gets executed anyway.
To be clear, I am intentionally following this method rather than a switch case.
I think I'm executing the process in a wrong way, could anyone highlight me where? Many thanks.

Send a string command to a socket

I am not very familiar with telnet so I would appreciate the help from any willing.
I have smart plugs which can be switch on or off through a telnet interface.
I always use telnet via command prompt to connect to the server Digi X4 connect port (via >telnet ). If I want to switch the socket on/off, I have to now type: "12 set pow=on/off" and press enter.
I would like to implement this through java using the telnet client. I am now able to connect to the port (thanks to the answers posted on this platform), but to send the command to switch devices on/off is proving difficult for me. I still have to type "12 set pow=on/off" and press enter. I would like Java to send this command.
Below is my java code. I would appreciate your assistance. Bab
public class TelnetConnection {
static TelnetClient tc = null;
public static void main(String[] a) throws Exception
{
String[] args = {"122.1222.181.45","8085"};
System.out.println("arg value: "+args);
if(args.length < 1)
{
System.err.println("Usage: Error <remote-ip> [<remote-port>]");
System.exit(1);
}
String remoteip = args[0];
int remoteport;
if (args.length > 1)
{
remoteport = (new Integer(args[1])).intValue();
}
else
{
remoteport = 7000;
}
tc = new TelnetClient();
while (true)
{
boolean end_loop = false;
try
{
tc.connect(remoteip, remoteport);
Thread reader = new Thread (new TelnetClientExample());
tc.registerNotifHandler(new TelnetClientExample());
System.out.println("TelnetClientExample");
reader.start();
OutputStream outstr = tc.getOutputStream();
PrintWriter out = new PrintWriter(outstr);
String buff = "11 set pow=on";
//int ret_read = 0;
do
{
try
{
out.print(buff);
outstr.flush();
}
catch (IOException e)
{
System.err.println("Error");
end_loop = true;
}
}
while((true) && (end_loop == false));
try
{
tc.disconnect();
}
catch (IOException e)
{
System.err.println("Error");
}
}
catch (IOException e)
{
System.err.println("Exception while connecting:" + e.getMessage());
System.exit(1);
}
}
}
}

Try tring buff = "11 set pow=on\n"; the server may need the newline to detect end-of-command.
By the way, the loop that infinitely sends that to the server looks worrisome.

You need to send a line terminator corresponding to 'and press Enter'.
The line terminator in Telnet is defined as \r\n.

WriteUTF only works every 2nd time

I'm having a little trouble with a simple Java server, client application.
Basically the topics says it all: when I do a writeUTF on the server side it only sends every 2nd time it's being executed.
For an example:
Server:
public class Server {
/**
* #param args
*/
public static void main(String[] args) {
try {
ServerSocket server = new ServerSocket(7777);
Socket client = server.accept();
DataOutputStream out = new DataOutputStream(new BufferedOutputStream(client.getOutputStream()));
DataInputStream in = new DataInputStream(new BufferedInputStream(client.getInputStream()));
while(true) {
for(int i = 0; i < 100; i++) {
out.writeUTF("Test" + i);
out.flush();
}
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
And client:
public class Client {
/**
* #param args
*/
public static void main(String[] args) {
try {
Socket client = new Socket("localhost", 7777);
DataInputStream in = new DataInputStream(new BufferedInputStream(client.getInputStream()));
DataOutputStream out = new DataOutputStream(new BufferedOutputStream(client.getOutputStream()));
while(in.readUTF() != null) {
System.out.println(in.readUTF());
}
} catch (UnknownHostException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
And the output in the console looks like this:
Test1
Test3
Test5
Test7
Test9
Test11
What is causing this behavior?

It's because you're discarding data on your client.
When you check while(in.readUTF() != null), you're reading an entry from the stream every time to see if it's non-null. Then you discard this value, and read a new one within the loop. (As well as losing values, this has the bug that with an odd number of total values, the while condition will evaluate to true but the next call to readUTF() would return null within the loop.)
To fix this, you should read the value to a variable, and test this before using it - something like the following:
String value;
while((value = in.readUTF()) != null) {
System.out.println(value);
}
If you don't like the assignment and nullity check as a single expression, you can instead assign value = in.readUTF() initially and at the end of every loop, but personally I find this more error-prone.

This loop
while(in.readUTF() != null) {
System.out.println(in.readUTF());
}
throws away every second string it reads. You read one string while testing for end of file, discard it, then read another one and print it.

You are consuming the data in the while loop evaluation here:
while(in.readUTF() != null) {
System.out.println(in.readUTF());
}
Try this instead:
String line;
while( ((line = in.readUTF()) != null) {
System.out.println(line);
}

If you want your socket in UTF-8
you only need to add "UTF-8" in BufferedWriter and BufferedReader's contstructor
here is the sample
this.basicReader = this.Client.getInputStream();
this.basicWriter = this.Client.getOutputStream();
this.Reader= new BufferedReader(new InputStreamReader(basicReader,"UTF-8"));
this.Writer= new BufferedWriter(new OutputStreamWriter(basicWriter,"UTF-8"));
how to send data
this.Writer.write("data"+"\r\n");
this.Writer.flush();
and your main problem is your client didnt respond a msg when your client receive a msg
server to client
client to server
server to client
like this, try it.

Java io handle is invalid exception

I have a function that reads from the console using readPassword(). This function is called several times in one program iteration. However, I keep getting a java io exception once it gets to the readPassword() line. I noticed when i removed the close() statement from the finally-clause this error disappears. Why does this happen and when should I properly close the reader?
public void Func()
{
Console console = System.console();
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
if (console == null)
System.out.println("Error!");
try
{
char[] pwd = console.readPassword();
String password = new String(pwd);
System.out.println("PW: " + password);
String input = reader.readLine();
System.out.println("UserNm: " + input);
} catch (IOException e) {
System.out.println("IO EXCEPTION");
} finally {
if (reader != null)
{
try
{
reader.close();
}
catch (IOException e)
{
System.out.println("error");
}
}
}
return null;
}
Thanks in advance for the help!

There's only one console, and there's only one System.in. If you close it, then you can't read from it anymore! You don't need to close that BufferedReader, nor should you. That whole finally block can and should just go away.
On closer reading, I don't even see why you're creating the BufferedReader in the first place -- it seems to have no function. Just delete all the code that deals with it!

You don't need any reader here, just use the Console instance.
public String Func() {
Console console = System.console();
if (console == null)
throw new IllegalStateException("No console available");
try {
String username = console.readLine("Username: ");
String pwd = new String(console.readPassword("Password: "));
return pwd;
} catch (IOException e) {
e.printStackTrace();
return null;
}
}
Edited with your question edit. Just use the Console class, it can read/write, you don't need any reader/writer.

Use something like java.util.Scanner instead and as other people say don't worry about ever trying to close system.in.
So much cleaner:
Scanner in = new Scanner(System.in);
String password = in.nextLine();
String username = in.nextLine();
No tidy up/exception handling required.

You should not close your Console. Keep it open until your program does no longer need to read from it.

Java BufferedReader, how to only call if will not block?

I have 2 sockets and I am using BufferedReader around it's InputStreams. What I am trying to do is take all input from the first socket and send it to the other socket (and visa versa).
The problem is that if the first one does not send a message, it will still block on the first readLine() even though the 2nd socket has already sent some data and is ready. I would like to continue with this simple approach of using no additional threads.
Here's some code that I wrote up, as you can see I have 2 BufferedReaders (in0 and in1) , the program gets stuck at in0.readLine() (blocking).
private void network()
{
PrintWriter out0 = null, out1 = null;
BufferedReader in0 = null,in1 = null;
try{
//clients[] is an array of Socket[2]
in0 = new BufferedReader(new InputStreamReader(clients[0].getInputStream()));
out0 = new PrintWriter(clients[0].getOutputStream(), true);
in1 = new BufferedReader(new InputStreamReader(clients[1].getInputStream()));
out1 = new PrintWriter(clients[1].getOutputStream(), true);
} catch (IOException e) {
System.out.println("Accept failed: 4445");
System.exit(-1);
}
int count = 1;
while(true)
{
System.out.println("network check loop # " + count);
++count;
String nextMessage = null;
try {
if( (nextMessage = in0.readLine()) != null)
{
this.relayMessage(nextMessage,out1);
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println("Middle of network check loop");
nextMessage = null;
try {
if((nextMessage = in1.readLine()) != null)
{
this.relayMessage(nextMessage,out0);
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
How can I just skip that statement if in0 is not ready to give me some data? I have seen BufferedReader's ready() method and have attempted to use in0.ready() && readLine() but this causes an infinite loop as neither of the bufferedreaders appear to ever be 'ready'. As well, I am certain that the messages being sent over the socket end in newline characters so readLine() should process correctly!
Any ideas?

Try to use setSoTimeout to put a timeout on your read(), then you just need to catch the SocketTimeoutException if the timer has expired.

Here break and continue keywords are your friends.

The simplest approach is to use two threads. This way you don't have to write your own scheduling code to determine which thread should be running. BTW: The code to copy from one socket to another is the same in each thread, reducing duplication.
To manage your threads I would use an ExecutorService which will make shutting downt eh threads easier.