Develop Reference

How to retrieve data from a file very fast in Java

I have a situation like, I am provided with a log file that consists of Strings. What I have to do is , I need to retrieve each string from the file and pass through a Socket and when the End of the File reaches it has to go again to the beginning of the file and send again the Strings. I have written a simple code using an infinite thread that sends the strings and when the EOF comes I am closing the file and again re-opening the file using new BufferedReader object. And I am also giving a small amount of 5ms of thread sleep, but after some time my Process is entering into Pause state (Like a Dead Lock). Is there anyway to improve the speed of transfer? or else can I eliminate the Pause state.
Below is my Simple code:
public class Write extends Thread{
private static final String FileName = "Messages.txt";
private static final int port = 8080;
private final int time = 5;
ServerSocket serverSocket;
Socket writeSocket;
#Override
public void run()
{
try
{
serverSocket = new ServerSocket(port);
System.out.println("Server listening on port " + port+ " ...");
Socket writeSocket = serverSocket.accept();
System.out.println("Connected to Client : "+ writeSocket.getLocalSocketAddress());
OutputStream outStream = writeSocket.getOutputStream();
PrintWriter out = new PrintWriter(outStream, true);
BufferedReader input = new BufferedReader(new FileReader(FileName));
String str = "";
while(true)
{
str = input.readLine();
if(str==null ){
input.close();
input = new BufferedReader(new FileReader(FileName));
}
else{
System.out.println("Outgoing Message>>"+str);
out.println(str);
Thread.sleep(time);
}
}
}
catch(IOException e) {System.out.println(e); } catch (InterruptedException ex) {
Logger.getLogger(Write.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
Let me give you a simple explanation. Consider the above code is in a Server code. And when I run a client machine in the same PC, I can able to send the messages at some(high) speed but after sometime, both the client and the Server are entering into a Pause state. I feel this like a Dead Lock. The client is showing like the Server is disconnected and again Connected. When I close the Client then again Server is starting. Can anyone tell me is there a way to process the strings at a very high speed?

Re the program blocking, I would suggest:
put a System.out.print("A") before out.println() and a System.out.print("B") after. If it blocks with "A" as the last message in the output, then the problem is at the client side (they're not consuming the data, causing eventually the sender to block).
If the previous situation happens, write your own simple client which just reads data from the socket and throws it away, so you can demonstrate the problem is at the other side.
Re speed, you want to remove the sleep and System.out.println.

Why not use java nio to read all lines?
https://docs.oracle.com/javase/8/docs/api/java/nio/file/Files.html#readAllLines-java.nio.file.Path-java.nio.charset.Charset-
Or is the file too big to do this?

your code that reads the log file is just fine. no need to make it faster. see below (I commented the parts of the code that deal with the socket and the code works well at reading the log file multiple times. there is no sign of slowing down or deadlocks) :
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.logging.Level;
import java.util.logging.Logger;
public class Write extends Thread {
private static final String FileName = "/tmp/Messages.txt";
private static final int port = 8080;
private final int time = 5;
ServerSocket serverSocket;
Socket writeSocket;
public static void main(String[] args) {
Write write = new Write();
Thread thread = new Thread(new Write());
thread.start();
}
#Override
public void run() {
try {
// serverSocket = new ServerSocket(port);
// System.out.println("Server listening on port " + port + " ...");
// Socket writeSocket = serverSocket.accept();
// System.out.println("Connected to Client : " + writeSocket.getLocalSocketAddress());
//
// OutputStream outStream = writeSocket.getOutputStream();
// PrintWriter out = new PrintWriter(outStream, true);
BufferedReader input = new BufferedReader(new FileReader(FileName));
String str = "";
while (true) {
str = input.readLine();
if (str == null) {
input.close();
input = new BufferedReader(new FileReader(FileName));
} else {
System.out.println("Outgoing Message>>" + str);
//out.println(str);
Thread.sleep(time);
}
}
} catch (IOException e) {
System.out.println(e);
} catch (InterruptedException ex) {
Logger.getLogger(Write.class.getName()).log(Level.SEVERE, null, ex);
}
}
}

Simple Client Server Java Program not going into while loop

I had stumbled upon a dead block when doing my assignment. It's a simple server and client program.
The details of this program is as follows;
Create a server class EncryptServer that listens for incoming connections. If there is a connection, accept it and create a thread EncryptServerSession to handle the input and output stream.
Create a thread class EncryptServerSession that takes in the input and output stream from the server class and process it.
Create a client class EncryptClient that connects to the server class and takes output stream from EncryptServerSession through EncryptServer.
Somehow the while true loop of the EncryptClient class is not working. I cannot seem to get into the loop. Is something wrong with my code? Thanks in advance.
EncryptServer
import java.net.*;
import java.io.*;
public class EncryptServer
{
public EncryptServer() throws IOException
{
ServerSocket serverSocket = new ServerSocket(1122);
System.out.println("Server started.");
while (true)
{
Socket conSocket = serverSocket.accept();
System.out.println("Client connected from " +
conSocket.getLocalAddress().getHostName());
Thread session = new
EncryptServerSession(conSocket.getInputStream(),
conSocket.getOutputStream());
session.start();
}
}
public static void main(String[] args)
{
try
{
EncryptServer server = new EncryptServer();
}
catch (Exception e)
{
System.out.println(e);
}
}
}
EncryptServerSession
import java.net.*;
import java.io.*;
public class EncryptServerSession extends Thread
{
BufferedReader in;
Writer out;
public EncryptServerSession(InputStream inStream, OutputStream outStream)
{
Reader read = new InputStreamReader(inStream);
in = new BufferedReader(read);
out = new OutputStreamWriter(outStream);
}
public void strEncrypt()
{
try
{
String message = in.readLine();
out.write(message);
out.flush();
}
catch (Exception e)
{
}
}
public void run()
{
try
{
//System.out.println(in.readLine());
out.write("Please enter the message to be encrypted: ");
out.flush();
//strEncrypt();
}
catch (Exception e)
{
System.out.println(e);
}
}
}
EncryptClient
import java.net.*;
import java.io.*;
public class EncryptClient
{
BufferedReader input, userTerm;
Writer output;
String line;
public EncryptClient() throws IOException
{
Socket clientSocket = new Socket("localhost", 1122);
Reader read = new InputStreamReader(clientSocket.getInputStream());
input = new BufferedReader(read);
userTerm = new BufferedReader(new InputStreamReader(System.in));
output = new OutputStreamWriter(clientSocket.getOutputStream());
/////////////// Somehow I cannot get into this loop, why? //////////
while (true)
{
System.out.println("test ");
System.out.println(input.readLine());
System.out.println("Enter message to be encrypted: ");
output.write(userTerm.readLine());
output.flush();
}
/////////////// Somehow I cannot get into this loop, why? //////////
}
public static void main(String[] args)
{
try
{
EncryptClient client = new EncryptClient();
}
catch (Exception e)
{
System.out.println(e);
}
}
}

As I understand, you are trying to send a message to a server, do some logic, then send it back to the client. The above code seems to run well on my side. Here's what I've done:
run EncryptServer first. I expect this is the issue you are facing. or maybe your firewall isn't letting you listen on sockets.
in EncryptServerSession, You are reading lines but you aren't writing lines. either close the stream or write a new line after you finish.
...
out.write(message);
out.write("\r\n"); // write new line
out.flush();
...
} finally {
try {
out.close();
} catch (IOException e) {
}
}
OR
...
out.write(message);
out.write("\r\n"); // write new line
out.flush();
...

java multi client socket server echoing all clients

I was working on multi-client sockets and its working just fine, however it came to my mind on how to make the communication public by making the entered string being streamed to all clients.
e.g if there are lets say 3 clients A,B and C and client A sends "foo" to server, I want the server to stream "foo" to clients B and C as well.
The Server Module :
package multiclient;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
public class Server {
public static void main(String args[]) {
Socket s = null;
ServerSocket ss2 = null;
System.out.println("Server Listening......");
try {
ss2 = new ServerSocket(4445); // can also use static final PORT_NUM , when defined
} catch (IOException e) {
e.printStackTrace();
System.out.println("Server error");
}
while (true) {
try {
s = ss2.accept();
System.out.println("connection Established");
ServerThread st = new ServerThread(s);
st.start();
} catch (Exception e) {
e.printStackTrace();
System.out.println("Connection Error");
}
}
}
}
class ServerThread extends Thread {
String line = null;
BufferedReader is = null;
PrintWriter os = null;
Socket s = null;
public ServerThread(Socket s) {
this.s = s;
}
public void run() {
try {
is = new BufferedReader(new InputStreamReader(s.getInputStream()));
os = new PrintWriter(s.getOutputStream());
} catch (IOException e) {
System.out.println("IO error in server thread");
}
try {
line = is.readLine();
while (line.compareTo("QUIT") != 0) {
os.println(line);
os.flush();
System.out.println("Response to Client : " + line);
line = is.readLine();
}
} catch (IOException e) {
line = this.getName(); //reused String line for getting thread name
System.out.println("IO Error/ Client " + line + " terminated abruptly");
} catch (NullPointerException e) {
line = this.getName(); //reused String line for getting thread name
System.out.println("Client " + line + " Closed");
} finally {
try {
System.out.println("Connection Closing..");
if (is != null) {
is.close();
System.out.println(" Socket Input Stream Closed");
}
if (os != null) {
os.close();
System.out.println("Socket Out Closed");
}
if (s != null) {
s.close();
System.out.println("Socket Closed");
}
} catch (IOException ie) {
System.out.println("Socket Close Error");
}
}//end finally
}
}
The Client Module:
package multiclient;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.InetAddress;
import java.net.Socket;
public class Client {
public static void main(String args[]) throws IOException{
InetAddress address=InetAddress.getLocalHost();
Socket s1=null;
String line=null;
BufferedReader br=null;
BufferedReader is=null;
PrintWriter os=null;
try {
s1=new Socket(address, 4445); // You can use static final constant PORT_NUM
br= new BufferedReader(new InputStreamReader(System.in));
is=new BufferedReader(new InputStreamReader(s1.getInputStream()));
os= new PrintWriter(s1.getOutputStream());
}
catch (IOException e){
e.printStackTrace();
System.err.print("IO Exception");
}
System.out.println("Client Address : "+address);
System.out.println("Enter Data to echo Server ( Enter QUIT to end):");
String response=null;
try{
line=br.readLine();
while(line.compareTo("QUIT")!=0){
os.println(line);
os.flush();
response=is.readLine();
System.out.println("Server Response : "+response);
line=br.readLine();
}
}
catch(IOException e){
e.printStackTrace();
System.out.println("Socket read Error");
}
finally{
is.close();os.close();br.close();s1.close();
System.out.println("Connection Closed");
}
}
}

The server can keep a collection of all client sockets (until one is closed). When a client message arrives, server writes it to all client sockets.
There's a problem though, socket.write() is blocking, so if we do it in a loop, a slow client will block the rest of the clients. You can spawn a new thread to write to each individual socket, if there aren't too many clients.
In the blocking IO world, to implement a true full-duplex protocol, it is necessary for server to have two threads per client, one for read, one for write.
You may also try NIO if you are brave enough...

There are many examples. Search for chat server. One good one if you don't mind using a framework is Netty, check the SecureChat example for working code. It is a short and focused example.
Edit: the link takes you to the example code.

I suggest:
1. Keep the threads you create in an ArrayList
2. Create a method in Server called writeString and a lock
private final Lock mutex = new ReentrantLock(true);
private ArrayList<ServerThread> list = new ArrayList<ServerThread>();
public void writeString(ServerThread t,String s)
{
mutex.lock();
for(ServerThread th:list)
if(th!=null && th!=t) //different from the thread receiving the string
th.writeString(s); //send string to other threads
mutex.unlock();
}
3. in ServerThread class, implement writeString method and add a Lock
private final Lock mutex = new ReentrantLock(true);
public void writeString(String s)
{
mutex.lock();
os.println(s);
os.flush();
mutex.unlock();
}
4. Keep a reference to the main Server thread by modifying the constructor
//in ServerThread
private Server parent=null;
SeverThread(Socket s, Server parent)
{
this.parent=parent;
/*the rest of the code*/
}
//in Server
ServerThread st = new ServerThread(s,this);
st.start();
list.add(st);
When you read the string in ServerThread, call the Server writeString method in order to notify all the clients
parent.writeString(this,s); //calls the method we created at 2.

is it possible to check what the client is sending to the server using java

I am writing a client server based java program. I have two queries I was hoping someone will be able to answer.
First query, Is there a way to check what the client has sent to the server?
Second query is, is there code that will allow the server to check the file they have received from the client? I have been unable to find answers to this online
this is my server code
package servers;
import java.io.*;
import java.net.*;
public class Servers {
public static void main(String [] args)throws Exception
{
try
{
// server variable
ServerSocket server=new ServerSocket(9999);
Socket client=server.accept();
BufferedReader fromClient=new BufferedReader(new InputStreamReader(client.getInputStream()));
String temp=fromClient.readLine();
System.out.println(temp);
System.out.println("Recieved files");
server.close();
while ((temp = fromClient.readLine()) != null)
{
System.out.println(temp);
}
}
catch (Exception ex)
{
}
}
}
this is my client code
package client;
import java.io.*;
import java.net.*;
public class Client{
public static void main(String [] args)throws Exception
{
try
{
File file=new File("C:\\Users\\User\\Desktop\\College 2013\\FYP\\Attribute Data\\Alex.txt");
BufferedReader br=new BufferedReader(new FileReader(file));
String line;
while ((line = br.readLine()) != null)
{
System.out.println(line);
}
Socket socket=new Socket("Localhost", 9999);
PrintWriter toServer=new PrintWriter(socket.getOutputStream(),true);
BufferedReader fromServer=new BufferedReader(new InputStreamReader(socket.getInputStream()));
String toSend,rec="";
if(!file.exists())
{
System.out.println("File not found terminating program.");
}
br.close();
toServer.println("this is the end");
System.out.println("Finished sending file.");
System.out.println("Begining to receive Server output.");
while (!(rec = fromServer.readLine()).equals("this is the end"))
{
System.out.println(rec);
}
toServer.close();
br.close();
socket.close();
return;
}
catch (Exception e)
{
}
}
}
Any advice would be greatly appreciated

Use a program such as tcpdump or wireshark to watch the network traffic going back and forth. I usually use tcpdump from a command line; however, wireshark has a GUI and maybe some people like that better.
I think it is better to use a separate program to watch the traffic. That way you don't have to complicate your program with extra stuff, and also the external program can be applied to anything that generates network traffic.

You could also setup an intercepting proxy such as OWASP Hatkit Proxy Project

tcptrace works quite well, is very small, for Windows only
http://www.pocketsoap.com/tcptrace/

Not able to run multithreaded server program in Java

Here is the server code
package echoserver;
import java.net.*;
import java.io.*;
public class EchoServer {
public static void main(String[] args) {
try {
//establish server socket
ServerSocket s = new ServerSocket(1981);
//Thread client connectionsincoming
while (true) {
//wait for incoming connection
Socket incoming = s.accept();
Runnable r = new ThreadedEchoHandler(incoming);
Thread t = new Thread(r);
t.start();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
package echoserver;
import java.net.*;
import java.util.*;
import java.io.*;
class ThreadedEchoHandler implements Runnable {
public ThreadedEchoHandler(Socket i) {
//initializing socket
incoming = i;
}
public void run() {
try {
try {
//recieve input stream from socket
InputStream inStream = incoming.getInputStream();
//recieve output stream from socket
OutputStream outStream = incoming.getOutputStream();
//Create a scanner from input stream
Scanner scan = new Scanner(inStream);
//Create printer writer from output stream and enabled auto flushing
PrintWriter out = new PrintWriter(outStream, true);
//prompt users on how to exit program soon as a long in into the server
out.println("Enter BYE to exit");
boolean done = false;
//while done is not true and scanner has next line loop
while (!done && scan.hasNextLine()) {
//reading text that came in from the socket
String line = scan.nextLine();
//On the server print the ip address of where the text is coming from and the text they typed
System.out.println("Recieved from " + incoming.getInetAddress().getHostAddress() + ": " + line);
//Echo back the text the client typed to the client
out.println("Echo: " + line);
//if they type BYE in caps terminate there connection and I also trimmed whitespaces
if (line.trim().equals("BYE")) {
done = true;
}
}
} //finally close the socket connection
finally {
incoming.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
private Socket incoming;
}
and here is the code for client
package client;
import java.net.*;
import java.io.*;
public class Client {
public static void main(String[] args) throws IOException {
PrintWriter out = null;
try {
Socket s = new Socket(InetAddress.getLocalHost(), 1981);
System.out.println("Connected to server on port 1981");
out = new PrintWriter(s.getOutputStream());
out.println("Hello");
s.close();
} catch (Exception ex) {
System.err.println(ex.getMessage());
}
}
}
Socktes are getting created successfully but when control goes to t.start() method call it is not calling run() method of ThreadedEchoHandler class.
Why is this happening? any idea?

The client writes "Hello" to the PrintWriter. So far, so good.
You may expect that the PrintWriter sends this text directly to the socket, but it doesn't. The documentation from the PrintWriter(OutputStream) constructor says that it creates a PrintWriter without automatic line flushing. This means that you have to call out.flush() whenever you want something to be actually sent.
Until you call out.flush() the text only exists in some internal buffer, and the server will not be able to see it.

My guess would be that the acept statement is blocking forever because no client is connecting to the server. You could wrap accept() in prints to prove or disprove.