To understand the concept of socket programming, I created a server and a client. The client will send a file and server should save it some location. (ie. a file upload).
Server:
package com.test.socket.server;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.ServerSocket;
import java.net.Socket;
public class WebServer {
public static void main(String[] args) throws IOException {
ServerSocket serverSocket = new ServerSocket(8081);
Socket socket = serverSocket.accept();
System.out.println("Received request");
InputStream inputStream = socket.getInputStream();
OutputStream out = new FileOutputStream("yoyo.png");
System.out.println("Reading....");
byte[] bytes = new byte[16 * 1024];
int count = 0;
while((count = inputStream.read(bytes)) > 0){
System.out.print(". ");
out.write(bytes,0,count);
System.out.println("Some bytes are written");
}
System.out.println("written....");
socket.getOutputStream().write("Written.....".getBytes());
out.close();
inputStream.close();
socket.close();
serverSocket.close();
}
}
Java client follows:
package com.test.socket.client;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.Socket;
import java.net.UnknownHostException;
public class WebClient {
public static void main(String[] args) throws UnknownHostException, IOException {
Socket socket = null;
String host = "127.0.0.1";
socket = new Socket(host, 8081);
///home/renju/Desktop/frame.png
File file = new File("/home/renju/Desktop/frame.png");
InputStream inputStream = new FileInputStream(file);
OutputStream os = socket.getOutputStream();
byte[] bytes = new byte[16 * 1024];
int count = 0;
while((count = inputStream.read(bytes)) > 0){
os.write(bytes);
}
System.out.println("Sending....");
os.close();
inputStream.close();
socket.close();
}
}
This works fine and writes the uploaded file to my projects root folder.
Now I changed the client to an HTML page.
HTML:
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
<form action="http://127.0.0.1:8081/" method="POST">
<input type="file" name="file" />
<button type="submit" name="submit">Upload</button>
</form>
</body>
</html>
This is not working in the same fashion as the Java client. For some reason, the execution does not go beyond the out.write(bytes); of server code.
Console log..
Received request
Reading....
. Some bytes are written
What can be the possible reason?
One more question...
Ultimately what I am trying to understand is the purpose of 'multipart/form-data' while uploading a file(once I got the above code working, that is what I am planning to experiment). If someone could give me a hint on that, it will be really helpful.
This works fine.
No it doesn't. It writes junk at the end of the file, and possibly in other places as well. Your copy loop should be:
while((count = inputStream.read(bytes)) > 0){
System.out.print(". ");
out.write(bytes, 0, count);
}
in both server and client.
For some reason, the execution does not go beyond the out.write(bytes); of server code.
Actually it is blocking in read(), not write(). That is because you are now getting an HTTP request, and specifically it is because of HTTP keepalive. See RFC 2616 and successors. The server code you've written will write all the HTTP headers to the target file and then block until the client browser releases the connection, which can take an arbitrary amount of time. You need to read and parse the headers, specifically the Content-length and Content-encoding headers, and process the body of the request accordingly, which means only trying to read the number of bytes given in Content-length, not read to end of stream, and if the Content-encoding is chunked, you need to write some unchunking code.
From oracle docs:
A socket is one end-point of a two-way communication link between two
programs running on the network. Socket classes are used to represent
the connection between a client program and a server program. The
java.net package provides two classes--Socket and ServerSocket--that
implement the client side of the connection and the server side of the
connection, respectively.
Simple socket client is :
Socket echoSocket = new Socket(hostName, portNumber);
PrintWriter out =
new PrintWriter(echoSocket.getOutputStream(), true);
BufferedReader in =
new BufferedReader(
new InputStreamReader(echoSocket.getInputStream()));
The Socket constructor used here requires the name of the computer and the port number to which you want to connect.
Simple socket server is:
ServerSocket serverSocket = new ServerSocket(portNumber);
Socket clientSocket = serverSocket.accept();
PrintWriter out =
new PrintWriter(clientSocket.getOutputStream(), true);
BufferedReader in = new BufferedReader(
new InputStreamReader(clientSocket.getInputStream()));
ServerSocket is a java.net class that provides a system-independent implementation of the server side. To accept connection from client ServerSocket does:
clientSocket = serverSocket.accept();
Related
I was trying to do a chat and I notice that readUTF() and writeUTF() did not work. readUTF() stays waiting when I already used writeUTF(). I made a simple test and does not work, what I am doing bad?
(I know that I could use Data Streams instead of Object Streams but in my chat I want to write objects and strings)
Server code:
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.ServerSocket;
import java.net.Socket;
public class Server {
public static void main(String[] args) throws IOException {
ServerSocket server = new ServerSocket(40001);
Socket s = server.accept();
ObjectOutputStream out = new ObjectOutputStream(s.getOutputStream());
ObjectInputStream in = new ObjectInputStream(s.getInputStream());
System.out.println(in.readUTF());
out.writeUTF("E");
}
}
Client code:
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.Socket;
public class Client {
public static void main(String[] args) throws IOException {
Socket s = new Socket("localhost", 40001);
ObjectOutputStream out = new ObjectOutputStream(s.getOutputStream());
ObjectInputStream in = new ObjectInputStream(s.getInputStream());
out.writeUTF("A");
System.out.println(in.readUTF());
}
}
I could use writeObject("A") and cast the String with readObject(), but I want to know why this way does not work.
You need to call flush() after writing using writeUTF. The reason that writeObject just seems to work is that writeObject will switch to a specific mode before it starts writing, and switch back after it is done. This switching back will automatically flush the buffered data (at least in Java 11). This is not the case for writeUTF, and an explicit call to flush() is needed.
ObjectOutputStream uses an internal buffer, so you should try out.flush() after writes if you want content to be available to read on the InputStream.
The javadoc for ObjectOutputStream includes:
callers may wish to flush the stream immediately to ensure that constructors for receiving ObjectInputStreams will not block when reading the header
Im working on a project that involves sending a string from an android phone to my laptop running a 32 bit windows VM (VMWare Fusion). After doing some searching on how to do such a thing, I get the client (phone) working, but for the server (laptop) end, it never seems to receive anything.
Im sharing bluetooth with the VM, & the device is paired to the host, yet when I send the data it connects to the host, but the VM running the "server" never seems to receive it.
I got the code for the receiver from here, but just for clarifying, heres the code im using for the receiver/server/VM:
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import javax.bluetooth.RemoteDevice;
import javax.bluetooth.UUID;
import javax.microedition.io.Connector;
import javax.microedition.io.StreamConnection;
import javax.microedition.io.StreamConnectionNotifier;
public class server {
// TODO: Update this to use the window, instead of the console
public void startServer() throws IOException {
// Create a UUID for SPP
UUID uuid = new UUID("1101", true);
//UUID uuid = new UUID("00001101-0000-1000-8000-00805F9B34FB", false);
// Create the servicve url
String connectionString = "btspp://localhost:" + uuid + ";name=SpudSPPServer";
// open server url
StreamConnectionNotifier streamConnNotifier = (StreamConnectionNotifier) Connector.open(connectionString);
// Wait for client connection
System.out.println("\nServer Started. Waiting for clients to connect…");
StreamConnection connection = streamConnNotifier.acceptAndOpen();
RemoteDevice dev = RemoteDevice.getRemoteDevice(connection);
System.out.println("Remote device address: " + dev.getBluetoothAddress());
System.out.println("Remote device name: " + dev.getFriendlyName(true));
// read string from spp client
InputStream inStream = connection.openInputStream();
BufferedReader bReader = new BufferedReader(new InputStreamReader(inStream));
String lineRead = bReader.readLine();
System.out.println(lineRead);
// send response to spp client
OutputStream outStream = connection.openOutputStream();
PrintWriter pWriter = new PrintWriter(new OutputStreamWriter(outStream));
pWriter.write("Response String from SPP Server\r\n");
pWriter.flush();
pWriter.close();
streamConnNotifier.close();
}
}
& in the main file:
public static void main(String args[]) throws IOException {
display d = new display();
server blueToothServer = new server();
d.makePanel();
if (selectFile.fileMissing()) {
d.feed.setText("File missing, creating new file");
selectFile.makeFile();
d.feed.setText("File created! Awaiting data...");
} else {
d.feed.setText("File found! Awaiting data...");
d.MACAddress.setText("MAC Address: " + LocalDevice.getLocalDevice().getBluetoothAddress().replace("-", ":").toUpperCase());
}
blueToothServer.startServer();
}
If you need the code for the client (phone), I can post that if asked
Figured it out, turns out it was on the VMs end, so I just installed windows normally as opposed to a VM, & that fixed it
I have created a simple class which sends a string to a server, both communicate using Java Sockets API. The server reads what the client have sent, and responds with another string. But the client can not read that response.
This is the client class:
import java.io.IOException;
import java.net.Socket;
public class Client {
public static void main(String[] args) throws IOException {
Socket socket = new Socket("localhost", 8181);
socket.getOutputStream().write("Hello".getBytes());
int read;
while ((read = socket.getInputStream().read()) > -1) {
System.out.print((char) read);
}
socket.close();
}
}
And this is the server class:
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
public class Server {
public static void main(String[] args) throws IOException {
ServerSocket serverSocket = new ServerSocket(8181);
while (true) {
Socket socket = serverSocket.accept();
int read;
while ((read = socket.getInputStream().read()) > -1) {
System.out.print((char) read);
}
socket.getOutputStream().write("Hi!".getBytes());
}
}
}
I imagine that the problem may be in the client execution flow, because I don`t know how canI do it wait for a server response. In other words, how to implement a client able to read the server response?
You aren't closing the sockets.
The server is attempting to read until end of stream and then send a reply. End of stream only happens when the peer closes the connection, so it won't be possible to send a reply even after you fix (1). You need to read a message, whatever that means in your application protocol.
You need to flush or close the outputstream.
I am quite a newbie to Java. Please excuse me if you find this as a very basic question.There are many answers available already in stack overflow about this and I went through almost all the possible helps i can get in Stack overflow and also in some other forums. Unfortunately none of them helped me.
I have client/server program in which the client send a string to server and server just attaches another string to the string sent by client and sends it back to the client.
Server program looks like this.
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.ServerSocket;
import java.net.Socket;
public class server {
public static void main(String[] args) {
try
{
ServerSocket server = new ServerSocket(7300);
Socket s = server.accept();
DataInputStream inp = new DataInputStream(s.getInputStream());
DataOutputStream out = new DataOutputStream(s.getOutputStream());
String str =inp.readUTF();
str = str+" buddy!";
out.writeUTF(str);
}
catch(Exception e)
{
e.printStackTrace();
}
}
}
Client looks like This.
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.net.*;
public class client {
public static void main(String[] args) {
try
{
Socket s = new Socket("192.168.1.3",7300);
DataInputStream inp = new DataInputStream(s.getInputStream());
DataOutputStream out = new DataOutputStream(s.getOutputStream());
out.writeUTF("hi");
System.out.println(inp.readUTF());
Thread.sleep(2000);
out.writeUTF("hello");
System.out.println(inp.readUTF());
}
catch(Exception e)
{
e.printStackTrace();
}
}
}
Everything works fine while client writes "hi" and when client starts sending "hello" i am getting Connection reset error. I am not getting what mistake am i doing please help me in resolving this.
The output with the error i am getting looks like this.
hi buddy!
java.net.SocketException: Connection reset by peer: socket write error
at java.net.SocketOutputStream.socketWrite0(Native Method)
at java.net.SocketOutputStream.socketWrite(Unknown Source)
at java.net.SocketOutputStream.write(Unknown Source)
at java.io.DataOutputStream.write(Unknown Source)
at java.io.DataOutputStream.writeUTF(Unknown Source)
at java.io.DataOutputStream.writeUTF(Unknown Source)
at sokry.client.main(client.java:18)
In your server example, readUTF is only called once on the DataInputStream, even though the client wrote to the DataOutputStream twice. Thus, simply adding
str = inp.readUTF();
str = str + " buddy!";
out.writeUTF(str);
to your server example, after the last out.writeUTF(str), will solve your problem.
do comment on following line of your client.java file and try.it will work
Thread.sleep(2000);
`//out.writeUTF("hello");;
//System.out.println(inp.readUTF());
because when you are sending "hi" from client to server and server gives reply then it finished it work and it stop connection but in client.java you sending another request to server but server is at rest.
you should start server until client finish it work..
hope it will wait
I'm trying to make a simple HTML server that will read a request from my browser, parse the requested file from the request, then serve the appropriate HTML back to the browser. I need to be able to handle multiple requests, so I currently have a Server class acting as a parent of another runnable class RequestHandler. Each time a connection is made on the server, a new instance of the runnable class RequestHandler is run.
package server;
import java.io.IOException;
import java.net.ServerSocket;
public class Server {
public static void main(String[] args){
try{
ServerSocket serverSocket = new ServerSocket(8000);
for(;;){
Object block = new Object();
RequestHandler handler = new RequestHandler(block, serverSocket);
handler.start();
try{
synchronized(block){
System.out.println("Server thread paused...");
block.wait();
System.out.println("Server thread creating new RequestHandler...");
}
}catch(InterruptedException e){
System.out.println("Can't be interrupted!");
e.printStackTrace();
}
}
}catch(IOException e){
System.out.println("IOException!");
e.printStackTrace();
}
}
}
package server;
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 RequestHandler extends Thread {
Object block;
ServerSocket serverSocket;
BufferedReader socketReader;
PrintWriter socketWriter;
public RequestHandler(Object block, ServerSocket serverSocket){
this.block = block;
this.serverSocket = serverSocket;
}
#Override
public void run() {
try{
System.out.println("Waiting for request...");
Socket clientSocket = serverSocket.accept();
System.out.println("Connection made.");
synchronized(block){
System.out.print("Notifying server thread...");
block.notify();
System.out.println("...done");
}
socketReader = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
socketWriter = new PrintWriter(clientSocket.getOutputStream(), true);
String input;
while((input = socketReader.readLine()) != null){
System.out.println(input);
}
}catch(IOException e){
System.out.println("IOException!");
e.printStackTrace();
}
}
}
The problem I'm running into is that I'm not sure how to combine all the lines of the request so that I can parse the requested file. If it's just constantly waiting on request input, I'll never get to a point where I can parse the entirety of the request. How can I solve this problem?
your while loop will only break once the connection between the client and the server is closed. Since the client is waiting on the same connection for a response after sending the request the connection will remain open, so your readline() will block. In your while loop you have to check after every line whether you have reached the end of the request data. For GET requests, you have to look for a blank line following HTTP headers. For POST requests, you have to parse incoming headers looking for <Content-Length: N>. THen process the remaining headers looking for the blank line (just like in the GET case). Once you find the blank like, you have to read <N> bytes. At this point you know you've finished processing request data and should break out of the read loop.
Read the HTTP spec for details.
The first line gives you the request method as well as the requested path, the following lines are the request headers, the header block ends with a blank line.
That said, you are reinventing the wheel: you could use com.sun.net.httpserver.HttpServer