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Why did parseFrom() function hang using protobuf in java socket?

I just want to create echo server/client using protobuf and java.
I tested with protobuf-java-2.4.1 and jdk1.7.
I wrote echo server code like below
// create server socket and accept for client connection.
// ...
link = servSock.accept();
Person person = Person.parseFrom(link.getInputStream()); // blocking position
person.writeTo(link.getOutputStream());
I think it is not necessary to note Person.proto.
The client code is only send Person object using socket input stream and receive echo Person object.
// socket connect code was omitted.
Person person = Person.newBuilder().setId(1).setName("zotiger").build();
person.writeTo(echoSocket.getOutputStream());
person = Person.parseFrom(echoSocket.getInputStream());
But server was blocked in parseFrom function when the server and client both run.
I found if i use writeDelimitedTo() and parseDelimitedFrom(), then that is ok. I don't understand why the writeTo() and parseFrom() function does not working.
Why did the server blocking in there?
Is it necessary to send some end signal from client side?

The reason you have to use writeDelimitedTo()/parseDelimitedFrom() is that otherwise protocol buffers may have no idea how much data it needs to read from the socket. That presents a problem (I say may because you could of course create a message with only fixed length fields that wouldn't require this ... but protocol buffers has to deal with both cases)
The writeDelimitedTo() method writes the length of the message to the OutputStream then the message itself. Its counterpart parseDelimitedFrom() reads the length, then the message.
You can use writeTo() and pasrseFrom() with streams but only if you want to write/read a single message and are closing the stream after writing. The reader will then get an EOF to indicate the end of the message (also the case when reading from a file that contains only a single message).

Don't write your own Client/Server, ie. RPC solution. There is one here......https://code.google.com/p/protobuf-rpc-pro/ which has some nice features already for java.

How to send a variable of type File[] through sockets in JAVA

I have implemented a Java Client Server Application.
The server is having a list of files stored in the folder as:
File[] list=folder.listFiles();
I want to send this variable list through socket to the client.
How to do this in JAVA
Thanx in advance

Well, basically you can't. You should think of a socket as transmitting a stream of bytes. A File object contains local-machine state, like the file pointer. If you want to do something similar, you should store something like path names for each File's underlying file and then create File objects on the other side.

Send each file in the File[] my looping over them and following the below simple steps:
- Open ServerSocket on server side.
- Create Socket on client side. Connect to server with bind.
- Using getOutputStream method on Socket get the output stream.
- Write your file to the output stream. // most important part
(Use FileInputStream, BufferedInputStream)
- Close the socket.

How to transfer data from one jsp to another jsp with sockets

I have 3 .jsp's. The first one asks the user for their username. Once the form is submitted it is taken to a 2nd jsp where a unique passcode is created for the user. How would I go about taking this passcode and passing it to a 3rd jsp using a socket?

You can use java.net.URL and java.net.URLConnection to fire and handle HTTP requests programmatically. They make use of sockets under the covers and this way you don't need to fiddle with low level details about the HTTP protocol. You can pass parameters as query string in the URL.
String url = "http://localhost:8080/context/3rd.jsp?passcode=" + URLEncoder.encode(passcode, "UTF-8");
InputStream input = new URL(url).openStream();
// ... (read it, it contains the response)
This way the passcode request parameter is available in the 3rd JSP by ${param.passcode} or request.getParameter("passcode") the usual way.
Better is however to just include that 3rd JSP in your 2nd JSP.
request.setAttribute("passcode", passcode);
request.getRequestDispatcher("3rd.jsp").include(request, response);
This way the passcode is available as request attribute in the 3rd JSP by ${passcode} or request.getAttribute("passcode") the usual way.
See also:
Using java.net.URLConnection to fire and handle HTTP requests
Unrelated to the concrete question, this is however a terribly nasty hack and the purpose of this is beyond me. There's somewhere a serious design flaw in your application. Most likely those JSPs are tight coupled with business logic which actually belongs in normal and reuseable Java classes like servlets and/or EJBs and/or JAX-WS/RS which you just import and call in your Java class the usual Java way. JSPs are meant to generate and send HTML, not to act as business services, let alone web services. See also How to avoid Java code in JSP files?

So, you want the username to be submitted from the first JSP to the second, by submitting a form to the second, right?
But, for interaction between the second and third, you want to avoid using the communication mechanisms behind the the JSP files and use your own, right?
Well, how you might implement doing this depends on where you're sending your communication from and to. For instance, are they on the same machine, or on different machines?
Generally speaking, you'll need a client-server type of relationship to be set up here. I imagine that you would want your third JSP to act as the server.
What the third JSP will do is will sit and wait for a client to try to communicate with it. But, before you can do that, you'll first need to bind a port to your application. Ports are allocated by the Operating System and are given to requesting processes.
When trying to implement this in Java, you might want to try something like the following:
int port_number = 1080;
ServerSocket server = new ServerSocket(port_number);
In the above example, the ServerSocket is already bound to the specified port 1080. It doesn't have to be 1080 - 1080 is just an example.
Next, you will want to listen and wait for a request to come in. You can implement this step in the following:
Socket request = null;
while((request = server.accept()) == null)
{}
This will cause the server socket to keep looping until it finally receives a request. When the request comes in, it will create a new Socket object to handle that request. So, you could come back to your loop later on and continue to wait and accept requests, while a child thread handles communication using your newly created request Socket.
But, for your project, I would guess that you don't need to communicate with more than one client at a time, so it's okay if we just simply stop listening once we receive a request, I suppose.
So, now onto the client application. Here, it's a little bit different from what we had with the server. First off, instead of listening in on the port and waiting for are request, the client's socket will actively try to connect to a remote host on their port. So, if there is no server listening in on that port, then the connection will fail.
So, two things will need to be know, those are:
What's the IP Address of the server?
What port is the server listening in on?
There are short-cuts to getting the connection using the Java Socket class, but I assume that you're going to test this out on the same machine, right? If so, then you will need two separate ports for both your client and server. That's because the OS won't allow two separate processes to share the same port. Once a process binds to the port, no other process is allowed to access it until that port releases it back to the OS.
So, to make the two separate JSP's communicate on the same physical machine, you'll need both a local port for your client, and you'll need the server's port number that it's listening in on.
So, let's try the following for the client application:
int local_port = 1079;
int remote_port = 1080;
InetSocketAddress localhost = new InetSocketAddress(local_port);
Socket client = new Socket(); //The client socket is not yet bound to any ports.
client.bind(localhost); //The client socket has just requested the specified port number from the OS and should be bound to it.
String remoteHostsName = "[put something here]";
InetSocketAddress remotehost = new InetSocketAddress(InetAddress.getByName(remoteHostsName), remote_port); //Performs a DSN lookup of the specified remote host and returns an IP address with the allocated port number
client.connect(remotehost); //Connection to the remote server is being made.
That should help you along your way.
A final note should be made here. You can't actually run these two applications using the same JVM. You'll need two separate processes for client and server applications to run.

Writing to servlet stream

I'm not sure if what I'm trying to do is possible, it might not. Here is my problem:
I'm trying to use a Servlet to pass information from a client to a server via HTTP. This communication is very frequent (I'm passing UI information, so every single mouse event), so I want to have as little overhead as possible to avoid latency issues, which is why I would like to not do a GET call for each transmission. HTTP is a requirement. I'm using an older Tomcat version (Servlet API 2.4). I guess this is somewhat of a web sockets use case, but I don't have any web sockets support available.
What I tried was to open a URL connection on the client side, and to open the input stream (otherwise the doGet() of the servlet never gets called). I'm passing an argument for initialization purposes to the client.
URLConnection uiConnection = url.openConnection();
uiConnection.setRequestProperty("Authorization", "Basic " + encode("xyz" + ":"
+ "xyz"));
uiConnection.setReadTimeout(0);
uiConnection.setDoOutput(true);
uiConnection.setAllowUserInteraction(true);
DataInputStream is = new DataInputStream(
uiConnection.getInputStream());
When I later try to retrieve an ouput stream from this connection, I'm getting a ProtocolException (cannot write output after reading input).
out = new BufferedWriter(new OutputStreamWriter(
uiConnection.getOutputStream()));
out.write(uiUpdate);
On the servlet end I did something like this:
DataInputStream is = new DataInputStream(
request.getInputStream());
Am I completely on the wrong track or is something like this possible without using a new connection for each transmission?
Thanks,
Mark

I think the key question for this, is do you also have http traffic going to this IP? If so, there may not be anything you can do using just java. If not, then create a servlet to listen in on port 80, and parse the incoming data directly.
http://download.oracle.com/javase/tutorial/networking/sockets/clientServer.html

using sockets to fetch a webpage with java

I'd like to fetch a webpage, just fetching the data (not parsing or rendering anything), just catch the data returned after a http request.
I'm trying to do this using the high-level Class Socket of the JavaRuntime Library.
I wonder if this is possible since I'm not at ease figuring out the beneath layer used for this two-point communication or I don't know if the trouble is coming from my own system.
.
Here's what my code is doing:
1) setting the socket.
this.socket = new Socket( "www.example.com", 80 );
2) setting the appropriate streams used for this communication.
this.out = new PrintWriter( socket.getOutputStream(), true);
this.in = new BufferedReader( new InputStreamReader( socket.getInputStream() ) );
3) requesting the page (and this is where I'm not sure it's alright to do like this).
String query = "";
query += "GET / HTTP/1.1\r\n";
query += "Host: www.example.com\r\n";
...
query += "\r\n";
this.out.print(query);
4) reading the result (nothing in my case).
System.out.print( this.in.readLine() );
5) closing socket and streams.

If you're on a *nix system, look into CURL, which allows you to retrieve information off the internet using the command line. More lightweight than a Java socket connection.
If you want to use Java, and are just retrieving information from a webpage, check out the Java URL library (java.net.URL). Some sample Java code:
URL ur = new URL("www.google.com");
URLConnection conn = ur.openConnection();
InputStream is = conn.getInputStream();
String foo = new Scanner(is).useDelimiter("\\A").next();
System.out.println(foo);
That'll grab the specified URL, grab the data (html in this case) and spit it out to the console. Might have to tweak the delimiter abit, but this will work with most network endpoints sending data.

Your code looks pretty close. Your GET request is probably malformed in some way. Try this: open up a telnet client and connect to a web server. Paste in the GET request as you believe it should work. See if that returns anything. If it doesn't it means there is a problem with the GET request. The easiest thing to do that point would be write a program that listens on a socket (more or less the inverse of what you're doing) and point a web browser to localhost:[correct port] and see what the web browser sends you. Use that as your template for the GET request.
Alternatively you could try and piece it together from the HTTP specification.

I had to add the full URL to the GET parameter. To make it work. Although I see you can specify HOST also if you want.
Socket socket = new Socket("youtube.com",80);
PrintWriter out = new PrintWriter(new BufferedWriter(new
OutputStreamWriter(socket.getOutputStream())));
out.println("GET http://www.youtube.com/yts/img/favicon_48-vflVjB_Qk.png
HTTP/1.0");
out.println();
out.flush();

Yes, it is possible. You just need to figure out the protocol. You are close.
I would create a simple server socket that prints out what it gets in. You can then use your browser to connect to the socket using a url like: http://localhost:8080. Then use your client socket to mimic the HTTP protocol from the browser.

Not sure why you're going lower down than URLConnection - its designed to do what you want to do: http://download.oracle.com/javase/tutorial/networking/urls/readingWriting.html.
The Java Tutorial on Sockets even says: "URLs and URLConnections provide a relatively high-level mechanism for accessing resources on the Internet. Sometimes your programs require lower-level network communication, for example, when you want to write a client-server application." Since you're not going lower than HTTP, I'm not sure what the point is of using a Socket.