sending request to server using socket in java

Question

I'm using socket to establish a streaming connection with server. By creating a socket, I tried to send a request to the server using the socket. but the request isn't received by server no matter which method I use. these are the methods I used to send request.

PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
out.println(query);

or the other one is

 out = new ObjectOutputStream(connection.getOutputStream());
 out.writeObject(msg);
 out.flush();

the request I'm trying to send is something like this:

String query = String.format("cmd=%s&version=%s", "handshake", "1.0");

I know that sending this query is much easier by using Httpconnection, but this is the way that it has to be done. so please help me with this. this is the httpconnection commands

 String charset = "UTF-8";
 String query = String.format("cmd=%s&version=%s", "handshake", "1.0");
 String charset = "UTF-8";
 URL url = new URL("serveraddress:8080");           
 URLConnection conn = url.openConnection();         
 conn.setDoOutput(true);            
 conn.connect();            
 OutputStream output = conn.getOutputStream();              
 output.write(command.getBytes(charset));                                       

 InputStreamReader content = new InputStreamReader(conn.getInputStream());                              
 String result ="";
 int c = content.read();
 while (c != -1) {
    result = result + ((char) c);  
        c = content.read();
} 
 Log.v(logTag, "Received: [" + result + "]");

and this is what I did in socket which didn't work

 URL url = new URL("serveraddress:8080");               
 String server_name = url.getHost();
 int port = url.getPort();
 Socket socket = new Socket(server_name, port);                         

 String query = "post /swarm HTTP/1.1\nHost: serveraddress\n" +
 "content-length: 27\nkeep-alive: 300\nconnection: keep-alive\n\n" +
 "cmd=handshake&version=1.0\n"; 

 PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
 out.println(query);

according to the server log the socket connection opened and closed without getting any request

Can you telnet to the port on which the server is listening? — lobster1234
– lobster1234, Commented Jan 26, 2012 at 7:22
I got a proper reply by using httpconnection, do you think using socket is different? I mean if httpconnection works so the port is ok. right? — Daniel
– Daniel, Commented Jan 26, 2012 at 7:24
Yes, then the port should be okay. Are you seeing any exceptions whatsoever when you use the socket? — lobster1234
– lobster1234, Commented Jan 26, 2012 at 7:37
no, I'm not. I saw the log file on server. The socket opened and then closed without getting any request. — Daniel
– Daniel, Commented Jan 26, 2012 at 7:39
@Daniel: Nevertheless, if your server requires the HTTP protocol, then you have to send the request in the proper format. It depends on your server requirements. — home
– home, Commented Jan 26, 2012 at 8:08

Jiddo · Accepted Answer · 2012-01-26 10:02:55Z

5

The three methods you mention (PrintWriter, ObjectOutputStream and HTTPConnection) will all result in something being sent to the server, but what is actually sent will differ greatly between the various methods.

First of all, the Java ObjectOutputStream class will encode the objects that you write to it along with information about the classes that these objects are instances of, especially class names, signatures etc. This is practically only appropriate when you are communicating with another Java application that is using an ObjectInputStream on the other end to read it. It will especially not adhere to the HTTP protocol and as such you would most likely not be able to use it at all with anything that you can use an HTTPConnection to.

Using a HttpURLConnection will actually construct and send complete (and most importantly, valid) HTTP requests to the server you are trying to connect to. For example, if you were to execute the following code:

URL url = new URL("http://localhost/test?cmd=handshake&version=1.0");
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("GET");
connection.connect();

Then the result will be that your application connects to localhost:80 and writes something like the following: (This is a simplified request. There will be additional headers and information in the actual request.)

GET /test?cmd=handshake&version=1.0 HTTP/1.1
Host: localhost

Finally, if you are using a PrintWriter then that will actually send pure text to the server. However, if the server is a HTTP server, which is likely since you say it responds to the HTTP connection, then it is not enough just to send the command part of the request. You will have to send the rest as well, including the GET, the HTTP version, maybe some headers, the trailing empty lines and the CRLF line endings. This can all be done using a PrintWriter.

It could be a good idea to install a network packet analyzer such as Wireshark and use it to actually see what is sent to the server when you perform your connection using a httpconnection and then trying to mimic that by manually constructing the request.

I would also recommend reading up on some more details regarding the HTTP protocol. A good starting point can be the Wikipedia article.

Edit based on new information in the OP:

There are some small inconsistencies in the updated code, some of which I can assume is copy-paste mistakes, others that I would like to point out just in case.

The solution based on a URLConnection does not specify the "/swarm" resource anywhere. Adding that will not change whether a request is actually sent or not, or even if its valid or not, but it could affect whether you can find the request in the logs or not.

The query string does overall look reasonable with the exception that POST is written using lowercase letters. At first I didn't think that this would make any difference, but when trying "get" vs. "GET" against www.google.com over Telnet, it DOES seem to make a difference. If the web server doesn't recognize the request as a request then it won't be able to process it and thus it might not show up in the logs as you expect.

I would recommend that you actually read the server response and print it to System.out so that you see if the server is reporting any particular error.

edited Jan 26, 2012 at 10:02

answered Jan 26, 2012 at 9:02

Jiddo

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8 Comments

Daniel Over a year ago

first of all thanks for your full and comprehensive explanation. this is the actual request that I'm sending to the server:

Daniel Over a year ago

String request = "post /swarm HTTP/1.1\nHost: serveraddress\ncontent-length: 27\n keep-alive: 300\nconnection: keep-alive\n\n cmd=handshake&version=1.0\n

Daniel Over a year ago

I mentioned all the thing that should be mentioned in a HTTP request, however, having network packet analyzer is a good idea. I'm going to try that too.

Jiddo Over a year ago

In that case, may I suggest that you post the full code that you use to create and send the request for both the PrintWriter and the httpconnection solutions? The OP only shows query being the actual "cmd=handshake&version=1.0" part.

Daniel Over a year ago

I changed the main question and added the httpconnection commands and socket commands

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