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i try to write simplest possible server app in Java, displaying html form with textarea input, which after submitting gives me possibility to parse xml typed in that textarea. For now i build simple serversocket based server like that:
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
public class WebServer {
protected void start() {
ServerSocket s;
String gets = "";
System.out.println("Start on port 80");
try {
// create the main server socket
s = new ServerSocket(80);
} catch (Exception e) {
System.out.println("Error: " + e);
return;
}
System.out.println("Waiting for connection");
for (;;) {
try {
// wait for a connection
Socket remote = s.accept();
// remote is now the connected socket
System.out.println("Connection, sending data.");
BufferedReader in = new BufferedReader(new InputStreamReader(
remote.getInputStream()));
PrintWriter out = new PrintWriter(remote.getOutputStream());
String str = ".";
while (!str.equals("")) {
str = in.readLine();
if (str.contains("GET")){
gets = str;
break;
}
}
out.println("HTTP/1.0 200 OK");
out.println("Content-Type: text/html");
out.println("");
// Send the HTML page
String method = "get";
out.print("<html><form method="+method+">");
out.print("<textarea name=we></textarea></br>");
out.print("<input type=text name=a><input type=submit></form></html>");
out.println(gets);
out.flush();
remote.close();
} catch (Exception e) {
System.out.println("Error: " + e);
}
}
}
public static void main(String args[]) {
WebServer ws = new WebServer();
ws.start();
}
}
After form (textarea with xml and one additional text input) is submitted in 'gets' String-type variable I have Urlencoded values of my variables (also displayed on the screen, it looks like that:
gets = GET /?we=%3Cnetwork+ip_addr%3D%2210.0.0.0%2F8%22+save_ip%3D%22true%22%3E%0D%0A%3Csubnet+interf_used%3D%22200%22+name%3D%22lan1%22+%2F%3E%0D%0A%3Csubnet+interf_used%3D%22254%22+name%3D%22lan2%22+%2F%3E%0D%0A%3C%2Fnetwork%3E&a=fooBar HTTP/1.1
What can i do to change GET to POST method (if i simply change it in form and than put " if (str.contains("POST")){" it gives me string like
gets = POST / HTTP/1.1
with no variables. And after that, how i can use xml from my textarea field (called 'we')?
776
Here, two classes are being used: Socket and ServerSocket. The Socket class is used to communicate client and server. Through this class, we can read and write message. The ServerSocket class is used at server-side.
What does the ServerSocket method accept () return? Upon accepting a connection request from a TCP based client, the accept() method called on the server socket returns a socket that is connected to the client. Data can be sent and received using the socket returned by the accept() method.
Reading Binary Data from a Socket The simplest protocol which we can define is called TLV (Type Length Value). It means that every message written to the socket is in the form of the Type Length Value. So we define every message sent as: A 1 byte character that represents the data type, like s for String.
To post HTML form data to the server in URL-encoded format using Java, you need to make an HTTP POST request to the server and provide the HTML form data in the body of the Java POST message. You also need to specify the data type using the Content-Type: application/x-www-form-urlencoded request header.
As there is a blank line following the headers, here is my relatively simple way of getting the post payload data, after having read the header information using the readLine() method of BufferedReader.
//socket is an instance of Socket
InputStream is = socket.getInputStream();
InputStreamReader isReader = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isReader);
//code to read and print headers
String headerLine = null;
while((headerLine = br.readLine()).length() != 0){
System.out.println(headerLine);
}
//code to read the post payload data
StringBuilder payload = new StringBuilder();
while(br.ready()){
payload.append((char) br.read());
}
System.out.println("Payload data is: "+payload.toString())
A typical HTTP POST request looks like this:
POST / HTTP/1.1
Host: www.example.com
Accept: text/html,*/*;q=0.5
User-Agent: BrowserName/1.0
Referer: http://www.example.com/
Content-type: application/x-www-form-urlencoded; charset=utf-8
foo=1&bar=2
The first line contains the method (typically GET or POST, but there's more, like HEAD, PUT, DELETE), the request URI, and the protocol version. Then there are a number of request headers, which may not be so important for a simple server. If the method is one that takes a request body (POST and PUT), then after the headers there's a blank line followed by the request body. In the case of a POST from an HTML form, the body will consists of key=value pairs for all form elements, joined by &. The values will be %-encoded.
You just need to take care of properly parsing the entire request.
You should be aware that line endings in HTTP are supposed to be Windows-style (\r\n). The readline() method might interpret this as two linebreaks, so it might look like there's an empty line between each of the real lines.
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