Web Science/Part1: Foundations of the web/Hypertext Transfer Protocol/A simple web server

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A simple web server

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Script

SimpleWebServer.java[edit]

/*
 * Copyright (C) 2013 Rene Pickhardt
 * Contact via http://www.rene-pickhardt.de or rene@rene-pickhardt.de
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package demo;
 
import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.Reader;
import java.net.ServerSocket;
import java.net.Socket;
 
/**
 * The purpose is to demonstrate how to build a simple Web Server on top
 * of TCP / IP. Therefore, we just make a very simple HTTP GET request. 
 */
public class SimpleWebServer {
 
	/**
	 * @param args
	 */
	public static void main(String[] args) {
		try {
			ServerSocket httpServerSocket = new ServerSocket(8080);
 
			Socket incommingHttpConnection = null;
 
			while ((incommingHttpConnection = httpServerSocket.accept()) != null){
				BufferedReader br = new BufferedReader(new InputStreamReader(incommingHttpConnection.getInputStream()));
 
				String line = br.readLine();
				// GET /test/simiple.html HTTP/1.0
 
				String path = processFirstLine(line, incommingHttpConnection);
 
				if (path != null){
					SimpleWebRequest request = new SimpleWebRequest(path);
					while ((line = br.readLine())!= null){
						if (line.equals("")){
							makeResponse(request, incommingHttpConnection);
							break;
						}
						// Example
						// Host:studywebscience.org\r\n
						request.addHeaderField(line);
					}
				}
				br.close();
				incommingHttpConnection.close();
				incommingHttpConnection = null;
			}
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
 
	}
 
	private static void makeResponse(SimpleWebRequest request,
			Socket incommingHttpConnection) {
		// /test/simple.html
		String body = fetchAsciiFile(request.getPath());
		if (body == null){
			makeErrorResponse("404 Not Found", incommingHttpConnection);
		} else {
			SimpleWebResponse resp = new SimpleWebResponse(incommingHttpConnection);
			resp.setStatusCode("200 Ok");
			resp.setBody(body);
			resp.writeToSocket();
		}
 
	}
 
	private static String fetchAsciiFile(String path) {
		try {
			StringBuilder body = new StringBuilder(100000);
			BufferedReader br = new BufferedReader(new FileReader(new File(System.getProperty("user.dir") + "/webdirectory" + path)));
			String tmp = null; 
			while ((tmp = br.readLine())!= null){
				body.append(tmp + "\n");
			}
			br.close();
			return body.toString();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return null;
	}
 
	private static String processFirstLine(String line, Socket incommingHttpConnection) {
		if (line == null)
			return null;
		String path = null;
		if (!line.startsWith("GET") && line.split("\\s").length !=3 ){
			makeErrorResponse("400 Bad Request", incommingHttpConnection);
		} else {
			String [] values = line.split("\\s");
			path = values[1];
			if (!(values[2].equals("HTTP/1.0") || values[2].equals("HTTP/1.1"))){
				makeErrorResponse("400 Bad Request", incommingHttpConnection);
			}
		}
		return path;
	}
 
	private static void makeErrorResponse(String errorCode,
			Socket incommingHttpConnection) {
		SimpleWebResponse resp = new SimpleWebResponse(incommingHttpConnection);
		resp.setStatusCode(errorCode);
		resp.writeToSocket();
	}
 
}

SimpleWebRequest.java[edit]

/*
 * Copyright (C) 2013 Rene Pickhardt
 * Contact via http://www.rene-pickhardt.de or rene@rene-pickhardt.de
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package demo;
 
import java.util.HashMap;
 
/**
 * The purpose is to demonstrate how to build a simple Web Server on top
 * of TCP / IP. Therefore, we just make a very simple HTTP GET request. 
 */
public class SimpleWebRequest {
	private HashMap<String, String> headerFields = null;
 
	public SimpleWebRequest(String path) {
		headerFields = new HashMap<String, String>();
		headerFields.put("path", path);
		// TODO Auto-generated constructor stub
	}
 
	public String getPath(){
		return headerFields.get("path");
	}
 
	public void addHeaderField(String line) {
		int index = line.indexOf(":");
		if (index < 0) return;
		String key = line.substring(0, index).trim();
		String value = line.substring(index+1, line.length());
		headerFields.put(key, value);
	}
 
}

SimpleWebResponse.java[edit]

/*
 * Copyright (C) 2013 Rene Pickhardt
 * Contact via http://www.rene-pickhardt.de or rene@rene-pickhardt.de
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package demo;
 
import java.io.IOException;
import java.io.OutputStream;
import java.net.Socket;
import java.util.Date;
 
/**
 * The purpose is to demonstrate how to build a simple Web Server on top
 * of TCP / IP. Therefore, we just make a very simple HTTP GET request. 
 */
public class SimpleWebResponse {
	private Socket connection = null;
	private String statusCode = null;
	private String body = "";
 
 
	public SimpleWebResponse(Socket incommingHttpConnection) {
		connection = incommingHttpConnection;
	}
 
	public void setStatusCode(String statusCode) {
		this.statusCode = statusCode;
 
	}
 
	public void setBody(String body){
		this.body = body;
	}
 
	public void writeToSocket() {
		try {
			OutputStream os = connection.getOutputStream();
 
			String response = "HTTP/1.0 " + statusCode + "\r\n";
 
			response += "Date:" + new Date(System.currentTimeMillis()) + "\r\n";
 
			response += "\r\n";
 
			response += body;
 
			os.write(response.getBytes());
			os.flush();
			os.close();
 
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
}

script[edit]

  • Java API for a server socket
  • Some directory in the file system
  • being able to respond to any get request
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