Shaokang's Blog

A simple JSP Java emulator was built to demonstrate the solution code behavior of the DSC 30 final project, where I served as a TA. The entire program was deployed to azure, containing code for handling different threads to run the solution code in the cloud instantly and render the running result on https://myplayer.azurewebsites.net

The Servlet part of managing, rendering, and connecting applications and front-end:

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package website;

import java.io.BufferedReader;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
 * Servlet implementation class hello
 */
public class hello extends HttpServlet {
	private static final long serialVersionUID = 1L;

	private static final HashMap<String, Process> runner = new HashMap<String, Process>();
	private static final HashMap<String, Long> runtime = new HashMap<String, Long>();

	/**
	 * @see HttpServlet#HttpServlet()
	 */
	public hello() {
		super();
		// TODO Auto-generated constructor stub
	}

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
	 *      response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		// TODO Auto-generated method stub
		HttpSession session = request.getSession();
		try {
			if (runner.containsKey(session.getId())) {
				// continue
				String code = request.getParameter("code");
				if (code.isEmpty()) {
					response.setContentType("application/json");
					PrintWriter out = response.getWriter();
					out.print("");
					out.flush();
				} else if (code.trim().compareTo("13") == 0) {
					if (runner.containsKey(session.getId())) {
						runner.get(session.getId()).destroy();
					}
					runner.remove(session.getId());
					runtime.remove(session.getId());
					response.setContentType("application/json");
					PrintWriter out = response.getWriter();
					out.print("Exit, please close browser.");
					out.flush();
				} else {
					Process p = runner.get(session.getId());
					OutputStream os = p.getOutputStream();
					InputStream in = p.getInputStream();
					os.write((code + System.lineSeparator()).getBytes());
					os.flush();
					BufferedReader dis = new BufferedReader(new InputStreamReader(in));
					String disr = "";
					while (true) {
						String newLine = dis.readLine();
						if (newLine.trim().equalsIgnoreCase("end")) {
							break;
						}
						disr += newLine + "\n";
					}

					response.setContentType("application/json");
					PrintWriter out = response.getWriter();
					out.print(disr);
					out.flush();

					runtime.put(session.getId(), session.getLastAccessedTime());
				}
			} else {
				String javaHome = System.getProperty("java.home");
				String javaBin = javaHome + File.separator + "bin" + File.separator + "java";
				File f = new File(MyPlayer.class.getProtectionDomain().getCodeSource().getLocation().getPath());
				String className = MyPlayer.class.getName();
				List<String> command = new LinkedList<String>();
				command.add(javaBin);
				command.add("-cp");
				command.add(f.getAbsolutePath());
				command.add(className);
				ProcessBuilder builder = new ProcessBuilder(command);

				Process p = builder.start();
				OutputStream os = p.getOutputStream();
				InputStream in = p.getInputStream();
				BufferedReader dis = new BufferedReader(new InputStreamReader(in));
				String disr = "";
				while (true) {
					String newLine = dis.readLine();
					if (newLine.trim().equalsIgnoreCase("end")) {
						break;
					}
					disr += newLine + "\n";
				}

				response.setContentType("application/json");
				PrintWriter out = response.getWriter();
				out.print(disr);
				out.flush();

				runner.put(session.getId(), p);
				runtime.put(session.getId(), session.getLastAccessedTime());
			}
		} catch (Exception e) {
			if (runner.containsKey(session.getId())) {
				runner.get(session.getId()).destroy();
			}
			runner.remove(session.getId());
			runtime.remove(session.getId());
			response.setContentType("application/json");
			PrintWriter out = response.getWriter();
			e.printStackTrace(out);
			out.flush();
		}

		// remove all long running job
		for (String a : runtime.keySet()) {
			if ((session.getLastAccessedTime() - runtime.get(a)) >= 180000) {// 3 minutes
				if (runner.containsKey(a)) {
					runner.get(a).destroy();
				}
				runner.remove(a);
				runtime.remove(a);
			}
		}
	}

	public void destroy() {
		for (String a : runner.keySet()) {
			runner.get(a).destroy();
			runner.remove(a);
			runtime.remove(a);
		}
	}

}
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