Web Science/Part1: Foundations of the web/Dynamic Web Content/Handling a post request in a Java Servlet

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Handling a post request in a Java Servlet

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Learning goals

  1. See how a POST request is handled in a Java Servlet
  2. get to know the Request object
  3. see how a data base query and more advanced technology can be included to a servlet
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Video

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Script

Register.java

import java.io.IOException;

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

import org.eclipse.jetty.server.Server;
import org.eclipse.jetty.webapp.WebAppContext;

public class Register extends HttpServlet {

	private Connection connect = null;
	private Statement statement = null;
	private ResultSet resultSet = null;

	public Register() {
		try {
			Class.forName("com.mysql.jdbc.Driver");
			// Setup the connection with the DB
			connect = DriverManager
					.getConnection("jdbc:mysql://localhost/mooc?"
							+ "user=mooc&password=studywebscience");

			// Statements allow to issue SQL queries to the database
			statement = connect.createStatement();
			// Result set get the result of the SQL query
		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

	protected void doGet(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		resp.getWriter().write("hello world");
	}

	protected void doPost(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		String sql = "insert into mooc.users values(default, '"
				+ req.getParameter("username") + "', '"
				+ req.getParameter("email") + "')";

		resp.setContentType("text/html");
		
		try {
			statement.execute(sql);
			resp.getWriter().write(
					"received username:<b>" + req.getParameter("username")
							+ "</b>, with email: <em>"
							+ req.getParameter("email") + "</em>");
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}

	}

	public static void main(String[] args) throws Exception {
		Server server = new Server(8080);

		WebAppContext context = new WebAppContext();
		context.setDescriptor("WEB-INF/web.xml");
		context.setResourceBase("");
		context.setContextPath("");
		context.setParentLoaderPriority(true);

		server.setHandler(context);

		server.start();
		server.join();
	}
}
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Quiz

1 How can HTTP header fields of an HTTP request be accessed in the Java code snippet which uses Jetty as an embedded servlet?

Retrieve the data from the socket using a reader class.
Retrieve the data from the socket using an input stream class.
There are methods on the request object for accesing HTTP header fields
Inside of the doGet and doPost methods exist objects which have access to the header fields.

2 What should one do when accessing request parameters or HTTP headers and processing them inside a server?

The user input retrieved from the fields should be escaped before running database queries
The video demonstrated everything that should happen. Nothing more needs to be done.

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Further reading

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Discussion