AddBlogEntry: Error

Listing 3: AddBlogEntry.java, which adds a new entry to our Weblog.

/* A servlet to add a new entry to our Weblog ("blog").

   The Weblog is stored in a PostgreSQL database table.

 */

import java.io.*;
import java.text.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.sql.*;

public class AddBlogEntry extends HttpServlet 
{

    // Keep the connection common to the entire instance
    private Connection con;
				
    // Our "init" method sets up a database connection
    public void init(ServletConfig config) throws ServletException
	{
	    // Some private variables for logging into the database
	    String loginJdbc = "org.postgresql.Driver";
	    String loginUser = "reuven";
	    String loginPasswd = "";
	    String loginUrl = "jdbc:postgresql://localhost/atf";

	    // Load the PostgreSQL driver
	    try 
	    {
		Class.forName(loginJdbc);
		con = 
		    DriverManager.getConnection(loginUrl, 
						loginUser, loginPasswd);
	    }
	    catch (ClassNotFoundException e)
	    {
		throw new
		    UnavailableException("Cannot load the PostgreSQL driver: "
					 + e);
	    }
	    catch (SQLException e)
	    {
		throw new
		    UnavailableException("Error connecting to PostgreSQL: "
					 + e);
	    }
	}

    // Our "doGet" method returns an error message indicating
    // that only "POST" is acceptable.

    public void doGet(HttpServletRequest request, HttpServletResponse response)
        throws IOException, ServletException
	{
	    // Set the MIME content type for the response
	    response.setContentType("text/html");

	    // Get the output stream to STDOUT
	    PrintWriter out = response.getWriter();

	    // Tell the user that GET isn't going to work with this servlet.
	    out.println("<HTML>\n" +
			"<Head><Title>AddBlogEntry: Error</Title></Head>\n" +
			"<Body>\n" +
			"<P>Sorry, but this servlet can only be invoked" +
			"with the POST method.</P>\n" +
			"</Body></HTML>\n");
	}

    // This is the real workhorse for our servlet, when someone submits
    // information

    public void doPost(HttpServletRequest request, 
		       HttpServletResponse response)
        throws IOException, ServletException
	       
	{
	    // Set the MIME content type for the response
	    response.setContentType("text/html");

	    // Get the output stream to STDOUT
	    PrintWriter out = response.getWriter();

	    // Initialize the message that we will send to the end user
	    String message = "";

	    // Get the headline, and make sure that it contains something
	    String entry_headline = request.getParameter("entry_headline");
	    if ((entry_headline == null) || (entry_headline == ""))
	    {
		message = message +
		    "<P>You must provide a headline for the blog entry.</P>";
	    }

	    // Get the text, and make sure that it contains something
	    String entry_text = request.getParameter("entry_text");
	    if ((entry_text == null) || (entry_text == ""))
	    {
		message = message +
		    "<P>You must provide text for the blog entry.</P>";
	    }
	
	    // If we have not produced any messages so far, we can
	    // go ahead with the insertion
	    if (message == "")
	    {
		try
		{
		    // Create our SQL statement
		    PreparedStatement statement = 
			con.prepareStatement(
			    "INSERT INTO BlogEntries " +
			    "  (entry_date, entry_headline, entry_text) " +
			    "  VALUES " +
			    "  (NOW(), ?, ?)"
			    );

			// Associate a variable with the placeholder
			statement.setString(1, entry_headline);
			statement.setString(2, entry_text);
		
			// Perform the INSERT
			int updateCount = statement.executeUpdate();
			
			// If we did not insert a row, indicate as such
			if (updateCount != 1)
			{
			    // Send output to the user's browser
			    out.println("<HTML>" +
					"<Head><Title>" +
					"AddBlogEntry: Error" +
					"</Title></Head>\n<Body>" +
					"<P>Sorry, but we could not " +
					"insert the entry." +
					"</Body></HTML>");
			    return;
			}
		}
		// Catch SQL exceptions
		catch(SQLException e)
		{
		    out.println("<HTML>" +
				"<Head><Title>" +
				"AddBlogEntry: Error" +
				"</Title></Head>\n<Body>");
		    

		    out.println("<P>SQL error in doPost: " + 
				e.getMessage() + "</P>");

		    while ((e = e.getNextException()) != null)
		    {
			out.println("<P>SQL error: " + 
				    e.getMessage() + "</P>");
		    }

		    out.println("</Body></HTML>");
		    
		    return;
		}

		// Catch all other exceptions
		catch(Exception e)
		{
		    out.println("<HTML>" +
				"<Head><Title>" +
				"AddBlogEntry: Error" +
				"</Title></Head>\n<Body>");

		    out.println("<P>Exception in doPost: " + 
				e.getMessage() + "</P>");

		    out.println("</Body></HTML>");
		    
		    return;
		}
	    }

	    // Send output to the user's browser
	    out.println("<HTML>" +
			"<Head><Title>" +
			"AddBlogEntry: Success!" +
			"</Title></Head>\n<Body>" +
			"<P>Your new entry was added." +
			"</Body></HTML>");
	}
}