Java Servlets Frequently Asked Questions

1.   Which servlet runner does SVWH use?

We're using the JServ Servlet Runner from the Apache group. This is a top-notch standards based open source project. More information on the Apache JServ project (including documentation and frequently asked questions pertaining to JServ) can be found here:

           http://java.apache.org/

2.   How do I add a directory or jar file to my classpath? How do I add servlet aliases?

Directories and jar files can are added to your classpath as repositories in the zone.properties file (located in your personal servlet directory). The zone.properties file is well documented; making changes to this configuration file is easy to do. To add "/local/home/a0000/code/my_jar_file.jar" to your classpath, simply add the following line to your zone.properties file:

           repositories=/local/home/a0000/code/my_jar_file.jar

Servlet aliases are also added to the zone.properties file. For example, to alias "SnoopServlet" to "snoop" you would make this entry in the zone.properties file:

           servlet.snoop.com=SnoopServlet

3.   Where do I upload my servlets and how do I access them via my browser?

In your home directory there will be a subdirectory named "servlet". Any class files that you upload to that directory will be picked up by JServ and available for use.

You may add additional directories by adding them as "repositories" to your zone.properties file (see Question 2).

Once you've uploaded a new class file it will be mapped into your virtual web server as "/servlet/your_class_file". For example, if you were to upload "TestServlet.class" to your "/servlet" directory it would be accessible as follows:

           http://www.your_domain.com/servlet/TestServlet

4.   How do I use Java Server Pages?

To make use of Java Server Pages (JSP) simply name your files with a .jsp extension. JSP is Java's answer to Microsoft's Active Server Pages. JSP has some significant advantages over ASP.

5.   How do I use Java HTML pages?

To make use of Java HTML pages (JHTML) simply name your files with a .jhtml extension. Java HTML pages allow you to make use of the <servlet> tag in your HTML code.

6.   How do I use the JDBC Drivers?

This is a common question that's usually best answered with an example. When your account was set up an "examples" directory placed in your home directory. In this directory there are, among other things, examples on using JSP pages, JHTML pages, and a sample database application written with JDBC drivers. This sample program illustrates the use of JDBC; a smaller, more concise example is given below. The below example simply creates a new table in the "jdbctestdb" database (it's assumed that the "jdbctestdb" database has already been created).

Further information (including full documentation of the MM JDBC drivers that are preinstalled) can be found at the MM JDBC Driver web site.

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

public class DBTableTestCreate extends HttpServlet
{
public void doGet (HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException
{
Connection con = null;
Statement stmt = null;
ResultSet rs = null;

String login = "YourUsername";
String password = "YourPassword";
String domain = "db.your_domain.com";
String driver = "org.gjt.mm.mysql.Driver";
String database = login + "_jdbctestdb";
String url = "jdbc:mysql://" + domain + ":3306/" + database +
"?autoReconnect=true&maxReconnects=30";

String createString = "CREATE TABLE TableTest " +
"(name varchar(32), id int)";

res.setContentType("text/html");
PrintWriter out = res.getWriter();

try
{
// Load (and therefore register) the MM Driver
Class.forName(driver);

// Get a connection to the database
con = DriverManager.getConnection(url, login, password);

// Create a Statement object
stmt = con.createStatement();

rs = stmt.executeQuery(createString);

out.println("");
out.println("");
out.println("Table Created");
out.println(" ");
out.println("");
}
catch (ClassNotFoundException e)
{
out.println("Couldn't load database driver: " + e.getMessage());
}
catch (SQLException e)
{
out.println("SQLException caught: " + e.getMessage());
}
finally
{
try
{
if (con != null) con.close();
}
catch (SQLException ignored) { }
}
}
}

7.   How do I restart my servlet runner?

Typically JServ will pick up and automatically reload any changed class files. However, if you're uploading a large class file through a relatively slow link (ie. a modem) it is possible for JServ to reload the class file when it's only partially loaded. If this happens you may want to restart your personal servlet runner. You can restart your runner using the Account Controller here:

           http://www.svwh.net/support/update.shtml