- JDBC Architecture
- Accessing a Database
- Advanced Database Concepts
- Database Connection Pooling
- Introduction to the MySQL Database
- Summary
Introduction to the MySQL Database
Most of the samples presented in this chapter make use of the MySQL database server. MySQL (pronounced "My Ess Que Ell") was chosen because of its popularity and the fact that it is an open source product that is available free of charge on UNIX, Windows, and MacOS. The source code for MySQL is made available under the GNU General Public License (GPL). (To demonstrate functionality not provided by MySQL, Oracle was chosen because of its cross-platform availability.)
Despite the fact that MySQL is free, it is still a powerful industrial-strength database. For instance, the creators of MySQL describe running this product in a production environment comprised of more than 40 databases consisting of 10,000 tables. Of these tables, more than500 contained more than 7 million rows. In addition, on some benchmarks, MySQL's performance has exceeded the performance of many commercial databases by an order of magnitude. As you can see, MySQL is a free database capable of handling many of your toughest mission-critical database requirements.
NOTE
It should be noted that MySQL does not implement many of the functions that are commonly supported by commercial databases. For example, MySQL currently does not support database triggers, stored procedures, or transactions. Fortunately, however, the exclusion of these features does, in many areas, improve database performance by reducing processing overhead. For instance, triggers can greatly reduce a database's performance as they are executed for each row in an insert, update, or delete operation. Therefore, if you choose to deploy MySQL in your organization, you will need to consider these limitations as you design your systems.
Finding and Installing MySQL
You can locate the MySQL installation file for your platform on the accompanying CD or you can download the latest version from http://www.mysql.com/. The MySQL installation files are usually named using the following format:
mysql-VERSION-OS.extension
For example, a file containing MySQL version 3.22.32 for a Sun machine running Solaris 5 would look like mysql-3.22.32-SunOS5.tgz. And similarly, the installation file for MySQL running on Windows NT/2000/9x might look like mysql-3.23.21-win.zip.
After finding the appropriate file for your platform, install it according to the installation instructions contained on the CD or available at http://www.mysql.com/ . On UNIX, installation involves expanding a compressed TAR file and following some additional simple instructions. On Windows, MySQL is installed by simply running the executable installation file. Once MySQL is installed and running, you're ready to create a new database.
MySQL includes numerous useful utilities within its /bin directory. These utilities include programs to import and export data, create and delete databases, and execute SQL statements. For example, to view all of the current databases, run the mysqlshow executable like this:
shell> mysqlshow
+-----------------+
| Databases |
+-----------------+
| mysql |
| phonebook |
| test |
+-----------------+
To create a new database, run the mysqladmin program using its create command while passing the name of the database as a command-line parameter. For instance, a database called phonebook can be created like this:
mysqladmin create phonebook
Similarly, a database can be dropped using the drop command like this:
mysqladmin drop phonebook
Once a database has been created, tables can be built using the mysql utility. In order to build the sample tables presented in Listing 16.1, retrieve the SQL script called phonebook.sql from the accompanying CD or use a text editor to create the phonebook.sql text file from Listing 16.1. Once you have the SQL script, build the tables by directing the SQL script instructions into the phonebook database using the mysql program like this:
mysql phonebook < phonebook.sql
The mysql utility is extremely useful for viewing data within database tables as well as creating, updating, and deleting rows. To perform these tasks, enter the mysql interactive shell and activate the phonebook database like this:
shell> mysql phonebook Welcome to the MySQL monitor. Commands end with ; or \g. Your MySQL connection id is 9 to server version: 3.21.29a-gamma- debug Type 'help' for help. mysql>
Once you're at the mysql> prompt, you can perform a variety of tasks. For instance, you can examine a table within the database like this:
mysql> show columns from employee; +---------------+-------------+------+------+----------+---------+ | Field | Type | Null | Key | Default | Extra | +---------------+-------------+------+------+----------+---------+ | EMPLOYEE_ID | int(11) | | PRI | 0 | auto-inc| | DEPARTMENT_ID | int(11) | YES | | NULL | | | FIRST_NAME | varchar(20) | YES | | NULL | | | LAST_NAME | varchar(20) | YES | | NULL | | | PHONE | varchar(20) | YES | | NULL | | | EMAIL | varchar(50) | YES | | NULL | | | HIRE_DATE | date | YES | | NULL | | +---------------+-------------+------+------+----------+---------+ 7 rows in set (0.07 sec) mysql>
You can also execute SQL SELECT , UPDATE , and DELETE commands like this:
mysql> select FIRST_NAME, LAST_NAME, PHONE, EMAIL from EMPLOYEE where EMPLOYEE_ID > 5; +------------+-----------+----------+------------------+ | FIRST_NAME |LAST_NAME | PHONE | EMAIL | +------------+-----------+----------+------------------+ | John | Dehlin | 555-1116 | johnd@email.com | | John | Schuch | 555-1118 | johns@email.com | | Ray | Babcock | 555-1120 | ray@email.com | | Darin | Callaway | 555-1121 | darin@email.com | | Gordon | Augat | 555-1122 | gordon@email.com | +------------+-----------+----------+------------------+ 5 rows in set (0.00 sec) mysql> update EMPLOYEE set PHONE = 'UNLISTED'; Query OK, 10 rows affected (0.00 sec) mysql> delete from EMPLOYEE where EMPLOYEE_ID <= 5; Query OK, 5 rows affected (0.01 sec) mysql>
Of course, we have only scratched the surface of the full array of configuration and database management utilities provided by MySQL. In addition, if you prefer a graphical interface, there are many useful GUI tools available for managing MySQL databases. Visit http://www.mysql.com/ for a comprehensive list of free MySQL applications (many include source code).
Accessing MySQL from a Servlet
There are several free JDBC drivers available for MySQL. The driver used in this chapter is an open source JDBC driver called MM MySQL developed by Mark Matthews. This driver, along with its source code, is included on the accompanying CD or it can be downloaded from the following URL:
The MM MySQL driver is packaged in a JAR file. Before using the Class.forName().newInstance() method to load the driver, its JAR file must be added to the CLASSPATH so that the Java class loader can locate the driver class file. The fully qualified class name (including package information) of the MM MySQL driver is org.gjt.mm.mysql.Driver and its JDBC URL uses this format:
jdbc:mysql://SERVER[:PORT]/DATABASE_NAME
Therefore, the URL for a database called phonebook residing on the local computer will look like jdbc:mysql://localhost/phonebook. To illustrate, the following code demonstrates how to establish a database connection using the MM MySQL JDBC driver from within a servlet's init() method.
Connection dbConn = null;
/**
* Creates a persistent connection to a MySQL database.
*/
public void init() throws ServletException
{
String jdbcDriver = "org.gjt.mm.mysql.Driver";
String dbURL ="jdbc:mysql://localhost/phonebook";
try
{
Class.forName(jdbcDriver).newInstance();
dbConn = DriverManager.getConnection(dbURL);
}
catch (ClassNotFoundException e)
{
throw new UnavailableException("JDBC driver not found:" +
jdbcDriver);
}
catch (SQLException e)
{
throw new UnavailableException("Unable to connect to: " +
dbURL);
}
}