http://www.developer.com/java/data/article.php/3417381/Using-JDBC-with-MySQL-Getting-Started.htm#Preface
Preface
Purpose
The purpose of this lesson is to get you beyond the initial hurdles involved in:
- Downloading and installing a MySQL database server.
- Preparing that database for use with JDBC.
- Writing and testing your first JDBC programs to administer the database and to manipulate the data stored in the MySQL database.
What is JDBC?
JDBC technology is an API (included in both J2SE and J2EE) that provides cross-DBMS connectivity to a wide range of SQL databases and access to other tabular data sources, such as spreadsheets or flat files.
What is MySQL?
The MySQL database server is probably the world's most popular open source database software, with more than five million active installations as of September 2004.
The database server software from MySQL is available under a "dual licensing" model. Under this model, users may choose to use MySQL products under the free software/open source GNU General Public License (commonly known as the "GPL") or under a commercial license.
A powerful combination
Simply stated, JDBC makes it possible to write platform independent Java programs that can be used to manipulate the data in a wide range of SQL databases without the requirement to modify and/or recompile the Java programs when moving from platform to platform or from DBMS to DBMS.
MySQL is available for a wide variety of platforms.
Since both JDBC and MySQL are freely available for many purposes, the combination of JDBC and MySQL is a powerful combination that should be of interest for a wide variety of applications.
Viewing tip
You may find it useful to open another copy of this lesson in a separate browser window. That will make it easier for you to scroll back and forth among the different listings and figures while you are reading about them.
Supplementary material
I recommend that you also study the other lessons in my extensive collection of online Java tutorials. You will find those lessons published at Gamelan.com. However, as of the date of this writing, Gamelan doesn't maintain a consolidated index of my Java tutorial lessons, and sometimes they are difficult to locate there. You will find a consolidated index at www.DickBaldwin.com.
Preview
Download, install, and prepare the database server
It is often possible to use the same Java program to manipulate the data in a wide variety of SQL databases without a requirement to modify and/or recompile the Java program.
However, the installation and preparation procedures for different SQL databases vary widely. A large part of the battle in using JDBC with a particular database is getting the database installed and properly prepared for use with JDBC.
In this lesson, I will show you how to download, install, and prepare a MySQL database as a localhostserver on a Windows platform for use with JDBC. Then I will show you how to write three simple JDBC programs to administer the database server and to manipulate data stored on the database server after it is installed.
(I will assume that you already have Java SDK v1.4.2 or later, which includes JDBC, installed on your computer.)
URLs and version numbers for downloading
I will provide specific URLs and version numbers for downloading MySQL software and documentation as of September 2004. The version numbers will certainly change over time as new versions of the software are released. Hopefully, the folks at MySQL will preserve the integrity of the URLs.
At least one URL, http://www.mysql.com/ should remain constant over time. If the other links to MySQL in this lesson become broken with time, you should revert to the main MySQL URL given above and begin your search for the software and documentation from that point.
Saving time
If you are a newcomer to the installation of database server software and the preparation of that software for use with JDBC, the information that I will provide in this lesson should save you several days of effort in pouring through documentation trying to figure out how to download, install, and tie everything together.
Even if you are experienced in these matters, this information should save you several hours of effort.
Installation and Preparation of MySQL
Getting things up and running
As a minimum, getting up and running with MySQL and JDBC involves at least the following steps:
- Download and install the appropriate release of the MySQL database server software (several different releases are available).
- Download and install the MySQL Connector/J -- for connecting to a MySQL database server from Java.
- Download and install the documentation for the MySQL database server.
- Download and install the documentation for the Connector, which is a separate documentation package from the database server documentation.
- Write and test one or more JDBC programs that will act as a database administrator, creating one or more users and possibly one or more databases on the database server. (I will show you three different ways to accomplish this.)
- Write and test a JDBC program that will log in as a user and manipulate data stored in one of those databases.
Additional MySQL software
Beyond the minimum, there are a variety of additional software packages, (such as GUI administrator packages) that can be downloaded from MySQL and installed on your computer.
Since the main thrust of this lesson has to do with JDBC rather than database administration, I won't get into that. Rather, I will show you how to use a command-line monitor program that is included with the MySQL database software to perform the minimal database administrative tasks required to satisfy the objectives of this lesson.
Documentation
I will begin with a discussion of the available documentation for both the MySQL database server and the MySQL Connector/J.
MySQL database server documentation
The MySQL Reference Manual can be downloaded from http://dev.mysql.com/doc/. In addition, there is an online searchable version of the Reference Manual available athttp://dev.mysql.com/doc/mysql/en/Reference.html.
The downloadable version is available in several different formats, including:
You would probably do well to have both of these formats locally available on your computer if you have sufficient disk space.
The one-page-per-chapter formatted manual
The first format in the above list consists of a large number of HTML files. There is one HTML file for the table of contents plus about thirty-three additional files containing the text of the reference manual.
This format has a major advantage over the second format in terms of speed. It is relatively fast to click on a hyperlink in the table of contents and to see that material appear in the browser window.
There are a couple of downsides to this format, however. One downside is that this format is not very useful for searching the entire manual for keywords, (using your browser) because it is broken down into a large number of separate HTML files.
A second downside is that even though MySQL 4.0 is the recommended release in September of 2004, this manual contains information up through version 5.0.1-alpha. Sometimes information about the newer versions tends to obscure information about version 4.0.
Installing the one-page-per-chapter formatted manual
All that you need to do to install the database server documentation in this format is to download the zip file and extract the various HTML files into a folder on your disk. Then open the file namedmanual_toc.html in your browser to view the manual.
For convenience, I created a desktop icon that links to the table of contents file.
The all-on-one-page formatted manual
This format is very useful for searching (using your browser) because all of the text is in a single HTML file.
(There are actually two HTML files. One file contains a hyperlinked table of contents. The second file contains the text of the entire manual.)
The primary downside to this format is speed, or lack thereof. The HTML file containing the text of the manual is about four megabytes in size. On my machine, navigating this manual in a browser is a very slow process.
The downloadable version in this format also contains information up through version 5.0.1-alpha, resulting in the same disadvantage mentioned earlier.
Included in the software distribution
When you download and install the currently recommended version of MySQL, (which is version 4.0.21), the Docs folder in the installation tree structure will contain a copy of the manual in the all-on-one-page format that purports to be for version 4.0.21. Thus, you don't need to download this format separately. You will get it when you download the software.
(Even though this version purports to be for version 4.0.21, it also contains a lot of information about later versions. It may be exactly the same as the version that can be downloaded separately except that the title page is different.)
Installation of the all-on-one-page formatted manual
As mentioned above, you don't need to do anything special to install this format of the manual. It will be installed automatically when you install the MySQL 4.0.21 version of the database.
(Presumably, later versions of the software will also contain a copy of the current manual in this format.)
Once you have installed the database, the Docs folder of the installation tree will contain the files named manual_toc.html and manual.html. The first file contains a hyperlinked table of contents, and the second file contains the entire text of the manual.
Once again, for convenience, I created a desktop icon linked to the table of contents file to make it convenient to open in my browser.
Using both formats
Because I have plenty of space on my disk, I have both formats installed on my computer with an icon on the desktop for each. I occasionally open the version that contains the entire manual in a single HTML file when I need to search the entire document for something. Most of the time, however, I open and use the multi-file version due to its increased speed.
MySQL Connector/J documentation
I did not find a separate downloadable version of the connector documentation at the MySQL site. However, I did find an online version at http://dev.mysql.com/doc/connector/j/en/index.html. I was able to save the connector documentation locally by selecting the Save Page As... item on the File menu of my Netscape 7.2 browser.
(I was unable to save the page locally using Internet Explorer version 6 for some reason. However, I also discovered later that essentially the same documentation is contained in the downloadable zip file for the connector software in a file named mysql-connector-java-3.0.15-ga/docs/index.html.)
Saving the page in Netscape 7.2 resulted in a local file named index.html and an associated folder named index_files. The file contains the text of the connector documentation. The folder contains style sheets and other related material.
Installation of the connector documentation consisted simply of saving this material locally and creating a desktop icon linked to the file named index.html.
Downloading the MySQL Database Server
The download page
The main download page for both the database server and the connector as of September 2004 ishttp://dev.mysql.com/downloads/. Hopefully, this URL will also remain intact as MySQL releases later versions of the software.
Several different versions of the database server are available for downloading as of September 2004, including:
- MySQL 4.0 -- Generally Available (GA) release (recommended)
- MySQL 4.1 -- Gamma release (use this for new development)
- MySQL 5.0 -- Alpha release (use this for previewing and testing new features)
- MySQL 5.0.1 -- Snapshot release (use this for previewing and testing new features)
- Older releases -- older releases (only recommended for special needs)
- Snapshots -- source code snapshots of the development trees
This list can be expected to change over time as new versions of the database server are released. Thus, the links in the above list will become obsolete. When that happens, you should revert back to the download page at http://dev.mysql.com/downloads/ and download the version that best suits your needs at that time.
The different versions of the database server
As of September 2004, the database server documentation has this to say about these different versions:
- MySQL 5.0 is the newest development release series and is under very active development for new features. Alpha releases have been issued to allow more widespread testing.
- MySQL 4.1 is in gamma status, soon moving to production status.
- MySQL 4.0 is the current stable (production-quality) release series. New releases are issued for bugfixes. No new features are added that could diminish the code stability.
- MySQL 3.23 is the old stable (production-quality) release series. This series is retired, so new releases are issued only to fix critical bugs.
I elected MySQL 4.0
I elected to download MySQL 4.0 since it is the stable production quality version as of September 2004. This resulted in the downloading of a distribution file named mysql-4.0.21-win.zip.
(The distribution file name is likely to be different for future versions of the MySQL database server.)
Installing MySQL Database Server
Installation instructions
Installation instructions for the database server are provided in the database server documentation, Section 2, entitled Installing MySQL.
Since I was installing on Windows XP and had no desire to deal with source code, I quickly skipped down to Section 2.2.1.2 entitled Installing a Windows Binary Distribution.
In my case, installation was easy
Because I did not have an earlier version of MySQL installed and I was logged onto Windows as an administrator, all that I needed to do was to execute the following instructions from the database server documentation to install the MySQL database server on my computer.
- Unzip the distribution file to a temporary directory.
- Run the setup.exe program to begin the installation process. If you want to install MySQL into a location other than the default directory (`C:/mysql'), use the Browse button to specify your preferred directory. If you do not install MySQL into the default location, you will need to specify the location whenever you start the server. The easiest way to do this is to use an option file, as described in Section 2.2.1.3 Preparing the Windows MySQL Environment.
Because I didn't want to deal with option files, I elected to allow the software to be installed in the default directory, C:/mysql.
Testing the installation
After completing the installation, I performed some of the procedures shown in the database server documentation, Section 2.4.1 entitled Windows Post-Installation Procedures. Although I didn't get exactly the same results as those shown in the documentation, my results were close enough to convince me that the MySQL database server was correctly installed on my computer.
(The reason that I didn't get exactly the same results was that I didn't log in with administrator privileges.)
Not installed as a Windows service
Section 2.2.1.7 of the database server documentation entitled Starting MySQL as a Windows Servicecontains the following:
"On the NT family (Windows NT, 2000, or XP), the recommended way to run MySQL is to install it as a Windows service. Then Windows starts and stops the MySQL server automatically when Windows starts and stops."
I have no desire for the MySQL database server to start running every time I start Windows running. I already waste enough time waiting for Windows XP to become ready for use on my laptop each time I start it.
Therefore, I did not install the database server as a service. I will explain how I manually start and stopthe database server whenever I need to use it later in this lesson.
Downloading MySQL Connector/J
What is MySQL Connector/J?
For those who don't know, let me begin by explaining the purpose of MySQL Connector/J.
The JDBC API is designed to make it possible for you to write a single Java program and to use it to manipulate the data in a variety of different SQL database servers without a requirement to modify and/or recompile the program. In order to do this, it is necessary for you to:
- Inform the Java program as to the URL of the database server. You can accomplish this with input data when you start the program.
- Provide the Java program with a programming interface to the specific database server that you intend to use. Assuming that the programming interface has been installed on your computer, you can also accomplish this with input data when you run the program.
The programming interface
The programming interface deals with the interface peculiarities of the different database servers.
Sun refers to the process of providing this information to the program as registering the database server with the Java program. You will see how this is done in the sample programs later in this lesson.
The connector download page
The download page for MySQL Connector/J is http://dev.mysql.com/downloads/index.html. As of September 2004, the following versions are available for downloading from this page:
- MySQL Connector/J 3.1 -- development release
- MySQL Connector/J 3.0 -- production release
- Older releases -- older releases (only recommended for special needs)
- Snapshots -- source code snapshots of the development trees
As with the MySQL database server software, these individual links are likely to become obsolete as new versions of the software are released. Hopefully the link tohttp://dev.mysql.com/downloads/index.html will remain intact.
The MySQL Connector/J 3.0 distribution file
Because I was very interested in stability, I elected to download and install MySQL Connector/J 3.0, identified above as the production release. This resulted in the download of a file named mysql-connector-java-3.0.15-ga.zip.
This zip file encapsulates 194 individual files in different folders including source code files, class files, pdf files, xml files, jar files, license files, files with no extensions, a manifest file, HTML files, and other file types not listed here.
The zip file also contains several java programs in a folder named testsuite that can be used to test your installation. You may find them useful for that purpose. In addition, these programs illustrate a variety of database operations using JDBC, so you may find them useful as example programs as well.
Fortunately, as I will explain below, all but one of these files can be ignored insofar as installation of the connector software is concerned.
Installing MySQL Connector/J
General installation instructions
The following statement appears in the connector documentation Section 2.2.1. entitled Setting the CLASSPATH (For Standalone Use).
"Once you have un-archived the distribution archive, you can install the driver in one of two ways: Either copy the "com" and "org" subdirectories and all of their contents to anywhere you like, and put the directory holding the "com" and "org" subdirectories in your classpath, or put mysql-connector-java-[version]-bin.jar in your classpath, either by adding the FULL path to it to your CLASSPATH environment variable, or by copying the .jar file to $JAVA_HOME/jre/lib/ext."
My installation
Actually, the above quotation describes three options instead of just two. To make a long story short, I elected the third option. I extracted the jar file named mysql-connector-java-3.0.15-ga-bin.jar from the zip file and copied it into the folder named c:/j2sdk1.4.2/jre/lib/ext, which is the installation directory tree for the currently installed version of Java on my computer.
The advantage of doing it this way was that I didn't have to modify the classpath environment variable. The disadvantage is that the next time I upgrade to a new version of Java, I must remember to save the MySQL connector jar file and copy it into the directory tree for my new Java installation.
Your installation
If you prefer the first option, the connector documentation contains a wealth of information to help you perform the necessary steps to modify the classpath, etc.
Testing the installation
I didn't use any of the test programs mentioned above in the folder named testsuite. Rather, I tested my installation using JDBC programs that I had developed earlier using a different SQL database server.
You can use the test programs mentioned earlier in the testsuite folder to test your installation. Also, I will provide and explain three sample JDBC programs later in this lesson that you can use to test your installation. Before you can test the installation, however, you must start the MySQL database server running.
Starting the database server
At this point, all of the software necessary to use the database server in a JDBC program should be installed on your computer ready for use. The next step is to confirm that you can start the database server running.
Selecting a Windows server
I found it necessary to pull together several pieces of information from the database server documentation to determine the best way to start the server from a command line. For example, the following table is found in the database server documentation, Section 2.2.1.4 entitled Selecting a Windows Server.
| Binary | Description |
| mysqld | Compiled with full debugging and automatic memory allocation checking, symbolic links, and InnoDB and BDB tables. |
| mysqld-opt | Optimized binary. From version 4.0 on, InnoDB is enabled. Before 4.0, this server includes no transactional table support. |
| mysqld-nt | Optimized binary for Windows NT, 2000, and XP with support for named pipes. |
| mysqld-max | Optimized binary with support for symbolic links, and InnoDB and BDB tables. |
| mysqld-max-nt | Like mysqld-max, but compiled with support for named pipes. |
Explaining the different types of servers
The following explanation follows the table:
"We have found that the server with the most generic name (mysqld) is the one that many users are likely to choose by default. However, that is also the server that results in the highest memory and CPU use due to the inclusion of full debugging support. The server namedmysqld-opt is a better general-use server choice to make instead if you don't need debugging support and don't want the maximal feature set offered by the -max servers or named pipe support offered by the -nt servers."
Changes in MySQL 4.1.2
This is followed by another explanation indicating that beginning with MySQL 4.1.2, the server names were changed eliminating the server name mysqld-opt and replacing the debug version (mysqld) withmysqld-debug. Therefore, if you are installing MySQL 4.1.2 or a later version, you should use the syntax mysqld instead of mysqld-opt to start the server running from an optimized binary file.
Starting MySQL 4.0.21
Since I am running MySQL 4.0.21 and need to make certain that what I am doing is compatible with a large number of students having different operating systems, I concluded that I should start the server running by using the syntax mysqld-opt.
Section 2.2.1.5 of the database server documentation entitled Starting the Server for the First Timeindicates that the following command should be used at the command prompt to start the server running:
C:/mysql/bin/mysqld --console
As I understand it, the purpose of --console is to cause error messages to be displayed on the standard error device (typically the screen) rather than to be entered into an error log file. This is what I want to happen.
Combining the two pieces of information given above, I concluded that I should start the MySQL database server by entering the following command at a command prompt:
C:/mysql/bin/mysqld-opt --console
Encapsulated in a batch file
Therefore, I created a batch file named MySqlStart.bat and linked that file to an icon on the desktop for convenience. The batch file contains the two commands shown in Listing 1 and repeated later in Listing 30 near the end of the lesson.
C:/mysql/bin/mysqld-opt --console pause |
The startup screen output
Figure 1 shows the screen output following the execution of the batch file named MySqlStart.bat.
(Note that it was necessary for me to manually enter a line break ahead of the word port to cause the screen output to fit in this narrow publication format.)
C:/mysql>C:/mysql/bin/mysqld-opt --console 040918 13:59:47 InnoDB: Started C:/mysql/bin/mysqld-opt: ready for connections. Version: '4.0.21' socket: '' port: 3306 Source distribution Figure 1 MySQL database server startup sequence |
The process window shown in Figure 1 remains open and active until the server is stopped. It should be possible to connect to the server using JDBC during this period.
Stopping the database server
It is probably a good idea to shut down the server before shutting down the computer. Section 2.2.1.6 of the database server documentation entitled Starting MySQL from the Windows Command Linestates that you can stop the MySQL server by executing the following command:
C:/mysql/bin/mysqladmin -u root shutdown
Therefore, I created a batch file named MySqlStop.bat and linked that file to an icon on my desktop to make it convenient to stop the server. The batch file contains the two commands shown in Listing 2 and repeated in Listing 31 near the end of the lesson.
C:/mysql/bin/mysqladmin -u root shutdown pause |
The screen output at server shutdown
Figure 2 shows the screen output in the server process window when the file named MySqlStop.bat is executed.
040918 14:00:02 C:/mysql/bin/mysqld-opt: Normal shutdown 040918 14:00:03 InnoDB: Starting shutdown... 040918 14:00:05 InnoDB: Shutdown completed 040918 14:00:05 C:/mysql/bin/mysqld-opt: Shutdown Complete C:/mysql>pause Press any key to continue . . . Figure 2 Screen output when MySQL server is
stopped.
|
(As before, it was necessary for me to manually enter line breaks in Figure 2 to cause the screen output to fit in this narrow publication format.)
Once the server is shut down, attempts to connect to the server from JDBC will fail.
Creating a New Database using the Monitor Program
Now that you know how to start the MySQL database server, it's time to learn how to:
- Create a database that can be manipulated using JDBC in a Java program.
- Create a new user having the necessary privileges to manipulate the database using JDBC in a Java program.
Three different approaches
I'm going to show you three different ways to accomplish this:
- Using a command-line program named mysql coupled with manual data entry at runtime. (I will refer to this as the monitor program for reasons that will become self-evident later.)
- Using the monitor program coupled with data input derived from a text file.
- Using JDBC in a Java program.
I will illustrate the first approach in this and the later section entitled Creating a New User using the Monitor Program .
I will illustrate the second approach in the section entitled Administering the Database Server using Text Files.
I will illustrate the third approach in the section entitled Discussion and Sample Code, which shows how to use JDBC to manage and manipulate the database server.
The monitor program and manual data entry
The monitor program is named mysql.exe. It is located in c:/mysql/bin. This program makes it possible to log onto the database server and to enter commands at the command line to:
- Create databases
- Add new users
- Modify databases
- Perform ad-hoc queries, etc.
(Unless you really enjoy typing, the monitor program is not a lot of fun to use.)
To really learn MySQL ...
In order to really learn how to use MySQL, you will need to study the MySQL database server documentation in detail and probably some good SQL books as well.
The purpose of this lesson is to teach you just enough to get you started. When you finish this lesson, you should be able to successfully write and execute simple JDBC programs that will manipulate database tables on the MySQL database server.
The default administrative user
As I understand it, when the MySQL database server is first installed, there is a default user namedroot with full administrative privileges and no password. At this point, the server is totally wide open and insecure.
(The server documentation provides various suggestions as to what you should do to add security to the server.)
The user named root has the ability to create new databases as well as to create new users and to register those users on the databases.
Existing databases at MySQL installation
Also, as I understand it, there are two existing databases on the server when it is first installed. There is a database named test, which is wide open with no password requirements. Any user can access this database.
There is also a database named mysql, which is apparently used to keep track of things such as databases, users, etc. I believe that this database is accessible only by users having administrative privileges.
Adding a new database using the monitor program
The first step in adding a new database using the monitor program is to log onto the database server as the administrative user named root with access to the database named mysql. Until a password is assigned to the root user, login can be accomplished by entering the following command at the command prompt:
c:/mysql/bin/mysql --user=root mysql
(In case it isn't clear on your display, the word user is preceded by two minus sign characters.)
The screen output
Assuming that the MySQL database server is running, the screen output produced by entering this command is shown in Figure 3.
(Note that in Figure 3, and several of the figures that follow, it was necessary for me to manually enter line breaks in the screen output to force the material to fit in this narrow publication format.)
C:/jnk>c:/mysql/bin/mysql --user=root mysql Welcome to the MySQL monitor. Commands end with ; or /g. Your MySQL connection id is 26 to server version: 4.0.21 Type 'help;' or '/h' for help. Type '/c' to clear the buffer. mysql> Figure 3 Monitor output for administrator login. |
The monitor program
Note that this program refers to itself as the MySQL monitor. That explains why I refer to it as the monitor or the monitor program.
The purpose of this program is to make it possible for you to enter SQL database commands from the keyboard. Note in particular the prompt shown in boldface at the end of Figure 3, which reads:
mysql>
This is not a command-line prompt, which typically looks something like:
C:/jnk>
Rather, this is a program-generated prompt where the monitor program is requesting input from the user.
SQL command terminators
As indicated in Figure 3, SQL commands end with either a semicolon character or /g (note the difference in typeface for the character g in this text relative to that shown in Figure 3).
SQL commands are often quite long. You can enter successive portions of SQL commands at successive program prompts.
(Later, we will see that the monitor program uses a different syntax for continuation prompts.)
It is not until you enter a semicolon character or a /g that the program responds to and attempts to execute the entire SQL command.
Terminating the monitor program
You can terminate the monitor program by entering a /q at the program prompt.
(Note that this is a q as in quit and is not a g as in good.)
Creating a new database named JunkDB
Figure 4 shows the screen output for the use of the monitor program by the user named root to create a new database named JunkDB and then to terminate the monitor program.
C:/jnk>c:/mysql/bin/mysql --user=root mysql Welcome to the MySQL monitor. Commands end with ; or /g. Your MySQL connection id is 27 to server version: 4.0.21 Type 'help;' or '/h' for help. Type '/c' to clear the buffer. mysql> CREATE DATABASE JunkDB; Query OK, 1 row affected (0.13 sec) mysql> /q Bye C:/jnk> Figure 4 Creating database named JunkDB |
The new material in Figure 4 is shown in boldface in the bottom half of the figure. The material in the top half of Figure 4 is a repeat of the material shown in Figure 3.
Using a batch file and a text file
Shortly, I will show you how to create a new database using a Windows batch file and an associated text file. Later on, I will show you how to create a new database using a Java JDBC program.
Creating a New User with the Monitor Program
Figure 5 shows the screen output for the use of the monitor program by the user named root to add a new user named auser.
The new material is shown in boldface in the lower half of the figure.
C:/jnk>c:/mysql/bin/mysql --user=root mysql Welcome to the MySQL monitor. Commands end with ; or /g. Your MySQL connection id is 30 to server version: 4.0.21 Type 'help;' or '/h' for help. Type '/c' to clear the buffer. mysql> GRANT SELECT,INSERT,UPDATE, -> DELETE,CREATE,DROP -> ON JunkDB.* -> TO 'auser'@'localhost' -> IDENTIFIED BY 'drowssap'; Query OK, 0 rows affected (0.01 sec) mysql> /q Bye C:/jnk> Figure 5 Adding new user named auser. |
A longer SQL command
This SQL command is much longer than the command used to create the new database. This command requires several continuation lines to complete to prevent it from exceeding the screen width.
(Note the difference in the syntax of new program prompts and continuation program prompts. The prompts that look like an arrow are the continuation prompts.)
I won't try to explain the SQL command is detail. I will simply refer you to the MySQL database documentation and a good SQL book for that purpose. However, the SQL command is relatively self explanatory.
The meaning of the SQL command
This SQL command grants a list of six different privileges on the database named JunkDB to a user named auser who will be accessing the database from localhost.
(Granting access to the same user from a different machine on the network would require a different syntax.)
The user named auser will be allowed to access the database named JunkDB using the passworddrowssap, (which is password spelled backwards to make it easy for me to remember).
Administering the Database Server using Text Files
As mentioned earlier, unless you really enjoy typing, using the monitor program in manual data entry mode is not a fun way to work with the database. For example, if you make a typing error, you must go back and retype the entire command from the beginning.
Fortunately, there is a better approach. That approach is to provide the commands to the monitor program using a text file as input. Then if you make an error, you can simply edit the text file and rerun the process.
How does it work?
To make a long story short, you start the monitor program by redirecting the input so that the input is derived from a text file instead of from the keyboard. This process is described in the database server documentation, Section 3.5 entitled Using mysql in Batch Mode.
Creating a new database
There are probably several ways to set this process up. I elected to use a combination of a batch file and a text file. The batch file starts the monitor program, logging in as root, and redirects input to the associated text file.
For example, the files used to create a new database named JunkDB are shown in Listing 32 and Listing 33 near the end of the lesson.
Making a new user
The files used to make a new user named auser are shown in Listing 34 and Listing 35.
Compare the contents of these two files with the manual data entry shown earlier in Figure 5. The new user is granted six different privileges on the database named JunkDB from localhost with a password of drowssap.
The files used to remove the user named auser are shown in Listing 36 and Listing 37. The procedure for revoking a user's privileges and removing the user is explained near the end of Section 14.5.1.1 entitled DROP USER Syntax in the database server documentation.
Deleting the database named JunkDB
The files used to delete the database named JunkDB are shown in Listing 38 and Listing 39. The procedure for deleting a database is explained in the database server documentation, Section 14.2.8 entitled DROP DATABASE Syntax.
Discussion and Sample Code for JDBC Programs
With all of the above as preparation, it is now time to learn how to write JDBC programs to administer and manipulate the data on the MySQL database server.
Three separate programs
I will explain three programs. The first program, named Jdbc11 shows how to:
- Log onto the server as the administrator named root.
- Create a new database named JunkDB.
- Register a new user named auser on the database named JunkDB with six different privileges and a password of drowssap.
The second program named Jdbc12 shows how to:
- Log onto the server as the administrator named root.
- Revoke the privileges of and remove the user named auser.
- Delete the database named JunkDB.
The third program named Jdbc10 shows how to log onto the server as the user named auser and to manipulate the database named JunkDB in a variety of ways.
I will break each of these programs down into fragments and discuss the fragments. Complete listings of all the programs are shown in Listings 40, 41, and 42 near the end of the lesson.
Jdbc11 - Create a database and make a new user
The purpose of the program named Jdbc11 is to log onto the master database named mysql as the default administrator named root whose password is blank in order to perform the following updates on the MySQL database server:
- Create a new database named JunkDB.
- Create a new user named auser with a password of drowssap with six different privileges on the database named JunkDB.
The output, or lack thereof
These two operations produce no visible output when successful. However, they produce error messages in the output when unsuccessful.
(Note, however, that print statements in the program produce several lines of output that are independent of the operations being performed on the database server.)
Server must be running
The MySQL server must be running on localhost before this program is started. Instructions for starting and stopping the database server were provided earlier (see Listing 1, Figure 1, Listing 2, and Figure 2).
The program was tested using Java SDK 1.4.2 under WinXP, MySQL version 4.0.21-win, and JDBC connector version mysql-connector-java-3.0.15-ga.
There are five critical steps in using JDBC to manipulate a database:
- Load and register the JDBC driver classes (programming interface) for the database server that you intend to use.
- Get a Connection object that represents a connection to the database server (analogous to logging onto the server).
- Get one or more Statement objects for use in manipulating the database.
- Use the Statement objects to manipulate the database.
- Close the connection to the database.
I will highlight these five steps in the discussion of the sample program that follows.
Beginning of class definition for Jdbc11
The first program fragment for the program named Jdbc11 is shown in Listing 3. The entire program is shown in Listing 40 near the end of the lesson.
public class Jdbc11 {
public static void main(String args[]){
System.out.println(
"Copyright 2004, R.G.Baldwin");
try {
Statement stmt;
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The code in Listing 3 is straightforward, showing the beginning of the class, the beginning of the mainmethod, and a print statement.
Listing 3 also declares a local variable of type Statement. I will have more to say about the Statementinterface later.
Register the JDBC driver for MySQL
Listing 4 shows the statement that implements the first critical step listed earlier (load and register the JDBC driver classes). This statement registers the MySQL driver classes with the Java program, making it possible for this program to manipulate data on the MySQL server.
Class.forName("com.mysql.jdbc.Driver");
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Reference to the driver class
The following statement appears in the MySQL Connector documentation, Section 2.2.1. entitledSetting the CLASSPATH (For Standalone Use).
"If you are going to use the driver with the JDBC DriverManager, you would use "com.mysql.jdbc.Driver" as the class that implements java.sql.Driver."
This information is also provided in the connector documentation in Section 2.2.2. entitled Driver Class Name and JDBC URL Format.
The Driver interface
Note the reference to the Driver interface in the above quotation. Here is some of what Sun has to say about the Driver interface:
"The interface that every driver class must implement.
The Java SQL framework allows for multiple database drivers.
Each driver should supply a class that implements the Driver interface.
The DriverManager will try to load as many drivers as it can find and then for any given connection request, it will ask each driver in turn to try to connect to the target URL. ...
When a Driver class is loaded, it should create an instance of itself and register it with theDriverManager. This means that a user can load and register a driver by calling
Class.forName("foo.bah.Driver")"
The name of the driver class
In order to use a JDBC program with a specific database server, you must obtain the name of this critical driver class from the database vendor (or from some third party that supports the database server). You must then cause your program to load the class.
This is the class that connects the other classes in the connector package to the Java program. Without it, the Java program would be unable to communicate successfully with the database server.
Loading the driver class
The statement in Listing 4 causes this class to be loaded as described in the Sun documentation quoted above.
(If you are unfamiliar with the use of the forName method of the class named Class, see The Essence of OOP using Java: Static Members for a brief introduction to the class named Class. Then open your Google search engine, set the number of results to 100, and search for all of the keywords java forname richard baldwin. This should point you to several previous lessons that I have published that discuss this topic. If you don't find what you need there, click on the link on the bottom of the last Google page that reads repeat the search with the omitted results included to see even more lessons.)
Specification of Driver class as a String
There are several alternative ways to register the Driver class, only one of which is shown in Listing 4. The statement in Listing 4 makes it possible to specify the Driver class as a String. The primary advantage of this approach is that this string can be obtained by the program in a variety of ways at runtime.
Although the string was hard coded into this simple program, that is not a requirement. For a more general program intended to be used with two or more database servers, this string would most likely be provided as some form of user input.
The URL of the database server
MySQL and other similar database engines behave as servers on a network. They are identified by a URL much as other types of servers (such as HTTP servers and FTP servers) are identified. The next fragment defines the URL for the MySQL database server that I used in this sample program.
The code in Listing 5 defines the URL of the master database named mysql on the MySQL database server residing on localhost and servicing the default port number 3306.
(I could have omitted the default port number from the URL, but I decided to include it to remind me to mention it. Note that the "//" characters shown to the right of "mysql:" form part of the URL. They are not comment indicators.)
String url =
"jdbc:mysql://localhost:3306/mysql";
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The URL format is provided in the connector documentation in Section 2.2.2. entitled Driver Class Name and JDBC URL Format. The URL format contains several optional elements. This URL will be referenced in the statement in Listing 6 for the purpose of getting a connection to the database.
Get a connection to the database
The code in Listing 6 implements the second critical step listed earlier (get a connection object).
Listing 6 gets a connection to the database at the specified URL (mysql on localhost port 3306) for a user named root with a blank password. As you are already aware, this user is the default administrator having full privileges to do anything, including creating new databases and registering new users on those databases.
Connection con =
DriverManager.getConnection(
url,"root", "");
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In effect, Listing 6 logs the JDBC program onto the MySQL database server in a manner that is analogous to the first line in Figures 3, 4, and 5 as well as the statements in the batch files shown in Listings 32, 34, 36, and 38.
The getConnection method
The getConnection method is a static method of the DriverManager class. When getConnection is invoked, the DriverManager will attempt to locate a suitable driver from among those loaded at initialization and those loaded explicitly using the same classloader as the current applet or application.
There are several overloaded versions of the getConnection method. The version used in Listing 6 attempts to establish a connection to the given database URL for a specific user with a specific password.
If the attempt to get a connection to the database server is successful, the method returns an object of type Connection. In this program, a reference to the Connection object is stored in the reference variable named con.
If the attempt is not successful, an exception of type SQLException will be thrown. Information pertinent to the nature of the problem will be encapsulated in the SQLException object.
As you will see later, SQL statements are executed and results are returned within the context of a connection.
Display some information
The code in Listing 7 is not critical to the program. This code simply displays information about the URL and the connection.
System.out.println("URL: " + url);
System.out.println("Connection: " + con);
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Get a Statement object
The code in Listing 8 implements the third critical step listed earlier (get one or more Statementobjects).
This code invokes the createStatement method of the Connection interface to get an object of typeStatement.
stmt = con.createStatement(); |
Recall that con is a reference to an object of type Connection. A Connection object defines a connection (session) with a specific database. SQL statements are executed and results are returned within the context of a connection.
According to Sun, a Statement object is:
"... used for executing a static SQL statement and returning the results it produces."
The results that are returned
The results, if any, are retur