I am trying to learn Java and need an example program with MySql
database.
I am sure there are many who have made an invoice program in Java with
MySql database. The program must have routines that are similar to
those an invoice program has: customers, orders, products. Screens
like orders head and orderlines.
Can you please send me a copy of the source files for such a program
or a different program?
Try this out, besure to download MySQL JDBC connector from:
http://www.mysql.com/downloads/api-jdbc.html
then to run it type the following at the command line.
java -cp .\;mysql-connector-java-3.0.10-stable-bin.jar TestMySQL
--- cut ---
/*
* TestMySQL.java
*
*/
import java.sql.*;
public class TestMySQL {
public static void main(String argv[]) throws Exception {
// --- Load the driver class.
try {
Class.forName("org.gjt.mm.mysql.Driver").newInstance();
}
catch (Exception ex) {
System.out.println("Can't load driver.");
System.exit(1);
}
// --- Try to connect to MySQL Server.
java.sql.Connection MySQLConnection = null;
try {
/*
The format for a connection string is as follows:
jdbc:mysql: -- Connection type
//my_host -- MySQL Host or IP address.
/my_database -- Database to open
?user=my_user_name -- user name
&password=my_password -- password
*/
MySQLConnection =
java.sql.DriverManager.getConnection(
"jdbc:mysql://localhost/my_database"+
"?user=user&password=my_pass");
}
catch (Exception ex) {
System.out.println(
"Can't connect to MySQL Server.");
System.exit(1);
}
// --- Create table and add Values.
java.sql.Statement SQLStatement =
MySQLConnection.createStatement();
int count;
SQLStatement.executeUpdate (
"DROP TABLE IF EXISTS animal");
SQLStatement.executeUpdate (
"CREATE TABLE animal ("
+ "id INT UNSIGNED NOT NULL AUTO_INCREMENT,"
+ "PRIMARY KEY (id),"
+ "name CHAR(40), category CHAR(40))");
count = SQLStatement.executeUpdate (
"INSERT INTO animal (name, category)"
+ " VALUES"
+ "('snake', 'reptile'),"
+ "('frog', 'amphibian'),"
+ "('tuna', 'fish'),"
+ "('racoon', 'mammal')");
SQLStatement.close ();
System.out.println (count + " rows were inserted");
// --- Show records.
SQLStatement = MySQLConnection.createStatement();
SQLStatement.executeQuery(
"SELECT id, name, category FROM animal");
java.sql.ResultSet SQLResultSet = SQLStatement.getResultSet();
count = 0;
while (SQLResultSet.next()) {
int idVal = SQLResultSet.getInt("id");
String nameVal = SQLResultSet.getString("name");
String catVal = SQLResultSet.getString("category");
System.out.println("id = " + idVal
+ ", name = " + nameVal
+ ", category = " + catVal);
++count;
}
SQLResultSet.close();
SQLStatement.close();
System.out.println(count + " rows were retrieved");
// --- Close connection.
MySQLConnection.close();
}
}
-- cut --
Reference material
-- begin --
Writing JDBC Applications with MySQL
Paul DuBois
(e-mail address removed)
Document revision: 1.01
Last update: 2003-01-24
Table of Contents
• Preliminary Requirements
• Connecting to the MySQL Server
• Issuing Queries
o Issuing Queries That Return No Result Set
o Issuing Queries That Return a Result Set
Using Placeholders
o Error Handling
• Resources
• Acknowledgment
You can write MySQL applications in a variety of languages. The
languages that most people use with MySQL are PHP and Perl, but a
sometimes overlooked option is the MySQL Connector/J driver, which
allows you to develop Java applications that interact with your MySQL
server.
MySQL Connector/J works within the framework of the Java JDBC
interface, an API that allows Java programs to use database servers in
a portable way. JDBC is based on an approach similar to that used in
the design of Perl and Ruby DBI modules, Python's DB-API module, and
PHP's PEAR:
B class. This approach uses a two-tier architecture:
• The top level is visible to application programs and presents an
abstract interface for connecting to and using database engines. The
application interface does not depend on details specific to
particular engines.
• The lower level consists of drivers for individual database engines.
Each driver handles the details necessary to map the abstract
application interface onto operations that a specific engine will
understand.
The JDBC interface allows developers to write applications that can be
used with different databases with a minimum of porting effort. Once a
driver for a given server engine is installed, JDBC applications can
communicate with any server of that type. By using MySQL Connector/J,
your Java programs can access MySQL databases.
Note: MySQL Connector/J is the successor to the MM.MySQL driver. If
you have JDBC programs written for MM.MySQL, they should work with
MySQL Connector/J as well, although you may want to update the driver
class name used in your programs. Just replace instances of
org.gjt.mm.mysql in your Java source files with com.mysql.jdbc and
recompile.
Preliminary Requirements
To use Java applications with MySQL, you may need to install some
additional software:
• If you want to compile and run Java programs, you'll need a Java
compiler (such as javac or jikes) and a runtime environment. If these
are not already installed on your system, you can get them by
obtaining a Java Software Development Kit (SDK) from java.sun.com.
• If you want only to run precompiled applications, no compiler is
necessary, but you'll still need a Java Runtime Environment (JRE).
This too may be obtained from java.sun.com.
This article assumes that you'll write and compile your own programs,
and thus that you have a Java SDK installed. Once you compile a Java
program, however, you can deploy it to other machines, even ones that
have only a runtime environment. This works even in heterogenous
installations, because Java is platform-independent. Applications
compiled on one platform can be expected to work on other platforms.
For example, you can develop on a Linux box and deploy on Windows.
Connecting to the MySQL Server
To connect to the MySQL server, register the JDBC driver you plan to
use, then invoke its getConnection() method. The following short
program, Connect.java, shows how to connect to and disconnect from a
server running on the local host. It accesses a database named test,
using a MySQL account with a user name and password of testuser and
testpass:
import java.sql.*;
public class Connect
{
public static void main (String[] args)
{
Connection conn = null;
try
{
String userName = "testuser";
String password = "testpass";
String url = "jdbc:mysql://localhost/test";
Class.forName ("com.mysql.jdbc.Driver").newInstance ();
conn = DriverManager.getConnection (url, userName,
password);
System.out.println ("Database connection established");
}
catch (Exception e)
{
System.err.println ("Cannot connect to database
server");
}
finally
{
if (conn != null)
{
try
{
conn.close ();
System.out.println ("Database connection
terminated");
}
catch (Exception e) { /* ignore close errors */ }
}
}
}
}
Compile Connect.java to produce a class file Connect.class that
contains executable Java code:
% javac Connect.java
Then invoke the class file as follows and it should connect to and
disconnect from your MySQL server:
% java Connect
Database connection established
Database connection terminated
If you have trouble compiling Connect.java, double check that you have
a Java Software Development Kit installed and make sure that the MySQL
Connector/J driver is listed in your CLASSPATH environment variable.
The arguments to getConnection() are the connection URL and the user
name and password of a MySQL account. As illustrated by Connect.java,
JDBC URLs for MySQL consist of jdbc:mysql:// followed by the name of
the MySQL server host and the database name. An alternate syntax for
specifying the user and password is to add them as parameters to the
end of the connection URL:
jdbc:mysql://localhost/test?user=testuser&password=testpass
When you specify a URL using this second format, getConnection()
requires only one argument. For example, the code for connecting to
the MySQL server in Connect.java could have been written like this:
String userName = "testuser";
String password = "testpass";
String url = "jdbc:mysql://localhost/test?user="
+ userName
+ "&password="
+ password;
Class.forName ("com.mysql.jdbc.Driver").newInstance ();
conn = DriverManager.getConnection (url);
getConnect() returns a Connection object that may be used to interact
with MySQL by issuing queries and retrieving their results. (The next
section describes how to do this.) When you're done with the
connection, invoke its close() method to disconnect from the MySQL
server.
To increase the portability of your applications, you can store the
connection parameters (host, database, user name, and password) in a
Java properties file and read the properties at runtime. Then they
need not be listed in the program itself. This allows you to change
the server to which the program connects by editing the properties
file, rather than by having to recompile the program.
Issuing Queries
To process SQL statements in a JDBC-based application, create a
Statement object from your Connection object. Statement objects
support an executeUpdate() method for issuing queries that modify the
database and return no result set, and an executeQuery() method for
queries that do return a result set. The query-processing examples in
this article use the following table, animal, which contains an
integer id column and two string columns, name and category:
CREATE TABLE animal
(
id INT UNSIGNED NOT NULL AUTO_INCREMENT,
PRIMARY KEY (id),
name CHAR(40),
category CHAR(40)
)
id is an AUTO_INCREMENT column, so MySQL automatically assigns
successive values 1, 2, 3, ... as records are added to the table.
Issuing Queries That Return No Result Set
The following example obtains a Statement object from the Connection
object, then uses it to create and populate the animal table. DROP
TABLE, CREATE TABLE, and INSERT all are statements that modify the
database, so executeUpdate() is the appropriate method for issuing
them:
Statement s = conn.createStatement ();
int count;
s.executeUpdate ("DROP TABLE IF EXISTS animal");
s.executeUpdate (
"CREATE TABLE animal ("
+ "id INT UNSIGNED NOT NULL AUTO_INCREMENT,"
+ "PRIMARY KEY (id),"
+ "name CHAR(40), category CHAR(40))");
count = s.executeUpdate (
"INSERT INTO animal (name, category)"
+ " VALUES"
+ "('snake', 'reptile'),"
+ "('frog', 'amphibian'),"
+ "('tuna', 'fish'),"
+ "('racoon', 'mammal')");
s.close ();
System.out.println (count + " rows were inserted");
The executeUpdate() method returns the number of rows affected by a
query. As shown above, the count is used to report how many rows the
INSERT statement added to the animal table.
A Statement object may be used to issue several queries. When you're
done with it, invoke its close() method to dispose of the object and
free any resources associated with it.
Issuing Queries That Return a Result Set
For statements such as SELECT queries that retrieve information from
the database, use executeQuery(). After calling this method, create a
ResultSet object and use it to iterate through the rows returned by
your query. The following example shows one way to retrieve the
contents of the animal table:
Statement s = conn.createStatement ();
s.executeQuery ("SELECT id, name, category FROM animal");
ResultSet rs = s.getResultSet ();
int count = 0;
while (rs.next ())
{
int idVal = rs.getInt ("id");
String nameVal = rs.getString ("name");
String catVal = rs.getString ("category");
System.out.println (
"id = " + idVal
+ ", name = " + nameVal
+ ", category = " + catVal);
++count;
}
rs.close ();
s.close ();
System.out.println (count + " rows were retrieved");
executeQuery() does not return a row count, so if you want to know how
many rows a result set contains, you should count them yourself as you
fetch them.
To obtain the column values from each row, invoke getXXX() methods
that match the column data types. The getInt() and getString() methods
used in the preceding example return integer and string values. As the
example shows, these methods may be called using the name of a result
set column. You can also fetch values by position. For the result set
retrieved by the SELECT query in the example, id, name, and category
are at column positions 1, 2 and 3 and thus could have been obtained
like this:
int idVal = rs.getInt (1);
String nameVal = rs.getString (2);
String catVal = rs.getString (3);
ResultSet objects, like Statement objects, should be closed when
you're done with them.
To check whether or not a column value is NULL, invoke the result set
object's wasNull() method after fetching the value. For example, you
could check for a NULL value in the name column like this:
String nameVal = rs.getString ("name");
if (rs.wasNull ())
nameVal = "(no name available)";
Using Placeholders
Sometimes it's necessary to construct queries from values containing
characters that require special treatment. For example, in queries,
string values are written enclosed within quotes, but any quote
characters in the string itself should be doubled or escaped with a
backslash to avoid creating malformed SQL. In this case, it's much
easier to let JDBC handle the escaping for you, rather than fooling
around trying to do so yourself. To use this approach, create a
different kind of statement (a PreparedStatement), and refer to the
data values in the query string by means of placeholder characters.
Then tell JDBC to bind the data values to the placeholders and it will
handle any special characters automatically.
Suppose you have two variables nameVal and catVal from which you want
to create a new record in the animal table. To do so without regard to
whether or not the values contain special characters, issue the query
like this:
PreparedStatement s;
s = conn.prepareStatement (
"INSERT INTO animal (name, category) VALUES(?,?)");
s.setString (1, nameVal);
s.setString (2, catVal);
int count = s.executeUpdate ();
s.close ();
System.out.println (count + " rows were inserted");
The '?' characters in the query string act as placeholders--special
markers indicating where data values should be placed. The setString()
method takes a placeholder position and a string value and binds the
value to the appropriate placeholder, performing any special-character
escaping that may be necessary. The method you use to bind a value
depends on the data type. For example, setString() binds string values
and setInt() binds integer values.
Error Handling
If you want to trap errors, execute your JDBC operations within a try
block and use an exception handler to display information about the
cause of any problems that occur. JDBC provides getMessage() and
getErrorCode() methods that may be invoked when an exception occurs to
obtain the error message and the numeric error code. The following
example deliberately issues a malformed query. When it runs, the
executeQuery() method fails and raises an exception that is handled in
the catch block:
try
{
Statement s = conn.createStatement ();
s.executeQuery ("XYZ"); // issue invalid query
s.close ();
}
catch (SQLException e)
{
System.err.println ("Error message: " + e.getMessage ());
System.err.println ("Error number: " + e.getErrorCode ());
}
Resources
The following sites provide information about the tools discussed in
this article:
• Sun's Java site is a clearinghouse for all kinds of Java-related
information:
•
http://java.sun.com/
•
You can obtain the Java Software Development Kit or Java Runtime
Environment here. The specification for the JDBC API is also available
on this site, should you wish to read more about it.
• The MySQL Connector/J driver is supported by MySQL AB. Connector/J
author Mark Matthews maintains the driver, which is available at:
•
http://www.mysql.com/
•
• Introductory articles describing other MySQL APIs based on an
architecture similar to that used for JDBC may be found at:
•
http://www.kitebird.com/articles/
•
APIs discussed in the articles include Perl DBI, PHP PEAR:
B, Python
DB-API, and Ruby DBI.
Acknowledgment
The original version of this article was written for NuSphere
Corporation. The current version is an updated revision of the
original.
-- End
