1. Lecture 11 Database Connection
Jaeki Song

2. Outline
Introduction
Java Database Connectivity

3. Introduction File processing Database systems
Random access or sequential
Only allow access to data
Cannot query
Database systems
Mechanisms to organize and store data
Allow sophisticated queries
Relational database - most popular style
Microsoft Access, Sybase, Oracle
Structured Query Language (SQL, "sequel")
Queries relational databases
Can write Java programs to use SQL queries

4. Database Language Database language Used to access database
Can use high-level languages
Java, C, C++, Visual Basic, COBOL, PL/I, Pascal
Make requests using a specially designed query language
Host language

5. Relational Database Model
Database models
Hierarchal, network, relational (most popular)
Focus on relational
Relational Database Model
Composed of tables
Rows called records
Columns are fields (attributes)
First field usually primary key
Unique for each record
Primary key can be more than one field (column)
Primary key not required

6. Relational Database Structure
Table: Employee
Number
Name
Department
Salary
Location
23603
JONES, A.
413
1100
NEW JERSEY
24568
KERWIN, R.
413
2000
NEW JERSEY
A record
34589
LARSON, P.
642
1800
LOS ANGELES
35761
MYERS, B.
611
1400
ORLANDO
47132
NEUMANN, C.
413
9000
NEW JERSEY
78321
STEPHENS, T.
611
8000
ORLANDO
Primary Key
A column

7. Advantages Tables easy to use, understand, and implement
Easy to convert other database structures into relational scheme
Universal
Projection and join operations easy to implement
Searches faster than schemes with pointers
Easy to modify - very flexible
Greater clarity and visibility than other models

8. Java Database Connectivity
You can access data files in Java using JDBC
JDBC classes handle communication between your Java program and a database driver
Java uses JDBC-ODBC Bridge

9. Data Source Name (DSN)
Before using JDBC in a Window environment, you need to create a DSN
DSN registers your database files on the computer
Setting up a DSN
Step1: From the start menu, select control panel
Step2: select ODBC Data source
Step3: On the User DSN tab, click on the Add button

10. Data Source Name (DSN)

11. Data Source Name (DSN)
Step4: Select the database type (Microsoft Access database), and click Finish

12. Data Source Name (DSN)
Step5: Type in the Data Source Name

13. Data Source Name (DSN)
Step6: Use the Select (or Browse) button to locate the file, then close the dialog boxes

14. JDBC-ODBC Bridge Driver
In Java code, you must connect to the driver using the Class.forName method
Connect to Microsoft’s driver
Class.forName(“com.ms.jdbc.odbc.JdbcOdbcDriver”);
Connect to Sun’s driver
Class.forName(“sun.jdbc.odbc.JdbcOdbcDriver”);

15. JDBC-ODBC Bridge Driver
If you need to be able to load either driver, you can use try/catch block
try
{ Class.forName(“com.ms.jdbc.odbc.JdbcOdbcDriver”); }
catch
{ try
{Class.forName(“sun.jdbc.odbc.JdbcOdbcDriver”);}
catch(ClassNotFoundException err)
{ System.err.println(“Driver did not load properly”);} }

16. Connecting to the Database
Next step is to connect to the database using the name that your registered as a DSN
“jdbc:odbc:EX1”
Use DriverManager.getConnection method and assign it to a Connection object
conEmployees = DriverManager.getConnection(“jdbc:odbc:EX1”);

17. Connecting to the Database
//Declare a Connection object
Connection conEmployees;
//Connect to the database
try {
conEmployees = DriverManager.getConnection (“jdbc:odbc:EX1”); }
catch(SQLException err)
statement // “No connection to database”

18. Creating a ResultSet
A ResultSet object contains a collection of records from the database
To create ResultSet, you must declare a Statement object and call the Connection objects’ createStatement method
Statement cmdEmployees;
ResultSet rsEmployees;
You create a ResultSet with an SQL query with executeQuery method
Select * from Employees
cmdEmployees.executeQuery(“Select * from Employees”);

19. Example try { Connection conEmployees;
conEmployees = DriverManager.getConnection (“jdbc:odbc:EX1”);
//create a ResultSet
Statement cmdEmployees = conEmployees.createStatement();
ResultSet rsEmployees = cmdEmployees.executeQuery (“Select * from Employees”); }
catch(SQLException err)
statement // “No connection to database”

20. Example
You can create an SQL statement to create a ResultSet that matches a given condition
ResultSet rsEmployees = cmdEmployees.executeQuery ( “Select * from Employees Where [Last Name] = ‘Song’ ”);
ResultSet rsEmployees = cmdEmployees.executeQuery ( “Select * from Employees Where [Last Name] = ‘ “ + strLastName + ” ’ ”);

21. Retrieving a Record Looping through a ResultSet
Displaying the fields from a record

22. Retrieving a Record
When you first open a ResutSet, the current-record is located just prior to the first record
You call the ResultSet’s next method
The next method moves the current-record pointer to the first record and returns boolean value
true: the next record exists
false: no more records exists

23. Example try { rsEmployees.next( );
The getString method retrieves the data
for the specified string field
try {
rsEmployees.next( );
lstNames.add(rsEmployees.getString (“Last Name”)); }
catch (SQLException err)
System.err.println(“Error : “ + err.toString());

24. Looping through a ResultSet
You can step through all records in a ResultSet using a loop
while (rsResultSet.next( )) to control the loop
The boolean condition tests true as long as records remain in the ResultSet
while(rsEmployees.next( ))
lstNames.add(rsEmployees.getString(“Last Name”));

25. Displaying the Fields try { //display information
if (rsEmployees.next( )) {
lblFirstName.setText(rsEmployees.getString(“ First Name”);
lblSSN.setText(rsEmployees.getString(“SSN”));
lblSSN.setText(rsEmployees.getString(“Phone Number”)); }
else
//Statement
catch (SQLException err)
System.err.println(“Error : “ + err.toString());

26. Accessing the Data Fields
Access the data in database fields by using the appropriate method for the data type
getString for string field
getFloat or getInt for float or int fields
Convert the value to a string format to display the value in a label or text field

27. Closing the Connection
Make sure that the database connection is closed at the termination of the program
Place the statement in the stop method
Place the code in your exit routine
public void stop( ) {
if (conEmployees != null)
conEmployees.close( ); }

28. SQL
Java’s JDBC uses Structured Query Language (SQL) to create a ResultSet
ResultSet rsEmployees = cmdEmployees.executeQuery(“Select * from Employees”);
ResultSet rsEmployees = cmdEmployees.executeQuery(“Select * from Employees where [Last Name] = ‘ “ + strLastName + ” ’; ”);

29. Types of SQL Statement
For the field(s), you can list the field names or use an asterisk to indicate all fields from the named table.
Multiple-world field names must be enclosed in square brackets or accent grave marks (‘)
The closing semicolon(;) is specified in the SQL standards

30. SQL Examples SELECT Where “Select * from Employees;”
“Select * from Employees where [Last Name] = ‘ ABC’ ”;
“Select * from Employees where [Last Name] = ‘ “ + strLastName + ”’; ”

31. Adding a Record SQL insert statement-General format
Insert Into TableName (FieldList) Values (ListOfValue)
Use the statement object’s executeUpdate method to excute the SQL Insert Into statement

32. Example
cmdEmplyees.executeUpdate (“ Insert Into Employees” + “( [Last Name] , [First Name], SSN, [Phone Number]) ”
+ “Values( ‘ “
+ txtLastName.getText() + ” ’, ‘ “
+ txtFirstName.getText( ) + ” ’)”);

33. Finding a Record SQL Statement strLastName = txtLastName.getText();
String query = “Select *from Employees where [Last Name] = ‘ “ + strLastName + ’ ” ”;
rsEmployees = statement.executeQuery(query);