1. JDBC – Java Database Connectivity
CS , Spring 2008/9

2. Today’s Menu JDBC Architecture Using JDBC Timeout ResultSet Object
Null Values
Prepared Statements

3. JDBC (Java Database Connectiveity) is an API (Application Programming Interface)
That is, a collection of classes and interfaces
JDBC is used for accessing databases from Java applications
Information is transferred from relations to objects and vice-versa

4. JDBC Architecture

5. JDBC Architecture Java code calls JDBC library JDBC loads a driver
The driver talks to a particular DBMS
An application can work with several DBMS by using corresponding drivers

6. “Movies” Relation movieName producer releaseDate Movie1 Producer1
Movie2
Producer2
Movie3
Producer3

7. 7 Steps for Using JDBC Load the driver Define the connection URL
Establish the connection
Create a Statement object
Execute a query using the Statement
Process the result
Close the connection

9. Loading the Driver Class.forName loads the given class dynamically
Class.forName(“com.mysql.jdbc.Driver ”);
Class.forName loads the given class dynamically
When the driver is loaded, it automatically
creates an instance of itself
registers this instance within DriverManager
Another way:
Driver driver = new com.mysql.jdbc.Driver();
DriverManager.registerDriver(driver);
MySql JDBC driver can be downloaded from here.

11. Define the connection URL
Every database is identified by a URL
Given a URL, DriverManager looks for the driver that can talk to the corresponding database
DriverManager tries all registered drivers,until a suitable one is found

12. An Example // A driver for imaginary1
Class.forName("ORG.img.imgSQL1.imaginary1Driver");
// A driver for imaginary2
Driver driver = new ORG.img.imgSQL2.imaginary2Driver();
DriverManager.registerDriver(driver);
//A driver for PostgreSQL
Class.forName("org.postgresql.Driver");

13. Establish the connection
Connection con = DriverManager.getConnection("jdbc:imaginaryDB1://localhost:3306/");

15. 4. Create a Statement object
We use Statement objects in order to
Query the DB
Update the DB(insert, update, create, drop, …)

17. 5. Execute a query using the Statement
executeQuery returns a ResultSet object representing the query result (discussed later…)

19. Manipulating DB with Statement
String deleteStr =
“delete from movies where movieName=‘Movie1’ ”;
Statement stmt = con.createStatement();
int rowsDeleted = stmt.executeUpdate(deleteStr);
executeUpdate is for data manipulation: insert, delete, update, create table, etc.
executeUpdate returns the number of rows modified (or 0 for DDL commands)

20. 6. Process the result
We will discuss ResultSet in a while…

22. 7. Close the connection Close Connections, Statements, and Result Sets
con.close();
stmt.close();
rs.close();
‘finally’ block is a good place…

24. ResultSet
ResultSet objects provide access to the tables generated as results of executing Statement queries.
Only one ResultSet per Statement can be open at a given time!
The table rows are retrieved in sequence:
A ResultSet maintains a cursor pointing to its current row.
next() moves the cursor to the next row

25. ResultSet Methods
boolean next()
Activates the next row
First call to next() activates the first row
Returns false if there are no more rows
Not all of the next calls actually involve the DB
void close()
Disposes of the ResultSet
Allows to re-use the Statement that created it
Automatically called by most Statement methods
Type getType(int columnIndex)
Returns the given field as the given type
Indices start at 1 and not 0!
Add the column name as a comment if it is known!
Type getType(String columnName)
Same, but uses name of field
int findColumn(String columnName)
Looks up column index given column name
Type = int || double || long || boolean || byte || time || date …

26. Timeout
Use setQueryTimeOut(int seconds) of Statement class to set a timeout for the driver to wait for a query to be completed.
If the operation is not completed in the given time, an SQLException is thrown
What is it good for?

27. Mapping Java Types to SQL Types

28. Null Values In SQL, NULL means the field is empty
Not the same as 0 or “”!
In JDBC, you must explicitly ask if the last read field was null
ResultSet.wasNull(column)
For example, getInt(column) will return 0 if the value is either 0 or NULL!

29. Database Time Times in SQL are notoriously non-standard
Java defines three classes to help
java.sql.Date
year, month, day
java.sql.Time
hours, minutes, seconds
java.sql.Timestamp
year, month, day, hours, minutes, seconds, nanoseconds
Usually use this one

30. Exceptions
An SQLException is actually a list of exceptions

31. Prepared Statements
The PreparedStatement object contains not just an SQL statement, but an SQL statement that has been precompiled.
This means that when the PreparedStatement is executed, the DBMS can just run the PreparedStatement SQL statement without having to compile it first.
Most often used for SQL statements that take parameters.

32. Creating a PreparedStatement Object
As with Statement objects, you create PreparedStatement objects with a Connection method.
The following code create a PreparedStatement object that takes two input parameters:

33. Supplying Values for PreparedStatement Parameters
You need to supply values to be used in place of the question mark placeholders (if there are any) before you can execute a PreparedStatement object. You do this by calling one of the setXXX methods defined in the PreparedStatement class.

34. Example updateSales.setInt(1, 75);
the following line of code sets the first question mark placeholder to a Java int with a value of 75:
updateSales.setInt(1, 75);
The next example sets the second placeholder parameter to the string " Colombian":
updateSales.setString(2, "Colombian");

35. Another Example

36. Callable Statements Execute a call to a database stored procedure.
We will not go into details

37. Resources used for this presentation