1. JDBC – Java Database Concentricity
Representation and Management of Data on the Internet

2. Relational Databases
Data stored in records (tuples) which live in tables (relations)
Maps row (record) to column (field) in a single table A B C D 1 2 3 4 4 3 2 1

3. A (very short) Reminder of SQL
Creating tables:
CREATE TABLE books (
isbn INTEGER primary key,
title VARCHAR2(40) not null,
abstract TEXT);

4. A (very short) Reminder of SQL
Inserting tuples into the tables
INSERT INTO books(isbn, title)
VALUES (12345, “Foundations
of Database”)

5. A (very short) Reminder of SQL
Updating tuples in the tables
UPDATE books SET
title=“Foundation of Databases”
WHERE isbn=12345;

6. A (very short) Reminder of SQL
Deleting tuples from the tables
DELETE FROM books
WHERE title like ‘%goblin%;

7. A (very short) Reminder of SQL
Queries
SELECT title
FROM books
WHERE abstract like ‘%hobbit%;

8. Transactions
Transaction = more than one statement which must all succeed (or all fail) together
If one fails, the system must reverse all previous actions
Also can’t leave DB in inconsistent state halfway through a transaction
COMMIT = complete transaction
ROLLBACK = abort

9. Working With Oracle Add to your .cshrc the following:
if ($HOST == sol4) then
setenv ORACLE_HOME /opt/oracle
else
setenv ORACLE_HOME /usr/local/oracle8i
endif
setenv PATH $ORACLE_HOME/bin:$PATH
setenv ORACLE_SID stud

10. sqlplus snoopy/snoopy@stud.cs
Calling Oracle
If a student whose login is Snoopy wants to work directly with Oracle:
sqlplus
Note: we use the login for a password!

11. Introduction to JDBC
JDBC is used for accessing databases from Java applications
Information is transferred from relations to objects and vice-versa
databases optimized for searching/indexing
objects optimized for engineering/flexibility

12. Overview
RMI
JDBC
CORBA
java.net
TCP/IP
Network OS

13. JDBC Drivers (Fig.) JDBC Type I “Bridge” ODBC ODBC Driver Type II
“Native”
CLI (.lib)
Type III
“Middleware”
Middleware
Server
Type IV
“Pure”

14. Java Package
JDBC is implemented in
Java in the package
java.sql

15. Seven Steps Load the driver Define the Connection URL
Establish the Connection
Create a Statement object
Execute a query
Process the result
Close the connection

16. Important Classes DriverManager Driver Connection Statement ResultSet
loads, chooses drivers
Driver
connects to actual database
Connection
a series of SQL statements to and from the DB
Statement
a single SQL statement
ResultSet
the records returned from a Statement

17. DriverManager
Driver
Connection
Statement
ResultSet

18. Loading the Driver Registering the Driver directly automatically:
Class.forName(
“oracle.jdbc.driver.OracleDriver");
Calling Class.forName, automatically
creates an instance of the driver
registers the driver with the DriverManager

19. Another Option
Another option is to create an instance of the driver and register it with the Driver Manager:
Driver driver = new oracle.jdbc.OracleDriver();
DriverManager.registerDriver(driver);

20. The DriverManager The DriverManager tries all the drivers
Uses the first one that works
When a driver class is first loaded, it registers itself with the DriverManager
Therefore, to load a driver, just register it!

21. Creating a Connection
Use getConnection on the Driver
Connection getConnection
(String url,
String user,
String password)
Connects to given JDBC URL with given user name and password
Throws java.sql.SQLException
returns a Connection object

22. URLS
Gives the required information for making the connection to the database
For example, Snoopy will use the URL
Path to driver
User name
Password
Port
Host
Database name

23. Connection A Connection represents a session with a specific database
Within the context of a Connection, SQL statements are executed and results are returned

24. Connections There can be multiple connections to a database
A connection provides “metadata”, i.e., information about the database, tables, and fields
Connection object has methods to deal with transactions

25. Creating a Connection
String url =
try {
Class.forName (“oracle.jdbc.OracleDriver");
Connection con = DriverManager.getConnection(url); }
catch (ClassNotFoundException e)
{ e.printStackTrace(); }
catch (SQLException e)

26. Statements Why all these different kinds of statements?
Statement createStatement()
returns a new Statement object
PreparedStatement prepareStatement(String sql)
returns a new PreparedStatement object
CallableStatement prepareCall(String sql)
returns a new CallableStatement object
Why all these different kinds of statements?

27. Statements
A Statement object is used for executing a static SQL statement and obtaining the results produced by it
executeQuery is used for statements that return an output result
executeUpdate is used for statements that need not return an output

28. Executing Queries and Updates
ResultSet executeQuery(String)
Execute a SQL statement that returns a single ResultSet
int executeUpdate(String)
Execute a SQL INSERT, UPDATE or DELETE statement
Used for CREATE TABLE, DROP TABLE and ALTER TABLE
Returns the number of rows changed

29. Timeout
Use setQueryTimeOut to set a timeout for the driver to wait for a statement to be completed
If the operation is not completed in the given time, an SQLException is thrown
What is it good for?

30. Cursor What is the result of a query?
Is a remote connection different from a direct access to the database?
How can a database send the result of a query through communication lines?
The answer: using a cursor

31. Result Set
A ResultSet provides access to a table of data generated by executing a Statement
Only one ResultSet per Statement can be open at once
The table rows are retrieved in sequence
A ResultSet maintains a cursor pointing to its current row of data
The 'next' method moves the cursor to the next row
you can’t rewind

32. Working with ResultSet
boolean next()
activates the next row
the first call to next() activates the first row
returns false if there are no more rows
void close()
disposes of the ResultSet
allows you to re-use the Statement that created it
automatically called by most Statement methods

33. Getting Values from Rows
Type getString(int columnIndex)
returns the given field as the given type
fields indexed starting at 1 (not 0)
Type getString(String columnName)
same, but uses name of field
less efficient
int findColumn(String columnName)
looks up column index given column name
getType

34. Example
Code Example

36. Optimized Statements Prepared Statements Stored Procedures
SQL calls that you make again and again
allows driver to optimize (compile) queries
created with Connection.prepareStatement()
Stored Procedures
written in DB-specific language
stored inside database
accesed with Connection.prepareCall()

37. Metadata Connection: ResultSet: DatabaseMetaData getMetaData()
ResultSetMetaData getMetaData()

38. Useful Methods of Metadata
getColumnCount
getColumnDisplaySize
getColumnName
getColumnType
isNullabale
Imagine the case where you want to print the result

39. Transaction Management
Transactions are not explicitly opened and closed
Instead, the connection has a state called AutoCommit mode
if AutoCommit is true, then every statement is automatically committed
default case: true

40. AutoCommit
Connection.setAutoCommit(boolean)
if AutoCommit is false, then every statement is added to an ongoing transaction
you must explicitly commit or rollback the transaction using Connection.commit() and Connection.rollback()

41. Connection Manager
For a large threaded database server, create a Connection Manager object
It is responsible for maintaining a certain number of open connections to the database
When your applications need a connection, they ask for one from the CM’s pool
Why? Because opening and closing connections takes a long time
Warning: the CM should always setAutoCommit(false) when a connection is returned