Jdbc (database in java)

JDBC
(Java Database Connectivity)

Overview (1/2)
 JDBC
 JDBC is a standard interface for connecting to relational databases
from Java
 The JDBC Classes and Interfaces are in the java.sql package
 JDBC is Java API for executing SQL statements

Provides a standard API for tool/database developers

Possible to write database applications using a pure Java API

Easy to send SQL statements to virtually any relational database
 What does JDBC do?
 Establish a connection with a database
 Send SQL statements
 Process the results
JDBC Driver
JAVA Applet/
Application Database
JDBC Call
Database
Command

 Reason for JDBC
 Database vendors (Microsoft Access, Oracle etc.) provide
proprietary (non standard) API for sending SQL to the server
and receiving results from it
 Languages such as C/C++ can make use of these proprietary
APIs directly

High performance

Can make use of non standard features of the database

All the database code needs to be rewritten if you change
database vendor or product
 JDBC is a vendor independent API for accessing relational
data from different database vendors in a consistent way
CCTM: Course material developed by James King (james.king@londonmet.ac.uk)
Overview (2/2)

History of JDBC (1/2)
 JDBC 1.0 released 9/1996.
 Contains basic functionality to connect to database, query database,
process results
 JDBC classes are part of java.sql package
 Comes with JDK 1.1
 JDBC 2.0 released 5/1998
 Comes with JDK 1.2
 javax.sql contains additional functionality
 Additional functionality:

Scroll in result set or move to specific row

Update database tables using Java methods instead of SQL
commands

Send multiple SQL statements to the database as a batch

Use of SQL3 datatypes as column values

History of JDBC (2/2)
 JDBC 3.0 released 2/2002
 Comes with Java 2, J2SE 1.4

Support for:

Connection pooling

Multiple result sets

Prepared statement pooling

Save points in transactions

JDBC Model
 JDBC consists of two parts:
 JDBC API, a purely Java-based API
 JDBC driver manager

Communicates with vendor-specific
drivers
 Connection con =
DriverManager.getConnection( "jd
bc:myDriver:myDatabase",
username, password);
JAVA Applet/
Application
JDBC API
Driver Manager
Driver API
Vendor Specific
JDBC Driver
JDBC-ODBC Bridge
Database
Vender Specific
ODBC Driver
Database
Java Application
Developer
JDBC Developer
Vender Specific
JDBC developer

JDBC Programming Steps
Connect
Query
Process Results
Close
1) Register the driver
2) Create a connection to the database
1) Create a statement
2) Query the database
1) Get a result set
2) Assign results to Java variables
1) Close the result set
2) Close the statement
3) Close the connection

Skeleton Code
Class.forName(DRIVERNAME);
Connection con = DriverManager.getConnection(
CONNECTIONURL, DBID, DBPASSWORD);
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery(“SELECT a, b, c FROM member);
While(rs.next())
{
Int x = rs.getInt(“a”);
String s = rs.getString(“b”);
Float f = rs.getFloat(“c”);
}
rs.close();
stmt.close();
con.close();
Loading a JDBC driver
Connecting to a database
Processing the result set
Closing the connections
Executing SQL

Step 1 : Loading a JDBC Driver
 A JDBC driver is needed to connect to a database
 Loading a driver requires the class name of the driver.
Ex) JDBC-ODBC: sun.jdbc.odbc.JdbcOdbcDriver
Oracle driver: oracle.jdbc.driver.OracleDriver
MySQL: com.mysql.jdbc.Driver
 Loaing the driver class
Class.forName("com.mysql.jdbc.Driver");
 It is possible to load several drivers.
 The class DriverManager manages the loaded driver(s)

Step 2 : Connecting to a Database (1/2)
 JDBC URL for a database
 Identifies the database to be connected
 Consists of three-part:
jdbc:<subprotocol>:<subname>
Protocol: JDBC is
the only protocol in
JDBC
Protocol: JDBC is
the only protocol in
JDBC
Subname: indicates the location and
name of the database to be
accessed. Syntax is driver specific
Subname: indicates the location and
name of the database to be
accessed. Syntax is driver specific
Sub-protocol:
identifies a
database
driver
Sub-protocol:
identifies a
database
driver
Ex) jdbc:mysql://oopsla.snu.ac.kr/mydb
The syntax for the name of the database is a little messy and is
unfortunately vendor specific

JDBC URL
Vendor of database, Location of
database server and name of
database
Username Password
Step 2 : Connecting to a Database (2/2)
 The DriverManager allows you to connect to a database using
the specified JDBC driver, database location, database name,
username and password.
 It returns a Connection object which can then be used to
communicate with the database.
Connection connection =
DriverManager.getConnection("jdbc:mysql://oopsla.snu.ac.kr/mydb",“useri
d",“password");
JDBC URL
Vendor of database, Location of
database server and name of
database
Username Password

Step 3 : Executing SQL (1/2)
 Statement object
 Can be obtained from a Connection object
 Sends SQL to the database to be executed
 Statement has three methods to execute a SQL statement:
 executeQuery() for QUERY statements

Returns a ResultSet which contains the query results
 executeUpdate() for INSERT, UPDATE, DELETE statements

Returns an integer, the number of affected rows from the SQL
 execute() for either type of statement
Statement statement = connection.createStatement();

Statement stmt = conn.createStatement();
ResultSet rset = stmt.executeQuery
("select RENTAL_ID, STATUS from ACME_RENTALS");
Statement stmt = conn.createStatement();
int rowcount = stmt.executeUpdate
("delete from ACME_RENTAL_ITEMS
where rental_id = 1011");
Step 3 : Executing SQL (2/2)
 Execute a select statement
 Execute a delete statement

Step 4 : Processing the Results (1/2)
 JDBC returns the results of a query in a ResultSet object
 ResultSet object contains all of the rows which satisfied the conditions
in an SQL statement
 A ResultSet object maintains a cursor pointing to its current
row of data
 Use next() to step through the result set row by row

next() returns TRUE if there are still remaining records
 getString(), getInt(), and getXXX() assign each value to a Java
variable
Record 1 Record 2 Record 3 Record 4
ResultSetInternal Pointer
The internal pointer starts one before the first record

Step 4 : Processing the Results (2/2)
 Example
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery(“SELECT ID, name, score FROM table1”);
While (rs.next()){
int id = rs.getInt(“ID”);
String name = rs.getString(“name”);
float score = rs.getFloat(“score”);
System.out.println(“ID=” + id + “ ” + name + “ ” + score);}
NOTE
You must step the cursor to the first record before read the results
This code will not skip the first record
ID name score
1 James 90.5
2 Smith 45.7
3 Donald 80.2
Table1
Output
ID=1 James 90.5
ID=2 Smith 45.7
ID=3 Donald 80.2

Step 5 : Closing Database Connection
 It is a good idea to close the Statement and Connection objects
when you have finished with them
 Close the ResultSet object
rs.close();
 Close the Statement object
stmt.close();
 Close the connection
connection.close();

The PreparedStatement Object
 A PreparedStatement object holds precompiled SQL
statements
 Use this object for statements you want to execute more than
once
 A PreparedStatement can contain variables (?) that you supply
each time you execute the statement
// Create the prepared statement
PreparedStatement pstmt = con.prepareStatement(“
UPDATE table1 SET status = ? WHERE id =?”)
// Supply values for the variables
pstmt.setString (1, “out”);
pstmt.setInt(2, id);
// Execute the statement
pstmt.executeUpdate();

Jdbc (database in java)

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