1. Java Access to RDB Relational databases (RDBs) dominate today, due to:
Representational simplicity and flexibility
Maturity
Scalability
Broad accessibility
But applications are increasingly object oriented
Especially with Java
These apps view RDBs as persistent object systems
How can this view be supported?
Basically two choices
Use low level, standard access facility: JDBC
Use middleware: an object-relational gateway product

2. Accessing RDBs From Java
Illustrated by access of an Oracle9i database
Details on the two approaches
JDBC
Java DB Connectivity
Send SQL strings to relational DB
Receive enumerations of records as result
Each query is an individual transaction
Object relational gateway
Presents OO view of relational data
Each row is an object (exactly one!)
Foreign key -> primary key mappings converted to references
Lazy loading
Transaction semantics

3. JDBC
Provides platform and vendor independent access to relational DBs from Java clients
Principal classes
java.sql.Connection: manages DB connection
java.sql.Statement: presents SQL query as String
java.sql.ResultSet: returns collection of query result rows
Two varieties of JDBC packages
JDBC-ODBC bridge Uses ODBC database connectivity support in Windows
Thin JDBC clients Pure Java solutions – good esp. for Web clients (applets)

4. Selecting a driver Java Application Driver Manager ODBC Microsoft
Access
Java
Application
Driver
Manager
Oracle
Driver
Oracle
Connection
object
Other
DB Driver
Other DB

5. Sample code import java.sql.*; public class ConnectionDemo {
public static void main( String av[] )
Connection conn;
try {
DriverManager.registerDriver(
new oracle.jdbc.driver.OracleDriver() );
conn = DriverManager.getConnection(
“scott", “tiger");
Statement statement = conn.createStatement();
ResultSet rs = statement.executeQuery(
"select * from branch" );

6. Sample code // iterate through rows in result set while ( rs.next() ){
// extract column values in current row
String branchName = rs.getString( "branch_name" );
String branchCity = rs.getString( "branch_city" );
long assets = rs.getLong( "assets" );
System.out.println( branchName + " " +
branchCity + " " + assets ); }
// catch any SQLException in this block
} catch ( SQLException e ) {
System.out.println( e.toString() );
e.printStackTrace();

7. Connection Load DB driver DriverManager.registerDriver(
new oracle.jdbc.driver.OracleDriver() );
Create a connection
conn = DriverManager.getConnection(
“scott", “tiger");
Close a connection
conn.close();

8. Statement Statement object Create statement
an envelope into which you put your message
Create statement
Statement statement = conn.createStatement();
Execute statement
ResultSet rs = statement.executeQuery(
"select * from branch" );
ResultSet rs = statement.executeUpdate(
“delete from loan
where loan-number=‘L-101’" );

9. Statement A generic execute statement is available
String command = “..”;
boolean hasResultSet = statement.execute(command);
if (hasResultSet) {
ResultSet result = statement.getResultSet(); ……
} else {
int count = statement.getUpdateCount(); }

10. PreparedStatement Provide better performance when frequently used
PreparedStatement pstmt = conn.prepareStatement(
insert into loan values (?, ?, ?));
pstmt.setString(1, “L-201”);
pstmt.setString(2, “Downtown”);
pstmt.setInt(1, 1500);
int insCount = pstmt.executeUpdate();
System.out.println(“Inserted “ + insCount + “ rows.”);

11. ResultSet ResultSet organized into logical rows and columns
Use next() to move to the next record
Get columns by name and type
while ( rs.next() ) {
String branchName = rs.getString( "branch_name" );
String branchCity = rs.getString( "branch_city" );
long assets = rs.getLong( "assets" );
System.out.println( branchName + " " +
branchCity + " " + assets ); }