CS124-L9-JDBC.ppt Add more information to your upload

JDBC
 Java Database Connectivity
 Database Access Interface
 provides access to a relational database (by
allowing SQL statements to be sent and executed
through a Java program)
 JDBC package: set of Java classes that facilitate
this access (java.sql.*)
 Comes with JDK (since 1.1)

JDBC Driver
Need a driver, specific to the DB product, to
mediate between JDBC and the database
 the driver is a Java class that needs to be loaded
first
Relational
DBMS
Java Program
- load driver
- establish connection
- send SQL statements

JDBC-ODBC Bridge
 Driver that interfaces with ODBC (Object
Database Connectivity--also an access
interface)
 Easiest way to access databases created by
Microsoft products
 register database as an ODBC data source
 use JDBC-ODBC bridge as the JDBC driver
(included in JDK distribution)

Key Classes in JDBC
 Connection
 need to create an instance of this class when
establishing a connection to the database
 Statement
 for issuing SQL statements
 ResultSet (interface)
 a ResultSet object represents the table returned
by an SQL select statement

Establishing a Connection
Use the getConnection() method
 under the DriverManager class
 String argument: "jdbc:driver:name”
 returns a Connection object
Class.forName(“sun.jdbc.odbc.JdbcOdbcDriver”);
// above line loads the jdbc-odbc driver
String dbname = “jdbc:odbc:MyDB”;
Connection c = DriverManager.getConnection(dbname);

Creating a
Statement Object
Execute the createStatement() method on the
Connection object
 returns a Statement object
 afterwards, run methods on the Statement object
to execute an SQL statement
Statement s = c.createStatement();

Methods of the
Statement Class
 Methods of the Statement class require a string
parameter containing the SQL statement
 executeQuery()
 requires a String argument (a SELECT statement)
 returns a ResultSet object representing the table returned
 executeUpdate()
 requires a String argument
(an INSERT, UPDATE, or DELETE statement)
 returns an int (row count, in most cases)

The ResultSet Interface
 A ResultSet object represents the table
returned by the select statement sent
 Navigation/retrieval methods
 next(): moves to the next row (first row if called
for the first time), returns false if no rows remain
 getXXX() methods return the value of a field for
the current row

ResulSet example
ResultSet rs;
rs = s.executeQuery(“SELECT * FROM [ORDER]”);
rs.next(); // gets the first row (use in a loop for multiple rows)
// suppose the ORDER table has an integer field
// called quantity
int myvar = rs.getInt(“quantity”);
// if you knew that quantity is the 2nd field in the table
myvar = rs.getInt(2);
Need braces because
ORDER is a reserved
word in SQL

Exercise
 Create a Microsoft Access table
 insert sample rows
 Add an ODBC data source
 use the Microsoft Access driver
 associate with the created database
 Create a Java program
 use JDBC-ODBC bridge
 create a loop that lists all rows of the table

executeQuery( ) example
…
Statement s = con.createStatement();
ResultSet rs = s.executeQuery(
“SELECT * FROM STUDENT WHERE QPI > 3.0”
);
while ( rs.next() )
{
String name = rs.getString(“LastName”);
int y = rs.getInt(“Year”);
double qpi = rs.getDouble(“QPI”);
System.out.println( name + “ ” + y + “ ” + qpi);
}

executeUpdate( ) example
…
int result;
result = s.executeUpdate(
“DELETE FROM EMPLOYEE WHERE DeptCode=‘CS’”
);
System.out.println( result + “ rows deleted.” );

The PreparedStatement class
 PreparedStatement: a Statement that
specifies parameters through Java code
 The SQL statements take different forms
when you specify different parameter values
 Useful when query is performed repeatedly
 Formatting of literal values is easier

Version 1 (Statement)
// suppose lastName is a String variable
ResultSet rs = s.executeQuery(
“SELECT * FROM STUDENT WHERE LastName = ‘” + lastName +”’”
);
while ( rs.next() )
{
String name =
rs.getString(“LastName”) + rs.getString(“FirstName”);
}
Query string is built manually

Version 2 (PreparedStatement)
// suppose lastName is a String variable
PreparedStatement s = con.prepareStatement(
“SELECT * FROM STUDENT WHERE LastName = ?”
);
s.setString( 1, lastName );
ResultSet rs = s.executeQuery();
while ( rs.next() )
{
String name =
rs.getString(“LastName”) + rs.getString(“FirstName”);
}
the appropriate literal
is “inserted” in the query

Summary
 JDBC allows you to write Java programs that
manipulate a database
 A driver (often a separate product) is required
that facilitates access
 Key classes: Connection, Statement,
PreparedStatement, and ResultSet
 Other features: metadata and stored-proc
invocation

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