JDBC Overview

Autumn 2001

Lecturer: C. DeJong

Relational Databases

• widespread use

• used via SQL (Structured Query Language)

• freely available

• powerful

• text-based

What is JDBC?

• An API for Java database connectivity

• A collection of Java classes from Sun

• A set of interfaces for database programming

• java.sql.*

Steps for setting up JDBC

• install Java and JDBC (available from java.sun.com)

• install a driver

• install a relational database – MySQL, PostgreSQL (free!)– Oracle, Sybase, IBM’s DB2 (commercial)

Establishing a connection

• Load the database driver

• Make the connection

Loading the driver

• driver should be provided with database

• one line of code:Class.forName(<driver class name>);

• ex: Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");

Make the connection

• Returns a Connection object

• Syntax:Connection con = DriverManager.getConnection(

url, "myLogin",

"myPassword");

URL for connecting

• should be in documentation with JDBC driver

• starts with “jdbc:”

• can connect across a network

Statements

• used to send SQL to the database

• syntax:

Statement stmt = con.createStatement();

Using statements

• creating a tablestmt.executeUpdate(

"CREATE TABLE COFFEES "

+ "(COF_NAME VARCHAR(32), SUP_ID INTEGER, PRICE FLOAT, "

+ "SALES INTEGER, TOTAL INTEGER)");

Using statements

• inserting datastmt.executeUpdate(

"INSERT INTO COFFEES "

+ "VALUES ('Colombian', 101, 7.99, 0, 0)");

Sample query

• in SQL:

SELECT COF_NAME, PRICE FROM COFFEES

Query result

COF_NAME PRICE

------------------ -----

Colombian 7.99

French_Roast 8.99

Espresso 9.99

Colombian_Decaf 8.99

French_Roast_Decaf 9.99

Retrieving data with ResultSet

• Statements can run a query on a database

• This returns an object.

• This object is a ResultSet.

Running the query in Java

Statement stmt = con.createStatement();

ResultSet rs = stmt.executeQuery(

"SELECT COF_NAME, PRICE FROM COFFEES");

Inspecting the ResultSet

while (rs.next()) {

String s =

rs.getString("COF_NAME");

float n = rs.getFloat("PRICE");

System.out.println(s + " " + n);

}

Output

• The output will look something like this:

Colombian 7.99

French_Roast 8.99

Espresso 9.99

Colombian_Decaf 8.99

French_Roast_Decaf 9.99

alternative syntax

while (rs.next()) {

String s =

rs.getString(1);

float n = rs.getFloat(2);

System.out.println(s + " " + n);

}

• note: starts at 1, not 0!

some ResultSet retrieval methods

• getString()

• getInt()

• getFloat()

• getObject()

• … many others

Closing

• When finished, call close() on– ResultSet objects– Statement objects– Connection objects

• … or you may have a memory leak!

Exceptions

• Most methods on classes in the java.sql package throw java.sql.SQLException

• SQLException.getMessage() shows database error

• SQLException is a checked exception

• so: try/catch/finally or throws