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( ); 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 table stmt.executeUpdate( "CREATE TABLE COFFEES " + "(COF_NAME VARCHAR(32), SUP_ID INTEGER, PRICE FLOAT, " + "SALES INTEGER, TOTAL INTEGER)");

Using statements inserting data stmt.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