 2004 Keith Vander Linden. All Rights Reserved. Calvin CollegeDepartment of Computer Science(1/25) Database Programming with JDBC Keith Vander Linden Calvin College

 2004 Keith Vander Linden. All Rights Reserved. Calvin CollegeDepartment of Computer Science(2/25) Overview Introduction An Example Exercise 1 – a simple JDBC connectionExercise 1 JDBC Classes Summary Exercise 2 – recursive SQL with Java/JDBCExercise 2

 2004 Keith Vander Linden. All Rights Reserved. Calvin CollegeDepartment of Computer Science(3/25) Database Programming The world of information technology revolves around databases. While interactive interfaces to database systems are useful, most database work is done though database programs. Approaches to database programming:  Embedding commands in a programming language (e.g., SQLJ)  Using a database API (e.g., JDBC, ODBC, ADO.net)  Designing a database programming language (e.g., PL/SQL, T-SQL)

 2004 Keith Vander Linden. All Rights Reserved. Calvin CollegeDepartment of Computer Science(4/25) Impedance Mismatch Relational databases fields records tables General-purpose programming languages standard data types classes The problem is to bind: relational fields, records and tables native 4GL variables, arrays and classes

 2004 Keith Vander Linden. All Rights Reserved. Calvin CollegeDepartment of Computer Science(5/25) JDBC Sun Microsystem’s database API for Java.  cf. ODBC/ADO.net Supports Sun’s mantra: “Write once, run anywhere”  JDBC supports portability across DBMS vendors.  Java supports portability across hardware platforms. The typical JDBC interaction sequence: 1. Establish a connection to a database 2. Interact with the database 3. Close the connection

 2004 Keith Vander Linden. All Rights Reserved. Calvin CollegeDepartment of Computer Science(6/25) A JDBC Example import java.sql.*; class SimpleJDBC { public static void main (String args[]) throws SQLException { DriverManager.registerDriver(new oracle.jdbc.OracleDriver()); Connection conn = DriverManager.getConnection “login", “pswd"); Statement stmt = conn.createStatement(); try { ResultSet rset = stmt.executeQuery ("SELECT firstName, lastName FROM Student"); while (rset.next ()) System.out.println (rset.getString(1) + " " + rset.getString(2)); rset.close(); } catch (SQLException se) { System.out.println("oops! can't query the Student table. Error:"); se.printStackTrace(); } stmt.close(); conn.close(); }

 2004 Keith Vander Linden. All Rights Reserved. Calvin CollegeDepartment of Computer Science(7/25) The Output % /usr/java/j2sdk1.4.2/bin/javac -classpath /opt/oracle/product/9ir2/jdbc/lib/ojdbc14.jar:. SimpleJDBC.java % /usr/java/j2sdk1.4.2/bin/java -classpath /opt/oracle/product/9ir2/jdbc/lib/ojdbc14.jar:. SimpleJDBC Adam Adams Bert Benson Cathy Cahill Derrick De Vries Ernest Evers Francetta Franks Gabby Gonzales Harold Hornby Inez Inglewood Jack Jansma Kevin Kline Laurance Lancaster Valery Vander Meiden

 2004 Keith Vander Linden. All Rights Reserved. Calvin CollegeDepartment of Computer Science(8/25) A JDBC Example import java.sql.*; class SimpleJDBC { public static void main (String args[]) throws SQLException { DriverManager.registerDriver(new oracle.jdbc.OracleDriver()); Connection conn = DriverManager.getConnection “login", “pswd"); Statement stmt = conn.createStatement(); try { ResultSet rset = stmt.executeQuery ("SELECT firstName, lastName FROM Student"); while (rset.next ()) System.out.println (rset.getString(1) + " " + rset.getString(2)); rset.close(); } catch (SQLException se) { System.out.println("oops! can't query the Student table. Error:"); se.printStackTrace(); } stmt.close(); conn.close(); } Import the JDBC API definition.

 2004 Keith Vander Linden. All Rights Reserved. Calvin CollegeDepartment of Computer Science(9/25) A JDBC Example import java.sql.*; class SimpleJDBC { public static void main (String args[]) throws SQLException { DriverManager.registerDriver(new oracle.jdbc.OracleDriver()); Connection conn = DriverManager.getConnection “login", “pswd"); Statement stmt = conn.createStatement(); try { ResultSet rset = stmt.executeQuery ("SELECT firstName, lastName FROM Student"); while (rset.next ()) System.out.println (rset.getString(1) + " " + rset.getString(2)); rset.close(); } catch (SQLException se) { System.out.println("oops! can't query the Student table. Error:"); se.printStackTrace(); } stmt.close(); conn.close(); } Create a “standard” Java application.

 2004 Keith Vander Linden. All Rights Reserved. Calvin CollegeDepartment of Computer Science(10/25) A JDBC Example import java.sql.*; class SimpleJDBC { public static void main (String args[]) throws SQLException { DriverManager.registerDriver(new oracle.jdbc.OracleDriver()); Connection conn = DriverManager.getConnection “login", “pswd"); Statement stmt = conn.createStatement(); try { ResultSet rset = stmt.executeQuery ("SELECT firstName, lastName FROM Student"); while (rset.next ()) System.out.println (rset.getString(1) + " " + rset.getString(2)); rset.close(); } catch (SQLException se) { System.out.println("oops! can't query the Student table. Error:"); se.printStackTrace(); } stmt.close(); conn.close(); } Load the JDBC driver for your DBMS and establish a connection to that DBMS.

 2004 Keith Vander Linden. All Rights Reserved. Calvin CollegeDepartment of Computer Science(11/25) A JDBC Example import java.sql.*; class SimpleJDBC { public static void main (String args[]) throws SQLException { DriverManager.registerDriver(new oracle.jdbc.OracleDriver()); Connection conn = DriverManager.getConnection “login", “pswd"); Statement stmt = conn.createStatement(); try { ResultSet rset = stmt.executeQuery ("SELECT firstName, lastName FROM Student"); while (rset.next ()) System.out.println (rset.getString(1) + " " + rset.getString(2)); rset.close(); } catch (SQLException se) { System.out.println("oops! can't query the Student table. Error:"); se.printStackTrace(); } stmt.close(); conn.close(); } Create an SQL statement and pass it to the DBMS. Handle any error that might occur.

 2004 Keith Vander Linden. All Rights Reserved. Calvin CollegeDepartment of Computer Science(12/25) A JDBC Example import java.sql.*; class SimpleJDBC { public static void main (String args[]) throws SQLException { DriverManager.registerDriver(new oracle.jdbc.OracleDriver()); Connection conn = DriverManager.getConnection “login", “pswd"); Statement stmt = conn.createStatement (); try { ResultSet rset = stmt.executeQuery ("SELECT firstName, lastName FROM Student"); while (rset.next ()) System.out.println (rset.getString(1) + " " + rset.getString(2)); rset.close(); } catch (SQLException se) { System.out.println("oops! can't query the Student table. Error:"); se.printStackTrace(); } stmt.close(); conn.close(); } Process the results of the SQL query.

 2004 Keith Vander Linden. All Rights Reserved. Calvin CollegeDepartment of Computer Science(13/25) A JDBC Example import java.sql.*; class SimpleJDBC { public static void main (String args[]) throws SQLException { DriverManager.registerDriver(new oracle.jdbc.OracleDriver()); Connection conn = DriverManager.getConnection “login", “pswd"); Statement stmt = conn.createStatement(); try { ResultSet rset = stmt.executeQuery ("SELECT firstName, lastName FROM Student"); while (rset.next ()) System.out.println (rset.getString(1) + " " + rset.getString(2)); rset.close(); } catch (SQLException se) { System.out.println("oops! can't query the Student table. Error:"); se.printStackTrace(); } stmt.close(); conn.close(); } Close the record set, the statement, and the connection.

 2004 Keith Vander Linden. All Rights Reserved. Calvin CollegeDepartment of Computer Science(14/25) Exercise 1 Create a simple application with Java and JDBC to print out the contents of a relational table.  The stub code in exercise1 assumes the existence of a MS Access database called lab10.mdb.

 2004 Keith Vander Linden. All Rights Reserved. Calvin CollegeDepartment of Computer Science(15/25) JDBC Connections Connection conn = “login", “pswd"); The URL string for the connection contains:  the protocol (jdbc)  the vendor (oracle)  the driver (oci8, oci7, thin)  the server (mydb) The Connection class is an interface, so you cannot create Connection objects directly. All interactions between the java program and the database will be done through this object.

 2004 Keith Vander Linden. All Rights Reserved. Calvin CollegeDepartment of Computer Science(16/25) JDBC Statements There are three classes for sending SQL statements:  Statement – for SQL statements without parameters  PreparedStatement – for precompiled/parameterized statements  CallableStatement – for executing stored procedures These “statements” are Java classes, not individual SQL statements. They can be reused. JDBC Statements are executed with:  executeUpdate() – executes SQL data definition statements  executeQuery() – returns the results of the SQL query JDBC Statements support dynamic SQL statements.

 2004 Keith Vander Linden. All Rights Reserved. Calvin CollegeDepartment of Computer Science(17/25) JDBC Updates The executeUpdate() statement performs updates: Statement stmt = conn.createStatement(); stmt.executeUpdate("CREATE TABLE Part (" + " id INTEGER PRIMARY KEY, " + " name VARCHAR2(10), " + " cost REAL )"); stmt.executeUpdate("INSERT INTO Part VALUES (1, 'simple', 10)"); When used for DDL statements, executeUpdate() returns 0. When used to modify data, it returns the number of rows affected by the update.

 2004 Keith Vander Linden. All Rights Reserved. Calvin CollegeDepartment of Computer Science(18/25) JDBC ResultSets The executeQuery() command returns a ResultSet. ResultSet rset = stmt.executeQuery ("SELECT firstName, lastName FROM Student"); while (rset.next()) System.out.println(rset.getString(1) + " " + rset.getString(2)); The ResultSet provides:  a cursor pointing just before the first result row  next(), to get the next row, returning true if successful  getXXX() to retrieve column values of Java type XXX The argument to getXXX() may either be an index number, getInt(1), or a field name, getDouble(“cost”). ResultSet cursors can be:  Forward-only or scrollable  Read-only or read-write

 2004 Keith Vander Linden. All Rights Reserved. Calvin CollegeDepartment of Computer Science(19/25) JDBC PreparedStatements Sometimes it is more convenient or efficient to work with precompiled statements. PreparedStatement pstmt = conn.prepareStatement( “SELECT FROM Student WHERE lastName LIKE ?"); The statement can then be configured and run. pstmt.setString(1, ‘Vander%’); ResultSet rset = pstmt.executeQuery() ; The PerparedStatement provides:  setXXX() functions to set the statement values for Java type XXX As with getXXX(), setXXX() arguments may be an index number or a field name.

 2004 Keith Vander Linden. All Rights Reserved. Calvin CollegeDepartment of Computer Science(20/25) JDBC Transactions JDBC Connections can support transactions. try { conn.setAutoCommit(false); stmt.executeUpdate(“CREATE TABLE t (id INTEGER, name VARCHAR2(10))"); stmt.executeUpdate(“INSERT INTO t VALUES (10, ‘some name’)”); conn.commit(); conn.setAutoCommit(true); } catch (SQLException se) { System.out.println(“SQL Exception:“ + se.getMessage()); conn.rollback(); connsetAutoCommit(true); } This code will rollback() for any form of exception thrown by the code in the try block.

 2004 Keith Vander Linden. All Rights Reserved. Calvin CollegeDepartment of Computer Science(21/25) Summary This lecture covered the basic concepts for accessing databases from 4 th generation programming languages. It illustrated the concepts using JDBC:  Connections  Statements  ResultSets It also discussed JDBC support for transactions. References ( )

 2004 Keith Vander Linden. All Rights Reserved. Calvin CollegeDepartment of Computer Science(22/25) Exercise 2 Use the remaining time to work through the following JDBC exercise.  SQL is not recursive, so it can’t be used to compute the cost of a part and all its sub-parts (and their sub- parts and so forth).  Java is recursive, so it can be used with JDBC to perform this computation.  Start with the code given in exercise2 and then write:  code to load the appropriate database values into the tables.  a recursive Java function that uses JDBC to compute the total cost for potentially complex part. You’ll find the algorithm in the code.

 2004 Keith Vander Linden. All Rights Reserved. Calvin CollegeDepartment of Computer Science(23/25) Exercise 2: The Database The parts database has the following relational table design:  Here, a part has its own cost and can have potentially many sub-parts. The count indicates the number of sub-parts required by the super-part. Part name ID cost m SubPart m count

 2004 Keith Vander Linden. All Rights Reserved. Calvin CollegeDepartment of Computer Science(24/25) Part ID name price 1 simple complex sub sub subsub subsub Exercise 2: Sample Data Here we see that part 1 is simple in that it has no sub-parts mentioned in the SubPart table. Part 2 is complex in that it has two sub-parts (3 & 4) one of which (4) has its own sub-parts (5 & 6) SubPart PID CID count

 2004 Keith Vander Linden. All Rights Reserved. Calvin CollegeDepartment of Computer Science(25/25) Exercise 2: Hints You may assume that the database contains no “cycles”, e.g., part 1 is made up of part 2’s, which are each made up of part 1’s. Get the trivial case, i.e., part 1, working first. It has no sub-parts. Print out appropriate error message if the given part doesn’t exist.