Database Programming with JDBC

2004 Keith Vander Linden. All Rights Reserved. Calvin CollegeDepartment of Computer Science(1/25)

Database Programming with JDBC

Keith Vander Linden

Calvin College


Overview

Introduction

An Example

Exercise 1 – a simple JDBC connection

JDBC Classes

Summary

Exercise 2 – recursive SQL with Java/JDBC


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)


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


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


A JDBC Exampleimport java.sql.*;

class SimpleJDBC { public static void main (String args[]) throws SQLException { DriverManager.registerDriver(new oracle.jdbc.OracleDriver()); Connection conn = DriverManager.getConnection ("jdbc:oracle:oci8:@mydb", “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(); }}


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:. SimpleJDBCAdam AdamsBert BensonCathy CahillDerrick De VriesErnest EversFrancetta FranksGabby GonzalesHarold HornbyInez InglewoodJack JansmaKevin KlineLaurance LancasterValery Vander Meiden







Import the JDBC API definition.







Create a “standard” Java

application.







Load the JDBC driver for your DBMS and establish a connection to that DBMS.







Create an SQL statement and pass it to the DBMS.

Handle any error that might occur.




Statement stmt = conn.createStatement (); try { ResultSet rset = stmt.executeQuery ("SELECT firstName, lastName FROM Student");



Process the results of the SQL query.







Close the record set, the statement, and the

connection.


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.


JDBC ConnectionsConnection conn = DriverManager.getConnection("jdbc:oracle:oci8:@mydb", “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.


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.


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.


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


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.


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.


Summary

• This lecture covered the basic concepts for accessing databases from 4th generation programming languages.

• It illustrated the concepts using JDBC: Connections Statements ResultSets

• It also discussed JDBC support for transactions.• References (http://java.sun.com/products/jdbc/ )


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.


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.

Partname

ID

costm

SubPart

m

count


Part ID name price 1 simple 10.00 2 complex 5.00 3 sub1 4.00 4 sub2 3.00 5 subsub1 2.00 6 subsub2 1.00

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)

SubPartPID CID count 2 3 1 2 4 2 4 5 1 4 6 2


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.

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Database Programming with JDBC