Download 10.jdbc - Calvin College

Database Programming
with JDBC
Keith Vander Linden
Calvin College
(1/25)
2004 Keith Vander Linden. All Rights Reserved.
Department of Computer Science
Calvin College
Overview
Introduction
An Example
Exercise 1 – a simple JDBC connection
JDBC Classes
Summary
Exercise 2 – recursive SQL with Java/JDBC
(2/25)
2004 Keith Vander Linden. All Rights Reserved.
Department of Computer Science
Calvin College
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)
(3/25)
2004 Keith Vander Linden. All Rights Reserved.
Department of Computer Science
Calvin College
Impedance Mismatch
Relational databases
General-purpose
programming languages
• fields
• records
• tables
• standard data types
• classes
The problem is to bind:
• relational fields, records and tables
• native 4GL variables, arrays and classes
(4/25)
2004 Keith Vander Linden. All Rights Reserved.
Department of Computer Science
Calvin College
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
(5/25)
2004 Keith Vander Linden. All Rights Reserved.
Department of Computer Science
Calvin College
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 ("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();
}
}
(6/25)
2004 Keith Vander Linden. All Rights Reserved.
Department of Computer Science
Calvin College
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
(7/25)
2004 Keith Vander Linden. All Rights Reserved.
Department of Computer Science
Calvin College
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 ("jdbc:oracle:oci8:@mydb", “login", “pswd");
Import the JDBC
API definition.
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();
}
}
(8/25)
2004 Keith Vander Linden. All Rights Reserved.
Department of Computer Science
Calvin College
Create a
A JDBC Example
“standard” Java
import java.sql.*;
application.
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();
}
}
(9/25)
2004 Keith Vander Linden. All Rights Reserved.
Department of Computer Science
Calvin College
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 ("jdbc:oracle:oci8:@mydb", “login", “pswd");
Statement stmt = conn.createStatement();
try {
ResultSet rset =
stmt.executeQuery ("SELECT firstName, lastName FROM Student");
Load the JDBC driver for
your DBMS and establish a
connection to that DBMS.
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();
}
}
(10/25)
2004 Keith Vander Linden. All Rights Reserved.
Department of Computer Science
Calvin College
A JDBC Example
Create an SQL statement
and pass it to the DBMS.
class SimpleJDBC {
Handle
any error
public static void main (String args[]) throws
SQLException
{ that
DriverManager.registerDriver(new oracle.jdbc.OracleDriver());
might occur.
Connection conn =
import java.sql.*;
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();
}
}
(11/25)
2004 Keith Vander Linden. All Rights Reserved.
Department of Computer Science
Calvin College
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 ("jdbc:oracle:oci8:@mydb", “login", “pswd");
Process the results
the SQL query.
conn.createStatementof
();
Statement stmt =
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();
}
}
(12/25)
2004 Keith Vander Linden. All Rights Reserved.
Department of Computer Science
Calvin College
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 ("jdbc:oracle:oci8:@mydb", “login", “pswd");
Statement stmt = conn.createStatement();
try {
ResultSet rset =
stmt.executeQuery ("SELECT firstName, lastName FROM Student");
Close the record set,
the statement, and the
connection.
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();
}
}
(13/25)
2004 Keith Vander Linden. All Rights Reserved.
Department of Computer Science
Calvin College
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.
(14/25)
2004 Keith Vander Linden. All Rights Reserved.
Department of Computer Science
Calvin College
JDBC Connections
Connection 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.
(15/25)
2004 Keith Vander Linden. All Rights Reserved.
Department of Computer Science
Calvin College
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.
(16/25)
2004 Keith Vander Linden. All Rights Reserved.
Department of Computer Science
Calvin College
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.
(17/25)
2004 Keith Vander Linden. All Rights Reserved.
Department of Computer Science
Calvin College
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
(18/25)
2004 Keith Vander Linden. All Rights Reserved.
Department of Computer Science
Calvin College
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.
(19/25)
2004 Keith Vander Linden. All Rights Reserved.
Department of Computer Science
Calvin College
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.
(20/25)
2004 Keith Vander Linden. All Rights Reserved.
Department of Computer Science
Calvin College
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/ )
(21/25)
2004 Keith Vander Linden. All Rights Reserved.
Department of Computer Science
Calvin College
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 subparts 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:


(22/25)
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.
Department of Computer Science
Calvin College
Exercise 2: The Database
• The parts database has the following relational
table design:
ID
m
name
SubPart
Part
count
m
cost
 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.
(23/25)
2004 Keith Vander Linden. All Rights Reserved.
Department of Computer Science
Calvin College
Exercise 2: Sample Data
Part
ID name
1 simple
2 complex
3 sub1
4 sub2
5 subsub1
6 subsub2
price
10.00
5.00
4.00
3.00
2.00
1.00
SubPart
PID CID
2
3
2
4
4
5
4
6
count
1
2
1
2
• 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)
(24/25)
2004 Keith Vander Linden. All Rights Reserved.
Department of Computer Science
Calvin College
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.
(25/25)
2004 Keith Vander Linden. All Rights Reserved.
Department of Computer Science
Calvin College