1. CS JDBC

2. Introducing JDBC
JDBC: is an API that provides “universal data access for the Java2 platform” Allows you to connect to a known data source using common OO semantics using Java
Allows you to issue standard SQL commands on that data source
Provides you with classes to facilitate access to and manipulation of:
returned data and,
generated exceptions

3. JDBC Driver Types Type 1 (JDBC-ODBC Bridge Technology)
Type 2 (JNI drivers for native connection libraries)
Type 3 (Socket-level Middleware Translator)
Type 4 (Pure Java-DBMS driver)

4. Driver Types
Type 2
Type 1
Type 3
Type 4

5. Type 1 Drivers: JDBC-ODBC Bridges
JDBC driver translates call into ODBC and redirects ODBC call to an ODBC driver on the DBMS
ODBC binary code must exist on every client
Translation layer compromises execution speed to small degree

6. Type 2 Drivers: Native-API + Java Driver
Java driver makes JNI calls on the client API (usually written in C or C++)
eg: Sybase dblib or ctlib
eg: Oracle Call Interface libs (OCI)
Requires client-side code to be installed
Often the fastest solution available
Native drivers are usually delivered by DBMS vendor
Bug in driver can crash JVMs

7. Type 3 Drivers: JDBC-Middleware Pure Java Driver
JDBC driver translates JDBC calls into a DBMS-independent protocol
Then, communicates over a socket with a middleware server that translates Java code into native API DBMS calls
No client code need be installed
Single driver provides access to multiple DBMSs, eg. WebLogic, Tengah drivers
Type 3 drivers auto-download for applets.
Communication is indirect via a middleware server

8. Type 4 Drivers: Pure Java Drivers
Java drivers talk directly to the DBMS using Java sockets
No Middleware layer needed, access is direct.
Simplest solution available.
No client code need be installed.
Type 4 drivers auto-download for applets

9. JDBC Drivers
JDBC drivers exist for every major database including: Oracle, SQL Server, Sybase, and MySQL.

10. Six Steps to Using JDBC (simple program…no connection pooling/middleware)
Load the JDBC Driver
Establish the Database Connection
Create a Statement Object
Execute a Query
Process the Results
Close the Connection

11. A standard simple JDBC application
// Load the JDBC driver
Class.forName("oracle.jdbc.OracleDriver").newInstance();
// Connect to the database
Connection conn = DriverManager.getConnection
(connect-string,user, pass);
// Create a statement
Statement stmt = conn.createStatement ();
// Execute the statement: select data from the emp table
boolean results = stmt.execute("select * from emp");
ResultSet rset = null;
if (results) rset = stmt.getResultSet();
// Process results: walk through the result set
while (rset.next ()) {
System.out.println (rset.getString (1) + rset.getString(2)); …. }

12. Overview: Connecting to a Database
// Load the Oracle JDBC driver
Class.forName("oracle.jdbc.OracleDriver").newInstance();
// Connect to the database
Connection conn = DriverManager.getConnection
(connect-string,user, pass);
// Create a statement
Statement stmt = conn.createStatement ();
// Select data from the emp table
boolean results = stmt.execute("SELECT * FROM EMP");
ResultSet rset = null;
if (results) rset = stmt.getResultSet();
// Walk through the result set
while (rset.next ()) {
System.out.println (rset.getString (1) + rset.getString(2)); …. }

13. The JDBC Driver Manager
Management layer of JDBC, interfaces between the client and the driver.
Keeps a list of available drivers
Manages driver login time limits and printing of log and tracing messages
Secure because manager will only allow drivers that come from local file system or the same initial class loader requesting a connection
Most popular use:
Connection getConnection(url, id, passwd);

14. Create a Connection to the database
Call the getConnection method on the DriverManager.
Connection conn =
DriverManager.getConnection(url, login, password)
URLs:
“jdbc:sybase:Tds:skunk:4100/myDB”
Only one requirement: the relevant Drivers must be able to recognize their own URL

15. Overview: Statements // Load the Oracle JDBC driver
Class.forName("oracle.jdbc.OracleDriver").newInstance();
// Connect to the database
Connection conn = DriverManager.getConnection
(connect-string,user, pass);
// Create a statement
Statement stmt = conn.createStatement ();
// Select data from the emp table
boolean results = stmt.execute("SELECT * FROM EMP");
ResultSet rset = null;
if (results) rset = stmt.getResultSet();
// Walk through the result set
while (rset.next ()) {
System.out.println (rset.getString (1) + rset.getString(2)); …. }

16. SQL Statements Types of statements:
Class Statement
Represents a basic SQL statement
Statement stmt = conn.createStatement();
Class PreparedStatement
A precompiled SQL statement, which can offer improved performance, especially for large/complex SQL statements
Class CallableStatement
Allows JDBC programs access to stored procedures
Can be used for both DDL and DML commands

17. Execute an SQL Statement
executeQuery(): execute a query and get a ResultSet back
executeUpdate(): execute an update and get back an int specifying number of rows acted on
UPDATE [table] set [column_name] = value where […]
DELETE from [table] where [column_name] = 5
execute(): exec. unknown SQL, returns true if a resultSet is available:
Statement genericStmt = conn.createStatement();
if( genericStmt.execute(SQLString)) {
ResultSet rs = genericStmt.getResultSet();
process(); }
else {
int updated = genericStmt.getUpdateCount();
processCount(); } …

18. Prepared Statements Use for complex queries or repeated queries
Features:
precompiled at database (statement usually sent to database immediately on creation for compilation)
supply with new variables each time you call it
Example:
PreparedStatement ps = conn.prepareStatement(“UPDATE TABLE SET SALES = ? WHERE CUSTNAME = ?”);
Set with values (use setXXX() methods on PreparedStatement:
ps.setInt(1, );
ps.setString(2, “United Airlines”);
Then execute:
int count = ps.executeUpdate();

19. Overview: ResultSets and Cursors
// Load the Oracle JDBC driver
Class.forName("oracle.jdbc.OracleDriver").newInstance();
// Connect to the database
Connection conn = DriverManager.getConnection
(connect-string,user, pass);
// Create a statement
Statement stmt = conn.createStatement ();
// Select data from the emp table
boolean results = stmt.execute("SELECT * FROM EMP");
ResultSet rset = null;
if (results) rset = stmt.getResultSet();
// Walk through the result set
while (rset.next ()) {
System.out.println (rset.getString (1) + rset.getString(2)); …. }

20. Result Sets and Cursors
Result Sets are returned from queries.
Possible number of rows: zero, one, or more
Cursors are ‘iterators’ that can be user to ‘walk’ through a result set
JDBC 2.0 allows for backward as well as forward cursors, including the ability to go to a specific row or a relative row

21. Result Sets Iterate over all rows: Extract data from the ResultSet
ResultSet rs = stmt.executeQuery(“select id, price from inventory”);
rs.next(), rs.previous(), rs.first(), …
call once to access first row: while(rs.next()) {}
Extract data from the ResultSet
getXXX(columnName/indexVal)
getInt()
getDouble()
getString() (highly versatile, inclusive of others; automatic conversion to String for most types)
getObject() (returns a generic Java Object)
rs.wasNull() - returns true if last get was Null

22. Example : Inserting Data via JDBC

23. import java.sql.*;
public class InsertCoffees {
public static void main(String args[]) throws SQLException {
System.out.println ("Adding Coffee Data");
ResultSet rs = null;
PreparedStatement ps = null;
String url = "jdbc:mysql://localhost/cerami";
Connection con;
Statement stmt;
try {
Class.forName("org.gjt.mm.mysql.Driver");
} catch(java.lang.ClassNotFoundException e) {
System.err.print("ClassNotFoundException: ");
System.err.println(e.getMessage()); } 1

24. 2 3 4 6 try { con = DriverManager.getConnection(url);
stmt = con.createStatement();
stmt.executeUpdate ("INSERT INTO COFFEES " +
"VALUES('Amaretto', 49, 9.99, 0, 0)");
"VALUES('Hazelnut', 49, 9.99, 0, 0)");
"VALUES('Amaretto_decaf', 49, 10.99, 0, 0)");
"VALUES('Hazelnut_decaf', 49, 10.99, 0, 0)");
stmt.close();
con.close();
System.out.println ("Done");
} catch(SQLException ex) {
System.err.println("-----SQLException-----");
System.err.println("SQLState: " + ex.getSQLState());
System.err.println("Message: " + ex.getMessage());
System.err.println("Vendor: " + ex.getErrorCode()); } 2 3 4 6

25. Example : Querying Data via JDBC

26. Class.forName("org.gjt.mm.mysql.Driver");
import java.sql.*;
public class SelectCoffees {
public static void main(String args[]) throws SQLException {
ResultSet rs = null;
PreparedStatement ps = null;
String url = "jdbc:mysql://localhost/cerami";
Connection con;
Statement stmt;
try {
Class.forName("org.gjt.mm.mysql.Driver");
} catch(java.lang.ClassNotFoundException e) {
System.err.print("ClassNotFoundException: ");
System.err.println(e.getMessage()); }
con = DriverManager.getConnection(url);
stmt = con.createStatement(); 1 2 3

27. 4 5 6 ResultSet uprs = stmt.executeQuery("SELECT * FROM COFFEES");
System.out.println("Table COFFEES:");
while (uprs.next()) {
String name = uprs.getString("COF_NAME");
int id = uprs.getInt("SUP_ID");
float price = uprs.getFloat("PRICE");
int sales = uprs.getInt("SALES");
int total = uprs.getInt("TOTAL");
System.out.print(name + " " + id + " " + price);
System.out.println(" " + sales + " " + total); }
uprs.close();
stmt.close();
con.close();
} catch(SQLException ex) {
System.err.println("-----SQLException-----");
System.err.println("SQLState: " + ex.getSQLState());
System.err.println("Message: " + ex.getMessage());
System.err.println("Vendor: " + ex.getErrorCode()); 4 5 6

28. Exception Handling SQL Exceptions
Nearly every JDBC method can throw a SQLException in response to a data access error
If more than one error occurs, they are chained together
SQL exceptions contain:
Description of the error, getMessage
The SQLState (Open Group SQL specification) identifying the exception, getSQLState
A vendor-specific integer, error code, getErrorCode
A chain to the next SQLException, getNextException

29. SQL Exception Example try { ... // JDBC statement.
} catch (SQLException sqle) {
while (sqle != null) {
System.out.println("Message: " + sqle.getMessage());
System.out.println("SQLState: " + sqle.getSQLState());
System.out.println("Vendor Error: " +
sqle.getErrorCode());
sqle.printStrackTrace(System.out);
sqle = sqle.getNextException(); }

30. Using the JDBC MetaData Interface
ResultSet: ResultSetMetaData m = rs.getMetaData()
ResultSetMetaData provides information about the types and properties of the DDL properties of a ResultSet object
ResultSetMetaData provides various methods for finding out information about the structure of a ResultSet:
getColumnClassName(int col): gets fully-qualified Java class name to which a column value will be mapped; eg. Java.lang.Integer, etc.
getColumnCount(): gets the number of columns in the ResultSet
getColumnName(int col): gets the name of column
int getColumnType(int col): gets the JDBC type (java.sql.Types) for the value stored in col; eg. Value 12 = JDBC VARCHAR, etc.
getPrecision(int col): for numbers, gets the mantissa length, for others, gets the number of bytes for column