1. 225 City Avenue, Suite 106 Bala Cynwyd, PA 19004 610.206.0101, phone 610.206.0102, fax www.learnquest.com Connecting to a Database

2. 2 Learning Objectives  Drivers  The DriverManager Class  Using JDBC Drivers  Database Connections  Connecting to a Database  Connection Failure  Read-Only Connections  Closing the Connection  Summary

3. 3 Drivers  The java.sql package defines interfaces that describe how Java will connect to a database  Vendors provide implementations of these interfaces which allow a Java program to connect to a particular RDBMS (Oracle, DB2 etc.)  This vendor provided code is called a “Driver”

4. 4  If your program needs to connect to two different RDBMSs (DB2, Oracle) it will need to have two sets of drivers loaded at the same time. The DriverManager class manages these drivers  DriverManager keeps track of the drivers that are available and handles establishing a connection between a database and the appropriate driver  It manages events such as driver login time limits and the printing of log and tracing messages The DriverManager Class

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7. 7  A Driver class is loaded and registered with the DriverManager in one of two ways : By calling the method Class.forName By adding the Driver class to the java.lang.System property jdbc.drivers Using JDBC Drivers

8. 8 The JDBC-ODBC Driver  Java contains a built-in driver called the JDBC-ODBC driver. It uses Open Database Connectivity to allow a program to connect to any database that is ODBC compliant. Such databases include Microsoft Access, SQL-Server, Cloudscape and others  The JDBC-ODBC driver does not perform well enough to be used for anything other than testing

9. 9 Example: Loading a Driver try { // loading the JDBC-ODBC Driver Class.forName( "sun.jdbc.odbc.JdbcOdbcDriver"); } catch(ClassNotFoundException e) { System.out.println("Message: “ + e.getMessage()); }

10. 10 Types of JDBC Drivers: Type 1JDBC-ODBC bridge third party API Type 2Native-API partly-Java driver Type 3JDBC-Net pure Java driver Type 4Native-protocol pure Java driver In general the higher numbered drivers are preferred. In practice you will simply use a driver provided by the vendor Using JDBC Drivers

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12. 12  Once the driver is loaded you must establish a connection to the database using the getConnection() method of the DriverManager class  getConnection() accepts a vendor specific string which holds the database location and other connection information  A user can get information about a Connection object's database by invoking the Connection.getMetaData method Database Connections

13. 13  The JDBC 2.0 Standard Extension API provides the DataSource interface as an alternative to the DriverManager for establishing a connection  Data sources create pools of connections that can be reused by different programs. If many different programs need to connect to the same database a datasource can provide better performance than simply setting up a separate connection in each and every program  Data sources are used in J2EE Data Sources

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15. 15  When an application uses the DriverManager to create a Connection object it must supply a URL to the DriverManager.getConnection method  A JDBC URL provides a way of identifying a data source so that the appropriate driver will recognize it and establish a connection with it  The standard syntax for JDBC URLs: jdbc: : Connecting to a Database (con’t)

16. 16 The JDBC URL  A URL (Uniform Resource Locator) gives information for locating a resource on the Internet. It can be thought of as an address  The JDBC URL is composed of: Jdbc – the protocol. The protocol in a JDBC URL is always jdbc - the name of the driver or the name of a database connectivity mechanism, which may be supported by one or more drivers - a way to identify the data source The subname can vary depending on the subprotocol and it can have any internal syntax the driver writer chooses including a subname The point of a subname is to give enough information to locate the data source

17. 17 Connection Example try { Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); // Define the DSN(Data Source Name) String url = "Jdbc:Odbc:JdbcLab"; String databaseUser = ""; String databasePassword = ""; Connection databaseConnection = DriverManager.getConnection(url,databaseUser, databasePassword); } catch(Exception e) { // error processing here… }

18. 18  If the Connection fails with the message “Class not found” it usually means that the Driver is not in the CLASSPATH  If the Connection fails with the message “Driver not found” it usually means that the Driver has not been registered with the DriverManager Common Connection Problems

19. 19  One can put the connection to the database in read-only mode as a hint to the driver to enable database optimizations  The method of Connection interface setReadOnly() is used to establish read-only connection  The method of Connection interface isReadOnly() is used to get an information whether Connection object is in read-only mode Read-Only Connections

20. 20  It is recommended that one explicitly closes database connections when they are no longer needed: myConnection.close();  A Connection object is automatically closed when it is garbage collected  Also certain fatal errors can close a Connection object Closing the Connection

21. 21  The DriverManager class provides a method to establish a connection with a database  The traditional way to establish a connection with a database is to use DriverManager.getConnection method  It is recommended that programmers explicitly close all connections with the method Connection.close() as soon as they are no longer needed, thereby freeing DBMS resources as early as possible Summary

22. 22 Any Questions?  After discussing this chapter with your instructor please complete the exercises in Lab 9