MIS 3023 Business Programming II Professor: Akhilesh Bajaj Introduction to JDBC © Akhilesh Bajaj, All Rights Reserved.

Goals for Today To understand the programs we wrote in the JDBC lab To understand the basic JDBC API

Advantages of JDBC JDBC = Java Database Connectivity (popular belief though not true) The API (Application Programming Interface) is meant to allow java programs to connect to a database, to retrieve, insert, update or delete data in the database, and to process the data in the java program. Some advantages of this: The java program will be largely unchanged across different platforms & databases. The only changes will be in the SQL part, in case we move across databases, that have slightly different SQL syntax. The bulk of the java program (the processing part) will be unchanged. This means potentially large increases in application programmer productivity and also in maintenance costs of the application.

JDBC Drivers JDBC connections to a database are done using a JDBC driver. Almost all vendors now offer JDBC drivers. We are using a jdbc-odbc bridge driver to talk to a MS Access Database or to a MYSL database. In case we want to run our programs on another database, like Oracle, we need to install the JDBC driver for that DBMS on our machine. has a searchable database of available drivers for different DBMSs. In addition, we can also check the sites for the DBMS vendors, like

Loading the Driver The JDBC API is in the java.sql package. We imported that in all the code that we wrote in the labs. The driver is loaded into a program with the following code: Class.forName(“sun.jdbc.odbc.JdbcOdbcDriver”); If we are using another driver, then it’s documentation will tell us its class name. E.g., A driver whose class name is jdbc.DriverXYZ will be loaded with: Class.forName(“jdbc.DriverXYZ”); Here, the java.lang.ClassLoader object locates and loads the driver class from the CLASSPATH.

Connecting to the Database java.sql.DriverManager is a static class that provides methods to obtain connections. The advantage is that this class provides a uniform method of accessing all the drivers, so we write the same code for all drivers, except that the driver class name is different for different drivers. The DriverManager.getConnection(url,user,password) method provides an easy way to access all databases. URL: Basic syntax: protocol: : Protocol is always jdbc. Subprotocol is supplied by the maker of that particular JDBC driver. In our case, it’s odbc. Subname is the way to identify the database. In our case,it’s simply the name of the database: MyGarage. If the database is on another machine, then the subname is where the address will be, e.g., //hostname:port/subsubname

Connection Interface The Connection interface offers 3 methods for sending SQL statements to the underlying database: createStatement(): For a simple, parameterless SQL statement prepareStatement(): For a prepared statement (with parameters) prepareCall(): For a stored procedure. We won’t be doing this method, because stored procedures are inherently DB specific and hence against the principle of portability of an application. In CreateGarage.java & DropGarage.java, we used the createStatement() method. This method gives a Statement Object. In InsertGarage.java, we used the prepareStatement() method. This method gives a PreparedStatement object.

Statement Interface A Statement object is created using the Connection method createStatement(). Statement objects are used to send SQL statements without parameters. The method we used in this interface is: int executeUpdate(String sql): Performs an Update, Insert or Delete on the database, and is also used for DDL statements (like create table). It returns the number of rows affected by the statement.

PreparedStatement Interface This is an extension of the Statement interface. Used for parametrized SQL queries. we wrote these in InsertGarage.java. The new methods here include setInt(int parameterIndex, int x): sets the given parameter to x. Similarly, we have setDouble, setString, SetDate, etc.

SQLException Class Is derived from java.lang.Exception. It contains a description of the error, and a chain to the next SQL Exception object, in case there was more than one exception. In our labs, we printed out only the current SQL exception. Below is useful code that prints out the chain of exceptions: catch(SQLException ex) { System.err.println(“\n---SQL EXCEPTION CAUGHT---\n”); while(ex!=null){ System.err.println("SQLException: "+ex.getMessage()); ex.printStackTrace(System.err); ex=ex.getNextException(); System.err.println( “ ” ); }//while }//catch

Conclusion We made sense of the lab we have done, and also got an overview of the portion of the JDBC API,that is used most often. For further reading, we can look at: 1. JDBC: Database Access with Java, by Hamilton, Cattell & Fisher Addison Wesley has a lot of useful information on JDBC, including features on new versions of the API.