1. JDBC

2. Java Database Connectivity (JDBC) Use the java.sql package to query and update the database. JDBC is an API that allows java to communicate with a database server using SQL commands. Most important members, such as Connection, Statement, and ResultSet, are interfaces instead of being classes. –This is because, the point of JDBC is to hide the specifics of accessing a particular database. –The implementation of the underlying classes is done in the vendor provided driver and associated classes.

3. Basics DriverManager is responsible for keeping track of all the JDBC drivers that are available on a system. First task of a JDBC program is to load an appropriate driver for the type of database being used. After that a JDBC program should connect to the database by calling DriverManager.getConnection(). –You specify the database to connect with a jdbc:URL. This URL has the following general syntax: jdbc:subprotocol:host:port:databasename import java.sql.*; class InsertMovie { public static void main (String args []) throws SQLException { DriverManager.registerDriver (new oracle.jdbc.driver.OracleDriver()); Connection conn = DriverManager.getConnection ("jdbc:oracle:thin:@oracle.csc.uvic.ca:1521:TEACH", "thomo", “password"); // @machineName:port:SID, userid, password …

4. Creating JDBC Statements A Statement object is what sends your SQL statement to the DBMS. You simply create a Statement object and then execute it: –For a SELECT statement, use executeQuery. –For statements that create or modify tables, use executeUpdate. It takes an instance of an active connection to create a Statement object. –In the following example, we use our Connection object conn to create the Statement object stmt: –Statement stmt = conn.createStatement(); At this point stmt exists, but it does not have an SQL statement to pass on to DBMS. –We need to supply that with execute…

5. import java.sql.*; class InsertMovie { public static void main (String args []) throws SQLException { DriverManager.registerDriver (new oracle.jdbc.driver.OracleDriver()); Connection conn = DriverManager.getConnection ("jdbc:oracle:thin:@oracle.csc.uvic.ca:1521:TEACH", "user", "password"); // @machineName:port:SID, userid, password String title = "Movie ABCDEF"; int year = 2005; int length = 200; String studioName = "UVic"; String statementString = "INSERT INTO Movie(title, year, length, studioName) " + "VALUES( '" + title + "'," + year + "," + length + ",'" + studioName + "')"; Statement stmt = conn.createStatement(); stmt.executeUpdate(statementString); stmt.close(); } No semicolon ending an SQL statement

6. Getting Data Example ResultSet rset = stmt.executeQuery( "SELECT title, year " + "FROM Movie"); while (rset.next()) … Variable rset, contains the rows of the query result. The first call of next() positions a "cursor" on the first row. Successive invocations of next() move the cursor down one row at a time.

7. Using the getXXX methods Use the getXXX method of the appropriate type to retrieve the value in each column. –getString() for VARCHAR, CHAR –getInt() for INT, NUMBER –etc. while (rset.next()) { String s = rset.getString("Title"); int n = rset.getInt("Year"); System.out.println(s + " " + n); } However we can also do instead: String s = rset.getString(1); int n = rset.getInt(2); Column Name Column Position

8. Using the getXXX methods (Continued) JDBC allows a lot of flexibility as far as which getXXX methods you can use to retrieve the different SQL types. For example, the method getInt can be used to retrieve any of the numeric or character types. The data it retrieves will be converted to an INT; –that is, if the SQL type is VARCHAR, JDBC will attempt to parse an integer out of the VARCHAR. The getString method can retrieve any other datatype. However, in such a case we should convert strings to numbers.

9. import java.sql.*; class dbAccess { public static void main (String args []) throws SQLException { DriverManager.registerDriver (new oracle.jdbc.driver.OracleDriver()); Connection conn = DriverManager.getConnection ("jdbc:oracle:thin:@orcus.csc.uvic.ca:1521:TEACH", "thomo", “password"); // @machineName:port:SID, userid, password Statement stmt = conn.createStatement(); ResultSet rset = stmt.executeQuery( "SELECT title, year " + "FROM Movie"); while (rset.next()) System.out.println (rset.getString("title") + " " + rset.getString("year")); stmt.close(); }

10. Prepared statements Sometimes it is more convenient or more efficient to use a PreparedStatement object for sending SQL statements to the database. When we want to execute a Statement object many times, it will normally reduce execution time to use a PreparedStatement object instead. –A PreparedStatement is given an SQL template statement when it is created. –This is precompiled and and ready to run many times without the need to be compiled each time a query conforming to it is given. Example PreparedStatement updateMovies = conn.prepareStatement( "UPDATE Movie SET studioName = ? WHERE studioName = ?");

11. import java.sql.*; class UpdateMovie { public static void main (String args []) throws SQLException { DriverManager.registerDriver (new oracle.jdbc.driver.OracleDriver()); Connection conn = DriverManager.getConnection ("jdbc:oracle:thin:@oracle.csc.uvic.ca:1521:TEACH", "thomo", “password"); // @machineName:port:SID, userid, password PreparedStatement updateMovieStatement; String updateMovieString = "UPDATE Movie " + "SET studioName = ? " + "WHERE studioName LIKE ?"; updateMovieStatement = conn.prepareStatement(updateMovieString);

12. String studiosBoughtByParamount [] = {"Disney", "Fox"}; for(int i=0; i<studiosBoughtByParamount.length; i++) { updateMovieStatement.setString(1, "Paramount"); updateMovieStatement.setString(2, "%"+studiosBoughtByParamount[i]+"%"); updateMovieStatement.executeUpdate(); } updateMovieStatement.close(); }