Java Database Connectivity (JDBC) 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 whole point of JDBC is to hide the specifics of accessing a particular database. An application programmer doesn’t have to worry about the implementation of the underlying classes. –All you have to do is to use the methods defined by the various interfaces. –The implementation of the underlying classes is done in the vendor provided driver and associated classes.

Basics The DriverManager class 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 "thomo", “password"); userid, password …

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, the method to use is executeQuery. –For statements that create or modify tables, the method to use is 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…

import java.sql.*; class InsertMovie { public static void main (String args []) throws SQLException { DriverManager.registerDriver (new oracle.jdbc.driver.OracleDriver()); Connection conn = DriverManager.getConnection "thomo", “password"); 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(); }

Getting Data Recall the impediance mismatch problem… Well, Java provides us a class ResultSet which helps us bridge the gap. ResultSet rset = stmt.executeQuery( "SELECT title, year " + "FROM Movie"); while (rset.next()) … The variable rset, which is an instance of ResultSet, contains the rows of the query result. In order to access the titles and years, we will go to each row and retrieve the values according to their types. The first call of the method next moves the cursor to the first row and makes it the current row. Successive invocations of the method next move the cursor down one row at a time from top to bottom.

Using the getXXX methods Use the getXXX method of the appropriate type to retrieve the value in each column. –For example, the first column in each row of the previous rset stores a value of SQL type VARCHAR. The method for retrieving a value of SQL type VARCHAR is getString. –The second column in each row stores a value of SQL type INT, and the method for retrieving values of that type is getInt. while (rset.next()) { String s = rset.getString("Title"); int n = rset.getInt("Year"); System.out.println(s + " " + n); } However we can also say instead: (which is slightly more efficient) String s = rset.getString(1); int n = rset.getInt(2); Column Name Column Position

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.

import java.sql.*; class dbAccess { public static void main (String args []) throws SQLException { DriverManager.registerDriver (new oracle.jdbc.driver.OracleDriver()); Connection conn = DriverManager.getConnection "thomo", “password"); 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(); }

Prepared statements Sometimes it is more convenient or more efficient to use a PreparedStatement object for sending SQL statements to the database. –This special type of statement is derived from the more general interface, Statement, that you already know. If you want to execute a Statement object many times, it will normally reduce execution time to use a PreparedStatement object instead. The main feature of a PreparedStatement object is that, unlike a Statement object, it is given an SQL statement when it is created. The advantage to this is that in most cases, this SQL statement will be sent to the DBMS right away, where it will be compiled. –As a result, the PreparedStatement object contains not just an SQL statement, but an SQL statement that has been precompiled. –This means that when the PreparedStatement is executed, the DBMS can just run the PreparedStatement 's SQL statement without having to compile it first.

Prepared statements (Continued) Using our open connection conn from previous examples, we create a PreparedStatement: PreparedStatement updateMovies = conn.prepareStatement( "UPDATE Movie SET studioName = ? WHERE studioName = ?"); The variable updateMovies now contains the SQL statement, "UPDATE Movie SET studioName = ? WHERE studioName = ?", which has also, been sent to the DBMS and been precompiled.

import java.sql.*; class UpdateMovie { public static void main (String args []) throws SQLException { DriverManager.registerDriver (new oracle.jdbc.driver.OracleDriver()); Connection conn = DriverManager.getConnection "thomo", “password"); userid, password PreparedStatement updateMovieStatement; String updateMovieString = "UPDATE Movie " + "SET studioName = ? " + "WHERE studioName LIKE ?"; updateMovieStatement = conn.prepareStatement(updateMovieString);

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(); }