Basic JDBC Celsina Bignoli

What is JDBC Industry standard for database- connectivity between the Java language and a wide range of databases Generic Leverage existing database APIs Simple

JDBC Architecture Sybase DB Java Application DriverManager Sybase DriverMySQL DriverOracle Driver MySQL DB Oracle DB

JDBC Drivers Vendor-specific implementation of the JDBC interfaces Transparent to the database application developers

JDBC specifications JDBC 2.0 Core API (java.sql package) Scrollable ResultSets Streams JDBC 2.0 Standard Extension API (javax.sql package) DataSource Connection pooling Distributed transactions Rowsets JDBC 2.0 Specification JDBC 1.0 Specification Basic database connectivity

Loading the Driver Class.forName(driverClassName).newInstance(); Class.forName(“com.mysql.jdbc.Driver”).newInstance(); dynamically load a java class at runtime executes newInstance() to create an object of class Driver calling the default constructor for the class. The constructor executes code to register the class with the DriverManager

Connecting to the Database Connection DriverManager.getConnection(String url); DriverManager.getConnection( “jdbc:mysql://localhost/accounts?user=ro ot&password=cis384“);

URL URL: : : jdbc mysql //localhost/accounts : // [: ][/ ] //localhost/accounts // /prod //db.mycompany.com/prod //db.mycompany.com:4544/prod when not specified, connector/J will default to port 3306.

DriverManager -getConnection() method static Connection getConnection(String url) Attempts to establish a connection to the given database URL. static Connection getConnection(String url, Properties info) Attempts to establish a connection to the given database URL using the specified properties. static Connection getConnection(String url, String user, String password) Attempts to establish a connection to the given database URL as used identified by password.

getConnection() – Example Properties info = new Properties(); info.setProperty(“user”, “username”); info setProperty(“password”, “pwd”); Connection con = DriverManager.getConnection(url, prop); OR String username=“username”; String password=“password”; Connection con = DriverManager.getConnection(url, username, password);

Queries – Statement Object used to send a SQL statement to the database executes the SQL statement returns back the results of the SQL statement

createStatement() StatementcreateStatement () Creates a Statement object for sending SQL statements to the database.

executeQuery() ResultSetexecuteQuery(String sql) Executes the given SQL statement, which returns a single ResultSet object no assumption is made on the validity of the query if the SQL execute successfully it returns a ResultSet object containing rows from the database if the SQL fails it will raise a SQLException

Executing a Statement - Example ResultSet rs = stmt.executeStatement(“select name from pets”); ResultSet: Fluffy Claws Buffy Fang Chirpy Whistler Slim Puffball Initial cursor position next()

ResultSet Object A table of data representing a database result set maintains a cursor pointing to its current row of data Initially the cursor is positioned before the first row The next() method moves the cursor to the next row next() returns false when there are no more rows in the ResultSet object A default ResultSet object is not updatable and has a cursor that moves forward only

Moving Through the ResultSet - Example while (rs.next()) { System.out.println(rs.getString((1))); } Fluffy Claws Buffy Fang Chirpy Whistler Slim Puffball

Basic Getter Methods int getInt(int columnIndex) int getInt(String columnName) String getString(int columnIndex) String getString(String columnName) Date getDate(int columnIndex) Date getDate(String columnName)

Handling Errors Connector/J Driver throws a SQLException –errors connecting with the database –errors executing SQL statements To know more about a single Exception use the SQLException methods –getMessage() –getSQLState() –getErrorCode()

executeUpdate() method intexecuteUpdate (String sql) Creates a Statement object for sending SQL statements to the database. Returns either the row count for INSERT, UPDATE or DELETE statements, or 0 for SQL statements that return nothing

Inserting a Row - Example Statement stmt = connection.createStatement(); int i= stmt.executeUpdate(“INSERT INTO pet VALUES(12, ’minou’, ’Gwen’, ’cat’)”);

Updating a Row - Example Statement stmt = connection.createStatement(); int i= stmt.executeUpdate(“UPDATE pet SET owner=‘Lucy’ where owner= ‘Gwen’ ”);

Deleting a Row - Example Statement stmt = connection.createStatement(); int i= stmt.executeUpdate(“DELETE FROM pet WHERE owner= ‘Gwen’ ”);

Prepared Statements - SQL ability to set up a statement once, and then execute it many times with different parameters. replace building ad hoc query strings, and do so in a more efficient manner. First implemented in the C API Available in Connector/J server-side starting from version 3.1

How databases execute queries parse the query invoke the optimizer to determine best query execution plan caches the plan – query is the key to fetch plan from cache

Prepared Statement - Example PREPARE sel_stmt FROM “SELECT name FROM pet WHERE id=?”; EXECUTE sel_stmt name Fluffy

JDBC – Dynamic Query Example Statement stmt = con.createStatement(); for int(i=1; i<=10; i++){ String stmtString = “select name from pet where id = “ +I; ResultSet rs = stmt.executeQuery(stmtString); while (rs.next()){ System.out.println(rs.getString(1)); } rs.close() } statement is parsed by the database each time new query plan is created for each select statement and cached (entire stmt being the key)

JDBC – PreparedStatement PreparedStatement ps = con.prepareStatement( “select name from pet where id =?“ ); for int(i=1; i<=10; i++){ ps.setInt(1, i); -- variable binding ResultSet rs = ps.executeQuery(); while (rs.next()){ System.out.println(rs.getString(1)); } rs.close(); } ? is called placeholder query is parsed only once and only 1 execution plan is created and caches for it executed many times after binding variables MUCH MORE EFFICIENT!

Placeholders- Setter methods voidsetInt(int parameterIndex, int value) voidsetString(int parameterIndex, String value) voidsetDate(int parameterIndex, java.sql.Date value) voidsetTimestamp(int parameterIndex, java.sql.Timestamp value) voidsetLong(int parameterIndex, long value)

Disconnecting from the database close a connection to the database to release resources Make sure you first close all component that use that connection Close components in the reverse order you opened them. rs.close() stmt.close() conn.close()