JDBC Java Database Connectivity

JDBC (Java Database Connectivity)

There are 4 different types of JDBC drivers: JDBC-ODBC Bridge drivers (follows ODBC standards) Partly Java – Partly Native (this does not use any standards) Pure Java – Net Protocol Drivers Pure Java Drivers (also called Type4Drivers, most popular one) Important Classes: DriverManager Driver Connection Statement ResultSet

1) How to get the database connection? There are two ways to get the database connection. 1) First is to load the the Driver using Class.forName() and use the DriverManager.getConnection() . 2) Second is to use the DataSource to get the connection .

Loading the driver : Getting the connection from DriverManager : Getting the connection from the DataSource: To make the data source we need to deploy the *-ds.xml file in the deploy directory of JBoss Application Server. You can find the sample *-ds.xml files for different databases in the jboss-eap-4.3/jboss-as/docs/examples/jca directory. Class.forName( "DriverName" ); e.g.Class.forName( "com.microsoft.jdbc.sqlserver.SQLServerDriver" ); Connection connection = DriverManager.getConnection( "jdbc:microsoft:sqlserver://127.0.0.1\\ABCD:1443;” + “ DatabaseName=JDBCDB" , "username" , "password" );

Sample *-ds.xml files for postgresql database : <datasources> <local-tx-datasource> <use-java-context> false </use-java-context> <jndi-name> PostgresDS </jndi-name> <connection-url> jdbc:postgresql://127.0.0.1:5432/ejb3db </connection-url> <!—- For ssl connection <connection- url>jdbc:postgresql://127.0.0.1:5432/ejb3db?ssl=true&sslfactory=org.postg resql.ssl.NonValidatingFactory&</connection-url> --> <driver-class> org.postgresql.Driver </driver-class> <user-name> x </user-name> <password> y </password>   <min-pool-size> 50 </min-pool-size> <max-pool-size> 80 </max-pool-size> <blocking-timeout-millis> 5000 </blocking-timeout-millis> <idle-timeout-minutes> 1 </idle-timeout-minutes>   <metadata> <type-mapping> PostgreSQL 8.0 </type-mapping> </metadata> </local-tx-datasource> </datasources>

How to get Connection from the database? jndi.properties InitialContext initialContext = new InitialContext(); DataSource dataSource = (DataSource) initialContext.lookup( "PostgresDS" ); Connection connection = dataSource.getConnection() java.naming.factory.initial=org.jnp.interfaces.NamingContextFactory java.naming.factory.url.pkgs=org.jboss.naming:org.jnp.interfaces java.naming.provider.url=127.0.0.1:1099

2) Setting up Tables: Creating a Table: Creating JDBC Statements : executeQuery() is used for select statements (DQL). executeUpdate() is used to create or modify tables (DDL and DML). String createTableCoffees = "CREATE TABLE COFFEES" + " (COF_NAM VARCHAR(32), SUP_ID INTEGER, PRICE FLOAT," + " SALES INTEGER, TOTAL INTEGER)"; Statement statement = connection.createStatement(); statement.executeUpdate(createTableCoffees);

Executing Statements : Entering Data into a Table : Getting Data from a Table : executeQuery( "SELECT statement..." ) executeUpdate( "DDL and DML statements..." ) Statement statement = connection.createStatement(); statement.executeUpdate( "INSERT INTO COFFEES " + "VALUES('Colombian', 101, 7.99, 0, 0" ); ResultSet resultSet = statement.executeQuery( "SELECT * FROM COFFEES" );

3) Updating Tables: String query = "SELECT COF_NAME, SALES FROM COFFEES “ + " WHERE COF_NAME LIKE 'Colombian'" ; ResultSet resultSet = statement.executeQuery(query); while(rs.next()){ String s = resultSet.getString( "COF_NAME" ); int n = resultSet.getInt( "SALES" ); System.out.println(n + " ponds of " + s + " sold this week." ); } String updateString = "UPDATE COFFEES " + "SET TOTAL = TOTAL + 75 " + "WHERE COF_NAME LIKE 'Colombian'" ; statement.executeUpdate(updateString); String query = "SELECT COF_NAME, TOTAL FROM COFFEES" + "WHERE COF_NAME LIKE 'Colombian'" ; ResultSet resultSet = statment.executeQuery(query); while(rs.next()) { String s = rs.getString(1); int n = rs.getInt(2); System.out.println(n + " ponds of " + s + " sold till date." ); }

4) Using PreparedStatement : When to use PreparedStatment ? 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 of this is that in most cases, the 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 PreparedStatemen’s SQL statement without having to compile it first. Although PreparedStatement objects can be used for SQL statements with no parameters, you will probably use them most often for SQL statements that take parameters. The advantage of using SQL statements that take parameters is that you can use the same statements and supply it with different values each time you execute it.

Creating a PreparedStatement Object: Supplying values for PreparedStatement Parameters: Code Fragment I: Code Fragment II: PreparedStatement updateSales = connection.preparedStatement( "UPDATE COFFEES SET SALES = ? WHERE COF_NAME" + " LIKE ? " ); String updateString = "UPDATE COFFEES SET SALES=75 " + " WHERE COF_NAME LIKE 'Colombian'" ; statement.executeUpdate(updateString); PreparedStatement updateSales = connection.preparedStatement( "UPDATE COFFEES SET SALES=? " + "WHERE COF_NAME LIKE ? " ); updateSales.setInt(1, 75); updateSales.setString(2, "Colombian" ); updateSales.executeUpdate();

Note: Once a parameter has been set with a value, it will retain that value until it is reset to another value or the method clearParameters is called. Using a loop to set values: updateSales.setInt(1, 100); updateSales.setString(2, "French_Roast" ); updateSales.executeUpdate(); updateSales.setString(2, "Espresso" ); updateSales.executeUpdate(); PreparedStatement updateSales; String updateString = "update COFFEES " + " set SALES = ? where COF_NAME like ?" ; updateSales = con.preparedStatement(updateString); int [] salesForWeek = {175, 150, 60, 155, 90}; String [] coffees = ( "Colombian" , "French_Roast" , "Colombian_Decaf" , "French_Roast_Decaf" ); int len = coffees.length; for(int i=0; I < len; i++) { updateSales.setInt(1, salesForWeek[i]); updateSales.setString(2, coffees[i]); updateSales.executeUpdate(); }

Return values for the method executeUpdate : * executeQuery returns a ResultSet object containing the results of the query sent to the DBMS, the return value for executeUpdate is an int that indicates how many rows of a table were updated. When the method executeUpdate is used to execute a DDL statement, such as in creating a table, it returns the int 0. Note that when the return value for executeUpdate is 0, it can mean one of two things: 1) the statement executed was an update statement that affected zero rows, or 2) the statement executed was a DDL statement. updateSales.setInt(1, 50); updateSales.setString(2, "Espresso" ); int n = updateSales.executeUpdate(); // n = 1 because one row had a change in it. int n = executeUpdate(createTableCoffees); // n = 0

5) Using Joins: String createSUPPLIERS = "create table SUPPLIERS " + "(SUP_ID INTEGER, SUP_NAME VARCHAR(40), " + "STREET VARCHAR(40), CITY VARCHAR(20), " + "STATE CHAR(2), ZIP CHAR(5))" ; statement.executeUpdate(createSUPPLIERS); statement.executeUpdate( "insert int SUPPLIER values (101, " + "'Acme, Inc.', '99 Market Street', 'Groundsville', " + "'CA', '95199'" ); statement.executeUpdate( "insert int SUPPLIERS values (49, " + "'Superior Coffee', '1 Party Place', 'Mendocino', 'CA' " + "'95460'" ); statement.executeUpdate( "Insert into SUPPLIERS value(150, " + "'The High Ground', '100 Coffee Lane', 'Meadows', 'CA‘, '93966'" ; ResultSet rs = statement.executeQuery( "select * from SUPPLIERS" ); String query = "SELECT COFFEES.COF_NAME " + "FROM COFFEES, SUPPLIERS " + "WHERE SUPPLIERS.SUP_NAME LIKE 'Acme, Inc.' " + "and SUPPLIER_ID = COFFEES.SUP_ID" ; ResultSet rs = statement.executeQuery(query); System.out.println( "Coffees bought from Acme, Inc.: " ); while(rs.next()) { String coffeeName = rs.getString( "COF_NAME" ); System.out.println( " " + coffeeName); }

6) Using Transactions: A transaction is a set of one or more statements that are executed together as a unit, so either all of the statements are executed or none of the statements is executed. Disabling Auto-Commit Mode where connection is an active connection. Committing a Transaction Once auto-commit mode is disabled, no SQL statements will be committed until you call the method commit explicitly. connection.setAutoCommit( false ); connection.setAutoCommit( false ); PreparedStatement updateSales = connection.preparedStatment( "UPDATE COFFEES SET TOTAL = TOTAL + " + " ? WHERE COF_NAME LIKE ?" ); updateTotal.setInt(1, 50); updateTotal.setString(2, "Colombian" ); updateTotal.executeUpdate(); connection.commit(); connnection.setAutoCommit( true );

Using Transaction to Preserve Data Integrity Transaction isolation levels 1) int TRANSACTION_NONE = 0; 2) int TRANSACTION_READ_UNCOMMITTED = 1; 3) int TRANSACTION_READ_COMMITTED = 2; 4) int TRANSACTION_REPEATABLE_READ = 4; 5) int TRANSACTION_SERIALIZABLE = 8; When to call method rollback ? If you are trying to execute one or more statements in a transaction and get an SQLException , you should call the method rollback to abort the transaction and start the transaction all over again. void setTransactionIsolation( int level) throws SQLException ; int getTransactionIsolation() throws SQLException ;

7) Using Stored Procedures: In SQL In Java (JDBC) Create procedure SHOW_SUPPLIERS As Select SUPPLIERS.SUP_NAME, COFFEES.COF_NAME from SUPPLIERS, COFFEES where SUPPLIERS.SUP_ID = COFFEES.SUP_ID Order by SUP_NAME String createProcedure = “Create procedure SHOW_SUPPLIERS” + “ as “ + “ select SUPPLIER.SUP_NAME, COFFEES.COF_NAME ” + “ from SUPPLIERS, COFFEES ” + “ where SUPPLIER.SUP_ID = COFFEES.SUP_ID ” + “ order by SUP_NAME”; Statement stmt = con.createStatement(); Stmt.executeUpdate(createProcedure);

Steps Putting code in a class definition. Importing classes to make them visible import java.sql.*; Using the main method. Using try and catch blocks. Retrieving Exceptions. 8) Creating Complete JDBC Applications:

try { - - - - - - } catch ( SQLException ex) { System .err.println( “SQLException: ” + ex.getMessage()); } try { Class.forName( “myDriverClassName” ); } catch ( ClassNotFoundException ex) { System .err.println( “ClassNotFoundException: ” + ex.getMessage()); }

Catching Exceptions try { - - - - - - } catch ( SQLException ex) { System .err.println( “SQLException Caught”); while (ex != null){ System .out.println( “Message: “ + ex.getMessage()); System .out.println( “SQLState: “ + ex.getSQLState()); System .out.println( “ErrorCode: “ + ex.getErrorCode()); ex = ex.getNextException(); System .out.println( “ ” ); } }

Retrieving Warnings SQLWarning objects are a subclass of SQLException that deal with database access warnings. Warnings do not stop the execution of an application, as exceptions do; they simply alert the user that something did not happen as planned. A warning can be reported on a # a connection object # a statement object (including PreparedStatment and CallableStatement objects) # a ResultSet object Each of these classes have a getWarnings method, which you mush invoke in order to see the first warning reported on the calling object. If getWarnings returns a warning, you can call the SQLWarning method getNextWarning on it to get any additional warnings. Executing a statement automatically clears the warnings from the previous statement, so they do not build up. This means, however that if you want to retrieve warnings reported on a statement you must do so before you execute another statement.

Example Statement stmt = con.createStatement(); ResultSet rs = stmt.executeQuery( “ Select COF_NAME from COFFEES” ); while(rs.next) { String CoffeName = rs.getString( “COF_NAME” ); System .out.println( “ Coffees available at the Coffee Break: ” ); System .out.println( “ ” + coffeeName); SQLWarning warning = stmt.getWarnings(); if(warning != null) { System.out.println( “—Warning-” ); while(warning != null){ System .out.println( “Message: ” + warning.getMessage()); System .out.println( “SQLState: ” + warning.getSQLState()); System .out.println( “Vendor Eror Code: ” + warning.getErrorCode()); warning = warning.getNextWarning(); } } ---

--- SQLWarning warn = rs.getWarnings(); if(warning != null) { System.out.println(“-- Warning --”); while(warn != null) { System.out.println(“Message: ” + warn.getMessage()); System.out.println(“SQLState: ” + warn.getSQLState()); System.out.println(“Vendor Error Code:” + warn.getErrorCode()); warn = warn.getNextWarning(); } } }

JDBC Java Database Connectivity

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JDBC Java Database Connectivity