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22-Jul-12 1Database Prorgaming with Java

Database Programming with Java JDBC Basics

Basic steps in using JDBCStatementResultSet PreparedStatement

22-Jul-12 Database Prorgaming with Java 2

JDBC Basics• JDBC (Java DataBase Connectivity) provides a standard library for accessing relational databases

• JDBC consists of two parts:o JDBC API, a purely Java-based API

o JDBC Driver Manager,which communicates with vendor-specific drivers that perform the real communication with the database.

• JDBC classes are in the java.sql package

• Current JDBC version: 4.0

22-Jul-12 3Database Prorgaming with Java

Advantages of JDBC• Continued usage of existing data• Vendor independent• Platform independent• Ease of use

4 types:• Type 1• Type 2• Type 3• Type 4


JDBC Driver types


Type 1: JDBC-ODBC Bridge plus ODBC Driver

This combination provides JDBC access via ODBC drivers. ODBC binary code -- and in many cases, database client code -- must be loaded on each client machine that uses a JDBC-ODBC Bridge.

Example: Sun ODBC

• AdvantagesThe JDBC-ODBC Bridge allows access to almost any database, since the database's ODBC drivers are already available.

• Disadvantages Since the Bridge driver is not written fully in Java, type 1 drivers are not portable.

A performance issue is. They are the slowest of all driver types.

The client system requires the ODBC Installation to use the driver.


Type 1: JDBC-ODBC Bridge plus ODBC Driver

This type of driver converts JDBC calls into calls on the client API for Oracle, Sybase, Informix, DB2, or other DBMS. Note that, like the bridge driver, this style of driver requires that some binary code be loaded on each client machine.


Type 2: A native API partly Java technology

• AdvantagesThe distinctive characteristic of type 2 jdbc drivers are that they are typically offer better performance than the JDBC-ODBC Bridge.

• Disadvantages Native API must be installed in the Client System and hence type 2 drivers cannot be used for the Internet.

It’s not written in Java Language which forms a portability issue.

If we change the Database we have to change the native api as it is specific to a database


Type 2: A native API partly Java technology

• Type 3 database requests are passed through the network to the middle-tier server. The middle-tier then translates the request to the database


Type 3: All Java/Net-protocol driver

• Advantages This driver is server-based, so there is no need for any vendor database library to be present on client machines.

This driver is fully written in Java and hence Portable. It is suitable for the web.

There are many opportunities to optimize portability, performance, and scalability.

The net protocol can be designed to make the client JDBC driver very small and fast to load.



The type 3 driver typically provides support for features such as caching (connections, query results, and so on), load balancing, and advanced system administration such as logging and auditing.

This driver is very flexible allows access to multiple databases using one driver.

They are the most efficient amongst all driver types.



• DisadvantagesIt requires another server application to install and maintain.

Traversing the recordset may take longer, since the data comes through the backend server.



This type of driver converts JDBC calls into the network protocol used directly by DBMSs, allowing a direct call from the client machine to the DBMS server and providing a practical solution for intranet access.


Type 4: Direct-to-Database Pure Java Driver

• AdvantagesType 4 jdbc drivers are completely written in Java to achieve platform independence and eliminate deployment administration issues. It is most suitable for the web.

Type 4 JDBC drivers don't have to translate database requests to ODBC performance is typically quite good.

Don’t need to install special software on the client or server.



• DisadvantagesWith type 4 drivers, the user needs a different driver for each database.




JDBC Driver types(Sumary)


Basic Steps in using JDBC 1. Load the driver 2. Define the connection URL and establish the connection

3. Create a Statement object 4. Executing the Statement 5. Getting data from executing result

6. Process the results. 7. Close the connection


Loading JDBC drivers• Class.forName("DriverXYZ");

o Use Class.forName() to load the Driver class

o No need to register with DriverManager.

• Some examples.o Class.forName("oracle.jdbc.driver.OracleDriver");

o Class.forName("org.gjt.mm.mysql.Driver");

o Class.forName(“com.mysql.jdbc.Driver");

o Class.forName(“com.ibm.db2j.jdbc.DB2jDriver");

o Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");

o Class.forName(“com.microsoft.sqlserver.jdbc.SQLServerDriver”);


Establish the DB connection• Need to know which database to connect too In JDBC you need to specify the URLo Need username, password

• Get a java.sql.Connection objecto Connection con = DriverManager.getConnection(url, “user”, “password”);

• Examples:o jdbc:oracle:thin:@localhost:1521:orclo jdbc:mysql://127.0.0.1:3306/bookso jdbc:sqlserver://localhost:1433; database = schoolManagement; user=sa;password=1234567";


JDBC Statement Object• A Statement object is what sends your SQL statement to the DBMS

• Create a Statement object and then execute it, supplying appropriate method with the SQL statement you want to send.o Statement stmt = con.createStatement();

• For a SELECT statement, the method to use is executeQuery.o stmt.executeQuery( “SELECT * FROM XXX");

• For statements that create or modify tables, the method to use is executeUpdate.o stmt.executeUpdate( "INSERT INTO XXX… “);


ResultSet object• A ResultSet object is a table of data representing a database result set, which is usually generated by executing a statement that queries the database.

• You access the data in a ResultSet object through a cursor. This cursor is a pointer that points to one row of data in the ResultSet. Initially, the cursor is positioned before the first row.


ResultSet type• TYPE_FORWARD_ONLY: The result set cannot be scrolled; its cursor moves forward only, from before the first row to after the last row.

• TYPE_SCROLL_INSENSITIVE: The result can be scrolled; its cursor can move both forward and backward relative to the current position, and it can move to an absolute position.

• TYPE_SCROLL_SENSITIVE: The result can be scrolledThe result set reflects changes made to the underlying data source while the result set remains open.

• The default ResultSet type is TYPE_FORWARD_ONLY.


ResultSet Concurrency• The concurrency of a ResultSet object determines what level of update functionality is supported.

• There are two concurrency levels:– CONCUR_READ_ONLY: The ResultSet object cannot be updated using the ResultSet interface.

– CONCUR_UPDATABLE: The ResultSet object can be updated using the ResultSet interface.

• The default ResultSet concurrency is CONCUR_READ_ONLY.


ResultSet navigationMethod Descriptionnext() Moves the cursor froward one row from its

current position. previous() Moves the cursor to the previous row in

this ResultSet object. first() Moves the cursor to the first row in this

ResultSet object. last() Moves the cursor to the last row in this

ResultSet object. beforeFirst()

Moves the cursor to the front of this ResultSet object, just before the first row. This method has no effect if the result set contains no rows.

afterLast() Moves the cursor to the end of this ResultSet object, just after the last row. This method has no effect if the result set contains no rows.

getRow() Retrieves the current row number. The first row is number 1, the second number 2, and so on.


ResultSet navigation (cont)Method Descriptionabsolute(int row)

Moves the cursor to the given row number in this ResultSet object.Row number is positive, the cursor moves to the given row number with respect to the beginning of the result set. The first row is row 1, the second is row 2, and so on.row number is negative, the cursor moves to an absolute row position with respect to the end of the result set. For example, calling the method absolute(-1) positions the cursor on the last row; calling the method absolute(-2) moves the cursor to the next-to-last row, and so on.

relative(int rows)

Moves the cursor a relative number of rows, either positive (forward) or negative (backward). Note: Calling the method relative(1) is identical to calling the method next() and calling the method relative(-1) is identical to calling the method previous(). Calling relative(0) is valid, but does not change the cursor position.


Methods of returning Scrollable ResultSet

• public Statement reateStatement(int resultSetType, int resultSetConcurrency) throws SQLException

• public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency) throws SQLException

• public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency) throws SQLException


Retrieving Column Values from Rows

• The ResultSet declares methods (example: getBoolean, getLong, …) for retrieving column values from the current row.

• Retrieve values using either the index number or the alias or name of the column.

• Columns are numbered from 1. • For maximum portability, result set columns within each row should be read in left-to-right order


Updating Rows in ResultSet Objects

• With CONCUR_UPDATABLE ResultSet, you can update values using updateXXX() method.

• Must call the method ResultSet.updateRow to update the database.


Inserting a row• Step 1: Positioning the Cursor

Statement st = cn.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_UPDATABLE)

ResultSet rs = st.executeQuery(“SELECT NAME, EMPLOEE_ID FROM EMPLOYEES”);

rs.first();• Step 2: Updating the columns: rs.update<Type>

• Step 3: inserting a row : rs.insertRow();


Example: Inserting Rowstry { stmt = con.createStatement( ResultSet.TYPE_SCROLL_SENSITIVE,

ResultSet.CONCUR_UPDATABLE); ResultSet uprs = stmt.executeQuery( "SELECT * FROM " + dbName + ".COFFEES");

uprs.moveToInsertRow();

uprs.updateString("COF_NAME", coffeeName); uprs.updateInt("SUP_ID", supplierID); uprs.updateFloat("PRICE", price); uprs.updateInt("SALES", sales); uprs.updateInt("TOTAL", total);

uprs.insertRow(); uprs.beforeFirst();

} catch (SQLException e ) {


Deleting a rowStep 1: Positioning the cursor

// Move the cursor to the last row of the result set

rs.last();Step 2: Deleting the row

// Deleting the row from the result setrs.deleteRow();


Connecting & Querying sample Database

• DisplayAuthorso Retrieves the entire authors tableo Displays the data in a JTextArea


DisplayAuthors.java1 // DisplayAuthors.java2 // Displaying the contents of the authors table.3 import java.awt.*;5 import java.sql.*;6 import java.util.*;7 import javax.swing.*;8 9 public class DisplayAuthors extends JFrame {10 11 // JDBC driver name and database URL 12 static String JDBC_DRIVER = "oracle.jdbc.driver.OracleDriver";13 String DATABASE_URL = "jdbc:oracle:thin:@localhost:1521:orcl"; 14 15 // declare Connection and Statement for accessing 16 // and querying database 17 private Connection connection; 18 private Statement statement; 19 20 // constructor connects to database, queries database, processes 21 // results and displays results in window22 public DisplayAuthors() 23 {24 super( "Authors Table of Books Database" );25


DisplayAuthors.java26 // connect to database books and query database27 try {28 293032 // load database driver class33 Class.forName( JDBC_DRIVER );34 35 // establish connection to database 36 connection = DriverManager.getConnection( DATABASE_URL );37 38 // create Statement for querying database39 statement = connection.createStatement();40 41 // query database 42 ResultSet resultSet = 43 statement.executeQuery( "SELECT * FROM authors" );44 45 // process query results46 StringBuffer results = new StringBuffer();47 ResultSetMetaData metaData = resultSet.getMetaData();48 int numberOfColumns = metaData.getColumnCount(); 49


DisplayAuthors.java50 for ( int i = 1; i <= numberOfColumns; i++ )51 results.append( metaData.getColumnName( i ) + "\t" );52 53 results.append( "\n" );54 55 while ( resultSet.next() ) {56 57 for ( int i = 1; i <= numberOfColumns; i++ )58 results.append( resultSet.getObject( i ) + "\t" );59 60 results.append( "\n" );61 }62 63 // set up GUI and display window64 JTextArea textArea = new JTextArea( results.toString() );65 Container container = getContentPane();66 67 container.add( new JScrollPane( textArea ) );68 69 setSize( 300, 100 ); // set window size70 setVisible( true ); // display window71 72 } // end try73


DisplayAuthors.java74 // detect problems interacting with the database 75 catch ( SQLException sqlException ) { 76 JOptionPane.showMessageDialog( null, sqlException.getMessage(), 77 "Database Error", JOptionPane.ERROR_MESSAGE ); 78 79 System.exit( 1 ); 80 } 81 82 // detect problems loading database driver 83 catch ( ClassNotFoundException classNotFound ) { 84 JOptionPane.showMessageDialog( null, classNotFound.getMessage(), 85 "Driver Not Found", JOptionPane.ERROR_MESSAGE ); 86 87 System.exit( 1 ); 88 } 89 90 // ensure statement and connection are closed properly 91 finally { 92 93 try { 94 statement.close(); 95 connection.close(); 96 } 97


DisplayAuthors.java98 // handle exceptions closing statement and connection99 catch ( SQLException sqlException ) { 100 JOptionPane.showMessageDialog( null, 101 sqlException.getMessage(), "Database Error", 102 JOptionPane.ERROR_MESSAGE ); 103 104 System.exit( 1 ); 105 } 106 } 107 108 } // end DisplayAuthors constructor109 110 // launch the application111 public static void main( String args[] )112 {113 DisplayAuthors window = new DisplayAuthors(); 114 window.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );115 }116 117 } // end class DisplayAuthors


PreparedStatement Object• An object that represents a precompiled SQL statement.

• PreparedStatement object is given an SQL statement when it is created

• When the PreparedStatement is executed, the DBMS can just run the PreparedStatement 's SQL statement without having to compile it first.

• PreparedStatement objects are used more for SQL statements that take parameters.


PreparedStatement ExamplePreparedStatement pstmt = con.prepareStatement(

"UPDATE authors SET lastName = ?WHERE authorID = ?");

pstmt.setString(1, “John”);pstmt.setInt(2, 3);pstmt.executeUpdate();

Set value “John” to the first placeholder.

Set value 3 to the second placeholder.

Assignments

Assignment 1 Assignment 2(See assignemt file)


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