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Lecture 11Java Database Connectivity

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Outline

• Introduction

• Java Database Connectivity

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Introduction

• File processing– Random access or sequential– Only allow access to data

• Cannot query

• Database systems– Mechanisms to organize and store data– Allow sophisticated queries– Relational database - most popular style

• Microsoft Access, Sybase, Oracle

• Structured Query Language (SQL, "sequel")– Queries relational databases– Can write Java programs to use SQL queries

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Database Language

• Database language– Used to access database– Can use high-level languages

• Java, C, C++, Visual Basic, COBOL, PL/I, Pascal• Make requests using a specially designed query

language• Host language

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Relational Database Model

• Database models– Hierarchal, network, relational (most popular)– Focus on relational

• Relational Database Model– Composed of tables

• Rows called records• Columns are fields (attributes)

– First field usually primary key• Unique for each record• Primary key can be more than one field (column)• Primary key not required

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Relational Database Structure

Number Name DepartmentSalary Location

2360324568

35761

34589

47132

78321

JONES, A.

KERWIN, R.

LARSON, P.

MYERS, B.

NEUMANN, C.

STEPHENS, T.

413

413

642

611

413

611

1100

2000

1800

1400

9000

8000

NEW JERSEY

NEW JERSEY

LOS ANGELES

ORLANDO

NEW JERSEY

ORLANDO

Table: Employee

A record

A columnPrimary Key

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Advantages

• Tables easy to use, understand, and implement• Easy to convert other database structures into

relational scheme– Universal

• Projection and join operations easy to implement• Searches faster than schemes with pointers• Easy to modify - very flexible• Greater clarity and visibility than other models

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Java Database Connectivity

• You can access data files in Java using JDBC– JDBC classes handle communication

between your Java program and a database driver

– Java uses JDBC-ODBC Bridge

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Data Source Name (DSN)

• Before using JDBC in a Window environment, you need to create a DSN– DSN registers your database files on the computer

• Setting up a DSN– Step1: From the start menu, select control panel– Step2: select ODBC Data source – Step3: On the User DSN tab, click on the Add button

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Data Source Name (DSN)

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Data Source Name (DSN)

– Step4: Select the database type (Microsoft Access database), and click Finish

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Data Source Name (DSN)

– Step5: Type in the Data Source Name

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Data Source Name (DSN)

– Step6: Use the Select (or Browse) button to locate the file, then close the dialog boxes

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JDBC-ODBC Bridge Driver

• In Java code, you must connect to the driver using the Class.forName method– Connect to Microsoft’s driver

Class.forName(“com.ms.jdbc.odbc.JdbcOdbcDriver”);

– Connect to Sun’s driverClass.forName(“sun.jdbc.odbc.JdbcOdbcDriver”);

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JDBC-ODBC Bridge Driver

• If you need to be able to load either driver, you can use try/catch block

try{ Class.forName(“com.ms.jdbc.odbc.JdbcOdbcDriver”); }catch{ try

{Class.forName(“sun.jdbc.odbc.JdbcOdbcDriver”);}catch(ClassNotFoundException err){ System.err.println(“Driver did not load properly”);}

}

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Connecting to the Database

• Next step is to connect to the database using the name that your registered as a DSN“jdbc:odbc:EX1”

• Use DriverManager.getConnection method and assign it to a Connection objectconEmployees =

DriverManager.getConnection(“jdbc:odbc:EX1”);

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Connecting to the Database

//Declare a Connection objectConnection conEmployees;

//Connect to the databasetry{conEmployees = DriverManager.getConnection (“jdbc:odbc:EX1”);}catch(SQLException err){ statement // “No connection to database”}

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Creating a ResultSet

• A ResultSet object contains a collection of records from the database– To create ResultSet, you must declare a Statement

object and call the Connection objects’ createStatement method

Statement cmdEmployees;

ResultSet rsEmployees;

– You create a ResultSet with an SQL query with executeQuery method

Select * from Employees

cmdEmployees.executeQuery(“Select * from Employees”);

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Example

try{ Connection conEmployees; conEmployees = DriverManager.getConnection (“jdbc:odbc:EX1”);

//create a ResultSet Statement cmdEmployees = conEmployees.createStatement(); ResultSet rsEmployees = cmdEmployees.executeQuery (“Select * from Employees”);}catch(SQLException err){ statement // “No connection to database”}

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Example

• You can create an SQL statement to create a ResultSet that matches a given condition

ResultSet rsEmployees = cmdEmployees.executeQuery ( “Select * from Employees Where [Last Name] = ‘Song’ ; ”);

ResultSet rsEmployees = cmdEmployees.executeQuery ( “Select * from Employees Where [Last Name] = ‘ “ + strLastName + ” ’ ; ”);

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Retrieving a Record

• Looping through a ResultSet

• Displaying the fields from a record

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Retrieving a Record

• When you first open a ResutSet, the current-record is located just prior to the first record

• You call the ResultSet’s next method– The next method moves the current-record

pointer to the first record and returns boolean value

• true: the next record exists• false: no more records exists

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Example

try{ rsEmployees.next( ); lstNames.add(rsEmployees.getString (“Last Name”));}catch (SQLException err){ System.err.println(“Error : “ + err.toString());}

The getString method retrieves the datafor the specified string field

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Looping through a ResultSet

• You can step through all records in a ResultSet using a loop– while (rsResultSet.next( )) to control the loop– The boolean condition tests true as long as

records remain in the ResultSet

while(rsEmployees.next( )) lstNames.add(rsEmployees.getString(“Last Name”));

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Displaying the Fields

try{ //display information if (rsEmployees.next( )) { lblFirstName.setText(rsEmployees.getString(“ First Name”); lblSSN.setText(rsEmployees.getString(“SSN”)); lblSSN.setText(rsEmployees.getString(“Phone Number”)); } else //Statement}catch (SQLException err){ System.err.println(“Error : “ + err.toString());}

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Accessing the Data Fields

• Access the data in database fields by using the appropriate method for the data type– getString for string field– getFloat or getInt for float or int fields

• Convert the value to a string format to display the value in a label or text field

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Closing the Connection

• Make sure that the database connection is closed at the termination of the program– Place the statement in the stop method– Place the code in your exit routine

public void stop( ){

if (conEmployees != null) conEmployees.close( );

}

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SQL

• Java’s JDBC uses Structured Query Language (SQL) to create a ResultSetResultSet rsEmployees =

cmdEmployees.executeQuery(“Select * from Employees”);

ResultSet rsEmployees = cmdEmployees.executeQuery(“Select * from Employees where [Last Name] = ‘ “ + strLastName + ” ’; ”);

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Types of SQL Statement

• For the field(s), you can list the field names or use an asterisk to indicate all fields from the named table.– Multiple-world field names must be enclosed

in square brackets or accent grave marks (‘)– The closing semicolon(;) is specified in the

SQL standards

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SQL Examples

• SELECT“Select * from Employees;”

• Where“Select * from Employees where [Last Name] = ‘

ABC’ ”;

“Select * from Employees where [Last Name] = ‘ “ + strLastName + ”’; ”

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Adding a Record

• SQL insert statement-General formatInsert Into TableName (FieldList) Values

(ListOfValue)

• Use the statement object’s executeUpdate method to excute the SQL Insert Into statement

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Example

cmdEmplyees.executeUpdate (“ Insert Into Employees” + “( [Last Name] , [First Name], SSN, [Phone Number]) ”

+ “Values( ‘ “

+ txtLastName.getText() + ” ’, ‘ “

+ txtFirstName.getText( ) + ” ’)”);

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Finding a Record

• SQL Statement

strLastName = txtLastName.getText();

String query = “Select *from Employees where [Last Name] = ‘ “ + strLastName + ’ ” ”;

rsEmployees = statement.executeQuery(query);