JDBC lecture

8/7/2019 JDBC lecture

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JDBC Java DatabaseJDBC Java DatabaseConnectivityConnectivity

Talking to Databases

Zulqarnain Hashmi


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Introduction to JDBCIntroduction to JDBC

JDBC is used for accessing databases

from Java applications

Information is transferred from relationsto objects and vice-versa

databases optimized for searching/indexing

objects optimized for engineering/flexibility


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JDBC ArchitectureJDBC Architecture

JavaApplication JDBC

MS AccessSQL Server

DB2

Oracle

Access

Driver

DB2

Driver

Oracle

Driver

These are

Java classes

Network

We willuse this one


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JDBC Architecture (cont.)JDBC Architecture (

cont.)

Application JDBC Driver

Java code calls JDBC library

JDBC loads a driver

Driver talks to a particular database

Can have more than one driver -> more than one

database

Ideal: can change database engines without changing

any application code


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JDBC DriversJDBC Drivers

Javaap

plication

JDBC-Driver manager

NativeAPI-driver

JDBC-ODBCbridge

Client libraryODBC

Client library

JDBC-API


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What is ODBC?What is ODBC?

ODBC is (Open Database Connectivity): A standard or open application programming

interface (API) for accessing a database.

By using ODBC statements (DSN, Data SourceName) in a program, you can access files in anumber of different databases, includingAccess, dBase, DB2, Excel, and Text.

ODBC handles the SQL request and converts itinto a request the individual database systemunderstands.


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Running a JDBC ApplicationRunning a JDBC Application

Phase Task Relevant java.sql classes

Initialisation

Processing

Termination

Load driverCreate connection

Generate SQL statements

Process result data

Terminate connectionRelease data structures

DriverManagerConnection

Statement

ResultSet etc.

ConnectionStatement etc.


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Seven StepsSeven Steps

Load the driver

Define the connection URL

Establish the connection Create a Statement object statement

Execute a query using statement Process the result

Close the connection


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Loading the DriverLoading the Driver

We can register the Driver indirectly using the

Java statement:Class.forName(sun.jdbc.odbc.JdbcOdbcDriver"); or

Class.forName(oracle.jdbc.driver.OracleDriver");

Calling Class.forName causes the Driver class to be

loaded

When this class is loaded, it automatically

creates an instance of itself

registers this instance with the DriverManager


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Connecting to the DatabaseConnecting to the Database

Every database is identified by a URL

Given a URL, DriverManager is asked to

find the driver that can talk to thecorresponding database

DriverManager tries all registereddrivers, until a suitable one is found


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Connecting to the DatabaseConnecting to the Database

Connection con = DriverManager.

getConnection("jdbc.odbc:Books,userName,password );

jdbc.odbc:Books URL

userName Login Name

Password Login Password


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Interaction with the DatabaseInteraction with the Database

We use Statement objects in order to

Extract data from the database

Update the database

Three different interfaces are used:

Statement, PreparedStatement, CallableStatement

All are interfaces, thus cannot be instantiated

They are created by the Connection


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Querying with StatementQuerying with Statement

The executeQuery method returns a ResultSetobject representing the query result.

Will be discussed later

String queryStr ="SELECT * FROM Member " +

"WHERE Name = 'harry potter'";

Statement stmt = con.createStatement();

ResultSet rs = stmt.executeQuery(queryStr);


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Changing DB with StatementChanging DB with Statement

String deleteStr =DELETE FROM Member " +

"WHERE Name = harry potter";


int delnum = stmt.executeUpdate(deleteStr);

executeUpdate is used for data manipulation: insert, delete, update,

create table, etc. (anything other than querying!)

executeUpdate returns the number of rows modified


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ResultSetResultSet

A ResultSet provides access to a table of datagenerated by executing a Statement

Only one ResultSet per Statement can be open at

once The table rows are retrieved in sequence

A ResultSet maintains a cursor pointing to its current

row of data The 'next' method moves the cursor to the next row


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ResultSet MethodsResultSet Methods

boolean next() activates the next row

the first call to next() activates the first row

returns false if there are no more rows

void close()

disposes of the ResultSet

allows you to re-use the Statement that created it

automatically called by most Statement methods


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TypegetType(int columnIndex)

returns the given field as the given type

fields indexed starting at 1 (not 0)

TypegetType(String columnName)

same, but uses name of field

less efficient

int findColumn(String columnName)

looks up column index given column name


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String getString(int columnIndex) boolean getBoolean(int columnIndex)

byte getByte(int columnIndex)

short getShort(int columnIndex)

int getInt(int columnIndex) long getLong(int columnIndex)

float getFloat(int columnIndex)

double getDouble(int columnIndex)

Date getDate(int columnIndex)

Time getTime(int columnIndex)

Timestamp getTimestamp(int columnIndex)


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String getString(String columnName) boolean getBoolean(String columnName)

byte getByte(String columnName)

short getShort(String columnName)

int getInt(String columnName)

long getLong(String columnName)

float getFloat(String columnName)

double getDouble(String columnName)

Date getDate(String columnName)

Time getTime(String columnName)

Timestamp getTimestamp(String columnName)


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ResultSet ExampleResultSet Example


ResultSet rs = stmt.

executeQuery("select name, age from Employees");

// Print the result

while(rs.next()) {

System.out.print(rs.getString(1) + :);

System.out.println(rs.getShort(age)+);}


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Null ValuesNull Values

In SQL, NULL means the field is empty

Not the same as 0 or

In JDBC, you must explicitly ask if a field

is null by calling ResultSet.isNull(column)

For example, getInt(column) will return 0if the value is either 0 or null!!


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ResultSet Meta-DataResultSet Meta-Data

ResultSetMetaData rsmd = rs.getMetaData();

int numcols = rsmd.getColumnCount();

for (int i = 1 ; i


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Mapping Java Types to SQLMapping Java Types to SQLTypesTypes

SQL type Java TypeCHAR, VARCHAR, LONGVARCHAR String

NUMERIC, DECIMAL java.math.BigDecimal

BIT boolean

TINY INT byte

SMALL INT short

INTEGER int

BIG INT long

REAL float

FLOAT, DOUBLE double

BINARY, VARBINARY, LONGVARBINARY byte[]

DATE java.sql.DateTIME java.sql.Time

TIMESTAMP java.sql.Timestamp


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Database TimeDatabase Time

Times in SQL are notoriously non-standard Java defines three classes to help

java.sql.Date

year, month, day

java.sql.Time

hours, minutes, seconds

java.sql.Timestamp year, month, day, hours, minutes, seconds, nanoseconds

usually use this one


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Cleaning Up After YourselfCleaning Up After Yourself

Remember to close the Connections, Statements and ResultSets

rs.close();

stmt.close();

con.close();


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Dealing With ExceptionsDealing With Exceptions

Jdbc normaly throw ClassNotFoundException and SQLException like.

try {Class.forName( "sun.jdbc.odbc.JdbcOdbcDriver);connection = DriverManager.getConnection(

url, username, password );

}catch (ClassNotFoundException cnfe) {

System.out.println(cnfe.getMessage());

}


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Dealing With ExceptionsDealing With Exceptions

An exception can have more exceptions in it.

catch (SQLException e) {while (e != null) {

System.out.println(e.getSQLState());

System.out.println(e.getMessage());

System.out.println(e.getErrorCode());e = e.getNextException();

}

}


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A Summary of JDBC applicationA Summary of JDBC application

loadDriver

getConnection

createStatement

execute(SQL)

Result handling

Lastexecution ?

closeStatment

closeConnection

no

yes

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

connection = DriverManager.getConnection(jdbc:odbc:Books,,);

stmt.close();

con.close();

while (resultSet.next()) {...

}

resultSet.close();

resultSet = statement.executeQuery(SELECT * FROM Authors");

statement = connection.createStatement();

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JDBC lecture

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