Java Database Connectivity Lecture1

8/3/2019 Java Database Connectivity Lecture1

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JDBC

Java DataBase Connectivity


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What is JDBC?

An API that lets you access virtually any tabular data

source from the Java programming language

JDBC Data Access API JDBC Technology Homepage

Whats an API? See J2SE documentation

Whats a tabular data source?

access virtually any data source, from relational

databases to spreadsheets and flat files. JDBC Documentation

Well focus on accessing Oracle databases


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General Architecture

What design pattern is

implied in this

architecture?

What does it buy for us? Why is this architecture

also multi-tiered?


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Part I: Overview of Databases

and Java


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Databases in the Enterprise

All corporate data stored in DB

SQL standardizes format (sort of)


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Database Architectures

Two-tier

Three-tier

N-tier


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Two-Tier Architecture

Client connects directly to

server

e.g. HTTP, email

Pro:

simple

client-side scripting offloads

work onto the client

Con: fat client

inflexible


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Three-Tier Architecture

Application Server sits between client and

database


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Three-TierPros

flexible: can change one part without

affecting others

can connect to different databases withoutchanging code

specialization: presentation / business logic /

data management

can cache queries

can implement proxies and firewalls


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Three-Tier Cons

higher complexity

higher maintenance

lower network efficiency more parts to configure (and buy)


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N-Tier Architecture

Design your application using as many tiers

as you need

Use Object-Oriented Design techniques Put the various components on whatever

host makes sense

Java allows N-Tier Architecture, especially

with RMI and JDBC


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Join example

People

name

homeaddress workaddress

Addresses

id

street

state

zip


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SQL

Structured Query Language

Standardized syntax for querying

(accessing) a relational database Supposedly database-independent

Actually, there are important variations from

DB to DB


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SQLSyntax

INSERT INTO table (field1, field2 )

VALUES (value1, value2 )

inserts a new record into the named table

UPDATE table SET (field1 = value1,field2 = value2 ) WHERE condition

changes an existing record or records

DELETE FROM table WHERE condition

removes all records that match conditionSELECT field1, field2 FROM table WHERE

condition

retrieves all records that match condition


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Part II: JDBC Overview


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JDBC Goals

SQL-Level

100% Pure Java

Keep it simple High-performance

Leverage existing database technology

why reinvent the wheel? Use strong, static typing wherever possible

Use multiple methods to express multiple

functionality


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JDBC Architecture

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 thanone database

Ideal: can change database engines without

changing any application code


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The Microsoft Access

Northwind Database

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Using Microsoft Access via

ODBC

Click Start, Settings, Control Panel, Administrative Tools, Data

Sources, System DSN, and select Add

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ODBC (Continued)

Select Microsoft Access Driver, Finish, type a name under Data

Source Name, and hit Select

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ODBC (Continued)

Navigate to the Samples directory of MS Office, select

Northwind.mdb, hit OK, then hit OK in following two windows

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Part III: JDBC APIs


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Basic steps to use

a database in Java

1.Establish a connection

2.Create JDBC Statements

3.Execute SQL Statements 4.GET ResultSet

5.Close connections


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1. Establish a connection

import java.sql.*;

Load the vendor specific driver Class.forName("oracle.jdbc.driver.OracleDriver");

What do you think this statement does, and how? Dynamically loads a driver class, for Oracle database

Make the connection Connection con = DriverManager.getConnection(

"jdbc:oracle:thin:@oracle-prod:1521:OPROD",username, passwd);

What do you think this statement does?

Establishes connection to database by obtaininga Connection object


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2. Create JDBC statement(s)

Statement stmt = con.createStatement() ;

Creates a Statement object for sending SQL statements

to the database


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Executing SQL Statements

String createLehigh = "Create table Lehigh " +

"(SSN Integer not null, Name VARCHAR(32), " +"Marks Integer)";

stmt.executeUpdate(createLehigh);

//What does this statement do?

String insertLehigh = "Insert into Lehigh values+ "(123456789,abc,100)";

stmt.executeUpdate(insertLehigh);


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Get ResultSet

String queryLehigh = "select * from Lehigh";

ResultSet rs = Stmt.executeQuery(queryLehigh);//What does this statement do?

while (rs.next()) {

int ssn = rs.getInt("SSN");

String name = rs.getString("NAME");

int marks = rs.getInt("MARKS");

}


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Close connection

stmt.close();

con.close();


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Transactions and JDBC

JDBC allows SQL statements to be grouped together into asingle transaction

Transaction control is performed by the Connection object,default mode is auto-commit, I.e., each sql statement is treated

as a transaction We can turn off the auto-commit mode with

con.setAutoCommit(false);

And turn it back on with con.setAutoCommit(true);

Once auto-commit is off, no SQL statement will be committed

until an explicit is invoked con.commit(); At this point all changes done by the SQL statements will be

made permanent in the database.


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Handling Errors with

Exceptions

Programs should recover and leave the database in

a consistent state.

If a statement in the try block throws an exception or

warning, it can be caught in one of thecorresponding catch statements

E.g., you could rollback your transaction in a

catch { } block or close database connection


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ODBC (Continued)

Use sun.jdbc.odbc.JdbcOdbcDriver as the

class name of the JDBC driver.

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

U

se "jdbc:odbc:N

orth

wind" as th

e databaseaddress, and use empty strings for the

username and password.

Connection connection =

DriverManager.getConnection("jdbc:odbc:Northwind",

"","");

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Simple Standalone Northwind

Test

import java.sql.*;

public class NorthwindTest {

public static void main(String[] args) {

String driver =

"sun.jdbc.odbc.JdbcOdbcDriver";

String url = "jdbc:odbc:Northwind";String username = "";

String password = "";

showEmployeeTable(driver, url,

username, password);

}

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public static void showEmployeeTable(String driver,

String url,

String username,

String password) {try {

// Load database driver if not already loaded.

Class.forName(driver);

// Establish network connection to database.

Connection connection =DriverManager.getConnection(url,

username, password);

System.out.println("Employees\n" +

"=========");

Statement statement = connection.createStatement();

String query =

"SELECT firstname, lastname FROM employees";

// Send query to database and store results.

ResultSet resultSet = statement.executeQuery(query);

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//Print results.

while(resultSet.next()) {

//First name

System.out.print(resultSet.getString(1) + " ");

//Last name

System.out.println(resultSet.getString(2));

}

} catch(ClassNotFoundException cnfe) {

System.err.println("Error loading driver: " + cnfe);

} catch(SQLException sqle) {

System.err.println("Error connecting: " + sqle);

}

}

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Simple Standalone Northwind

Test: Results

Prompt> java NorthwindTest

Employees

=========

Nancy Davolio

Andrew Fuller

Janet Leverling

Margaret Peacock

Steven Buchanan

Michael SuyamaRobert King

Laura Callahan

Anne Dodsworth

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Mapping types JDBC - Java


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JDBC 2 Scrollable Result Set

Statement stmt =

con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,

ResultSet.CONCUR_READ_ONLY);

String query = select students from class where type=not sleeping ;

ResultSet rs = stmt.executeQuery( query );

rs.previous(); / / go back in the RS (not possible in JDBC 1)

rs.relative(-5);/ / go 5 records backrs.relative(7);/ / go 7 records forward

rs.absolute(100);/ / go to 100th record


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Metadata from DB

A Connection's database is ableto provide schema informationdescribing its tables,

its supported SQL grammar,its stored proceduresthe capabilities of this connection, and so on What is a stored procedure?

Group of SQL statements that form a logical unit

and perform a particular taskThis information is made available through

a DatabaseMetaData object.


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Metadata from DB - example

Connection con = . ;

DatabaseMetaData dbmd = con.getMetaData();

String catalog = null;String schema = null;String table = sys%;String[ ] types = null;

ResultSet rs =dbmd.getTables(catalog , schema , table , types );


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JDBC Metadata from RS

public static void printRS(ResultSet rs) throws SQLException

{

ResultSetMetaData md = rs.getMetaData();

// get number of columns

int nCols = md.getColumnCount();// print column names

for(int i=1; i < nCols; ++i)

System.out.print( md.getColumnName( i)+",");

/ / output resultset

while ( rs.next() ){ for(int i=1; i < nCols; ++i)

System.out.print( rs.getString( i)+",");

System.out.println( rs.getString(nCols) );

}

}

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Java Database Connectivity Lecture1