Distributed Application Development

B. Ramamurthy

Working with Oracle

• Use the Oracle DBMS on UB machines. Information about this is available here.

• You can access UB db from your laptop as long you have enabled VPN and installed the appropriate driver and connected the data source. (and of course you have an internet connectivity).

Standard Access to DB

APPLICATION

DRIVER

MGR

DBMSDriver 1

DBMSDriver 2

DBMSDriver 3

DBMS 1

DBMS 2

DBMS 3

DB

DB

DB

ODBC Architecture

Application

Class1 Class2

Driver Manager

DriverType1 DriverType2 DriverType3

DataSource2DataSource1 DataSource3

ODBC

Open Database Connectivity (ODBC) Standard

• ODBC standard is an interface by which application programs can access and process SQL databases in a DBMS-independent manner. It contains:

• A Data Source that is the database, its associated DBMS, operating system and network platform

• A DBMS Driver that is supplied by the DBMS vendor or independent software companies

• A Driver Manager that is supplied by the vendor of the O/S platform where the application is running

ODBC Interface

• It is a system independent interface to database environment that requires an ODBC driver to be provided for each database system from which you want to manipulate data.

• The database driver bridges the differences between your underlying system calls and the ODBC interface functionality.

An Example

Application DriverManager

Access driver mySQL driver Oracle driver

odbc stan

dard API

Application in Java

Application inJava

DriverManager

Sybase driver mSQL driver Informix driver

odbc stan

dard API

jdbc API

Java Support for ODBC : JDBC

• When applications written in Java want to access data sources, they use classes and associated methods provided by Java DBC (JDBC) API.

• JDBC is specified an an “interface”. • An interface in Java can have many

“implementations”.• So it provides a convenient way to realize many

“drivers”

Java Support for SQL

• Java supports embedded SQL.• Also it provides an JDBC API as a standard way to

connect to common relational databases.• Java.sql package and an extensive exception

hierarchy.

Data Source

• Local relational database; Ex: Oracle• Remote relational database on a server; Ex:

InfoSource• On-line information service; Ex: Dow Jones,

Customer database

SQL Statements

• SELECT {what} FROM {table name}• SELECT {what} FROM {table name} WHERE

{criteria}• SELECT {what} FROM {table name} WHERE

{criteria} ORDER BY {field} • Others• Queries are embedded as strings in a

Statement object.

JDBC Components

• Driver Manager: Loads database drivers, and manages the connection between application & driver.

• Driver: Translates API calls to operations for a specific data source.

• Connection: A session between an application and a driver.• Statement: A SQL statement to perform a query or an update

operation.• Metadata: Information about the returned data, driver and

the database.• Result Set : Logical set of columns and rows returned by

executing a statement.

JDBC Classes

• Java supports DB facilities by providing classes and interfaces for its components

• DriverManager class• Connection interface (abstract class)• Statement interface (to be instantiated with

values from the actual SQL statement)• ResultSet interface

Driver Manager Class

• Provides static, “factory” methods for creating objects implementing the connection interface.– Factory methods create objects on demand

• When a connection is needed to a DB driver, DriverManager does it using it factory methods.

Connection interface

• Connection class represents a session with a specific data source.

• Connection object establishes connection to a data source, allocates statement objects, which define and execute SQL statements.

• Connection can also get info (metadata) about the data source.

Statement interface

• Statement interface is implemented by the connection object.

• Statement object provides the workspace for SQL query, executing it, and retrieving returned data.

• Types: Statement, PreparedStatement, CallableStatement

ResultSet interface

• Results are returned in the form of an object implementing the ResultSet interface.

• You may extract individual columns, rows or cell from the ResultSet using the metadata.

JDBC Application Architecture

Application

Connection

Driver Manager

Driver Driver Driver

DataSourceDataSource DataSource

Statement Result Set

JDBC Programming Steps• https://wiki.cse.buffalo.edu/services/content/how-use-jdbc-oracle

• Import necessary packages; Ex: import java.sql.*;• Include jdbc classes as a jar library.• Connect to the data source using “identifying” string ,

a user name and password.• Allocate Connection object, Statement object and

ResultSet object• Execute query using Statement object• Retrieve data from ResultSet object• Close Connection object.

Identifying Data Sources

• It is specified using URL format.• <scheme>: <sub_scheme>:<scheme-specific-part>Example(for local source): jdbc:odbc:tech_books• Alternatively, for remote connection,jdbc:odbc:thin:@aos.acsu.buffalo.edu:1521/aos.buffalo.edu

Connecting to a database on Netbeans

1. Add the driver jar file to the library for inclusion during compiling and building of the executable.

2. Add a new driver (jdbc:odbc) to the databases tab.3. Open connection to the data source (in this case to an

Oracle 11g instance)4. On successful connection you can view the data source

details (tables etc.).5. You can programmatically access the content of the

database from a Java program.6. You can execute SQL command from the source editor

window.

Connecting to UB’s Oracle 11g DB• Add the oracle driver to the library jars of your project.

Here is the oracle driver: • In order to load the JDBC driver in your Java programs,

include the line: • Class.forName("oracle.jdbc.driver.OracleDriver");• try { Class.forName ("oracle.jdbc.driver.OracleDriver"); } catch (ClassNotFoundException e){ System.out.println("Could not load the JDBC driver. Check your CLASSPATH."); System.exit(0); }

Connecting to UB’s Oracle

• Use this connection string syntax to connect to AOS:

Connection con = DriverManager.getConnection("jdbc:oracle:thin:"+user+"/"+

passwd+"@aos.acsu.buffalo.edu:1521/aos.buffalo.edu"); • Rest of the programming is similar to how we programmed

the Derby database..no difference!!• Essentially different drivers shield the differences in the

databases, exactly similar to how the device drivers operate!