jdbc connection in java

8/9/2019 jdbc connection in java

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Database access using Servlets


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Introduction JDBC is a Java API (set of classes and interfaces) for executing

database (SQL) statements in a Java program.

History

Part of JDK Since JDK 1.1

Package: java.sql

Use

Create tables, insert values into them, query tables, retrieve

results from queries, and update tables.


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JDBC Architecture

Application JDBC Driver Data Source

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


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JDBC drivers

Drivers are libraries used by applications to connect todatabases.

The JVM uses the JDBC driver to translate generalized JDBC

calls into vendor specific database calls.

JDBC drivers implement some of the JDBC API


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Types ofJDBC Driver Type 1: JDBC-ODBC Bridge

Type 2: Part Java, Part Native Driver

Type 3: Intermediate database Access Server

Type 4: Pure Java Drivers


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Type I

Bridge

Type II

Native

Type III

Middleware

Type IV

Pure

ODBC

API

ODBC

Layer

Middleware

Server

Native Code

Library

JDBC

Data

Source

Data

Source

Data

Source

Data

Source


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Type 1: JDBC-ODBC Bridge The JDBC to ODBC bridge driver connects Java Program to Microsoft

ODBC (Open Database Connectivity) data sources

The Java 2 Software Development kit from Sun Microsystems

includes the JDBC-ODBC bridge

This driver requires the ODBC driver on the client computer and

normally requires configuration of ODBC data sources

Uses bridge to connect Java client to an ODBC database system.

Translates all JDBC calls into ODBC and sends them to ODBC driver

This really refers to a C program, compiled to native code, thatinterfaces the Java Virtual Machine to ODBC.


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Java Application

JDBC-ODBC

BridgeJDBC

API

ODBC

Layer

ODBC

API

Data

SourceClient

Server

Translates query obtained by JDBC into corresponding ODBC query, which

is then handled by the ODBC driver.

There is some overhead associated with the translation work to go from

JDBC to ODBC


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Features Standard JDK includes classes for JDBC-ODBC bridge for e.g.

sun.jdbc.odbc.JdbcOdbcDriver.

Native library is not database specific. The bridge does not need to

know about every kind of database; it only needs to know how to usethe ODBC API

Advantages:

If ODBC driver is already available, then only bridge is required.

Almost any database for which ODBC driver is installed, can be accessed.


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Contd..Disadvantages

Slow

JDBC call goes thru the bridge to the ODBC driver then todatabase-specific driver.

Native code required

Data source to be defined on each client machine


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Type 2: Part Java, Part Native

Driver Uses mix of Java implementation and vendor-specific native API

for data access.

Requires vendor (database-specific) binary code to be present

on client machine.

Uses a native code library to access database, wrapping a thin

layer of Java around the native library.

Converts JDBC calls into database-specific calls for databasessuch as SQL server, Oracle, Sybase etc

e.g. Oracle Driver, WebLogic drivers


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J

ava Application

JDBC DriverVendor

APIJDBCAPI

Client

Data

Source

Server

Part Java, Part Native Driver


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Contd..Advantage

Type 2 drivers typically offer significantly better performancethan the JDBC-ODBC Bridge. Fast, as less layers to go

Disadvantage The vendor database library needs to be loaded on each client

machine. Consequently, type 2 drivers cannot be used for theInternet.

Type 2 drivers show lower performance than type 3 and type 4drivers.

ApplicationStandalone GUI- intensive program that always runs on NT mayuse Type 2 native code driver.


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Type 3: Intermediate database

Access Server Also known as JDBC-Net pure Java driver

Based on middleware database server that acts as a

gateway for multiple database servers. Uses database-independent protocol to communicate

with database gateway (vendor-neutral driver server).The middleware component might use any other typeof driver to provide actual database access.

Type 3 JDBC drivers are pure Java drivers fordatabase middleware.

e.g. Symantec


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ClientJava

Application

JDBC Driver JDBC Driver

Server

Native

Driver

Data

Source

Server

JDBCAPI

JDBC calls are translated into a middleware vendor's protocol, andthe middleware converts those calls into a database's API.

Type 3 JDBC drivers offer the advantage of being server-based,meaning that they do not require native client code, which makesType 3 drivers faster than Type 1 and Type 2 drivers.

Developers can also use a single JDBC driver to connect to multipledatabases.


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Contd..

Advantages:

Pure Java. No native code to be installed on client machine.

Flexible when client wants to communicate with multiple databasesfrom different vendors.

Useful for intranet applications.

Features of connection pooling, data caching etc.

Disadvantages

Type 3 drivers require database-specific coding to be done in themiddle tier.

Slow- presence of gateway. Gateway reads data from database thensends to client.


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Type 4: Pure Java Drivers Also known as Native-protocol pure Java driver

Type 4 JDBC drivers are direct-to-database pure Java drivers ("thin"drivers).

Convert JDBC API calls to direct network calls using vendor-specificnetworking protocols by making direct connections with database

They understand database-specific networking protocols and canaccess database directly without any additional software.

Are completely implemented in Java to achieve platform independence

Each DBMS requires its own Type 4 driver; therefore, there are more

drivers to manage in a heterogeneous computing environment, but thisis outweighed by the fact that Type 4 drivers provide faster

performance and direct access to DBMS features.

e.g. Oracle, mySQL


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ClientJava

Application

JDBC Driver

Data

Source

Server

JDBCAPI

JDBC drivers don't have to translate database requests to ODBC or anative connectivity interface or to pass the request on to another server


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Contd.. Advantages:

Simplest to deploy.

Platform-independent.

Fastest, no code needs to be deployed on client machine.

Disadvantages:

Database-specific- need different driver for each database.


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Driver Statement Connection ResultSet ResultSetMeta

Data

DatabaseMeta

Data

PreparedStatement

CallableStatementjava.lang.Object

java.util.date Driver Manager DriverPropertyInfo Types

Date Time TimeStamp


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InterfacesDriver

public interface Driver

The interface that every driver class must implement.

The Java SQL framework allows for multiple database drivers.

Each driver should supply a class that implements the Driver interface.

The DriverManager will try to load as many drivers as it can find andthen for any given connection request, it will ask each driver in turn totry to connect to the target URL.

When a Driver class is loaded, it should create an instance of itself andregister it with the DriverManager. This means that a user can load andregister a driver by calling

Class.forName("foo.bah.Driver")


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Contd.. Statement

The objective of the Statement interface is to pass to the database the

SQL string for execution and to retrieve any results from the database

in the form of a ResultSet


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Contd..

Connection

When a connection is opened, this represents a single instance of a

particular database session. As long as the connection remains open,

SQL queries may be executed and results obtained.

public Statement createStatement() throws SQLException

Creates a Statement object for sending SQL statements to the

database. SQL statements without parameters are normally

executed using Statement objects. If the same SQL statement is

executed many times, it may be more efficient to use a

PreparedStatement object.


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Contd..ResultSet

A ResultSet is the retrieved data from a currently executed SQL

statement.

The data from the query is delivered in the form of a table. The rows of

the table are returned to the program in sequence.


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Contd..ResultSetMetaData

Provides information on the type and properties of ResultSet.

An object that can be used to get information about the types and

properties of the columns in a ResultSet object.

Methods:

getColumnCount

public int getColumnCount() throws SQLException

Returns the number of columns in this ResultSet object


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Contd..isSearchable

public boolean isSearchable(int column) throws SQLException

Indicates whether the designated column can be used in a where

clause.

getColumnName

public String getColumnName(int column) throws

SQLException

Get the designated column's name.


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Contd..DatabaseMetaData

Provides information on the database as a whole

What tables are available?

Is the database in read-only mode?


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ClassesDriverManager

This is a very important class.

Its main purpose is to provide a means of managing thedifferent types ofJDBC database driver

On running an application, it is the DriverManager's

responsibility to load all the drivers found in the system


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Typical

JDBC Programming Procedure

1. Load the database driver

2. Obtain a connection

3. Create and execute statements

4. Use result sets to navigate through the results

5. Close the connection


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SQL

Code

import

java.sql.*;

class useDB

{

}

JDBC

Connectivity

UtilitiesDriver DB


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Database

DriverManager

Connection Statement ResultSet

Driver

SQL Data


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Used to provide common access layer on the top of differentdatabase drivers used in an application.

The DriverManager class keeps track of the registered JDBC

drivers and creates database connections. DriverManager requires that each driver required by the

application must be registered before use, so that theDriverManager is aware of it

DriverManager


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DriverManager

Sybase Driver

Oracle Driver

JDBC ODBC DriverConnection

getConnection(jdbc:odbc:myLib)


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DriverManager Application does not interacts directly with Driver object since

DriverManager is available.

getConnection() iterates thru the drivers that are registered with

the DriverManager and asks each one in turn if it can handle theURL that is passed.

First driver that can satisfy the connection defined by the URL creates

a connection object that is passed back to the application by the way of

DriverManager


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How to load DriverManager Load the database driver using ClassLoader:

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

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

} catch (ClassNotFoundException e) {/* Handle Exception */ }

When a Driver class is loaded, it should create an instance of itself and register

it with the DriverManager.

Class class: java.lang.Class- This method dynamically loads a class if it has

not already been loaded. The method returns a Class object that describes the

named classforName

public static Class forName(String className) throws ClassNotFoundException


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Connecting to a Database The Connection represents a single logical database transaction.

The Connection Interface has methods for sending a series ofSQL statements to the database and managing the committing

or aborting of those statements.Type 1 JDBC Driver

try

{

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

Connection con = DriverManager.getConnection

("jdbc:odbc:dsn");

}catch(SQLException e){

e.printStackTrace();

}


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Contd..Type 4 JDBC Driver

Oracle Server

try

{

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

Connection con = DriverManager.getConnection(

"jdbc:oracle:thin:@localhost:1521:ite",

"scott", tiger");



}


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Statement Statement interface provides workspace to create SQL query,

execute it and retrieve any results that are executed.

Created by createStatement() of Connection

createStatement() throws SQLException

Statement stat = con.createStatement();


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Executing SELECT

Statements A query is expected to return a set of tuples as the result, and

not change the state of the database. The executeQuery

method of the statement is used to execute a database query.

This returns a result set. The Stat.executeQuery() method is used when you want to

retrieve records from a database i.e. you are executing SELECT

SQL statements.

E.g.

ResultSet rs = stat.executeQuery("SELECT

*F

ROM

ells");ResultSet result = stat.executeQuery("SELECT name, cups FROM

JoltData ORDER BY cups DESC;");


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Executing INSERT/UPDATE/DELETE Query

To INSERT, UPDATE or DELETE records from a table, make use of

Stat.executeUpdate() method

When executeUpdate is used to call DDL statements, the return

value is always zero, while data modification statementexecutions will return a value greater than or equal to zero,which is the number of tuples affected in the relation


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Contd.. Create a simple table, which stores an employee ID and name

stat.executeUpdate (CREATE TABLE EMPLOYEE (Emp_Id

number(5), Emp_Name varchar(20)));

Insert data into employee, so the table contains datastat.executeUpdate (INSERT INTO EMPLOYEE VALUES (1,

'John')");

Commit changes

conn.commit();

Delete a record

int recordsUpdated;

recordsUpdated = st.executeUpdate("DELETE FROM

EMPLOYEE WHERE Emp_Id = 1");


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ResultSet The ResultSet interface allows to access data returned from an

SQL query.

ResultSet results = stmt.executeQuery( SELECT Emp_Id,

Emp_Name FROM EMPLOYEE);

while (results.next())

{

int Id = results.getInt(Emp_Id");

String Name = results.getString(Emp_Name");

}


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Contd.. The get method has two forms by which data can be accessed.

In the first form, column name of the table is specified while inthe second form the position of that column in the table isspecified.

Retrieving a result by index is faster than retrieving a result bycolumn name. But the disadvantage is that the code is harder tomaintain.

Updating data from ResultSet

Update values in result set and store updates back into

database. E.g.

results.updateString(column_name, new_value);

results.updateRow();

results.updateString(Emp_Name",Name.toUpperCase());


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import java.io.*;

import java.lang.Object;

import java.sql.*;

public class JdbcTest {

public static void main(String args[]){

Connection dbConn=null;

Statement stat=null;try{

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

dbConn=DriverManager.getConnection("jdbc:odbc:test2","scott","tiger");

stat = dbConn.createStatement();


System.out.println(e); }

catch(ClassNotFoundException e){System.out.println(e); }


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try{

ResultSet customers= stat.executeQuery("SELECT CustomerID, CompanyName, City,

Country FROM customers");

System.out.println("CUSTOMER LIST");

while(customers.next())

{

System.out.println( customers.getString("CustomerID"));

System.out.println(customers.getString("CompanyName"));

System.out.println(customers.getString("City"));

System.out.println(customers.getString("Country"));

}

}catch(Exception e){


}

}

}


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Handling database connections in Servlets

import java.io.*;

import java.sql.*;

import java.util.*;

import javax.servlet.*;

import javax.servlet.http.*;

public class JdbcServlet extends HttpServlet

Connection con = null; // dbase connection, 1 per pooled servlet instancepublic void init(ServletConfig config) throws ServletException{

super.init(config);

// Establish the connection for this instance

con = establishConnection();

con.setAutoCommit(false);

}


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public void doGet(HttpServletRequest req, HttpServletResponse res) throwsServletException, IOException {

res.setContentType("text/plain");

PrintWriter out = res.getWriter();

// Use the connection uniquely assigned to this instance

Statement stmt = con.createStatement();

// Update the database any number of ways Commit the transaction

con.commit();

}

public void destroy() {

if (con != null)

con.close();

}

}

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jdbc connection in java