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Web Design & Development ­ CS506
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Lesson 14
Java Database Connectivity
Introduction
Java Database Connectivity (JDBC) provides a standard library for accessing databases. The JDBC API
contains number of interfaces and classes that are extensively helpful while communicating with a
database.
The java.sql package
The java.sql package contains basic & most of the interfaces and classes. You automatically get this
package when you download the J2SETM. You have to import this package whenever you want to interact
with a relational database.
Connecting With Microsoft Access
In this handout, we will learn how to connect & communicate with Microsoft Access Database. We
chooses Access because most of you are familiar with it and if not than it is very easy to learn.
Create Database
In start create a database "PersonInfo" using Microsoft Access. Create one table named "Person". The
schema of the table is shown in the picture.
Add the following records into Person table as shown below.
Save the data base in some folder. (Your database will be saved as an .mdb file)
Setup System DSN
After creating database, you have to setup a system Data Source Name (DSN). DSN is a name
through which your system recognizes the underlying data source.
Select Start Settings Control Panel Administrative Tools Data Sources (ODBC).
The ODBC Data Source Administrator window would be opened as shown below. Select System
DSN tab. (If you are unable to use System DSN tab due to security restrictions on your machine,
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you can use the User DSN tab)
Press Add... button and choose Microsoft Access Driver (*.mdb) from Create New Data Source
window and press Finish button as shown in diagram.
After that, ODBC Microsoft Access Setup window would be opened as shown in following
diagram
Enter the Data Source Name personDSN and select the database by pressing Select button. The
browsing window would be opened, select the desired folder that contains the database (The
database .mdb file you have created in the first step) Press Ok button.
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Basic Steps in Using JDBC
There are eight (8) basic steps that must be followed in order to successfully communicate with a database.
Let's take a detail overview of all these one by one.
1. Import Required Package
Import the package java.sql.* that contains useful classes and interfaces to access & work with
database.
import java.sql.*;
2. Load Driver
Need to load suitable driver for underlying database.
Different drivers & types for different databases are available.
For MS Access, load following driver available with j2se.
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
For Oracle, load the following driver. You have to download it explicitly.
Class.forName("oracle.jdbc.driver.OracleDriver");
3. Define Connection URL
To get a connection, we need to specify the URL of a database (Actually we need to specify
the address of the database which is in the form of URL)
As we are using Microsoft Access database and we have loaded a JDBC-ODBC driver. Using
JDBC-ODBC driver requires a DSN which we have created earlier and named it personDSN.
So the URL of the database will be
String conURL = "jdbc:odbc:personDSN";
4. Establish Connection With DataBase
Use DriverManagerto get the connection object.
The URL of the database is passed to the getConnection method. Connection con =
DriverManager.getConnection(conURL);
If DataBase requires username & password, you can use the overloaded version of getConnection
method as shown below:
String usr = "umair";
String pwd = "vu";
Connection con = null;con = DriverManager.getConnection(conURL, usr, pwd);
5. Create Statement
A Statement object is obtained from a Connection object.
Statement stmt = con.createStatement( );
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Once you have a statement, you can use it for various kinds of SQL queries.
6. Execute a Query
The next step is to pass the SQL statements & to execute them.
Two methods are generally used for executing SQL queries. These are:
executeQuery(sql) method
Used for SQL SELECT queries.
Returns the ResultSET object that contains the results of the query and can be used to access the
query results.
String sql = "SELECT * from sometable";ResultSet rs =
stmt.executeQuery(sql);
executeUpdate(sql)method
.
This method is used for executing an update statement like INSERT, UPDATE or
7.
DELETE
Returns an Integer value representing the number of rows updated
String sql = "INSERT INTO tablename " + "(columnNames) Values (values)" ;
int count = stmt.executeUpdate(sql);
Process Results of the Query
The ResultSet provides various getXXX methods that takes a column index or name and returns
the data
The ResultSet maintains the data in the form tables (rows & columns)
First row has index 1, not 0.
The next method of ResultSet returns true or false depending upon whether the next row is
available (exist) or not and moves the cursor
Always remember to call next() method at-least once
To retrieve the data of the column of the current row you need to use the various getters provided
by the ResultSet.
For example, the following code snippet will iterate over the whole ResultSet and illustrates the
usage of getters methods
while ( rs.next() ){
//by using column name
String name = rs.getString("columnName");
// or by using column indexString name = rs.getString(1);
}
8. Close the Connection
An opening connection is expensive, postpone this step if additional database operations are
expected
con.close();
Example Code 14.1: Retrieving Data from ResultSet
The JdbcEx.java demonstrates the usage of all above explained steps. In this code example, we connect
with the PersonInfo database, the one we have created earlier, and then execute the simple SQL SELECT
query on Person table, and then process the query results.
// File JdbcEx.java
//step 1: import packageimport java.sql.*;
public class JdbcEx {
public static void main (String args[ ]) {
try {
//Step 2: load driverClass.forName("sun.jdbc.odbc.JdbcOdbcDriver");
//Step 3: define the connection URL
String url = "jdbc:odbc:personDSN";
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//Step 4: establish the connection
Connection con = DriverManager.getConnection(url);
//Step 5: create Statement
Statement st = con.createStatement();
//Step 6: preapare & execute the query
String sql = "SELECT * FROM Person";
ResultSet rs = st.executeQuery(sql);
//Step 7: process the results
while(rs.next()){
// The row name is "name" in database "PersonInfo,// hence specified in the getString()
method.
String name = rs.getString("name");String add = rs.getString("address");String
pNum = rs.getString("phoneNum");
System.out.println(name + " " + add + " " + pNum);}
//Step 8: close the connection
con.close();
}catch(Exception sqlEx){
System.out.println(sqlEx);
}
} // end main} // end class
The important thing you must notice that we have put all code inside try block and then handle (in the
above example, only printing the name of the exception raised) exception inside catch block.
Why? Because we are dealing with an external resource (database). If you can recall all IO related
operations involving external resources in java throw exceptions. These exceptions are checked exceptions
and we must need to handle these exceptions.
Compile & Execute
Since the Person table contains only three records, so the following output would be produced on executing
the above program.
References:
. Java ­ A Lab Course by Umair Javed
. Java tutorial by Sun: http://java.sun.com/docs/books/turorial
. Beginning Java2 by Ivor Hortan
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