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Database operations in Java
This article provides an example of how to create a simple JDBC application. This will show you how to open a database connection, execute a SQL query, and display the results.
Creating JDBC Application
There are following six steps involved in building a JDBC application −
Import the packages: Requires that you include the packages containing the JDBC classes needed for database programming. Most often, using import java.sql.* will suffice.
Register the JDBC driver: Requires that you initialize a driver so you can open a communication channel with the database.
Open a connection: Requires using the DriverManager.getConnection() method to create a Connection object, which represents a physical connection with the database.
Execute a query: Requires using an object of type Statement for building and submitting an SQL statement to the database.
Extract data from result set: Requires that you use the appropriate ResultSet.getXXX() method to retrieve the data from the result set.
Clean up the environment: Requires explicitly closing all database resources versus relying on the JVM's garbage collection.
Sample Code
This simple example can serve as a template when you need to create your own JDBC application in the future.
This sample code has been written based on the environment and database setup done in the previous chapter.
Copy and paste the following example in FirstExample.java, compile and run as follows −
//STEP 1. Import required packages
import java.sql.*;
public class FirstExample {
// JDBC driver name and database URL
static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
static final String DB_URL = "jdbc:mysql://localhost/EMP";
// Database credentials
static final String USER = "username";
static final String PASS = "password";
public static void main(String[] args) {
Connection conn = null;
Statement stmt = null;
try{
//STEP 2: Register JDBC driver
Class.forName("com.mysql.jdbc.Driver");
//STEP 3: Open a connection
System.out.println("Connecting to database...");
conn = DriverManager.getConnection(DB_URL,USER,PASS);
//STEP 4: Execute a query
System.out.println("Creating statement...");
stmt = conn.createStatement();
String sql;
sql = "SELECT id, first, last, age FROM Employees";
ResultSet rs = stmt.executeQuery(sql);
//STEP 5: Extract data from result set
while(rs.next()) {
//Retrieve by column name
int id = rs.getInt("id");
int age = rs.getInt("age");
String first = rs.getString("first");
String last = rs.getString("last");
//Display values
System.out.print("ID: " + id);
System.out.print(", Age: " + age);
System.out.print(", First: " + first);
System.out.println(", Last: " + last);
}
//STEP 6: Clean-up environment
rs.close();
stmt.close();
conn.close();
}catch(SQLException se) {
//Handle errors for JDBC
se.printStackTrace();
}catch(Exception e) {
//Handle errors for Class.forName
e.printStackTrace();
}finally {
//finally block used to close resources
try {
if(stmt!=null)
stmt.close();
}catch(SQLException se2) {}
// nothing we can do
try {
if(conn!=null)
conn.close();
}catch(SQLException se) {
se.printStackTrace();
}//end finally try
}//end try
System.out.println("Goodbye!");
}//end main
}//end FirstExampleNow let us compile the above example as follows −
C:\>javac FirstExample.java C:\>
When you run FirstExample, it produces the following result −
C:\>java FirstExample Connecting to database... Creating statement... ID: 100, Age: 18, First: Zara, Last: Ali ID: 101, Age: 25, First: Mahnaz, Last: Fatma ID: 102, Age: 30, First: Zaid, Last: Khan ID: 103, Age: 28, First: Sumit, Last: Mittal C:\>
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