JDBC: 5 Steps to connect to Database

5 Steps to connect to the database in java

There are 5 steps to connect any java application with the database in java using JDBC. They are as follows:

• Register the driver class
• Creating connection
• Creating statement
• Executing queries
• Closing connection

1) Register the driver class

The forName () method of Class class is used to register the driver class. This method is used to dynamically load the driver class.

Syntax of forName () method

public static void forName(String className)throws ClassNotFoundException  

Class.forName(“com.mysql.jdbc.Driver”);//For MySQL driver

2) Create the connection object

The getConnection () method of DriverManager class is used to establish connection with the database.

Syntax of getConnection () method

 1) public static Connection getConnection(String url)throws SQLException  

 2) public static Connection getConnection(String url,String name,String password)  

  throws SQLException.

Connection con=DriverManager.getConnection(“jdbc:mysql://localhost:3306/dbname”,”username”,”password”);     // For MySQL driver

3) Create the Statement object

The createStatement () method of Connection interface is used to create statement. The object of statement is responsible to execute queries with the database.

Syntax of createStatement () method

public Statement createStatement()throws SQLException  

Statement stmt=con.createStatement ();

4) Execute the query

The executeQuery () method of Statement interface is used to execute queries to the database. This method returns the object of ResultSet that can be used to get all the records of a table.

Syntax of executeQuery () method

public ResultSet executeQuery(String sql)throws SQLException

ResultSet rs=stmt.executeQuery("select * from TableName"); 

while(rs.next()){ 

System.out.println(rs.getInt(1)+" "+rs.getString(2)); 

5) Close the connection object

By closing connection object statment and ResultSet will be closed automatically. The close () method of Connection interface is used to close the connection.

Syntax of close () method

public void close()throws SQLException 

con.close();  

DriverManager Class:-

The DriverManager class acts as an interface between user and drivers. It keeps track of the drivers that are available and handles establishing a connection between a database and the appropriate driver. The DriverManager class maintains a list of Driver classes that have registered themselves by calling the method DriverManager.registerDriver ().

Connection interface:

A Connection is the session between java application and database. The Connection interface is a factory of Statement, PreparedStatement, and DatabaseMetaData i.e. object of Connection can be used to get the object of Statement and DatabaseMetaData. The Connection interface provide many methods for transaction management like commit(),rollback() etc.

By default, connection commits the changes after executing queries.

1) public Statement createStatement (): creates a statement object that can be used to execute SQL queries.

2) public Statement createStatement (int resultSetType,int resultSetConcurrency): Creates a Statement object that will generate ResultSet objects with the given type and concurrency.

3) public void setAutoCommit (boolean status): is used to set the commit status.By default it is true.

4) public void commit (): saves the changes made since the previous commit/rollback permanent.

5) public void rollback (): Drops all changes made since the previous commit/rollback.

6) public void close (): closes the connection and Releases a JDBC resources immediately.

Statement interface

The important methods of Statement interface are as follows:

1) public ResultSet executeQuery(String sql): is used to execute SELECT query. It returns the object of ResultSet.

2) public int executeUpdate (String sql): is used to execute specified query, it may be create, drop, insert, update, delete etc.

3) public boolean execute(String sql): is used to execute queries that may return multiple results.

4) public int[] executeBatch(): is used to execute batch of commands.

ResultSet interface

The object of ResultSet maintains a cursor pointing to a particular row of data. Initially, cursor points to before the first row.

By default, ResultSet object can be moved forward only and it is not updatable.

But we can make this object to move forward and backward direction by passing either TYPE_SCROLL_INSENSITIVE or TYPE_SCROLL_SENSITIVE in createStatement(int,int) method as well as we can make this object as updatable by:

Statement stmt = con.createStatement (ResultSet.TYPE_SCROLL_INSENSITIVE,              

ResultSet.CONCUR_UPDATABLE); 

For Example:-

package com.javacoreconcept.jeetendra;

import java.sql.Connection;

import java.sql.DriverManager;

import java.sql.ResultSet;

import java.sql.SQLException;

import java.sql.Statement;

public class JdbcSample {

        

            public static void main(String...jdbc) throws ClassNotFoundException, SQLException{

              Class.forName("com.mysql.jdbc.Driver");

              Connection con=DriverManager.getConnection("jdbc:mysql://localhost:3306/hibernatesample","root","admin");

              String query="Select * from UserDetails2";

            Statement

              ResultSet rs=stmt.executeQuery(query);

              rs.absolute(5);

              System.out.println(rs.getInt(1)+" "+rs.getString(2)+" "+rs.getString(3));

               con.close();}

}

Note:- boolean absolute( int row ) throws SQLException;

    /**

     * Moves the cursor a relative number of rows, either positive or negative.

     * Attempting to move beyond the first/last row in the

     * result set positions the cursor before/after the

     * the first/last row. Calling <code>relative(0)</code> is valid, but does

     * not change the cursor position.

PreparedStatement:

The PreparedStatement interface is a subinterface of Statement. It is used to exeucte parameterized query. Why use PreparedStatement?

The performance of the application will be faster if you use PreparedStatement interface because query is compiled only once.

The prepareStatement() method of Connection interface is used to return the object of PreparedStatement.Syntax:

public PreparedStatement prepareStatement(String query)throws SQLException{}