Five Steps to connect a database via JDBC driver
The fundamental steps involved in the process of connecting to a database and executing a query consist of the following:
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1) Load and register the JDBC driver
The forName() method of the java.lang.Class is used to load and register the JDBC driver:
Syntax
public static void forName(String className)throws ClassNotFoundException
Example
Class.forName("oracle.jdbc.driver.OracleDriver");
2) Create the connection object
The getConnection() method of java.sql.DriverManager is used to establish connection with database. It is an overloaded method that takes 3 parameters (URL, username, and password)
Syntax
1) public static Connection getConnection(String url, String name, String password) throws SQLException
In case, when the URL contains the username and password then the following method is used
2) public static Connection getConnection(String url)throws SQLException
Example
Connection connection=DriverManager.getConnection( "jdbc:oracle:thin:@localhost:1521:XE","UserName","Password");
3) Create the Statement object
The createStatement() method of java.sql.Connection interface is used to create statement object which is responsible for running & executing queries against the database.
Syntax:
public Statement createStatement()throws SQLException
Example:
Statement stmt=connection.createStatement();
4) Executing the query and processing the ResultSet
Once a Statement object has been constructed, the next step is to execute the query. This is done by using the executeQuery() method of the Statement object. On executing this method it returns the object of ResultSet which contains the ResultSet produced by executing the query.
Syntax:
public ResultSet executeQuery(String sql)throws SQLException
Execute query and process the ResultSet
ResultSet rset=stmt.executeQuery("select * from employee");
// Processing the ResultSet
while(rset.next())
{
System.out.println(rset.getInt(1)+" "+rset.getString(2));
}
5) Explicitly closing JDBC objects
Once the Resultset,statement & Connection objects have been used, they must be closed explicitly. This is done by calling close() method of the ResultSet ,Statement and Connection classes.
Syntax
public void close()throws SQLException
Example
connection.close(); rset.close();
If you do not explicitly call the close() method for each of these objects as soon as you are done with them, your programs are likely to run out of resources. The best practice is to Close JDBC objects in finally block and assign null value afterwards, so that it will be immediately eligible for garbage collection.
