How do we close resources automatically in Java?

You can close resources automatically using the try-with-resources in JDBC.

Syntax

try(Declaration of resource){
   body.....
} catch (SQLException e) {
   e.printStackTrace();
}

It is a try statement with one or more resources declared at try. where resource is an object which should be closed once it is no more required.

You can declare multiple resources in this and all those will be closed at the end of the statement automatically.

The objects/resources we declare in this should implement java.lang.AutoCloseable or java.io.Closeable, interfaces or, extend the java.lang.AutoCloseable class.

In JDBC we can use java.sql.CallableStatement, Connection, PreparedStatement, Statement, ResultSet, and RowSet in try-with-resources statement.

Example

Let us create a table with name MyPlayers in MySQL database using CREATE statement as shown below −

CREATE TABLE MyPlayers(
   ID INT,
   First_Name VARCHAR(255),
   Last_Name VARCHAR(255),
   Date_Of_Birth date,
   Place_Of_Birth VARCHAR(255),
   Country VARCHAR(255),
   PRIMARY KEY (ID)
);

Now, we will insert 7 records in MyPlayers table using INSERT statements −

insert into MyPlayers values(1, 'Shikhar', 'Dhawan', DATE('1981-12-05'), 'Delhi', 'India');
insert into MyPlayers values(2, 'Jonathan', 'Trott', DATE('1981-04-22'), 'CapeTown', 'SouthAfrica');
insert into MyPlayers values(3, 'Kumara', 'Sangakkara', DATE('1977-10-27'), 'Matale', 'Srilanka');
insert into MyPlayers values(4, 'Virat', 'Kohli', DATE('1988-11-05'), 'Delhi', 'India');
insert into MyPlayers values(5, 'Rohit', 'Sharma', DATE('1987-04-30'), 'Nagpur', 'India');
insert into MyPlayers values(6, 'Ravindra', 'Jadeja', DATE('1988-12-06'), 'Nagpur', 'India');
insert into MyPlayers values(7, 'James', 'Anderson', DATE('1982-06-30'), 'Burnley', 'England');

Following JDBC program demonstrates how usage of try-with-resources statement in JDBC −

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class TryWithResources_Example {
   public static void main(String args[]) {
      //Getting the connection
      String mysqlUrl = "jdbc:mysql://localhost/mydatabase";
      System.out.println("Connection established......");
      //Registering the Driver
      try(Connection con = DriverManager.getConnection(mysqlUrl, "root", "password");
      Statement stmt = con.createStatement(); ) {
         try(ResultSet rs = stmt.executeQuery("select * from MyPlayers");) {
            //Retrieving the data
            while(rs.next()) {
               System.out.print(rs.getInt("ID")+", ");
               System.out.print(rs.getString("First_Name")+", ");
               System.out.print(rs.getString("Last_Name")+", ");
               System.out.print(rs.getDate("Date_Of_Birth")+", ");
               System.out.print(rs.getString("Place_Of_Birth")+", ");
               System.out.print(rs.getString("Country"));
               System.out.println();
            }
         } catch (SQLException e) {
               e.printStackTrace();
         }
         } catch (SQLException e) {
            e.printStackTrace();
      }
   }
}

Output

Connection established......
1, Shikhar, Dhawan, 1981-12-05, Delhi, India
2, Jonathan, Trott, 1981-04-22, CapeTown, SouthAfrica
3, Kumara, Sangakkara, 1977-10-27, Matale, Srilanka
4, Virat, Kohli, 1988-11-05, Mumbai, India
5, Rohit, Sharma, 1987-04-30, Nagpur, India
6, Ravindra, Jadeja, 1988-12-06, Nagpur, India
7, James, Anderson, 1982-06-30, Burnely, England
8, Ryan, McLaren, 1983-02-09, Kumberly, null