How to commit a transaction in JDBC

Usually a Connection object is used to connect to a databse. By default a Connection object is in auto-commit mode, which means that it automatically commits changes after executing each statement. If auto-commit mode has been disabled, the method commit must be called explicitly in order to commit changes; otherwise, database changes will not be saved.

java.sql.Connection interface provides 'setAutoCommit' method to enable/disable auto commit mode.

void setAutoCommit(boolean autoCommit) throws SQLException

if autoCommit is true, enables the auto commit mode. Else disables auto commit mode. By default every connection to database is in auto-commit mode.

Lets take an example

/* Step 1: Import sql package */
import java.sql.*;

public class SampleApp {
    
    /* Update username, password and driver details here */
    static Connection getConnection() throws ClassNotFoundException, SQLException{
         /* Step 2: Load Driver */
        System.out.println("Loading/Registering driver");  
       
        Class.forName("com.mysql.jdbc.Driver");
         
        /* Step 3: Open connection to database */
        System.out.println("Connecting to database");
        String url = "jdbc:mysql://localhost/world";
        String userName = "root";
        String pasword = "tiger";
        return DriverManager.getConnection(url, userName, pasword);
    }
    
    public static void main(String args[]) throws SQLException, ClassNotFoundException{
        
        Connection conn = getConnection();
        conn.setAutoCommit(false);
          /* Create table employee */
        String query = "CREATE TABLE employee (id int, name varchar(30), PRIMARY KEY(id))";
        Statement stmt = conn.createStatement();
        stmt.execute(query);     
        
        /* Insert data to employee table */
        query = "INSERT INTO employee values(1, \"Krishna\")";
        stmt.execute(query);
        query = "INSERT INTO employee values(2, \"Arjun\")";
        stmt.execute(query);
        
        System.out.println("Calling roll back operation");
        conn.rollback();
        
        query = "SELECT * FROM employee";
        ResultSet rs = stmt.executeQuery(query);
        
        while(rs.next()){
            int id  = rs.getInt("id");
            String name = rs.getString("name");
            System.out.println(id +" " + name);
        }
        System.out.println("Dropping table employee");
        query = "DROP TABLE employee";
        stmt.execute(query);
        
    rs.close();
        stmt.close();
        conn.close();
    }
}

Output

Loading/Registering driver
Connecting to database
Calling roll back operation
Dropping table employee

As you observe in the above program,

conn.setAutoCommit(false);

statement disables the auto commit mode. So you must explicitly commit the transactions.

conn.rollback();

Undoes all changes made in the current transaction and releases any database locks currently held by this Connection object. So the records are not commited to the table employee.

Java.sql.Connection class provides 'commit' method to commit the transaction against the database.

void commit() throws SQLException

Makes all changes made since the previous commit/rollback permanent and releases any database locks currently held by this Connection object. Call this method if auto-commit mode has been disabled.

Will call 'commit' method just before calling rollback operation.

/* Step 1: Import sql package */
import java.sql.*;

public class SampleApp {
    
    /* Update username, password and driver details here */
    static Connection getConnection() throws ClassNotFoundException, SQLException{
         /* Step 2: Load Driver */
        System.out.println("Loading/Registering driver");  
       
        Class.forName("com.mysql.jdbc.Driver");
         
        /* Step 3: Open connection to database */
        System.out.println("Connecting to database");
        String url = "jdbc:mysql://localhost/world";
        String userName = "root";
        String pasword = "tiger";
        return DriverManager.getConnection(url, userName, pasword);
    }
    
    public static void main(String args[]) throws SQLException, ClassNotFoundException{
        
        Connection conn = getConnection();
        conn.setAutoCommit(false);
          /* Create table employee */
        String query = "CREATE TABLE employee (id int, name varchar(30), PRIMARY KEY(id))";
        Statement stmt = conn.createStatement();
        stmt.execute(query);     
        
        /* Insert data to employee table */
        query = "INSERT INTO employee values(1, \"Krishna\")";
        stmt.execute(query);
        query = "INSERT INTO employee values(2, \"Arjun\")";
        stmt.execute(query);
        
        System.out.println("Calling roll back operation");
        conn.commit();
        conn.rollback();
        
        query = "SELECT * FROM employee";
        ResultSet rs = stmt.executeQuery(query);
        
        while(rs.next()){
            int id  = rs.getInt("id");
            String name = rs.getString("name");
            System.out.println(id +" " + name);
        }
        System.out.println("Dropping table employee");
        query = "DROP TABLE employee";
        stmt.execute(query);
        
    rs.close();
        stmt.close();
        conn.close();
    }
}

Output

Loading/Registering driver
Connecting to database
Calling roll back operation
1 Krishna
2 Arjun
Dropping table employee 

 

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