Atomicity in Spring Boot JDBC and MySQL - mysql

Question

I am sure there are various similar questions regarding this. But I am still not sure about the atomicity in Spring boot JDBC.
So my project is a Basic Online Cloth Store. Where the user adds some products into the cart and then checkout. Each user has some credits (virtual money).
So to implement checkout I need to execute Atomic operation on the Database. Basically, there are two things that I have to check while checkout.
User has enough credits while checkout.
There is enough stock.
So instead of doing normal JDBCtemplate.update(), I performed the queries and update by obtaining Connection and Then using Prepared statement. Below is my code for the checkout function.
public boolean validCart(String username) throws SQLException {
Connection conn = DataSourceUtils.getConnection(template.getDataSource());
try {
conn.setAutoCommit(false);
PreparedStatement ps = conn.prepareStatement("SELECT credits from user where username = ?");
ps.setString(1, username);
ResultSet rs = ps.executeQuery();
rs.next();
int credits = rs.getInt(1);
ps = conn.prepareStatement("SELECT cart.quantity*stock.price from cart,stock where cart.username = ? and stock.cloth_id = cart.cloth_id and stock.size = cart.size");
ps.setString(1, username);
rs = ps.executeQuery();
rs.next();
int cost = rs.getInt(1);
Boolean flag = false;
if(credits >= cost){
String sql = "SELECT COUNT(*) from cart,stock where cart.username = ? and cart.size = stock.size and cart.cloth_id = stock.cloth_id and cart.quantity > stock.quantity";
ps = conn.prepareStatement(sql);
ps.setString(1, username);
rs = ps.executeQuery();
rs.next();
int bad = rs.getInt(1);
sql = "SELECT COUNT(*) FROM cart WHERE username = ? and (cloth_id,size) NOT IN (SELECT cloth_id,size from stock)";
ps = conn.prepareStatement(sql);
ps.setString(1, username);
rs = ps.executeQuery();
rs.next();
bad += rs.getInt(1);
if(bad == 0){
sql = "UPDATE cart INNER JOIN stock on cart.cloth_id = stock.cloth_id and stock.size = cart.size SET stock.quantity = stock.quantity - cart.quantity where cart.username = ?";
ps = conn.prepareStatement(sql);
ps.setString(1, username);
ps.executeUpdate();
sql = "UPDATE user SET credits = credits - ? where username = ?";
ps = conn.prepareStatement(sql);
ps.setInt(1, cost);
ps.setString(2, username);
ps.executeUpdate();
sql = "INSERT INTO order_details(username,cloth_id,size,quantity,price) SELECT cart.username,cart.cloth_id,cart.size,cart.quantity,stock.price from cart,stock where cart.username = ? and cart.cloth_id = stock.cloth_id and cart.size = stock.size";
ps = conn.prepareStatement(sql);
ps.setString(1, username);
ps.executeUpdate();
sql = "DELETE FROM cart WHERE username = ?";
ps = conn.prepareStatement(sql);
ps.setString(1, username);
ps.executeUpdate();
flag = true;
}
}
conn.commit();
conn.setAutoCommit(true);
return flag;
} catch (SQLException e) {
conn.rollback();
e.printStackTrace();
}
return false;
}
But I am still not sure If operations are atomic that is the problem of race condition will not happen here.
And what should be the best method to perform this type of operation in general?.