Retrieving an object

In this recipe, we create a DAO method to retrieve a database row, which we will use to create an object.

How to do it…

Use an SQL select query and create an object from the result using RowMapper:

1. In the DAO class, add an inline class implementing RowMapper. This class defines how to generate a User object from a database row:

   private class UserMapper implements RowMapper<User> {
     public User mapRow(ResultSet row, int rowNum) throws SQLException {
       User user = new User();
   
       user.setId(row.getLong("id"));
       user.setFirstName(row.getString("first_name"));
       user.setAge(row.getInt("age"));
       
       return user;
     }
   }

2. Add a DAO method which will perform an SQL select query and use a UserMapper object to generate a User object:

   public User findById(Long id) {
     String sql = "select * from user where id=?";
     User user = jdbcTemplate.queryForObject(sql, new Object[]{id}, new UserMapper());
     return user;
   }

How it works…

The queryForObject() method uses the UserMapper...