JdbcTemplate中的RowMapper有什么作用？代码举例讲解

在JdbcTemplate中,RowMapper用于将数据库查询结果集中的每一行映射为一个Java对象。常见的用法有:

1. BeanPropertyRowMapper:将列名映射到相同名称的JavaBean属性。

List<User> users = jdbcTemplate.query("SELECT * FROM user", 
    new BeanPropertyRowMapper<>(User.class));

2. RowMapper实现:

public class UserRowMapper implements RowMapper<User> {
    public User mapRow(ResultSet rs, int rowNum) throws SQLException {
        User user = new User();
        user.setId(rs.getInt("id"));
        user.setName(rs.getString("name"));
        user.setAge(rs.getInt("age"));
        return user;
    }
}

List<User> users = jdbcTemplate.query("SELECT * FROM user", new UserRowMapper());

3. Lambda表达式:

List<User> users = jdbcTemplate.query("SELECT * FROM user", 
    (ResultSet rs, int rowNum) -> {
        User user = new User();
        user.setId(rs.getInt("id"));
        user.setName(rs.getString("name"));
        user.setAge(rs.getInt("age"));
        return user;
    }); 

4. 元组/值对象:

List<User> users = jdbcTemplate.query("SELECT * FROM user", 
    (rs, rowNum) -> new User(
        rs.getInt("id"), 
        rs.getString("name"),
        rs.getInt("age")
    ));

所以,RowMapper的作用是方便我们将数据库查询结果映射为Java对象,避免手动遍历ResultSet来创建对象,代码简洁易读。