How to initialize variables in parent abstract class of spring bean using Kotlin? - spring

Question

I have the next structure of spring beans
abstract class GenericRepository<T> {
private val FIND_BY_ID_SQL = "SELECT * FROM ${this.getTableName()} WHERE id = ?"
abstract fun getTableName(): String
abstract fun jdbcTemplate(): JdbcTemplate
abstract fun getMapper(): RowMapper<T>
fun find(id: Long): T? {
return jdbcTemplate().queryForObject(FIND_BY_ID_SQL, arrayOf(id), getMapper())
}
}
User repository
#Repository
class UserRepository(
#Autowired
private val jdbcTemplate: JdbcTemplate
) : GenericRepository<User>() {
companion object {
private const val INSERT_SQL = "INSERT INTO \"user\"(name, age) VALUES (?,?)"
}
private class LogMapper : RowMapper<User> {
override fun mapRow(rs: ResultSet, rowNum: Int): User? {
return User(
id = rs.getLong("id"),
name = rs.getString("name"),
age = rs.getInt("operation")
)
}
}
override fun getTableName(): String {
return "user"
}
override fun jdbcTemplate(): JdbcTemplate {
return jdbcTemplate
}
override fun getMapper(): RowMapper<User> {
return LogMapper()
}
}
The problem when Spring creates proxy and creates bean of UserRepository it doesn't initialize FIND_BY_ID_SQL leaving it null.
The question: how usign abstract class make spring initialize FIND_BY_ID_SQL variable?
UPD
I used #Component instead of #Repository and the problem was solved. FIND_BY_ID_SQL is not null anymore.

Answer 1

You could work around the problem by making it lazy:
private val FIND_BY_ID_SQL by lazy { "SELECT * FROM ${this.getTableName()} WHERE id = ?" }
However, you should first be sure it's an actual problem (e.g. that when you call find you get an exception), because the proxy might simply delegate to a "real" UserRepository with non-null FIND_BY_ID_SQL (and jdbcTemplate etc.), depending on Spring's internal details.
In addition, you need to be careful when your superclass properties are initialized depending on subclass; I think your exact situation should work, but I'd prefer to write it as
abstract class GenericRepository<T>(val tableName: String) {
private val FIND_BY_ID_SQL = "SELECT * FROM ${tableName} WHERE id = ?"
abstract val jdbcTemplate: JdbcTemplate
abstract val mapper: RowMapper<T>
fun find(id: Long): T? {
return jdbcTemplate.queryForObject(FIND_BY_ID_SQL, arrayOf(id), mapper)
}
}
#Repository
class UserRepository(
#Autowired
override val jdbcTemplate: JdbcTemplate
) : GenericRepository<User>("user") { ... }