Mybatis dao pattern not autowiring field

Question

Trying to make a dao pattern for mybatis and spring. Want to use this sql queries anywhere i want, just using dependency injection. When i try to use this method (.getMaxId()) it gives me "Null pointer exception". Why field SqlSession is not autowiring(gives null)? Intellige idea shows this field as a canditate for autowiring.

I think there is 3 steps to achieve:

1) Autowire session

2) get mapper from session

3) execute queries from this mapper

I do this

@Autowired
 private Student_mapper sm;

sm.getMaxId();

Service

@Service
@Transactional
public class Student_mapperImpl {

    @Autowired
    private SqlSession session;

    @Autowired
    Student_mapper mapper = session.getMapper(Student_mapper.class);


    public Integer getMaxId() {

        Integer value = mapper.getMaxId();

        return value;
    }
}

Bean configuration file

 @org.springframework.context.annotation.Configuration
    @EnableTransactionManagement
    @ComponentScan
    public class DataSourceStudent_Mapper {

        @Bean
        public SqlSession getDataSource() {

         String user = "postgres";
         String password = "postgres";
         String databasenameURL = "jdbc:postgresql://localhost:5432/postgres";
         String dbDriver = "org.postgresql.Driver";
         DataSource dataSource = new org.apache.ibatis.datasource.pooled.PooledDataSource(
                 dbDriver, databasenameURL, user, password);
         TransactionFactory transactionFactory = new JdbcTransactionFactory();
         Environment environment = new Environment("development",
                 transactionFactory, dataSource);
         Configuration configuration = new Configuration(environment);
         SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder()
                 .build(configuration);
         SqlSession session = sqlSessionFactory.openSession();
         session.getConfiguration().addMapper(Student_mapper.class);

        return session;
        }
    }

Student_mapper - interface with a queries

@Repository
public interface Student_mapper {
    @Select("select max(id) from student")
    @Result(property = "id", column = "ID")
    Integer getMaxId();
}

Entity

public class Student {
    private int id;
    private String name;
    private String branch;
    private int percentage;
    private int phone;
    private String email;
    //(setters,getters, allArgs constructor are ommited)
}

I don't understand what's wrong. There is any examples how to realise this? I would like to execute my queries anywhere i want without constantly initializing the session, datasource etc. Thanks in advance

Answer 1

mybatis-spring Getting Started should be useful.