JdbcTemplate auto wiring only works from the main class

Question

Im new to spring and Jdbc, JdbcTemplate works when I auto wire it in the main class, but when I auto wire it in any other class it is null.

note: I comment out one of the JdbcTemplate when I test the other, I thought it might make a conflict.

Test class (Main)

@SpringBootApplication
public class Test implements CommandLineRunner {

    @Autowired
    private JdbcTemplate jdbcTemplate;  // this works

    public static void main(String[] args) {
        SpringApplication.run(Test.class, args);
    }

    @Override
    public void run(String... args) throws Exception {

        System.out.println("main class jdbc template = "+jdbcTemplate);

    }
}

StudentDaoImpl class

    public class StudentDaoImpl {

    @Autowired
    private JdbcTemplate jdbcTemplate; //this is null

}

Application.properties

spring.datasource.url=jdbc:mysql://localhost/db
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.username=username
spring.datasource.password=password
spring.jpa.database-platform=org.hibernate.dialect.MySQL5InnoDBDialect

I really have no clue why is this happening, any help will be appreciated.

Spring injects beans to other beans, not to arbitrary classes. Is StudentDaoImpl a spring-managed bean? — Lesiak, Apr 27 '22 at 10:40
i think i need to add some annotations, but i don't know which one and where? — sultanduwaik, Apr 27 '22 at 10:48
Not only you need to add one of spring annotations (`@Repository` looks good in your case) but also let Spring create it, and retrieeve it from Spring's context (or, preferably, inject it to another Spring-managed bean) — Lesiak, Apr 27 '22 at 10:53
You may want to read a good tutorial https://www.baeldung.com/spring-dependency-injection — Lesiak, Apr 27 '22 at 11:07

score 0 · Answer 1 · answered Apr 27 '22 at 12:09

0

Are you creating the StudentDaoImpl class yourself?

StudentDaoImpl dao = new StudentDaoImpl()?

If not, then annotate your StudentDaoImpl class with @Repository so it will be automatically picked up by Springs component scanning.

If yes then you have to set the JdbcTemplate yourself (in this case via a setter)

Note: Autowiring doesn’t work when you create an instance yourselves with the new keyword.

answered Apr 27 '22 at 12:09

MevlütÖzdemir

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yes im creating StudentDaoImpl in main class, and i tried to set JdbcTemplate it still is null – sultanduwaik Apr 27 '22 at 13:25
@Autowired public void setDataSource(DataSource dataSource) { System.out.println(dataSource); jdbcTemplate = new JdbcTemplate(dataSource); } – sultanduwaik Apr 27 '22 at 13:29
you mean this right? ^^^ – sultanduwaik Apr 27 '22 at 13:29
Do you create StudentDaoImp with new StudentDaoImpl(); ? – MevlütÖzdemir Apr 27 '22 at 16:43

JdbcTemplate auto wiring only works from the main class

1 Answers1