Spring Framework Autowired Null Pointer Exception

Question

I'm learning Spring and I'm having some problems trying to set up a relatively basic Spring project. I'm creating an application to simply read from a database, but I'm having problems with Autowiring, or lack thereof. My GetCustomerEvent class is throwing a null pointer exception in the GetCustomers() method, as the CustomerService variable hasn't been initialised. Can someone point me in the right direction here?

Application.class

package org.ben.test.main;
@Configuration
@ComponentScan(basePackages={"org.ben.test.persistence", "org.ben.test.main"})
public class Application {

    @Bean
    public CustomerService customerService() {
        return new CustomerService();
    }

    @Bean 
    public DataSource getDataSource() {
        DriverManagerDataSource dmds = new DriverManagerDataSource();
        dmds.setDriverClassName("org.postgresql.Driver");
        dmds.setUrl("jdbc:postgresql://localhost:5432/Customers");
        dmds.setUsername("postgres");
        dmds.setPassword("postgres");
        return dmds;

    }

    @Bean
    public JdbcTemplate jdbcTemplate() {
        DataSource ds = getDataSource();
        JdbcTemplate jdbc = new JdbcTemplate(ds);
        return jdbc;
    }

    public static void main(String[] args) {
        GetCustomerEvent ev = new GetCustomerEvent();
        ev.GetCustomers();
    }
}

CustomerService.class

package org.ben.test.persistence;

@Component
public class CustomerService {

    @Autowired JdbcTemplate jdbcTemplate;

    public CustomerService() {

    }

    public void getCustomers() {
        jdbcTemplate.query("SELECT * FROM Customers", new RowMapper() {
            @Override
            public Object mapRow(ResultSet arg0, int arg1) throws SQLException {
                System.out.println(arg0.getString("firstName"));
                return null;
            }
        });
    }

}

GetCustomerEvent.class

package org.ben.test.persistence;


@Component
public class GetCustomerEvent {

    @Autowired 
    CustomerService customerService;

    public GetCustomerEvent() {

    }

    public void GetCustomers() {
        customerService.getCustomers();
    }
}

Answer 1

You need to create the application context no matter if you are using xml or annotation based configuration. If your application is a web application, see this post Loading context in Spring using web.xml to load the application context

Once you have the application you can get the bean using context.getBean() method

Also, spring container does not manage the objects you create using new operator. In your example you need to autowire the GetCustomerEvent bean

@Autowired GetCustomerEvent getCustomerEvent;
//and call
getCustomerEvent.getCustomers();

Answer 2

Problem is with below line

GetCustomerEvent ev = new GetCustomerEvent();

You manually created instance using "new". Spring does not have idea about this object. See Why is my Spring @Autowired field null? for details.

Answer 3

You are not initializing the Spring Container.

You need to create your context in order for it to work.