Spring Framework自动连接的空指针异常 [英] Spring Framework Autowired Null Pointer Exception

问题描述

我正在学习Spring，但是在尝试建立一个相对基本的Spring项目时遇到了一些问题.我正在创建一个应用程序以简单地从数据库中读取数据，但是我在自动装配方面遇到了问题，或者缺少该问题.我的GetCustomerEvent类在GetCustomers()方法中引发了空指针异常，因为CustomerService变量尚未初始化.有人可以在这里向我指出正确的方向吗?

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

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

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

GetCustomerEvent.class

package org.ben.test.persistence;


@Component
public class GetCustomerEvent {

    @Autowired 
    CustomerService customerService;

    public GetCustomerEvent() {

    }

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

推荐答案

您没有初始化Spring容器.

You are not initializing the Spring Container.

您需要创建上下文以使其正常工作.

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

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