Property 'dataSource' is required

写了一个配置类，启动项目的时候报错：Property 'dataSource' is required
原代码如下：

@Configuration
public class SecurityConfig extends WebSecurityConfigurerAdapter {

    @Autowired
    private PersistentTokenRepository persistentTokenRepository;

    @Autowired
    private DataSource dataSource;

    @Bean
    PersistentTokenRepository getPersistentTokenRepository(){
        JdbcTokenRepositoryImpl jdbcTokenRepository = new JdbcTokenRepositoryImpl();
        DataSource dataSource = this.dataSource;
        jdbcTokenRepository.setDataSource(dataSource);
        return jdbcTokenRepository;
    }
}

解决办法：把DataSource 放到最上面即可，如下所示。spring在加载bean的时候，从上而下加载，按照上面的代码，先加载PersistentTokenRepository，此时还没加载DataSource，因此DataSource=null，jdbcTokenRepository.setDataSource(dataSource)这个方法执行的时候就会报错。调整了一下位置，问题解决

@Configuration
public class SecurityConfig extends WebSecurityConfigurerAdapter {
  
  
    @Autowired
    private DataSource dataSource;

    @Autowired
    private PersistentTokenRepository persistentTokenRepository;


    @Bean
    PersistentTokenRepository getPersistentTokenRepository(){
        JdbcTokenRepositoryImpl jdbcTokenRepository = new JdbcTokenRepositoryImpl();
        DataSource dataSource = this.dataSource;
        jdbcTokenRepository.setDataSource(dataSource);
        return jdbcTokenRepository;
    }
}