non-null object become empty json

I am trying write web application with spring boot, but found the object returned from controller method become empty json, hers is my code: Application.java ``` @Configuration @ComponentScan @EnableAutoConfiguration @EnableWebMvc public class Application { @Bean public DataSource ds() { BasicDataSource ds = new org.apache.commons.dbcp.BasicDataSource(); ds.setDriverClassName("com.mysql.jdbc.Driver"); ds.setUrl("jdbc:mysql://localhost:3306/test"); ds.setUsername("root"); ds.setPassword("test"); return ds; } @Bean public AbstractEntityManagerFactoryBean entityManagerFactory(DataSource dataSource, JpaVendorAdapter jpaVendorAdapter) { LocalContainerEntityManagerFactoryBean lef = new LocalContainerEntityManagerFactoryBean(); lef.setDataSource(ds()); lef.setJpaVendorAdapter(jpaVendorAdapter); lef.setPackagesToScan("hello"); return lef; } @Bean public JpaVendorAdapter jpaVendorAdapter() { HibernateJpaVendorAdapter hibernateJpaVendorAdapter = new HibernateJpaVendorAdapter(); hibernateJpaVendorAdapter.setShowSql(true); hibernateJpaVendorAdapter.setGenerateDdl(true); hibernateJpaVendorAdapter.setDatabase(Database.MYSQL); return hibernateJpaVendorAdapter; } @Bean public PlatformTransactionManager transactionManager() { return new JpaTransactionManager(); } public static void main(String[] args) { ConfigurableApplicationContext context = SpringApplication.run(Application.class); CustomerRepository repository = context.getBean(CustomerRepository.class); } } ``` Customer.java ``` @Entity @Table(name ="customer") public class Customer { @Id @GeneratedValue(strategy=GenerationType.AUTO) private long id; private String firstName; private String lastName; protected Customer() {} public Customer(String firstName, String lastName) { this.firstName = firstName; this.lastName = lastName; } @Override public String toString() { return String.format( "Customer[id=%d, firstName='%s', lastName='%s']", id, firstName, lastName); } } ``` MyController.java ``` @Controller @RequestMapping("/customer") public class MyController { @Autowired CustomerRepository customerRepository; @RequestMapping(method = RequestMethod.GET) public @ResponseBody List<Customer> getAll() { return (List<Customer>) customerRepository.findAll(); } @RequestMapping(value="/{id}", method = RequestMethod.GET) public @ResponseBody Customer findOne(@PathVariable long id) { Customer customer = customerRepository.findOne(id); System.out.println("--------------------------------"); System.out.println(customer); return customer; } } ``` I can see the customer printed in the console, so I guess the data access is working, the only problem is why the customer object is converted to empty json.