基础

Spring data 提供一个核心接口 CrudRepository<T, ID extends Serializable> 用来提供访问数据库的基本方法，T是访问数据库的实体类，ID是数据库主键数据类型

public interface CrudRepository<T, ID extends Serializable> extends Repository<T, ID> {
 
  <S extends T> S save(S entity);      ①
 
  Optional<T> findById(ID primaryKey); ②
 
  Iterable<T> findAll();               ③
 
  long count();                        ④
 
  void delete(T entity);               ⑤
 
  boolean existsById(ID primaryKey);   ⑥
 
  // … more functionality omitted.
}

① 保存数据
② 根据ID值查找数据
③ 返回所有数据
④ 返回数据的数量
⑤ 删除提供的数据
⑥ 提供的数据是否存在

Spring Data 已经实现了接口的方法，在使用中，只需要提供继承CrudRepository的接口，不需要自己实现相同的方法

下面进行测试

创建数据表

CREATE DATABASE jpa_demo;
USE jpa_demo;
CREATE TABLE t_user(
    id BIGINT PRIMARY KEY AUTO_INCREMENT,
    firstName VARCHAR(20) NOT NULL,
    lastName VARCHAR(20) NOT NULL
) ENGINE = INNODB;

配置Spring Data，这里采用JavaConfig配置

@Configuration                                   // 这里声明这个文件是配置文件
@EnableJpaRepositories({"com.lee.repository"})   // 这里制定repository所在的包(package)
public class DataSourceConfig {
 
  @Bean
  public DataSource dataSource() {
      Properties prop = new Properties();
      DriverManagerDataSource ds = new DriverManagerDataSource();
      
      try {
          String path = getClass().getClassLoader().getResource("db.properties").getPath();
 
          FileInputStream in = new FileInputStream(path);
          prop.load(in);
 
          String driver = prop.getProperty("driver");
          String url = prop.getProperty("url");
          String username = prop.getProperty("uname");
          String password = prop.getProperty("pass");
 
          ds.setDriverClassName(driver);
          ds.setUrl(url);
          ds.setUsername(username);
          ds.setPassword(password);
          in.close();
      } catch (FileNotFoundException e) {
 
      } catch (IOException e) {
 
      }
      
      return ds;
  }
 
  // JPA Hibernate
  @Bean
  public JpaVendorAdapter jpaVendorAdapter() {
     HibernateJpaVendorAdapter adapter = new HibernateJpaVendorAdapter();
     adapter.setDatabase(Database.MYSQL);
     adapter.setDatabasePlatform("org.hibernate.dialect.MySQL5InnoDBDialect");
     adapter.setShowSql(true);
     adapter.setGenerateDdl(false);
   
     return adapter;
  }
      
  @Bean
  public LocalContainerEntityManagerFactoryBean entityManagerFactory(DataSource dataSource, JpaVendorAdapter jpaVendorAdapter) {
     LocalContainerEntityManagerFactoryBean emfb = new LocalContainerEntityManagerFactoryBean();
     emfb.setDataSource(dataSource);
     emfb.setJpaVendorAdapter(jpaVendorAdapter);
     emfb.setPackagesToScan("com.lee.entity");
   
     return emfb;
  }
   
  @Bean
  pblic PlatformTransactionManager transactionManager(EntityManagerFactory entityManagerFactory) {
     return new JpaTransactionManager(entityManagerFactory);
  }
      
}

创建Entity，Entity需要提供getter, setter方法，用于关联数据表中的对应字段

@Entity                    // 声明这个类是实体类(Entity)
@Table(name = "t_user")    // 指定关联的数据表的名称
public class User {
    private Long id;
    private String firstName;
    private String lastName;
 
    public User() {
        this("testFirstName", "testLastName");
    }
 
    public User(String firstName, String lastName) {
        this.firstName = firstName;
        this.lastName = lastName;
    }
 
    @Id                   // 声明这个属性是数据库中的ID字段
    @GeneratedValue       // 声明这个ID值是自增长(数据库中 AUTO_INCREMENT)
    public Long getId() {
        return id;
    }
 
    public void setId(Long id) {
        this.id = id;
    }
 
    @Column(name = "firstName")    // 在getter方法声明这个属性关联数据库中firstName字段
    public String getFirstName() {
        return firstName;
    }
 
    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }
 
    @Column(name = "lastName")    // 在getter方法声明这个属性关联数据库中lastName字段
    public String getLastName() {
        return lastName;
    }
 
    public void setLastName(String lastName) {
        this.lastName = lastName;
    }
 
    /*
    用于打印信息
     */
    @Override
    public String toString() {
        return new StringBuilder()
                .append("id:").append(id)
                .append(", firstName:").append(firstName)
                .append(", lastName:").append(lastName)
                .toString();
    }
}

创建repository

public interface UserRepository extends CrudRepository<User, Long> {
}

JUnit测试

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes = {DataSourceConfig.class})
@FixMethodOrder(MethodSorters.NAME_ASCENDING)
public class UserRepositoryTest {
 
    @Autowired
    private UserRepository userRepository;
    private static User user;
 
    @Test
    public void test_00_init() {
        user = new User("Lee", "Fly");
        System.out.println(user);
    }
 
    @Test
    public void test_01_save() {
        user = userRepository.save(user);
        System.out.println(user);
        assertNotNull(user.getId());
    }
 
    @Test
    public void test_02_update() {
        String rename = "ModifyName";
        user.setFirstName(rename);
        user = userRepository.save(user);
        System.out.println(user);
        assertEquals(rename, user.getFirstName());
    }
 
    @Test
    public void test_10_delete() {
        userRepository.delete(user);
        assertNull(userRepository.findOne(user.getId()));
    }
}

注意：在配置文件中使用了数据库配置信息文件, db.properties, 没有给出, 可以更改成自己的配置方式, 或使用下面的源码
源码地址: https://github.com/LeeSpringFly/learnSpringData
如果运行正常，每一个测试都会显示绿条，表示成功