Java for Web学习笔记（一二五）映射（1）：再谈converter

try(Connection connection =  DriverManager.getConnection(
        "jdbc:mysql://localhost/test?user=test&password=123456");){
    DatabaseMetaData meta = connection.getMetaData();	
    log.info("Dirver version is {}",meta.getDriverVersion());
    log.info("JDBC version {}.{}",
            meta.getJDBCMajorVersion(),meta.getJDBCMinorVersion());
}

20180601 11:28:15.781 [localhost-startStop-1]  [INFO ] TestService:41 init() - Dirver version is mysql-connector-java-5.1.46 ( Revision: 9cc87a48e75c2d2e87c1a293b2862ce651cb256e )
20180601 11:28:15.781 [localhost-startStop-1]  [INFO ] TestService:42 init() - JDBC version 4.0

20180228 09:16:39.460 [localhost-startStop-1]  [DEBUG] (Hibernate) JdbcEnvironmentInitiator: Database ->
       name : MySQL
    version : 5.7.21-0ubuntu0.16.04.1
      major : 5
      minor : 7
20180228 09:16:39.460 [localhost-startStop-1]  [DEBUG] (Hibernate) JdbcEnvironmentInitiator: Driver ->
       name : MySQL Connector Java
    version : mysql-connector-java-5.1.44 ( Revision: b3cda4f864902ffdde495b9df93937c3e20009be )
      major : 5
      minor : 1
20180228 09:16:39.460 [localhost-startStop-1]  [DEBUG] (Hibernate) JdbcEnvironmentInitiator: JDBC version : 4.0
20180228 09:16:39.495 [localhost-startStop-1]  [INFO ] (Hibernate) Dialect: HHH000400: Using dialect: org.hibernate.dialect.MySQL5InnoDBDialect

// -------------- Read ---------------
//datetime在原生jdbc的api中可以转换为java.sql.timestamp,java.sql.date和java.sql.time。
java.sql.Date date = resultSet.getDate(1);
java.sql.Time time = resultSet.getTime(1);
java.sql.Timestamp timestamp = resultSet.getTimestamp(1);

//java.sql.timestamp可以很方便转换为java 8的Instant和LocalDateTime
LocalDateTime localDateTime = timestamp.toLocalDateTime();
Instant instant = timestamp.toInstant();

// 也可以通过getObject的方式直接转为java 8的LocalDateTime, LocalDate和LocalTime，但在我们的
// 测试中不能转成Instant, OffsetDateTime, ZonedDateTime，无论是JDBC4.0还是4.2，都不行。
// JDBC 4.2的API是提供了Instant, OffsetDateTime, ZonedDateTime，但具体的实现还在
// mysql-connector-java， 而mysql-connector-java上不支持。估计和Mysql里面的datetime和
// timestamp不带timezone信息有关。
LocalDateTime localDateTime = resultSet.getObject(1, LocalDateTime.class);
LocalDate localDate = resultSet.getObject(1, LocalDate.class);
LocalTime localTime = resultSet.getObject(1, LocalTime.class);

// -------------- Write ---------------
// LocalDateTime可以通过SetObject()直接设置，但Instant，OffsetDateTime，ZonedDateTime不行，
// 会抛出异常。同样JDBC 4.2的api是提供了相关接口，但是mysql-connector-java上不支持。
statement.setObject(1, LocalDateTime.now(),JDBCType.TIMESTAMP);
statement.setObject(1, LocalDateTime.now());

//【1】进行Converter的标记，并实现AttributeConverter接口
@Converter
public class InstantConverter implements AttributeConverter<Instant, Timestamp>{

   //【2】实现AttributeConverter，进行类型转换。这里需要提醒的是，一定要记得处理null。
    @Override
    public Timestamp convertToDatabaseColumn(Instant instant) {
        return instant == null ? null:new Timestamp(instant.toEpochMilli());
    }

    @Override
    public Instant convertToEntityAttribute(Timestamp dbData) {
        return dbData == null ? null:Instant.ofEpochMilli(dbData.getTime());
    }
}

@Bean
public LocalContainerEntityManagerFactoryBean entityManagerFactory(){
    ... ...
    LocalContainerEntityManagerFactoryBean factory = new LocalContainerEntityManagerFactoryBean();
    // 例子中entity放在cn.wei.flowingflying.chapter24.entities内，转换器放在
    // cn.wei.flowingflying.chapter24.converters包内
    factory.setPackagesToScan("cn.wei.flowingflying.chapter24.entities",
                              "cn.wei.flowingflying.chapter24.converters");
    ... ...
}

@Entity
public class MyEntity{
    @Convert(converter = InstantConverter.class)
    private Instant dateCreated;
    .....
}

@Entity
public class MyEntity{
    @Convert(converter = InstantConverter.class)
    private Instant dateCreated;
    .....
}

@Convert(attributeName = "dateCreated", converter = InstantConverter.class)
@Entity
public class MyEntity{
    private Instant dateCreated;
}

@Converts({
    @Convert(attributeName = "dateCreated", converter = InstantConverter.class),
    @Convert(attributeName = "dateModified", converter = InstantConverter.class)
})
@Entity
public class MyEntity{
    private Instant dateCreated;
}