Question

I need to access an existing MySQL database which uses BIGINT columns to store timestamps:

create table mytable (created bigint);

Now I prefer to work with java.util.Date or java.time.Instant instances instead of integers, so I’m trying to let Hibernate convert the values directly. Unfortunately Hibernate won’t recognize the column when annotated like this:

@Column(name = "created")
private Date created;

or like this:

@Column(name = "created")
@Temporal(TemporalType.TIMESTAMP)
private Calendar created;

This does return something in the future like 2017-07-01T04:14:00+02:00. How can I make Hibernate convert BIGINT columns properly so I don’t have to convert them in getters and setters?

Answer 1

Hibernate’s TemporalType.TIMESTAMP maps to java.sql.Timestamp. The Timestamp constructor takes Long values which is the number of milliseconds since the epoch. The values in database are stored as Unix timestamps which is the number of seconds since the epoch.

I wrote a UnixTimestampType that takes seconds instead of milliseconds and creates Date instances:

public class UnixTimestampType extends AbstractSingleColumnStandardBasicType<Date> implements IdentifierType<Date>, LiteralType<Date> {
    private static final long serialVersionUID = 1L;
    public static final UnixTimestampType INSTANCE = new UnixTimestampType();

    public UnixTimestampType() {
        super(UnixTimestampTypeDescriptor.INSTANCE, JdbcDateTypeDescriptor.INSTANCE);
    }

    @Override
    public String getName() {
        return "date";
    }

    @Override
    public String[] getRegistrationKeys() {
        return new String[] { getName(), java.sql.Date.class.getName() };
    }

    @Override
    public String objectToSQLString(Date value, Dialect dialect) throws Exception {
        final java.sql.Date jdbcDate = java.sql.Date.class.isInstance(value) ? (java.sql.Date) value : new java.sql.Date(value.getTime());
        return StringType.INSTANCE.objectToSQLString(jdbcDate.toString(), dialect);
    }

    @Override
    public Date stringToObject(String xml) {
        return fromString(xml);
    }
}

and

public class UnixTimestampTypeDescriptor implements SqlTypeDescriptor {
    private static final long serialVersionUID = 1L;
    public static final UnixTimestampTypeDescriptor INSTANCE = new UnixTimestampTypeDescriptor();

    @Override
    public int getSqlType() {
        return Types.INTEGER;
    }

    @Override
    public boolean canBeRemapped() {
        return true;
    }

    @Override
    public <X> ValueBinder<X> getBinder(final JavaTypeDescriptor<X> javaTypeDescriptor) {
        return new BasicBinder<X>(javaTypeDescriptor, this) {
            @Override
            protected void doBind(PreparedStatement st, X value, int index, WrapperOptions options) throws SQLException {
                Date date = javaTypeDescriptor.unwrap(value, Date.class, options);
                date.setTime(date.getTime() / 1000);
                st.setDate(index, date);
            }
        };
    }

    @Override
    public <X> ValueExtractor<X> getExtractor(final JavaTypeDescriptor<X> javaTypeDescriptor) {
        return new BasicExtractor<X>(javaTypeDescriptor, this) {
            @Override
            protected X doExtract(ResultSet rs, String name, WrapperOptions options) throws SQLException {
                Date date = new Date(rs.getLong(name) * 1000);
                return javaTypeDescriptor.wrap(date, options);
            }
        };
    }
}