increment   首先获取该表中最大主键值，然后加一插入 
identity    使用数据库自增
sequence    
native      根据数据库 从 identity sequence 中选择一种
assigned    手工指定
uuid        32位字符串



@GeneratedValue   指定主键生成策略
@GenericGenerator 自定义主键生成策略

@GeneratedValue  generator属性引用 @GenericGenerator定义的主键生成策略器的name值，strategy指定生成策略

@Id
@GeneratedValue(generator="increment")
@GenericGenerator(name="increment", strategy = "increment")
public Long getId() {
	return id;
}


   <class name="Event" table="EVENTS">
        <id name="id" column="EVENT_ID">
            <generator class="increment"/>
        </id>
        <property name="date" type="timestamp" column="EVENT_DATE"/>
        <property name="title"/>
    </class>


@GeneratedValue(generator="increment")
@GenericGenerator(name="increment", strategy = "increment")
	
@GeneratedValue(generator="identity")
@GenericGenerator(name="identity", strategy = "identity")
	
@GeneratedValue(generator="native")
@GenericGenerator(name="native", strategy = "native")	
	
@GeneratedValue(generator="sequence")
@GenericGenerator(name="sequence", strategy = "sequence")



hibernate5.3.28

org.hibernate.id.factory.internal.DefaultIdentifierGeneratorFactory

public DefaultIdentifierGeneratorFactory() {
	register( "uuid2", UUIDGenerator.class );
	register( "guid", GUIDGenerator.class );			// can be done with UUIDGenerator + strategy
	register( "uuid", UUIDHexGenerator.class );			// "deprecated" for new use
	register( "uuid.hex", UUIDHexGenerator.class ); 	// uuid.hex is deprecated
	register( "assigned", Assigned.class );
	register( "identity", IdentityGenerator.class );
	register( "select", SelectGenerator.class );
	register( "sequence", SequenceStyleGenerator.class );
	register( "seqhilo", SequenceHiLoGenerator.class );
	register( "increment", IncrementGenerator.class );
	register( "foreign", ForeignGenerator.class );
	register( "sequence-identity", SequenceIdentityGenerator.class );
	register( "enhanced-sequence", SequenceStyleGenerator.class );
	register( "enhanced-table", TableGenerator.class );
}