实际工作中遇到类似这样的问题，问题如下面 StackOverflow 中描述的

https://stackoverflow.com/questions/43424203/org-hibernate-annotationexception-unknown-id-generator-id-generator

# 下面是更改过后的代码（员工信息表对应的实体类），注意 id 的定义：

	import lombok.AllArgsConstructor;
	import lombok.Data;
	import lombok.NoArgsConstructor;
	import org.hibernate.annotations.GenericGenerator;

	import javax.persistence.Entity;
	import javax.persistence.GeneratedValue;
	import javax.persistence.Id;

	/**
	* <p>
	* <code>Employee</code>
	* </p>
	* Description:
	*
	* @author Mcchu
	* @date 2017/10/13 14:54
	*/
	@Entity
	@Data
	@AllArgsConstructor
	@NoArgsConstructor
	public class Employee {

	@GenericGenerator(name = "employeeSeqGenerator",
	strategy = "org.hibernate.id.enhanced.SequenceStyleGenerator",
	parameters = {
	@org.hibernate.annotations.Parameter(name = "sequence_name", value = "EMPLOYEE_SEQUENCE"),
	@org.hibernate.annotations.Parameter(name = "initial_value", value = "1000"),
	@org.hibernate.annotations.Parameter(name = "increment_size", value = "1")
	})
	@Id
	@GeneratedValue(generator = "employeeSeqGenerator")
	private Long id;

	private String employeeName;

	//... ...
	}

# 注解说明

@Id 注解：JPA 提供

顾名思义，该属性字段定义为主键，注意在源码注释中有讲只有下面几种类型才可以定义为主键

	import java.lang.annotation.Retention;
	import java.lang.annotation.Target;

	import static java.lang.annotation.ElementType.FIELD;
	import static java.lang.annotation.ElementType.METHOD;
	import static java.lang.annotation.RetentionPolicy.RUNTIME;

	/**
	* Specifies the primary key of an entity.
	* The field or property to which the <code>Id</code> annotation is applied
	* should be one of the following types: any Java primitive type;
	* any primitive wrapper type;
	* <code>String</code>;
	* <code>java.util.Date</code>;
	* <code>java.sql.Date</code>;
	* <code>java.math.BigDecimal</code>;
	* <code>java.math.BigInteger</code>.
	*
	* <p>The mapped column for the primary key of the entity is assumed
	* to be the primary key of the primary table. If no <code>Column</code> annotation
	* is specified, the primary key column name is assumed to be the name
	* of the primary key property or field.
	*
	* <pre>
	* Example:
	*
	* @Id
	* public Long getId() { return id; }
	* </pre>
	*
	* @see Column
	* @see GeneratedValue
	*
	* @since Java Persistence 1.0
	*/
	@Target({METHOD, FIELD})
	@Retention(RUNTIME)

	public @interface Id {
	}

@GeneratedValue 注解：JPA 提供

文档参考：http://docs.oracle.com/javaee/5/api/javax/persistence/GeneratedValue.html

源码定义如下：

	package javax.persistence;

	import java.lang.annotation.Retention;
	import java.lang.annotation.Target;

	import static java.lang.annotation.ElementType.FIELD;
	import static java.lang.annotation.ElementType.METHOD;
	import static java.lang.annotation.RetentionPolicy.RUNTIME;
	import static javax.persistence.GenerationType.AUTO;

	/**
	* Provides for the specification of generation strategies for the
	* values of primary keys.
	*
	* <p> The <code>GeneratedValue</code> annotation
	* may be applied to a primary key property or field of an entity or
	* mapped superclass in conjunction with the {@link Id} annotation.
	* The use of the <code>GeneratedValue</code> annotation is only
	* required to be supported for simple primary keys. Use of the
	* <code>GeneratedValue</code> annotation is not supported for derived
	* primary keys.
	*
	* <pre>
	*
	* Example 1:
	*
	* @Id
	* @GeneratedValue(strategy=SEQUENCE, generator="CUST_SEQ")
	* @Column(name="CUST_ID")
	* public Long getId() { return id; }
	*
	* Example 2:
	*
	* @Id
	* @GeneratedValue(strategy=TABLE, generator="CUST_GEN")
	* @Column(name="CUST_ID")
	* Long id;
	* </pre>
	*
	* @see Id
	* @see TableGenerator
	* @see SequenceGenerator
	*
	* @since Java Persistence 1.0
	*/
	@Target({METHOD, FIELD})
	@Retention(RUNTIME)

	public @interface GeneratedValue {

	/**
	* (Optional) The primary key generation strategy
	* that the persistence provider must use to
	* generate the annotated entity primary key.
	*/
	GenerationType strategy() default AUTO;

	/**
	* (Optional) The name of the primary key generator
	* to use as specified in the {@link SequenceGenerator}
	* or {@link TableGenerator} annotation.
	* <p> Defaults to the id generator supplied by persistence provider.
	*/
	String generator() default "";
	}

如上，包含两个属性，GenerationType 和 generator，其中 GenerationType 默认是 AUTO

GenerationType 几个属性的定义可以查看文档：http://docs.oracle.com/javaee/5/api/javax/persistence/GenerationType.html

generator 自己定义

四种数据库的对GeneratorValue4种策略的支持情况如下：来自http://blog.csdn.net/tianxiezuomaikong/article/details/64930151
 
mysql 
GenerationType.TABLE 
GenerationType.AUTO 
GenerationType.IDENTITY 
不支持GenerationType.SEQUENCE
 
oracle 
strategy=GenerationType.AUTO 
GenerationType.SEQUENCE 
GenerationType.TABLE 
不支持GenerationType.IDENTITY
 
postgreSQL 
GenerationType.TABLE 
GenerationType.AUTO 
GenerationType.IDENTITY 
GenerationType.SEQUENCE 
都支持
 
kingbase 
GenerationType.TABLE 
GenerationType.SEQUENCE 
GenerationType.IDENTITY 
GenerationType.AUTO 
都支持

@GenericGenerator 注解：Hibernate 提供

源码：

	package org.hibernate.annotations;
	import java.lang.annotation.Retention;
	import java.lang.annotation.Target;

	import static java.lang.annotation.ElementType.FIELD;
	import static java.lang.annotation.ElementType.METHOD;
	import static java.lang.annotation.ElementType.PACKAGE;
	import static java.lang.annotation.ElementType.TYPE;
	import static java.lang.annotation.RetentionPolicy.RUNTIME;

	/**
	* Generator annotation describing any kind of Hibernate generator in a generic (de-typed) manner.
	*
	* @author Emmanuel Bernard
	*/
	@Target({PACKAGE, TYPE, METHOD, FIELD})
	@Retention(RUNTIME)
	public @interface GenericGenerator {
	/**
	* unique generator name.
	*/
	String name();
	/**
	* Generator strategy either a predefined Hibernate strategy or a fully qualified class name.
	*/
	String strategy();
	/**
	* Optional generator parameters.
	*/
	Parameter[] parameters() default {};
	}