1.hibernate的主键生成器:
generator元素：表示了一个主键生成器，它用来为持久化类实例生成唯一的标识 。
准备工作:
hibernate.cfg.xml核心配置文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
	"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
	"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
	<hibernate-configuration>
		<session-factory>
			<property name="connection.username">root</property>
		<property name="connection.password">123</property>
		<property name="connection.url">jdbc:mysql://localhost:3306/t226?useUnicode=true&amp;characterEncoding=UTF-8
		</property>
		<property name="connection.driver_class">com.mysql.jdbc.Driver</property>
		<property name="dialect">org.hibernate.dialect.MySQLDialect</property>

		<!-- 配置本地事务（No CurrentSessionContext configured!） -->
		<property name="hibernate.current_session_context_class">thread</property>

		<!-- 2. 调试相关 -->
		<property name="show_sql">true</property>
		<property name="format_sql">true</property>

		<!-- 3. 添加实体映射文件 -->
		<mapping resource="com/qukang/one/entity/User.hbm.xml" />
		<!-- 4. 主键生成策略-->
		<mapping resource="com/qukang/two/entity/Student.hbm.xml" />
		<mapping resource="com/qukang/two/entity/Worker.hbm.xml" />
		</session-factory>
	</hibernate-configuration>

Student.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
	<class name="com.qukang.two.entity.Student" table="t_hibernate_student">
		<id name="sid" type="java.lang.Integer" column="sid">
			<generator class="assigned" />
<!-- 			<generator class="increment" /> -->
			<!-- <generator class="sequence" /> -->
			<!-- <generator class="sequence" > <param name="sequence_name">aaa</param> 
				</generator> -->
			<!-- <generator class="com.javaxl.two.id.Myts" /> -->
		</id>
		<property name="sname" type="java.lang.String" column="sname">
		</property>
	</class>
</hibernate-mapping>

对应的实体类

package com.qukang.two.entity;

public class Student {
	private Integer sid;
	private String sname;
	public Integer getSid() {
		return sid;
	}
	public void setSid(Integer sid) {
		this.sid = sid;
	}
	public String getSname() {
		return sname;
	}
	public void setSname(String sname) {
		this.sname = sname;
	}
	@Override
	public String toString() {
		return "Student [sid=" + sid + ", sname=" + sname + "]";
	}
	public Student(Integer sid,String sname) {
		this.sid=sid;
		this.sname=sname;
	}
	public Student() {}
	
}

Worker.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
	<class name="com.qukang.two.entity.Worker" table="t_hibernate_worker">
		<id name="wid" type="java.lang.String" column="wid">
			<generator class="assigned" />
			<!-- <generator class="sequence" /> -->
			<!-- <generator class="sequence" > <param name="sequence_name">aaa</param> 
				</generator> -->
			<!-- <generator class="com.javaxl.two.id.Myts" /> -->
		</id>

		<property name="wname" type="java.lang.String" column="wname">
		</property>
	</class>
</hibernate-mapping>

对应的实体类

package com.qukang.two.entity;

public class Worker {
	private String wid;
	private String wname;
	public String getWid() {
		return wid;
	}
	public void setWid(String wid) {
		this.wid = wid;
	}
	public String getWname() {
		return wname;
	}
	public void setWname(String wname) {
		this.wname = wname;
	}
	
	@Override
	public String toString() {
		return "Worker [wid=" + wid + ", wname=" + wname + "]";
	}
	public Worker(String wid, String wname) {
		this.wid = wid;
		this.wname = wname;
	}
	public Worker() {}
}

1.1 程序员自己控制：assigned
当你的主键ID引用的类是assigned时，不管你的数据库有没有设置自增长，都需要自己手动添加ID
不然就会报错

public static void main(String[] args) {
  	DemoDao dao=new DemoDao();
  	Student stu=new Student();
  	stu.setSname("哈哈哈");
  	dao.addStudent(stu);
  }

1.2 数据库控制: identity(标识列/自动增长) sequence

1.3 hibernate控制:increment uuid/uuid.hex

1.4 其它:native