为什么要批量插入

要插入10000条数据，如果不批量插入的话，那么我们执行的sql语句将是10000条insert

insert into member (group_id, user_id, role, extend) values (101, 100, 3, NULL)
insert into member (group_id, user_id, role, extend) values (101, 101, 3, NULL)
insert into member (group_id, user_id, role, extend) values (101, 102, 3, NULL)
insert into member (group_id, user_id, role, extend) values (101, 103, 3, NULL)

......

如果是批量插入，一批次插入50条，那么10000条数据将生成200条insert语句

insert into member (group_id, user_id, role, extend) VALUES (101, 100, 3, NULL), (101, 101, 3, NULL), ..., (101, 149, 3, NULL)

insert into member (group_id, user_id, role, extend) VALUES (101, 100, 3, NULL), (101, 101, 3, NULL), ..., (101, 149, 3, NULL)

好了，以上是jdbc级别的批量插入，换言之，我们需要JPA提供批量插入功能

JPA批量插入

搜索了Stackoverflow，似乎JPA本身并没有对批量插入的支持

http://stackoverflow.com/questions/7440397/how-to-do-the-batch-insert-in-jpa

Hibernate批量插入

因为使用Hibernate作为JPA的provider实现，因此我们可以使用Hibernate提供的批量插入功能

查阅hibernate文档

http://docs.jboss.org/hibernate/core/3.3/reference/en/html/batch.html

(1) 首先要在hibernate配置文件中配置属性

<property name="hibernate.jdbc.batch_size" value="20" /> <!-- value文档建议在10-50间 -->

(2) 批量插入代码示例

1 for ( int i=0; i<100000; i++ ) {
2     Customer customer = new Customer(.....);
3     session.save(customer);
4     if ( i % 20 == 0 ) { //20, same as the JDBC batch size
5         //flush a batch of inserts and release memory:
6         session.flush();
7         session.clear();
8     }
9 }

注意

如果批量插入的实体主键为@GeneratedValue(strategy=IDENTITY)类型，则hibernate会透明关闭在jdbc级别的批量插入；因为实际上，每次插入该实体的一个实例，hibernate都需要搜索该实例的主键；想想在代码中，我们persist实例之后，就能够通过get方法获取实例的主键；

实验结果也说明了这点

实体定义

 1 @Entity
 2 @Table (name="member")
 3 public class GroupUser {
 4 　　@Id
 5 　　@GeneratedValue(strategy=IDENTITY)
 6 　　@Column(name="id", nullable=true, unique=true)
 7 　　private Integer id;
 8
 9 　　......
10
11 }

实验代码

 1 Session session = (Session)em.getDelegate();
 2 session.setFlushMode(FlushMode.MANUAL);
 3
 4 for (int i = 0; i < userIds.size(); ++i) {
 5 　　session.save(new GroupUser(groupId, userIds.get(i), role));
 6 　　if (i % 20 == 0) {
 7 　　　　session.flush();
 8 　　　　session.clear();
 9 　　}
10 }

日志输出

Hibernate: insert into member (group_id, user_id, role, extend) values (?, ?, ?, ?)
Hibernate: insert into member (group_id, user_id, role, extend) values (?, ?, ?, ?)
Hibernate: insert into member (group_id, user_id, role, extend) values (?, ?, ?, ?)
Hibernate: insert into member (group_id, user_id, role, extend) values (?, ?, ?, ?)
......