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 (?, ?, ?, ?)
......