缓存 就是把本来应该放在硬盘里的东西放在内存里 将来存内存里读
一级缓存：
session缓存
二级缓存： sessionFactory级别的 （适合经常访问，数据量有限，改动不大）
很多的session缓存 找不到再去数据库拿
开启二级缓存
查询缓存 比如说 我查的是2-8的数据 然后呢我又查了3-9的数据 则3-8的数据就是查询缓存，三级缓存
缓存算法
内存对象满了 拿走什么
Lru Lfu fifo
1.最近很少被使用
2.最近不常被使用
3.缓存对象设置一个数组 来一个把第一个推走
例子
Category.java
package com.bjsxt.hibernate;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import org.hibernate.annotations.Cache;
import org.hibernate.annotations.CacheConcurrencyStrategy;
@Entity
//@BatchSize(size=5)
@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
public class Category {
private int id;
private String name;
@Id
@GeneratedValue
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
Msg.java
package com.bjsxt.hibernate; import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToOne; @Entity
public class Msg {
private int id;
private String cont;
private Topic topic;
@ManyToOne
public Topic getTopic() {
return topic;
}
public void setTopic(Topic topic) {
this.topic = topic;
}
@Id
@GeneratedValue
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
} public String getCont() {
return cont;
}
public void setCont(String cont) {
this.cont = cont;
} }
Msginfo.java
package com.bjsxt.hibernate; import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToOne; public class MsgInfo {
private int id;
private String cont;
private String topicName;
private String categoryName;
public MsgInfo(int id, String cont, String topicName, String categoryName) {
super();
this.id = id;
this.cont = cont;
this.topicName = topicName;
this.categoryName = categoryName;
}
public String getTopicName() {
return topicName;
}
public void setTopicName(String topicName) {
this.topicName = topicName;
}
public String getCategoryName() {
return categoryName;
}
public void setCategoryName(String categoryName) {
this.categoryName = categoryName;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
} public String getCont() {
return cont;
}
public void setCont(String cont) {
this.cont = cont;
} }
Topic.java
package com.bjsxt.hibernate; import java.util.ArrayList;
import java.util.Date;
import java.util.List; import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToOne;
import javax.persistence.NamedQueries;
import javax.persistence.NamedQuery;
import javax.persistence.OneToMany; import org.hibernate.annotations.BatchSize; @Entity
@NamedQueries(
{
@NamedQuery(name="topic.selectCertainTopic", query="from Topic t where t.id = :id")
}
)
/*
@NamedNativeQueries(
{
@NamedNativeQuery(name="topic.select2_5Topic", query="select * from topic limit 2, 5")
}
)
*/ public class Topic {
private int id;
private String title;
private Category category;
private Date createDate;
private List<Msg> msgs = new ArrayList<Msg>();
@OneToMany(mappedBy="topic")
public List<Msg> getMsgs() { return msgs;
}
public void setMsgs(List<Msg> msgs) {
this.msgs = msgs;
}
public Date getCreateDate() {
return createDate;
}
public void setCreateDate(Date createDate) {
this.createDate = createDate;
}
@ManyToOne
public Category getCategory() {
return category;
}
public void setCategory(Category category) {
this.category = category;
}
@Id
@GeneratedValue
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
} }
@Test
public void testCache1() {
Session session = sf.openSession();
session.beginTransaction();
Category c = (Category)session.load(Category.class, );
System.out.println(c.getName()); Category c2 = (Category)session.load(Category.class, ); //一级缓存
System.out.println(c2.getName());
session.getTransaction().commit();
session.close(); } //join fetch
@Test
public void testCache2() {
Session session = sf.openSession();
session.beginTransaction();
Category c = (Category)session.load(Category.class, );
System.out.println(c.getName()); session.getTransaction().commit();
session.close(); Session session2 = sf.openSession();
session2.beginTransaction();
Category c2 = (Category)session2.load(Category.class, ); //两个session 打开二级缓存 也只发送一次select
System.out.println(c2.getName()); session2.getTransaction().commit();
session2.close();
} //join fetch
@Test
public void testQueryCache() {
Session session = sf.openSession();
session.beginTransaction();
List<Category> categories = (List<Category>)session.createQuery("from Category")
.setCacheable(true).list(); session.getTransaction().commit();
session.close(); Session session2 = sf.openSession();
session2.beginTransaction();
List<Category> categories2 = (List<Category>)session2.createQuery("from Category") //三级缓存，List也不会重新发select 把共用的存储起来
.setCacheable(true).list(); session2.getTransaction().commit();
session2.close();
}