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我學習Hibernate的第二級緩存，是二級緩存是會話特定的休眠
這是我的實體
package com.hibernate.pojo;
import java.io.Serializable;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.NamedQuery;
import javax.persistence.Table;
import org.hibernate.annotations.Cache;
import org.hibernate.annotations.CacheConcurrencyStrategy;
@Entity
@Table(name = "customer")
@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
@NamedQuery(query = "select c.customerName from Customer c",name = "findCustomerNames")
public class Customer implements Serializable{
public Customer(){}
public Customer(Integer customerId){
this.customerId = customerId;
}
public Customer(Integer customerId,String customerName){
this.customerId = customerId;
this.customerName = customerName;
}
@Id
private Integer customerId;
private String customerName;
/**
* @return the customerId
*/
public Integer getCustomerId() {
return customerId;
}
/**
* @param customerId the customerId to set
*/
public void setCustomerId(Integer customerId) {
this.customerId = customerId;
}
/**
* @return the customerName
*/
public String getCustomerName() {
return customerName;
}
/**
* @param customerName the customerName to set
*/
public void setCustomerName(String customerName) {
this.customerName = customerName;
}
@Override
public String toString(){
StringBuffer strb = new StringBuffer();
strb.append("\n\n CUSTOMER-ID : ")
.append(this.customerId)
.append("\n CUSTOMER-NAME : ")
.append(this.customerName);
return strb.toString();
}
@Override
public int hashCode(){
return this.customerId * 29;
}
@Override
public boolean equals(Object object){
boolean flag = false;
if(object instanceof Customer){
Customer c = (Customer) object;
flag = (this.customerId == c.getCustomerId()) ? true : false;
}
return flag;
}
}
這是我的Hibernate配置文件
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<property name="hibernate.connection.driver_class">org.apache.derby.jdbc.ClientDriver</property>
<property name="hibernate.connection.url">jdbc:derby://localhost:1527/sun-appserv-samples</property>
<property name="hibernate.connection.username">app</property>
<property name="hibernate.connection.password">app</property>
<property name="hibernate.dialect">org.hibernate.dialect.DerbyDialect</property>
<property name="show_sql">true</property>
<property name="format_sql">true</property>
<property name="hibernate.cache.provider_class">org.hibernate.cache.EhCacheProvider</property>
<property name="hibernate.cache.use_query_cache">true</property>
<property name="hibernate.cache.use_second_level_cache">true</property>
<mapping class="com.hibernate.pojo.Customer" />
</session-factory>
</hibernate-configuration>
的下面的代碼是我的問題所在的地方
private static void getCustomer() throws Exception{
Session session = HibernateUtil.getSessionFactory().openSession();
Customer obj = null;
obj = (Customer)session.get(Customer.class, new Integer(2));
session.close();
session = HibernateUtil.getSessionFactory().openSession();
obj = (Customer)session.get(Customer.class, new Integer(2));
session.close();
session = HibernateUtil.getSessionFactory().openSession();
obj = (Customer)session.get(Customer.class, new Integer(2));
session.close();
System.out.println(obj);
}
從上面的代碼可以看出，我打開會話三次並關閉它三次。 在日誌中打印的查詢如下
Hibernate:
select
customer0_.customerId as customerId0_0_,
customer0_.customerName as customer2_0_0_
from
customer customer0_
where
customer0_.customerId=?
，
但是當我使用下面的代碼
private static void getCustomerFromSession() throws Exception{
Session [] session = new Session[]{
HibernateUtil.getSessionFactory().openSession(),
HibernateUtil.getSessionFactory().openSession(),
HibernateUtil.getSessionFactory().openSession()
};
Customer obj1 = (Customer) session[0].get(Customer.class, new Integer(2));
Customer obj2 = (Customer) session[1].get(Customer.class, new Integer(2));
Customer obj3 = (Customer) session[2].get(Customer.class, new Integer(2));
session[0].close();
session[1].close();
session[2].close();
}
我在這裏也說期待該查詢應打印一次，但日誌打印
Hibernate:
select
customer0_.customerId as customerId0_0_,
customer0_.customerName as customer2_0_0_
from
customer customer0_
where
customer0_.customerId=?
Hibernate:
select
customer0_.customerId as customerId0_0_,
customer0_.customerName as customer2_0_0_
from
customer customer0_
where
customer0_.customerId=?
Hibernate:
select
customer0_.customerId as customerId0_0_,
customer0_.customerName as customer2_0_0_
from
customer customer0_
where
customer0_.customerId=?
但查詢印三次。
那麼我的二級緩存配置是否正確？
是二級緩存特定會話嗎？
我應該對我的代碼做些什麼改變，這樣即使我創建了3個會話，從第一個會話'get'獲得的第一個客戶也應該由下兩個會話共享。
因此沒有打印2選擇同一客戶的查詢，因爲它存在於二級緩存中。