欢迎使用Hibernate二级缓存示例教程。今天我们将研究Hibernate EHCache，它是最受欢迎的Hibernate二级缓存提供程序。
目录[ 隐藏 ]
在大型应用程序中使用Hibernate的一个主要好处是它支持缓存，因此减少了数据库查询和更好的性能。在前面的例子中，我们研究了Hibernate First Level Cache，今天我们将使用Hibernate EHCache实现来研究Hibernate二级缓存。
Hibernate二级缓存提供程序包括EHCache和Infinispan，但EHCache更受欢迎，我们将它用于我们的示例项目。然而，在我们迁移到项目之前，我们应该知道缓存对象的不同策略。
由于EHCache支持所有上述缓存策略，因此当您在hibernate中寻找二级缓存时，它是最佳选择。我不会详细介绍EHCache，我的主要重点是让它适用于hibernate应用程序。
在Eclipse或您最喜欢的IDE中创建一个maven项目，最终实现将如下图所示。
让我们逐个查看应用程序的每个组件。
对于hibernate二级缓存，我们需要在我们的应用程序中添加ehcache-core和hibernate-ehcache依赖项。EHCache使用slf4j进行日志记录，因此我还添加了slf4j-simple用于日志记录。我正在使用所有这些API的最新版本，hibernate-ehcache API与ehcache-core API不兼容，在这种情况下你需要检查hibernate-ehcache的pom.xml以找出正确的版本使用。我们的最终pom.xml如下所示。
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><groupId>com.journaldev.hibernate</groupId><artifactId>HibernateEHCacheExample</artifactId><version>0.0.1-SNAPSHOT</version><description>Hibernate Secondary Level Cache Example using EHCache implementation</description><dependencies><!-- Hibernate Core API --><dependency><groupId>org.hibernate</groupId><artifactId>hibernate-core</artifactId><version>4.3.5.Final</version></dependency><!-- MySQL Driver --><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>5.0.5</version></dependency><!-- EHCache Core APIs --><dependency><groupId>net.sf.ehcache</groupId><artifactId>ehcache-core</artifactId><version>2.6.9</version></dependency><!-- Hibernate EHCache API --><dependency><groupId>org.hibernate</groupId><artifactId>hibernate-ehcache</artifactId><version>4.3.5.Final</version></dependency><!-- EHCache uses slf4j for logging --><dependency><groupId>org.slf4j</groupId><artifactId>slf4j-simple</artifactId><version>1.7.5</version></dependency></dependencies>
</project>
Hibernate默认情况下禁用二级缓存，因此我们需要启用它并添加一些配置才能使其正常工作。我们的hibernate.cfg.xml文件如下所示。
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration SYSTEM "classpath://org/hibernate/hibernate-configuration-3.0.dtd">
<hibernate-configuration><session-factory><property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property><property name="hibernate.connection.password">pankaj123</property><property name="hibernate.connection.url">jdbc:mysql://localhost/TestDB</property><property name="hibernate.connection.username">pankaj</property><property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property><property name="hibernate.current_session_context_class">thread</property><property name="hibernate.show_sql">true</property><property name="hibernate.cache.region.factory_class">org.hibernate.cache.ehcache.EhCacheRegionFactory</property><!-- For singleton factory --><!-- <property name="hibernate.cache.region.factory_class">org.hibernate.cache.ehcache.SingletonEhCacheRegionFactory</property>--><!-- enable second level cache and query cache --><property name="hibernate.cache.use_second_level_cache">true</property><property name="hibernate.cache.use_query_cache">true</property><property name="net.sf.ehcache.configurationResourceName">/myehcache.xml</property><mapping class="com.journaldev.hibernate.model.Employee" /><mapping class="com.journaldev.hibernate.model.Address" /></session-factory>
</hibernate-configuration>
关于休眠二级缓存配置的一些重要观点是：
org.hibernate.cache.ehcache.EhCacheRegionFactory它。如果您希望工厂类是单例，则应使用org.hibernate.cache.ehcache.SingletonEhCacheRegionFactory类。 如果您使用的是Hibernate 3，则相应的类将为net.sf.ehcache.hibernate.EhCacheRegionFactory和net.sf.ehcache.hibernate.SingletonEhCacheRegionFactory。
我们的EHCache配置文件myehcache.xml如下所示。
<?xml version="1.0" encoding="UTF-8"?>
<ehcache xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:noNamespaceSchemaLocation="ehcache.xsd" updateCheck="true"monitoring="autodetect" dynamicConfig="true"><diskStore path="java.io.tmpdir/ehcache" /><defaultCache maxEntriesLocalHeap="10000" eternal="false"timeToIdleSeconds="120" timeToLiveSeconds="120" diskSpoolBufferSizeMB="30"maxEntriesLocalDisk="10000000" diskExpiryThreadIntervalSeconds="120"memoryStoreEvictionPolicy="LRU" statistics="true"><persistence strategy="localTempSwap" /></defaultCache><cache name="employee" maxEntriesLocalHeap="10000" eternal="false"timeToIdleSeconds="5" timeToLiveSeconds="10"><persistence strategy="localTempSwap" /></cache><cache name="org.hibernate.cache.internal.StandardQueryCache"maxEntriesLocalHeap="5" eternal="false" timeToLiveSeconds="120"><persistence strategy="localTempSwap" /></cache><cache name="org.hibernate.cache.spi.UpdateTimestampsCache"maxEntriesLocalHeap="5000" eternal="true"><persistence strategy="localTempSwap" /></cache>
</ehcache>
Hibernate EHCache提供了很多选项，我不会详细介绍，但上面的一些重要配置是：
org.hibernate.cache.internal.StandardQueryCache和org.hibernate.cache.spi.UpdateTimestampsCache定义因为EHCache正在发出警告。
我们使用org.hibernate.annotations.Cache注释来提供缓存配置。org.hibernate.annotations.CacheConcurrencyStrategy用于定义缓存策略，我们还可以定义用于模型bean的缓存区域。
package com.journaldev.hibernate.model;import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToOne;
import javax.persistence.PrimaryKeyJoinColumn;
import javax.persistence.Table;import org.hibernate.annotations.Cache;
import org.hibernate.annotations.CacheConcurrencyStrategy;
import org.hibernate.annotations.GenericGenerator;
import org.hibernate.annotations.Parameter;@Entity
@Table(name = "ADDRESS")
@Cache(usage=CacheConcurrencyStrategy.READ_ONLY, region="employee")
public class Address {@Id@Column(name = "emp_id", unique = true, nullable = false)@GeneratedValue(generator = "gen")@GenericGenerator(name = "gen", strategy = "foreign", parameters = { @Parameter(name = "property", value = "employee") })private long id;@Column(name = "address_line1")private String addressLine1;@Column(name = "zipcode")private String zipcode;@Column(name = "city")private String city;@OneToOne@PrimaryKeyJoinColumnprivate Employee employee;public long getId() {return id;}public void setId(long id) {this.id = id;}public String getAddressLine1() {return addressLine1;}public void setAddressLine1(String addressLine1) {this.addressLine1 = addressLine1;}public String getZipcode() {return zipcode;}public void setZipcode(String zipcode) {this.zipcode = zipcode;}public String getCity() {return city;}public void setCity(String city) {this.city = city;}public Employee getEmployee() {return employee;}public void setEmployee(Employee employee) {this.employee = employee;}}
package com.journaldev.hibernate.model;import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToOne;
import javax.persistence.Table;import org.hibernate.annotations.Cache;
import org.hibernate.annotations.CacheConcurrencyStrategy;
import org.hibernate.annotations.Cascade;@Entity
@Table(name = "EMPLOYEE")
@Cache(usage=CacheConcurrencyStrategy.READ_ONLY, region="employee")
public class Employee {@Id@GeneratedValue(strategy = GenerationType.IDENTITY)@Column(name = "emp_id")private long id;@Column(name = "emp_name")private String name;@Column(name = "emp_salary")private double salary;@OneToOne(mappedBy = "employee")@Cascade(value = org.hibernate.annotations.CascadeType.ALL)private Address address;public long getId() {return id;}public void setId(long id) {this.id = id;}public Address getAddress() {return address;}public void setAddress(Address address) {this.address = address;}public String getName() {return name;}public void setName(String name) {this.name = name;}public double getSalary() {return salary;}public void setSalary(double salary) {this.salary = salary;}}
请注意，我使用的是与HQL示例中相同的数据库设置，您可能需要检查以创建数据库表并加载示例数据。
我们有一个简单的实用程序类来配置hibernate并获取SessionFactory单例实例。
package com.journaldev.hibernate.util;import org.hibernate.SessionFactory;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;public class HibernateUtil {private static SessionFactory sessionFactory;private static SessionFactory buildSessionFactory() {try {// Create the SessionFactory from hibernate.cfg.xmlConfiguration configuration = new Configuration();configuration.configure("hibernate.cfg.xml");System.out.println("Hibernate Configuration loaded");ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder().applySettings(configuration.getProperties()).build();System.out.println("Hibernate serviceRegistry created");SessionFactory sessionFactory = configuration.buildSessionFactory(serviceRegistry);return sessionFactory;}catch (Throwable ex) {System.err.println("Initial SessionFactory creation failed." + ex);ex.printStackTrace();throw new ExceptionInInitializerError(ex);}}public static SessionFactory getSessionFactory() {if(sessionFactory == null) sessionFactory = buildSessionFactory();return sessionFactory;}
}
我们使用Hibernate EHCache的hibernate二级缓存项目已准备就绪，让我们编写一个简单的程序来测试它。
package com.journaldev.hibernate.main;import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.stat.Statistics;import com.journaldev.hibernate.model.Employee;
import com.journaldev.hibernate.util.HibernateUtil;public class HibernateEHCacheMain {public static void main(String[] args) {System.out.println("Temp Dir:"+System.getProperty("java.io.tmpdir"));//Initialize SessionsSessionFactory sessionFactory = HibernateUtil.getSessionFactory();Statistics stats = sessionFactory.getStatistics();System.out.println("Stats enabled="+stats.isStatisticsEnabled());stats.setStatisticsEnabled(true);System.out.println("Stats enabled="+stats.isStatisticsEnabled());Session session = sessionFactory.openSession();Session otherSession = sessionFactory.openSession();Transaction transaction = session.beginTransaction();Transaction otherTransaction = otherSession.beginTransaction();printStats(stats, 0);Employee emp = (Employee) session.load(Employee.class, 1L);printData(emp, stats, 1);emp = (Employee) session.load(Employee.class, 1L);printData(emp, stats, 2);//clear first level cache, so that second level cache is usedsession.evict(emp);emp = (Employee) session.load(Employee.class, 1L);printData(emp, stats, 3);emp = (Employee) session.load(Employee.class, 3L);printData(emp, stats, 4);emp = (Employee) otherSession.load(Employee.class, 1L);printData(emp, stats, 5);//Release resourcestransaction.commit();otherTransaction.commit();sessionFactory.close();}private static void printStats(Statistics stats, int i) {System.out.println("***** " + i + " *****");System.out.println("Fetch Count="+ stats.getEntityFetchCount());System.out.println("Second Level Hit Count="+ stats.getSecondLevelCacheHitCount());System.out.println("Second Level Miss Count="+ stats.getSecondLevelCacheMissCount());System.out.println("Second Level Put Count="+ stats.getSecondLevelCachePutCount());}private static void printData(Employee emp, Statistics stats, int count) {System.out.println(count+":: Name="+emp.getName()+", Zipcode="+emp.getAddress().getZipcode());printStats(stats, count);}}
org.hibernate.stat.Statistics提供Hibernate SessionFactory的统计信息，我们用它来打印获取计数和二级缓存命中，未命中和放置计数。默认情况下禁用统计信息以获得更好的性能，这就是我在程序开始时启用它的原因。
当我们运行上面的程序时，我们会获得Hibernate和EHCache API生成的大量输出，但我们对正在打印的数据感兴趣。样本运行打印输出。
Temp Dir:/var/folders/h4/q73jjy0902g51wkw0w69c0600000gn/T/
Hibernate Configuration loaded
Hibernate serviceRegistry created
Stats enabled=false
Stats enabled=true
***** 0 *****
Fetch Count=0
Second Level Hit Count=0
Second Level Miss Count=0
Second Level Put Count=0
Hibernate: select employee0_.emp_id as emp_id1_1_0_, employee0_.emp_name as emp_name2_1_0_, employee0_.emp_salary as emp_sala3_1_0_, address1_.emp_id as emp_id1_0_1_, address1_.address_line1 as address_2_0_1_, address1_.city as city3_0_1_, address1_.zipcode as zipcode4_0_1_ from EMPLOYEE employee0_ left outer join ADDRESS address1_ on employee0_.emp_id=address1_.emp_id where employee0_.emp_id=?
1:: Name=Pankaj, Zipcode=95129
***** 1 *****
Fetch Count=1
Second Level Hit Count=0
Second Level Miss Count=1
Second Level Put Count=2
2:: Name=Pankaj, Zipcode=95129
***** 2 *****
Fetch Count=1
Second Level Hit Count=0
Second Level Miss Count=1
Second Level Put Count=2
3:: Name=Pankaj, Zipcode=95129
***** 3 *****
Fetch Count=1
Second Level Hit Count=2
Second Level Miss Count=1
Second Level Put Count=2
Hibernate: select employee0_.emp_id as emp_id1_1_0_, employee0_.emp_name as emp_name2_1_0_, employee0_.emp_salary as emp_sala3_1_0_, address1_.emp_id as emp_id1_0_1_, address1_.address_line1 as address_2_0_1_, address1_.city as city3_0_1_, address1_.zipcode as zipcode4_0_1_ from EMPLOYEE employee0_ left outer join ADDRESS address1_ on employee0_.emp_id=address1_.emp_id where employee0_.emp_id=?
4:: Name=Lisa, Zipcode=560100
***** 4 *****
Fetch Count=2
Second Level Hit Count=2
Second Level Miss Count=2
Second Level Put Count=4
5:: Name=Pankaj, Zipcode=95129
***** 5 *****
Fetch Count=2
Second Level Hit Count=4
Second Level Miss Count=2
Second Level Put Count=4
从输出中可以看出，统计信息最初被禁用，但我们启用它来检查我们的休眠二级缓存。
输出的逐步说明如下：
evict()方法从第一级缓存中删除employee对象，现在当我们尝试加载它时，hibernate在二级缓存中找到它。这就是为什么没有触发数据库查询并且获取计数仍为1.请注意，命中计数从0变为2，因为从二级缓存中读取了Employee和Address对象。二级未命中和计数仍保持在较早值。所以很明显我们的Hibernate二级缓存; Hibernate EHCache; 工作正常。Hibernate统计信息有助于找到系统中的瓶颈并对其进行优化，以减少获取次数并从缓存中加载更多数据。
这就是Hibernate EHCache示例的全部内容，我希望它能帮助您在hibernate应用程序中配置EHCache并通过hibernate二级缓存获得更好的性能。您可以从下面的链接下载示例项目，并使用其他统计数据来了解更多信息。
下载Hibernate EHCache项目
转载来源：https://www.journaldev.com/2980/hibernate-ehcache-hibernate-second-level-cache
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