Hibernate视频学习笔记（13）一级缓存_二级缓存_查询缓存

一级缓存：

hibernate一级缓存

一级缓存很短和session的生命周期一致，一级缓存也叫session级的缓存或事务级缓存

那些方法支持一级缓存：

* get()

* load()

* iterate（查询实体对象）

如何管理一级缓存：

* session.clear(),session.evict()

如何避免一次性大量的实体数据入库导致内存溢出

* 先flush，再clear

如果数据量特别大，考虑采用jdbc实现，如果jdbc也不能满足要求可以考虑采用数据本身的特定导入工具

Student student = (Student)session.load(Student.class, 1);

System.out.println("student.name=" + student.getName());

//不会发出sql，因为load使用缓存

student = (Student)session.load(Student.class, 1);

System.out.println("student.name=" + student.getName());

Student student = (Student)session.get(Student.class, 1);

System.out.println("student.name=" + student.getName());

//不会发出sql，因为get使用缓存

student = (Student)session.get(Student.class, 1);

System.out.println("student.name=" + student.getName());

Student student = (Student)session.createQuery("from Student s where s.id=1").iterate().next();

System.out.println("student.name=" + student.getName());

//会发出查询id的sql，不会发出查询实体对象的sql，因为iterate使用缓存

student = (Student)session.createQuery("from Student s where s.id=1").iterate().next();

System.out.println("student.name=" + student.getName());

String name = (String)session.createQuery("select s.name from Student s where s.id=1").iterate().next();

System.out.println("student.name=" + name);

//iterate查询普通属性，一级缓存不会缓存，所以发出sql

//一级缓存是缓存实体对象的

name = (String)session.createQuery("select s.name from Student s where s.id=1").iterate().next();

System.out.println("student.name=" + name);

//会发出查询语句，session间不能共享一级缓存的数据

//因为它会伴随session的生命周期存在和消亡

Student student = (Student)session.load(Student.class, 1);

System.out.println("student.name=" + student.getName());

Student stu = new Student();

stu.setName("王五");

Serializable id = session.save(stu);

//不会发出sql，因为save是使用缓存的

Student student = (Student)session.load(Student.class, id);

System.out.println("student.name=" + student.getName());

for (int i=0; i<1000; i++) {

Student student = new Student();

student.setName("s_" + i);

session.save(student);

//每20条数据就强制session将数据持久化

//同时清除缓存，避免大量数据造成内存溢出

if ( i % 20 == 0) {

session.flush();

session.clear();

}

}

一级缓存无法取消，但可以管理

hibernate二级缓存

二级缓存也称进程级的缓存或SessionFactory级的缓存，二级缓存可以被所有的session共享

二级缓存的生命周期和SessionFactory的生命周期一致，SessionFactory可以管理二级缓存

二级缓存的配置和使用：

* 将echcache.xml文件拷贝到src下

* 开启二级缓存，修改hibernate.cfg.xml文件

<property name="hibernate.cache.use_second_level_cache">true</property>

* 指定缓存产品提供商，修改hibernate.cfg.xml文件

<property name="hibernate.cache.provider_class">org.hibernate.cache.EhCacheProvider</property>

* 指定那些实体类使用二级缓存（两种方法）

* 在映射文件中采用<cache>标签，在id前面

* 在hibernate.cfg.xml文件中，采用<class-cache>标签

ehcache.xml

二级缓存是缓存实体对象的

了解一级缓存和二级缓存的交互

Session session = null;

try {

session = HibernateUtils.getSession();

session.beginTransaction();

Student student = (Student)session.load(Student.class, 1);

System.out.println("student.name=" + student.getName());

session.getTransaction().commit();

}catch(Exception e) {

e.printStackTrace();

session.getTransaction().rollback();

}finally {

HibernateUtils.closeSession(session);

}

try {

session = HibernateUtils.getSession();

session.beginTransaction();

//不会发出sql，因为开启了二级缓存，session是共享二级缓存的

Student student = (Student)session.load(Student.class, 1);

System.out.println("student.name=" + student.getName());

session.getTransaction().commit();

}catch(Exception e) {

e.printStackTrace();

session.getTransaction().rollback();

}finally {

HibernateUtils.closeSession(session);

}

Session session = null;

try {

session = HibernateUtils.getSession();

session.beginTransaction();

Student student = (Student)session.get(Student.class, 1);

System.out.println("student.name=" + student.getName());

session.getTransaction().commit();

}catch(Exception e) {

e.printStackTrace();

session.getTransaction().rollback();

}finally {

HibernateUtils.closeSession(session);

}

try {

session = HibernateUtils.getSession();

session.beginTransaction();

//不会发出sql，因为开启了二级缓存，session是共享二级缓存的

Student student = (Student)session.get(Student.class, 1);

System.out.println("student.name=" + student.getName());

session.getTransaction().commit();

}catch(Exception e) {

e.printStackTrace();

session.getTransaction().rollback();

}finally {

HibernateUtils.closeSession(session);

}

Session session = null;

try {

session = HibernateUtils.getSession();

session.beginTransaction();

Student student = (Student)session.load(Student.class, 1);

System.out.println("student.name=" + student.getName());

session.getTransaction().commit();

}catch(Exception e) {

e.printStackTrace();

session.getTransaction().rollback();

}finally {

HibernateUtils.closeSession(session);

}

//管理二级缓存

SessionFactory factory = HibernateUtils.getSessionFactory();

//factory.evict(Student.class);

factory.evict(Student.class, 1);

try {

session = HibernateUtils.getSession();

session.beginTransaction();

//会发出查询sql，因为二级缓存中的数据被清除了

Student student = (Student)session.load(Student.class, 1);

System.out.println("student.name=" + student.getName());

session.getTransaction().commit();

}catch(Exception e) {

e.printStackTrace();

session.getTransaction().rollback();

}finally {

HibernateUtils.closeSession(session);

}

Session session = null;

try {

session = HibernateUtils.getSession();

session.beginTransaction();

//仅向二级缓存读数据，而不向二级缓存写数据

session.setCacheMode(CacheMode.GET);

Student student = (Student)session.load(Student.class, 1);

System.out.println("student.name=" + student.getName());

session.getTransaction().commit();

}catch(Exception e) {

e.printStackTrace();

session.getTransaction().rollback();

}finally {

HibernateUtils.closeSession(session);

}

try {

session = HibernateUtils.getSession();

session.beginTransaction();

//发出sql语句，因为session设置了CacheMode为GET，所以二级缓存中没有数据

Student student = (Student)session.load(Student.class, 1);

System.out.println("student.name=" + student.getName());

session.getTransaction().commit();

}catch(Exception e) {

e.printStackTrace();

session.getTransaction().rollback();

}finally {

HibernateUtils.closeSession(session);

}

try {

session = HibernateUtils.getSession();

session.beginTransaction();

//只向二级缓存写数据，而不从二级缓存读数据

session.setCacheMode(CacheMode.PUT);

//会发出查询sql，因为session将CacheMode设置成了PUT

Student student = (Student)session.load(Student.class, 1);

System.out.println("student.name=" + student.getName());

session.getTransaction().commit();

}catch(Exception e) {

e.printStackTrace();

session.getTransaction().rollback();

}finally {

HibernateUtils.closeSession(session);

}

hibernate查询缓存

查询缓存是针对普通属性结果集的缓存

对实体对象的结果集只缓存id

查询缓存的生命周期，当前关联的表发生修改，那么查询缓存生命周期结束

查询缓存的配置和使用：

* 在hibernate.cfg.xml文件中启用查询缓存，如：

<property name="hibernate.cache.use_query_cache">true</property>

* 在程序中必须手动启用查询缓存，如：

query.setCacheable(true);

Query query = session.createQuery("select s.name from Student s");

//启用查询查询缓存

query.setCacheable(true);

List names = query.list();

for (Iterator iter=names.iterator();iter.hasNext(); ) {

String name = (String)iter.next();

System.out.println(name);

}

System.out.println("-------------------------------------");

query = session.createQuery("select s.name from Student s");

//启用查询查询缓存

query.setCacheable(true);

//没有发出查询sql，因为启用了查询缓存

names = query.list();

for (Iterator iter=names.iterator();iter.hasNext(); ) {

String name = (String)iter.next();

System.out.println(name);

}

Session session = null;

try {

session = HibernateUtils.getSession();

session.beginTransaction();

Query query = session.createQuery("select s.name from Student s");

//启用查询查询缓存

query.setCacheable(true);

List names = query.list();

for (Iterator iter=names.iterator();iter.hasNext(); ) {

String name = (String)iter.next();

System.out.println(name);

}

session.getTransaction().commit();

}catch(Exception e) {

e.printStackTrace();

session.getTransaction().rollback();

}finally {

HibernateUtils.closeSession(session);

}

System.out.println("-------------------------------------");

try {

session = HibernateUtils.getSession();

session.beginTransaction();

Query query = session.createQuery("select s.name from Student s");

//启用查询查询缓存

query.setCacheable(true);

//不会发出查询sql，因为查询缓存的生命周期和session无关

List names = query.list();

for (Iterator iter=names.iterator();iter.hasNext(); ) {

String name = (String)iter.next();

System.out.println(name);

}

session.getTransaction().commit();

}catch(Exception e) {

e.printStackTrace();

session.getTransaction().rollback();

}finally {

HibernateUtils.closeSession(session);

}

Session session = null;

try {

session = HibernateUtils.getSession();

session.beginTransaction();

Query query = session.createQuery("select s.name from Student s");

//启用查询查询缓存

query.setCacheable(true);

for (Iterator iter=query.iterate();iter.hasNext(); ) {

String name = (String)iter.next();

System.out.println(name);

}

session.getTransaction().commit();

}catch(Exception e) {

e.printStackTrace();

session.getTransaction().rollback();

}finally {

HibernateUtils.closeSession(session);

}

System.out.println("-------------------------------------");

try {

session = HibernateUtils.getSession();

session.beginTransaction();

Query query = session.createQuery("select s.name from Student s");

//启用查询查询缓存

query.setCacheable(true);

//查询缓存只对query.list()起作用，query.iterate不起作用，也就是query.iterate不使用

//查询缓存

for (Iterator iter=query.iterate();iter.hasNext(); ) {

String name = (String)iter.next();

System.out.println(name);

}

session.getTransaction().commit();

}catch(Exception e) {

e.printStackTrace();

session.getTransaction().rollback();

}finally {

HibernateUtils.closeSession(session);

}

Session session = null;

try {

session = HibernateUtils.getSession();

session.beginTransaction();

Query query = session.createQuery("select s from Student s");

//启用查询查询缓存

//query.setCacheable(true);

List students = query.list();

for (Iterator iter=students.iterator();iter.hasNext(); ) {

Student student = (Student)iter.next();

System.out.println(student.getName());

}

session.getTransaction().commit();

}catch(Exception e) {

e.printStackTrace();

session.getTransaction().rollback();

}finally {

HibernateUtils.closeSession(session);

}

System.out.println("-------------------------------------");

try {

session = HibernateUtils.getSession();

session.beginTransaction();

Query query = session.createQuery("select s from Student s");

//启用查询查询缓存

//query.setCacheable(true);

//会发出查询sql，因为list默认每次都会发出查询sql

List students = query.list();

for (Iterator iter=students.iterator();iter.hasNext(); ) {

Student student = (Student)iter.next();

System.out.println(student.getName());

}

session.getTransaction().commit();

}catch(Exception e) {

e.printStackTrace();

session.getTransaction().rollback();

}finally {

HibernateUtils.closeSession(session);

}

Session session = null;

try {

session = HibernateUtils.getSession();

session.beginTransaction();

Query query = session.createQuery("select s from Student s");

//启用查询查询缓存

query.setCacheable(true);

List students = query.list();

for (Iterator iter=students.iterator();iter.hasNext(); ) {

Student student = (Student)iter.next();

System.out.println(student.getName());

}

session.getTransaction().commit();

}catch(Exception e) {

e.printStackTrace();

session.getTransaction().rollback();

}finally {

HibernateUtils.closeSession(session);

}

System.out.println("-------------------------------------");

try {

session = HibernateUtils.getSession();

session.beginTransaction();

Query query = session.createQuery("select s from Student s");

//启用查询查询缓存

query.setCacheable(true);

//会发出n条查询语句，因为开启了查询缓存，关闭了二级缓存，那么查询缓存会缓存实体对象的id

//所以hibernate会根据实体对象的id去查询相应的实体，如果缓存中不存在相应的

//实体那么将发出根据实体id查询的sql语句，否则不会发出sql使用缓存中的数据

List students = query.list();

for (Iterator iter=students.iterator();iter.hasNext(); ) {

Student student = (Student)iter.next();

System.out.println(student.getName());

}

session.getTransaction().commit();

}catch(Exception e) {

e.printStackTrace();

session.getTransaction().rollback();

}finally {

HibernateUtils.closeSession(session);

}

Session session = null;

try {

session = HibernateUtils.getSession();

session.beginTransaction();

Query query = session.createQuery("select s from Student s");

//启用查询查询缓存

query.setCacheable(true);

List students = query.list();

for (Iterator iter=students.iterator();iter.hasNext(); ) {

Student student = (Student)iter.next();

System.out.println(student.getName());

}

session.getTransaction().commit();

}catch(Exception e) {

e.printStackTrace();

session.getTransaction().rollback();

}finally {

HibernateUtils.closeSession(session);

}

System.out.println("-------------------------------------");

try {

session = HibernateUtils.getSession();

session.beginTransaction();

Query query = session.createQuery("select s from Student s");

//启用查询查询缓存

query.setCacheable(true);

//不会发出查询sql，因为开启了二级缓存和查询缓存，查询缓存缓存了实体对象的id列表

//hibernate会根据实体对象的id列表到二级缓存中取得相应的数据

List students = query.list();

for (Iterator iter=students.iterator();iter.hasNext(); ) {

Student student = (Student)iter.next();

System.out.println(student.getName());

}

session.getTransaction().commit();

}catch(Exception e) {

e.printStackTrace();

session.getTransaction().rollback();

}finally {

HibernateUtils.closeSession(session);

}

变化不大的数据，相对静态的数据放入缓存比较合适

Client1

Client2

server

facade

Cache

Database

cache

cache

NRU最近不使用 FIFO先进先出 LRU最近最少使用