hibernate查詢緩存(hibernate默認(rèn)是關(guān)閉的)
查詢緩存是針對普通屬性結(jié)果集的緩存
對實(shí)體對象的結(jié)果集只緩存id
查詢緩存的生命周期，當(dāng)前關(guān)聯(lián)的表發(fā)生修改，那么查詢緩存生命周期結(jié)束
查詢緩存的配置和使用：
1. 啟用查詢緩存：在hibernate.cfg.xml中加入：
<property name=”hibernate.cache.use_query_cache”>true</property>
2. 在程序中必須手動(dòng)啟用查詢緩存，如：query.setCacheable(true);
測試查詢緩存：
一． 開啟查詢緩存，關(guān)閉二級緩存，開啟一個(gè)session，分別調(diào)用query.list （查詢屬性）
Query query = session.createQuery(“select s.name from Student s”);
//啟用查詢緩存
query.setCacheable(true);
List names = query.list();
for(Iterator iter = names.terator();iter.hasNext();){
String name = (String)iter.next();
System.out.println(name);
}
System.out.println(“------------------------------------------”);
query = session.createQuery(“select s.name from Student s”);
//啟用查詢緩存
query.setCacheable(true);
names = query.list();
for(Iterator iter = names.terator();iter.hasNext();){
String name = (String)iter.next();
System.out.println(name);
}
第二次沒有去查詢數(shù)據(jù)庫，因?yàn)閱⒂昧瞬樵兙彺?/p>
二． 開啟查詢緩存，關(guān)閉二級緩存，開啟兩個(gè)session，分別調(diào)用query.list （查詢屬性）
Query query = session.createQuery(“select s.name from Student s”);
//啟用查詢緩存
query.setCacheable(true);
List names = query.list();
for(Iterator iter = names.terator();iter.hasNext();){
String name = (String)iter.next();
System.out.println(name);
}
session.close();
System.out.println(“------------------------------------------”);
………
Query query = session.createQuery(“select s.name from Student s”);
//啟用查詢緩存
query.setCacheable(true);
List names = query.list();
for(Iterator iter = names.terator();iter.hasNext();){
String name = (String)iter.next();
System.out.println(name);
}
第二次沒有去查詢數(shù)據(jù)庫，因?yàn)椴樵兙彺嫔芷谂csession生命周期無關(guān)
三． 開啟查詢緩存，關(guān)閉二級緩存，開啟兩個(gè)session，分別調(diào)用query.iterate （查詢屬性）
Query query = session.createQuery(“select s.name from Student s”);
//啟用查詢緩存
query.setCacheable(true);
for(Iterator iter =query.iterate();iter.hasNext();){
String name = (String)iter.next();
System.out.println(name);
}
session.close();
System.out.println(“------------------------------------------”);
………
Query query = session.createQuery(“select s.name from Student s”);
//啟用查詢緩存
query.setCacheable(true);
for(Iterator iter = query.iterate();iter.hasNext();){
String name = (String)iter.next();
System.out.println(name);
}
第二去查詢數(shù)據(jù)庫，因?yàn)椴樵兙彺嬷粚uery.list()起作用，對query.iterate()不起作用,也就是說query.iterate()不使用查詢緩存
四． 關(guān)閉查詢緩存，關(guān)閉二級緩存，開啟兩個(gè)session，分別調(diào)用query.list （查詢實(shí)體對象）
Query query = session.createQuery(“ from Student s”);
//query.setCacheable(true);
List students = query.list();
for(Iterator iter = students.iterate();iter.hasNext();){
Student stu = (Student)iter.next();
System.out.println(stu.getName());
}
session.close();
System.out.println(“------------------------------------------”);
………
Query query = session.createQuery(“ from Student s”);
//query.setCacheable(true);
List students = query.list();
for(Iterator iter = students.iterate();iter.hasNext();){
Student stu = (Student)iter.next();
System.out.println(stu.getName());
}
第二去查詢數(shù)據(jù)庫，因?yàn)閘ist默認(rèn)每次都會(huì)發(fā)出查詢sql
五． 開啟查詢緩存，關(guān)閉二級緩存，開啟兩個(gè)session，分別調(diào)用query.list （查詢實(shí)體對象）
Query query = session.createQuery(“ from Student s”);
query.setCacheable(true);
List students = query.list();
for(Iterator iter = students.iterate();iter.hasNext();){
Student stu = (Student)iter.next();
System.out.println(stu.getName());
}
session.close();
System.out.println(“------------------------------------------”);
………
Query query = session.createQuery(“ from Student s”);
query.setCacheable(true);
List students = query.list();
for(Iterator iter = students.iterate();iter.hasNext();){
Student stu = (Student)iter.next();
System.out.println(stu.getName());
}
第二去查詢數(shù)據(jù)庫時(shí)，會(huì)發(fā)出N條sql語句，因?yàn)殚_啟了查詢緩存，關(guān)閉了二級緩存，那么查詢緩存會(huì)緩存實(shí)體對象的id，所以hibernate會(huì)根據(jù)實(shí)體對象的id去查詢相應(yīng)的實(shí)體，如果緩存中不存在相應(yīng)的實(shí)體，那么將發(fā)出根據(jù)實(shí)體id查詢的sql語句，否則不會(huì)發(fā)出sql，使用緩存中的數(shù)據(jù)
六． 開啟查詢緩存，開啟二級緩存，開啟兩個(gè)session，分別調(diào)用query.list （查詢實(shí)體對象）
Query query = session.createQuery(“ from Student s”);
query.setCacheable(true);
List students = query.list();
for(Iterator iter = students.iterate();iter.hasNext();){
Student stu = (Student)iter.next();
System.out.println(stu.getName());
}
session.close();
System.out.println(“------------------------------------------”);
………
Query query = session.createQuery(“ from Student s”);
query.setCacheable(true);
List students = query.list();
for(Iterator iter = students.iterate();iter.hasNext();){
Student stu = (Student)iter.next();
System.out.println(stu.getName());
}
第二不會(huì)發(fā)出sql，因?yàn)殚_啟了二級緩存和查詢緩存，查詢緩存緩存了實(shí)體對象的id列表，hibernate會(huì)根據(jù)實(shí)體對象的id列表到二級緩存中取得相應(yīng)的數(shù)據(jù)