以Hibernate中sessionFactory,Session举例
在Hibernate中sessionFactory是线程安全,在web应用中只要有一份实例就行,但是Session是每个线程都各自拥有一份实例,不然不同的线程持有同一个session对象进行CRUD,会引起数据操作混乱。因此为每一个线程都分配一个独自的Session实例,这里可以应用了ThreadLocal。下面进行简单模拟,说明ThreadLocal使用
//SessioinFactory类保存一个自定义的ThreadLocalSessionContext对象
package com.localthread;
public class SessionFactory {
public ThreadLocalSessionContext sc;
public SessionFactory(){
sc= new ThreadLocalSessionContext(this);
}
public Session currentSession(){
return sc.currentSession();
}
public Session createSession(){
return new Session();
}
}
package com.localthread;
import java.util.HashMap;
import java.util.Map;
//使用ThreadLocal来保存一个以SessionFactory-Session为key-value的Map。
public class ThreadLocalSessionContext {
private SessionFactory sessionFactory;
public ThreadLocalSessionContext(SessionFactory sessionFactory){this.sessionFactory=sessionFactory;}
public SessionFactory factory(){return sessionFactory;}
private static final ThreadLocal<Map> CONTEXT_TL=new ThreadLocal();//应用ThreadLocal,其中的Map的SessionFactory(key)-Session(value)
//获得当前线程的Session,没有则用SessioinFactory创建一个
public final Session currentSession(){
Session session=exsitSession(factory());
if(session==null){
session=factory().createSession();
bind(factory(),session);
}
return session;
}
public static Map sessionMap(){
return CONTEXT_TL.get();
}
public static Session exsitSession(SessionFactory factory){
Map sessionMap=sessionMap();
if(sessionMap==null)
return null;
return (Session) sessionMap.get(factory);
}
public static void bind(SessionFactory factory,Session session){
Map sessionMap=sessionMap();
if(sessionMap==null){
sessionMap=new HashMap();
CONTEXT_TL.set(sessionMap);
}
sessionMap.put(factory, session);
}
}
package com.localthread;
//打印sessionId
public class Session {
public int sessionId=0;
public void print(){
System.out.println(Thread.currentThread().getName()+":"+this+",sessionId:"+sessionId++);
}
}
//测试类
/***
启动三个线程共享一个SessionFactory,在每个线程的Run方法中获得每个线程各自对应的Session,测试输出如下图:
其中SessionId++按照预期运行。
**/
package com.localthread;
public class Main {
public static void main(String[] args) {
SessionFactory factory=new SessionFactory();
SessionThread s1=new SessionThread(factory);
SessionThread s2=new SessionThread(factory);
SessionThread s3=new SessionThread(factory);
s1.start();s2.start();s3.start();
}
}
class SessionThread extends Thread{
private int count=5;
private SessionFactory factory;
public SessionThread(SessionFactory factory){
this.factory=factory;
}
public void run(){
while(count>0){
factory.currentSession().print();
count--;
}
}
}
执行结果: