ThreadLocal浅析
try {
// 通过默认配置文件hibernate.cfg.xml创建SessionFactory
sessionFactory = new Configuration().configure().buildSessionFactory();
} catch (Throwable ex) {
log.error("初始化SessionFactory失败！", ex);
throw new ExceptionInInitializerError(ex);
}
}
//创建线程局部变量session，用来保存Hibernate的Session
public static final ThreadLocal session = new ThreadLocal();
* 获取当前线程中的Session
* @return Session
* @throws HibernateException
*/
public static Session currentSession() throws HibernateException {
Session s = (Session) session.get();
// 如果Session还没有打开，则新开一个Session
if (s == null) {
s = sessionFactory.openSession();
session.set(s); //将新开的Session保存到线程局部变量中
}
return s;
}
//获取线程局部变量，并强制转换为Session类型
Session s = (Session) session.get();
session.set(null);
if (s != null)
s.close();
}
}
package threadlocal;
public class Student {
private int age = 0; //年龄
public int getAge() {
return this.age;
}
public void setAge(int age) {
this.age = age;
}
}
package threadlocal;
import java.util.Random;
public class ThreadLocalDemo implements Runnable {
//创建线程局部变量studentLocal，在后面你会发现用来保存Student对象
private final static ThreadLocal studentLocal = new ThreadLocal();
public static void main(String[] agrs) {
ThreadLocalDemo td = new ThreadLocalDemo();
Thread t1 = new Thread(td, "a");
Thread t2 = new Thread(td, "b");
t1.start();
t2.start();
}
public void run() {
accessStudent();
}
/**
* 示例业务方法，用来测试
*/
public void accessStudent() {
//获取当前线程的名字
String currentThreadName = Thread.currentThread().getName();
System.out.println(currentThreadName + " is running!");
//产生一个随机数并打印
Random random = new Random();
int age = random.nextInt(100);
System.out.println("thread " + currentThreadName + " set age to:" + age);
//获取一个Student对象，并将随机数年龄插入到对象属性中,
//此时是a线程第一次调用Threadlocal的get方法，get返回null，实例化一个student并且将a线程放进threadlocal。
//当b线程到来是，与a线程相同的历程
getStudent().setAge(age);
//当a线程执行，此处调用getStudent方法，返回a线程的副本（student）
//当b线程执行，返回b线程的副本
System.out.println("thread " + currentThreadName + " first read age is:" + getStudent().getAge());
try {
Thread.sleep(1000);
}
catch (InterruptedException ex) {
ex.printStackTrace();
}
System.out.println("thread " + currentThreadName + " second read age is:" + getStudent().getAge());
}
protected Student getStudent() {
//获取本地线程变量并强制转换为Student类型
Student student = (Student) studentLocal.get();
//线程首次执行此方法的时候，studentLocal.get()肯定为null
if (student == null) {
System.out.println("--------");
//创建一个Student对象，并保存到本地线程变量studentLocal中
student = new Student();
studentLocal.set(student);
}
return student;
}
}
注释写的可能不是很明白，如果有疑问可以留言进行交流。
运行结果
a is running!
b is running!
thread a set age to:99
thread b set age to:56
--------
--------
thread b first read age is:56
thread a first read age is:99
thread b second read age is:56
thread a second read age is:99