同步静态方法如何在 Java 中工作，我可以使用它来加载 Hibernate 实体吗? [英] How do synchronized static methods work in Java and can I use it for loading Hibernate entities?

问题描述

如果我有一个带有静态方法的 util 类，它将调用 Hibernate 函数来完成基本的数据访问.我想知道使方法 synchronized 是否是确保线程安全的正确方法.

If I have a util class with static methods that will call Hibernate functions to accomplish basic data access. I am wondering if making the method synchronized is the right approach to ensure thread-safety.

我希望这样可以防止访问同一数据库实例的信息.但是，我现在确定以下代码是否会阻止在特定类调用 getObjectById 时为所有类调用它.

I want this to prevent access of info to the same DB instance. However, I'm now sure if the following code are preventing getObjectById being called for all Classes when it is called by a particular class.

public class Utils {
     public static synchronized Object getObjectById (Class objclass, Long id) {
           // call hibernate class
         Session session = new Configuration().configure().buildSessionFactory().openSession();
         Object obj = session.load(objclass, id);
         session.close();
         return obj;
     }

     // other static methods
}

推荐答案

通过在静态方法锁上使用同步，您将 同步类方法和属性(相对于实例方法和属性)

By using synchronized on a static method lock you will synchronize the class methods and attributes ( as opposed to instance methods and attributes )

所以你的假设是正确的.

So your assumption is correct.

我想知道使方法同步是否是确保线程安全的正确方法.

不是真的.您应该让您的 RDBMS 来完成这项工作.他们擅长这种东西.

Not really. You should let your RDBMS do that work instead. They are good at this kind of stuff.

通过同步对数据库的访问，你唯一会得到的就是让你的应用程序变得非常缓慢.此外，在您发布的代码中，您每次都在构建一个会话工厂，这样，您的应用程序将花费更多时间访问数据库而不是执行实际工作.

The only thing you will get by synchronizing the access to the database is to make your application terribly slow. Further more, in the code you posted you're building a Session Factory each time, that way, your application will spend more time accessing the DB than performing the actual job.

想象以下场景:

客户端 A 和 B 尝试将不同的信息插入表 T 的记录 X.

Client A and B attempt to insert different information into record X of table T.

使用您的方法，您唯一得到的是确保一个接一个地调用，而这无论如何都会在 DB 中发生，因为 RDBMS 将阻止它们插入来自 A 的一半信息和来自 B 的一半信息同时.结果将是相同的，但只会慢 5 倍(或更多).

With your approach the only thing you're getting is to make sure one is called after the other, when this would happen anyway in the DB, because the RDBMS will prevent them from inserting half information from A and half from B at the same time. The result will be the same but only 5 times ( or more ) slower.

可能最好看看 Hibernate 文档中的事务和并发" 一章.大多数情况下，您试图解决的问题已经得到解决，而且是一种更好的方法.

Probably it could be better to take a look at the "Transactions and Concurrency" chapter in the Hibernate documentation. Most of the times the problems you're trying to solve, have been solved already and a much better way.

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