1. Spring singleton mode is not thread-safe
In spring, singleton is the default scope. In the same container, all requests for the bean will return the same instance. Spring's singleton beans are not thread-safe, because they may have concurrency issues when accessed by multiple threads at the same time .
2. How to ensure the thread safety of Spring singleton beans?
(1) Change the scope of the Bean
By changing the scope of the Bean to the prototype , you can ensure that a new instance will be returned every time you get the Bean, thus avoiding the problem of sharing a Bean instance between multiple threads. The specific method is to use @scope("prototype") in the @Bean annotation on the Bean class to specify the scope of the Bean.
(2) Thread safety synchronization mechanism (locking)
For some beans that need to share state, a synchronization mechanism can be used to protect the shared state and prevent multiple threads from modifying the state of the same Bean instance at the same time. Generally speaking, keywords such as synchronized and Reentrantlock or lock objects are used to synchronize access to shared state code.
(3) Using ThreadLocal
If only a part of a certain Bean class needs to be synchronized, you can consider removing this part of the "state" information to Threadlocal at the Qingxiu level, so that each thread will have its own copy to avoid the problem of sharing state between multiple threads.
(4) Using concurrent collection classes
The Java Concurrency Package provides many thread-safe Concurrent classes, such as ConcurrentHashMap, CopyOnWriteArrayList, and so on. These classes implement various synchronization mechanisms internally to ensure correctness under multi-threading. Therefore, when dealing with shared beans in a multi-threaded environment, you can also use these thread-safe classes to replace ordinary collection classes, thereby avoiding concurrency problems that occur when multiple threads access the same Bean instance.