Instance variable in spring causing issues in multithreaded environment

Question

I have a spring bean Lets us say BeanA and scope is default injected via constructor.I have instance variable c which i am not using and its getting used in method1 and method2.Note that C is not injected.But in multithreaded environment I am facing issues because of variable C .As i unserstand default scope is singleton so this should work? The issues are like when diffrent users are trying to access the bean at same time They are getting stale instance of c Like example let user 1 instantiate c = hello .user 2 is seeing same hello.I want to understand how instance variable behave if not injected and used in diffrent methods?

class BeanA{
private A a,
private B b;
private C c;

public BeanA( A a, B b){

this.a=a;
this.b=b;
}

public method1(){
 c= //assignSomething
}

public method2(){
 c= //assignSomethingElse
}

}

What makes you think the bean being a Singleton would help? It sounds like you need to brush up on background knowledge. This question is not phrased in a way that can be answered more effectively then "it's doing exactly what it should, you need to figure out why that's not what you want" — Matt Whipple
– Matt Whipple, Commented Dec 3, 2014 at 3:58
Sounds like you need to add synchronized keyword for both methods. Otherwise race condition can happen. Singleton does not guarantee thread safety. — tonga
– tonga, Commented Dec 3, 2014 at 4:06

Panther · Accepted Answer · 2014-12-03 04:40:48Z

2

As you have only one instance of Bean A , all the users will be sharing same object. This will result in having only one variable C being used by all threads . So value of C is being shared between threads. This is the expected behavior.

It has nothing to with Spring injection. Its basic of java language itself. If you need different instance of BeanA,then you need to define its scope to request (in case of webapplicaton) or prototype as per your need.

It will be really helpful, if you state what you are trying to acheive.

answered Dec 3, 2014 at 4:40

Panther

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1 Comment

kiwiron Over a year ago

Be aware that setting the scope to prototype is only effective if you ask the Spring context to supply the bean. I've seen a lot of code where the author thought prototype bestowed some miraculous behavior that cured all their threading issues!

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