Sonar: Instance methods should not write to "static" fields

Question

I am getting this prompt from Sonar: Instance methods should not write to "static" fields

I'm not quite sure what I need to change to fix this issue.

Does "SemaMonitorProxy.applicationContext" have to equal a static method?

public class SemaMonitorProxy implements ApplicationContextAware {

    private static ApplicationContext applicationContext = null;

    public void registerFailedLoginAttempt(HttpServletRequest request, HttpServletResponse response) {
        final SemaMonitor semaMonitor = applicationContext.getBean(SemaMonitor.class);
        semaMonitor.registerFailedLoginAttempt(request, response);
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        SemaMonitorProxy.applicationContext = applicationContext;
    }
}

Im not a Sonar specialist, but what I can imagine is that it might be dangerous to write to a static field in parallel. Just try add a synchronize block on SemaMonitorProxy.class and see if the warning goes away. — loonytune, Nov 28 '17 at 10:34
The problem is you are setting the value of static field through a non-static field. Can you make the `setApplicationContext` method as `synchrozied`? I believe that should be enough to fix this. — utkarsh31, Nov 28 '17 at 10:42
There is a proper solution in [another question](https://stackoverflow.com/questions/21136302/findbugs-error-write-to-static-field-from-instance-method/21136731). — Mick Belker - Pseudonym, Aug 31 '18 at 07:12

gil.fernandes · Accepted Answer · 2017-11-28T12:46:21.857

2

In fact this method:

@Override
public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
    SemaMonitorProxy.applicationContext = applicationContext;
}

is an instance method writing to a static field:

private static ApplicationContext applicationContext

You cannot make the above method static. So the only solution would be to remove the static keyword from the applicationContext declaration.

private ApplicationContext applicationContext

edited Nov 28 '17 at 12:46

answered Nov 28 '17 at 11:26

gil.fernandes

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I can't set setApplicationContext to static because then it wont be able to override ApplicationContextAware, which isn't an interface I can't change since it's part of the spring framework. – Kevin M Nov 28 '17 at 12:41
@KevinM: absolutely right. I suggest to make the applicationContext non static. It is typically a singleton anyway which exists once in memory. I have updated the answer. – gil.fernandes Nov 28 '17 at 12:47

score 0 · Answer 2 · answered Sep 23 '22 at 06:47

Rule java:S2696

Correctly updating a static field from a non-static method is tricky to get right and could easily lead to bugs if there are multiple class instances and/or multiple threads in play. Ideally, static fields are only updated from synchronized static methods.

Check this answer from @G. Ann - SonarSource Team

Sonar: Instance methods should not write to "static" fields

2 Answers2