可能会抛出“NullPointerException”； “上下文”在这里可以为空

Question

So I have an issue with SonarQube that I can not solve.

if (result instanceof AsyncResult) {
    // Make sure handle async has been called
    context.handleAsync();
    Result newResult = context.controllerReturned();
    if (newResult != null) {
        result = newResult;
    }
 }

Answer 1

SonarQube claims that context may be null here. If you know this is incorrect, you could just suppress this warning as a false positive. Otherwise, you should explicitly check if context is not null :

if (result instanceof AsyncResult && context != null) {
    // Here -------------------------^

    // Make sure handle async has been called
    context.handleAsync();
    Result newResult = context.controllerReturned();
    if (newResult != null) {
        result = newResult;
    }
}

Answer 2

Your problem is probably here:

context.handleAsync();

What Sonar says is (given the context [...]) that somewhere in your code, your doing a null check on context but not in this part:

if (null == context) {
  // bla bla bla
}
...
context.handleAsync(); // yes, but context was tested for null, so it can be null.

Either recheck the context when using it, either remove the null check or fail at the beginning of your method:

if (null == context) {
  throw new IllegalStateException("context is null");
}

Or better:

  void yourMethod(Context context) {
    Objects.requireNonNull(context, "context");
    ... 
  }

The requireNonNull method is called as a precondition; its only purpose is to check for nulls and provide (if you don't omit) a default message.

Answer 3

Try this:

if (result instanceof AsyncResult) {
        if (context == null) {
            //appropriate error handling
        } else {
            // Make sure handle async has been called
            context.handleAsync();
            Result newResult = context.controllerReturned();
            if (newResult != null) {
                result = newResult;
            }
        }
}

Alternatively you could ensure that when context is initialised it can never get value null . You could also look into the @NotNull annotation from JSR303 if context is a method parameter.