Howe can I work around with singleton and component import?

[Tommy Chang]

I'm writing some tool class which should be a singleton. However, the functionality of the class requires dependencies on some service interfaces, i.e. PullRequestService. I'm facing the dilemma about how can I make it both singleton and correctly import those services.

When I was reading some documents from Java Bean, I realized that the Inject annotation can also be applied to a public setter. I tried writing something employing the setter, but it's no use. Any ideas?

public class ConflictStrategy extends AbstractMergeStrategy implements IMergeStrategy {

    static public final IMergeStrategy instance = new ConflictStrategy();

    @ComponentImport
    private PullRequestService pullRequestService; // this is null in runtime

    private ConflictStrategy() {}

    @Inject
    public void setComponents(PullRequestService pullRequestService) {
        this.pullRequestService = pullRequestService;
    }

    public MergeCheckResponse inspect(MergeCheckRequest request) {
        PullRequest pullRequest = request.getPullRequest();
        if (pullRequestCanMerge(pullRequest).isConflicted()) {
            return buildResponse(false, "Pull request conflicts");
        } else {
            return buildResponse(true, "No merge conflicts");
        }
    }

    private PullRequestMergeability pullRequestCanMerge(PullRequest pullRequest) {
        final long pullRequestID = pullRequest.getId();
        final int repoID = pullRequest.getFromRef().getRepository().getId();
        return this.pullRequestService.canMerge(repoID,pullRequestID);
    }

}