使用springboot，和mongo的repository，我定義了一個Comparator類，想實現自己的對象的比較方法。代碼如下： package com.story.utils; import java.util.Comparator; import javax.annotation.Resource; import org.springframework.stereotype.Service; import com.story.model.Phase; import com.story.model.Story; import com.story.repository.StoryRepository; @Service public class PhaseComparator implements Comparator<Phase>{ private String field; private Story story; @Autowired private StoryRepository storyRepository; public PhaseComparator() { super(); } public PhaseComparator (String field) { this.field = field; } @Override public int compare(Phase phase_1, Phase phase_2) { if (this.field.equals("createdDate")) { return phase_1.getCreatedDate() < phase_2.getCreatedDate() ? -1 : 1; } else { Story foundStory_1 = this.storyRepository.findOne(phase_1.getStoryId()); Story foundStory_2 = this.storyRepository.findOne(phase_1.getStoryId()); return foundStory_1.getLastUpdatedDate() < foundStory_2.getLastUpdatedDate() ? -1 : 1; } } } 但是，這樣的話，storyRepository就是null。請問應該如何處理呢？謝謝