我有一個(gè)Spring @Serviceclass（MileageFeeCalculator），它有一個(gè)@Autowiredfield（rateService），但該字段是null我嘗試使用它時(shí)。日志顯示正在創(chuàng)建MileageFeeCalculatorbean和MileageRateServicebean，但NullPointerException每當(dāng)我嘗試mileageCharge在我的服務(wù)bean上調(diào)用該方法時(shí)，我都會(huì)得到。為什么Spring沒(méi)有自動(dòng)裝配領(lǐng)域？控制器類：@Controllerpublic class MileageFeeController {        @RequestMapping("/mileage/{miles}")    @ResponseBody    public float mileageFee(@PathVariable int miles) {        MileageFeeCalculator calc = new MileageFeeCalculator();        return calc.mileageCharge(miles);    }}服務(wù)類：@Servicepublic class MileageFeeCalculator {    @Autowired    private MileageRateService rateService; // <--- should be autowired, is null    public float mileageCharge(final int miles) {        return (miles * rateService.ratePerMile()); // <--- throws NPE    }}應(yīng)該自動(dòng)裝配的服務(wù)bean，MileageFeeCalculator但它不是：@Servicepublic class MileageRateService {    public float ratePerMile() {        return 0.565f;    }}當(dāng)我嘗試時(shí)GET /mileage/3，我得到這個(gè)例外：java.lang.NullPointerException: null    at com.chrylis.example.spring_autowired_npe.MileageFeeCalculator.mileageCharge(MileageFeeCalculator.java:13)    at com.chrylis.example.spring_autowired_npe.MileageFeeController.mileageFee(MileageFeeController.java:14)    ...為什么我的Spring @Autowired字段為空？