java - 在 SpringBootApplication 类中使用服务会抛出 NullPointerException

Question

我对 SpringBoot 还很陌生。我创建了一个带有服务类的示例应用程序。

下面是我的SpringBootApplication类

@SpringBootApplication
public class SampleApplication {

    @Autowired
    static AWSService awsService;

    public static void main(String[] args) {

        SpringApplication.run(SampleApplication.class, args);
        awsService.getCertificate();  // Getting an NPE at this point

    }

}

AWSService 类

@Service
public class AWSService {

    public AWSService() {

    }

    private final Log log = new Log(getClass().getSimpleName());

    public void getCertificate() {
        String accessKey="";
        String secretKey="";
        try {
            Scanner awsCredentials = new Scanner(new File(Constants.AWS_CREDENTIALS));
            accessKey=awsCredentials.next();
            secretKey=awsCredentials.next();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
            log.error(e.getMessage());
        }
        BasicAWSCredentials basicAWSCredentials = new BasicAWSCredentials(accessKey,secretKey);
        AmazonS3 s3Client = AmazonS3ClientBuilder.standard().withCredentials(
                new AWSStaticCredentialsProvider(basicAWSCredentials)).build();
        S3Object s3object = s3Client.getObject(
                new GetObjectRequest(Constants.S3_BUCKET_NAME, Constants.S3_KEY_NAME));
        String temporaryCertificatePath = storeCertificate(s3object);
        Constants.setKeyStoreFile(temporaryCertificatePath);
    }

    private String storeCertificate(S3Object s3Object) {
        try {
            File certificate = File.createTempFile("signingKey",".p12");
            OutputStream outputStream = new FileOutputStream(certificate);
            byte buffer [] = IOUtils.toByteArray(s3Object.getObjectContent());
            outputStream.write(buffer);
            certificate.deleteOnExit();
            return certificate.getCanonicalPath();
        } catch (IOException e) {
            e.printStackTrace();
            log.error(e.getMessage());
        }
        return null;
    }
}

以下是我收到的错误

Exception in thread "main" java.lang.NullPointerException
2017-02-27 13:24:04.023 at in.juspay.SampleApplication.main(SampleApplication.java:18)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
 INFO   at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
798 at java.lang.reflect.Method.invoke(Method.java:498)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)

我在应用程序类中Autowired服务，但我收到了NullPointerException。如果我正确理解 Spring 的 @Service ，则 @Autowire 应该负责对象的初始化。那么为什么我会在那时获得 NPE 呢？

Answer 1

您无法 Autowiring 静态字段。使用应用程序上下文来访问它。

Can you use @Autowired with static fields?