在SpringBootApplication类中使用服务的java抛出NullPointerException
我对SpringBoot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课程
@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
}
}
AWS服务类
@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;
}
}
下面是我得到的错误
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)
我的应用程序类中有Autowired
服务,但是我得到了一个NullPointerException
。如果我正确理解Spring的@Service
,那么@Autowire
应该负责对象的初始化。那么,为什么我在那一点上得到了NPE
# 1 楼答案
不能自动关联静态字段。使用应用程序上下文来访问它
Can you use @Autowired with static fields?
# 2 楼答案
非常基本的一点是,静态字段甚至在创建bean之前就获得了优先级。 这就是为什么可以使用static关键字来访问实例
也请参阅Getting java.lang.NullPointerException when calling Method.invoke