Spring Boot can find resource file, but Java class fails with NullPointerException

Question

I am working on a project where in one class I need to load json file src/main/resources.

src/ 
   main/java/FirebaseTokenVerifier
   main/resources/staging_firebase.json

The class ForebaseTokenVerifier loads this JSON file in constructor as

@Component
public class FirebaseTokenVerifier implements TokenVerifier {

  private FirebaseAuth firebaseAuth;

  // TODO (hhimanshu): resourceFile and DatabaseURL are hardcoded, this should be picked by external file
  // or should be picked up conditionally based on environment
  public FirebaseTokenVerifier() throws IOException, URISyntaxException {
    final String resourceName = "staging_firebase.json";
    System.out.println("Getting Resource: " + resourceName);
    Path path = Paths.get(ClassLoader.getSystemClassLoader().getResource(resourceName).toURI());

    FileInputStream serviceAccount = new FileInputStream(path.toFile());
    FirebaseOptions options = new FirebaseOptions.Builder()
        .setCredential(FirebaseCredentials.fromCertificate(serviceAccount))
        .setDatabaseUrl("https://staging-myapp.firebaseio.com")
        .build();

    FirebaseApp defaultApp = FirebaseApp.initializeApp(options);
    firebaseAuth = FirebaseAuth.getInstance(defaultApp);

  }
 /// more things here .....
}

When I run mvn spring-boot:run, I see that the json file is loaded correctly as

2017-07-26 15:57:33.611  INFO 49104 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2017-07-26 15:57:33.611  INFO 49104 --- [ost-startStop-1] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 1424 ms
Getting Resource: staging_firebase.json
2017-07-26 15:57:33.799  INFO 49104 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'characterEncodingFilter' to: [/*]

and everything works fine. I then, try to do the following

 mvn clean package; java -jar target/myapp-core-0.0.1-SNAPSHOT.jar  

But this fails on runtime

at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:189) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireConstructor(AbstractAutowireCapableBeanFactory.java:1193) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1095) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:513) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:483) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:208) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1138) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1066) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:835) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:741) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    ... 35 common frames omitted
    Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'firebaseTokenVerifier' defined in URL [jar:file:/Users/Harit.Himanshu/bl/sources/idea/myapp-core/targ
    et/myapp-core-0.0.1-SNAPSHOT.jar!/BOOT-INF/classes!/com/myapp/api/auth/FirebaseTokenVerifier.class]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationEx
    ception: Failed to instantiate [com.myapp.api.auth.FirebaseTokenVerifier]: Constructor threw exception; nested exception is java.lang.NullPointerException
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1155) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1099) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:513) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:483) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:208) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1138) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1066) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:835) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:741) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    ... 49 common frames omitted
    Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.myapp.api.auth.FirebaseTokenVerifier]: Constructor threw exception; nested exception is java.lang.NullPointe
    rException
    at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:154) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:89) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1147) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    ... 61 common frames omitted
    Caused by: java.lang.NullPointerException: null
    at com.myapp.api.auth.FirebaseTokenVerifier.<init>(FirebaseTokenVerifier.java:31) ~[classes!/:0.0.1-SNAPSHOT]
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:1.8.0_131]
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) ~[na:1.8.0_131]
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[na:1.8.0_131]
    at java.lang.reflect.Constructor.newInstance(Constructor.java:423) ~[na:1.8.0_131]
    at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:142) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    ... 63 common frames omitted

It fails on L31 which is

Path path = Paths.get(ClassLoader.getSystemClassLoader().getResource(resourceName).toURI());  

I also confirm that the json file is present in the jar file as

✗ jar -tvf target/myapp-core-0.0.1-SNAPSHOT.jar| grep json
  2355 Wed Jul 26 16:00:44 NZST 2017 BOOT-INF/classes/staging_firebase.json
 64952 Tue Jan 07 19:29:24 NZDT 2014 BOOT-INF/lib/json-20140107.jar

What is going wrong here? and how come Spring-Boot is able to resolve this path correctly?

UPDATE
After looking at https://stackoverflow.com/a/36372773/379235, I changed my code to look like

FileInputStream serviceAccount = new FileInputStream(new ClassPathResource(resourceName).getFile());  

and it fails now saying

Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'firebaseTokenVerifier' defined in URL [jar:file:/Users/Harit.Himanshu/bl/sources/idea/myapp-core/target/myapp-core-0.0.1-SNAPSHOT.jar!/BOOT-INF/classes!/com/myapp/api/auth/FirebaseTokenVerifier.class]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationEx
    ception: Failed to instantiate [com.myapp.api.auth.FirebaseTokenVerifier]: Constructor threw exception; nested exception is java.io.FileNotFoundException: class path resource [staging_firebase.json] cannot be resolved to absolute file path because it does not reside in the file system: jar:file:/Users/Harit.Himanshu/bl/sources/idea/myapp-core/target/myapp-core-0.0.1-SNAPSHOT.jar!/BOO
    T-INF/classes!/staging_firebase.json
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1155) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1099) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:513) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:483) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:208) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1138) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1066) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:835) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:741) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    ... 49 common frames omitted
    Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.myapp.api.auth.FirebaseTokenVerifier]: Constructor threw exception; nested exception is java.io.FileNotFoundException: class path resource [staging_firebase.json] cannot be resolved to absolute file path because it does not reside in the file system: jar:file:/Users/Harit.Himanshu/bl/sources/idea/penn
    ytrak-core/target/myapp-core-0.0.1-SNAPSHOT.jar!/BOOT-INF/classes!/staging_firebase.json
    at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:154) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:89) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1147) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    ... 61 common frames omitted
    Caused by: java.io.FileNotFoundException: class path resource [staging_firebase.json] cannot be resolved to absolute file path because it does not reside in the file system: jar:file:/Users/Harit.Himanshu/bl/sources/idea/myapp-core/target/myapp-core-0.0.1-SNAPSHOT.jar!/BOOT-INF/classes!/staging_firebase.json
    at org.springframework.util.ResourceUtils.getFile(ResourceUtils.java:215) ~[spring-core-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at org.springframework.core.io.AbstractFileResolvingResource.getFile(AbstractFileResolvingResource.java:52) ~[spring-core-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    at com.myapp.api.auth.FirebaseTokenVerifier.<init>(FirebaseTokenVerifier.java:34) ~[classes!/:0.0.1-SNAPSHOT]
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:1.8.0_131]
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) ~[na:1.8.0_131]
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[na:1.8.0_131]
    at java.lang.reflect.Constructor.newInstance(Constructor.java:423) ~[na:1.8.0_131]
    at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:142) ~[spring-beans-4.3.8.RELEASE.jar!/:4.3.8.RELEASE]
    ... 63 common frames omitted

Even though I can see that in the jar file

✗ jar -tvf target/myapp-core-0.0.1-SNAPSHOT.jar| grep json
  2355 Wed Jul 26 16:54:02 NZST 2017 BOOT-INF/classes/staging_firebase.json
 64952 Tue Jan 07 19:29:24 NZDT 2014 BOOT-INF/lib/json-20140107.jar

Answer 1

cannot be resolved to absolute file path because it does not reside in the file system

This is pretty explicit. You're trying to access it as file, when it is NOT a file but a resource embedded in the JAR.

Research ClassLoader#getResourceAsStream().