在App Engine标准Java中初始化Firebase Admin

Question

I'm trying to use Firebase Auth in App engine standard Java to verify tokens from Android.

However, when I try to initialize Firebase admin, I get an Exception.

here is the exception:

java.lang.NoSuchMethodError: 
com.google.common.base.Preconditions.checkState
(ZLjava/lang/String;Ljava/lang/Object;)V
at com.google.firebase.FirebaseApp.checkNotDeleted (FirebaseApp.java:352)
at com.google.firebase.FirebaseApp.getOptions (FirebaseApp.java:267)
at com.google.firebase.FirebaseApp$TokenRefresher.<init> (FirebaseApp.java:434)
at com.google.firebase.FirebaseApp$TokenRefresher$Factory.create (FirebaseApp.java:535)
at com.google.firebase.FirebaseApp.<init> (FirebaseApp.java:113)
at com.google.firebase.FirebaseApp.initializeApp (FirebaseApp.java:201)
at com.google.firebase.FirebaseApp.initializeApp (FirebaseApp.java:188)
at com.google.firebase.FirebaseApp.initializeApp (FirebaseApp.java:175)

Most likely, because of conflict in Guava versions

here is my gradle:

dependencies {
    appengineSdk 'com.google.appengine:appengine-java-sdk:1.9.60'
    compile 'com.google.appengine.tools:appengine-gcs-client:0.7'
    compile ('com.google.firebase:firebase-admin:5.7.0') {
        exclude group: 'com.google.guava'
    }
    compile 'com.google.guava:guava:23.0'
    compile 'javax.servlet:servlet-api:2.5'
}

Here is the code:

InputStream in = filterConfig.getServletContext()
            .getResourceAsStream("/WEB-INF/PRIVATE_KEY_JSON.json");

FirebaseOptions options = null;
try {
     options = new FirebaseOptions.Builder()
            .setCredentials(GoogleCredentials.fromStream(in))
            .build();
} catch (IOException e) {
    e.printStackTrace();
}
FirebaseApp.initializeApp(options);

Answer 1

the solution is to add the jar file in the link

https://github.com/firebase/firebase-admin-java/pull/125

Answer 2

Since the question is related to initializing firebase admin SDK to app engine java environment, so there is a possibility that someone met with the exception:

java.lang.IllegalStateException: FirebaseApp with name [DEFAULT] already exist.

if all your dependencies are correct as described in above answers, then still you may get this exception.

Answer to the exception is "You must initialize firebase sdk only for once" or you need to provide unique app name during initializing.

Now where to put your initialization code that executes only for once so that before using firebase resource , sdk must be initialized.

Answer is using ServletContextListener docs

If you have custom logic that you want to run before any of your servlets is invoked:

Register a ServletContextListener in your web.xml file.

<listener>
  <listener-class>com.company.MyListener</listener-class>
</listener>

Supply a class alongside your servlet and filter code:

public class MyListener implements ServletContextListener {
  public void contextInitialized(ServletContextEvent event) {
    // This will be invoked as part of a warmup request, or
    // the first user request if no warmup request was invoked.
  }
  public void contextDestroyed(ServletContextEvent event) {
    // App Engine does not currently invoke this method.
  }
}

The ServletContextListener runs during a warmup request. If there is no warmup request, it runs upon the first request to a new instance. This might result in loading requests