Firebase admin sdk java 实时数据库监听器

Question

我正在尝试在 Kotlin 中实现 firebase admin SDK。我想在实时数据库中有一个监听器来监听来自这个数据库的更新。
我的问题是当我运行 main 函数时，运行开始然后立即完成该过程，而无需在实时数据库中监听更新。
这是我的代码:

fun main() {
    val serviceAccount = FileInputStream("path/to/key.json")
    val options = FirebaseOptions.Builder()
        .setCredentials(GoogleCredentials.fromStream(serviceAccount))
        .setDatabaseUrl("URLDATABASE")
        .build()

    FirebaseApp.initializeApp(options)

    val ref = FirebaseDatabase
            .getInstance()
            .getReference("/waitingList")
    ref.addValueEventListener(object : ValueEventListener {
        override fun onDataChange(dataSnapshot: DataSnapshot) {
            print("TEST")
        }

        override fun onCancelled(databaseError: DatabaseError) {
            println("The read failed: " + databaseError.code)
        }
    })
}

Answer 1

你的程序什么时候停止？您可以:
1 -> 在一个新的协程中启动它:

fun main() {
    GlobalScope.launch { // launch a new coroutine in background and continue

        val serviceAccount = FileInputStream("path/to/key.json")
        val options = FirebaseOptions.Builder()
            .setCredentials(GoogleCredentials.fromStream(serviceAccount))
            .setDatabaseUrl("URLDATABASE")
            .build()

        FirebaseApp.initializeApp(options)

        val ref = FirebaseDatabase
                .getInstance()
                .getReference("/waitingList")
        ref.addValueEventListener(object : ValueEventListener {
            override fun onDataChange(dataSnapshot: DataSnapshot) {
                print("TEST")
            }

            override fun onCancelled(databaseError: DatabaseError) {
                println("The read failed: " + databaseError.code)
            }
        })
    }
}

2 ->在最后添加一段时间 sleep :

fun main() {

    val serviceAccount = FileInputStream("path/to/key.json")
    val options = FirebaseOptions.Builder()
        .setCredentials(GoogleCredentials.fromStream(serviceAccount))
        .setDatabaseUrl("URLDATABASE")
        .build()

    FirebaseApp.initializeApp(options)

    val ref = FirebaseDatabase
            .getInstance()
            .getReference("/waitingList")
    ref.addValueEventListener(object : ValueEventListener {
        override fun onDataChange(dataSnapshot: DataSnapshot) {
            print("TEST")
        }

        override fun onCancelled(databaseError: DatabaseError) {
            println("The read failed: " + databaseError.code)
        }
    })

    while (true) {
        Thread.sleep(2000L) // block main thread for 2 seconds to keep JVM alive
    }
}