用java（非android）的Firebase检索信息 [英] Firebase with java (non-android) retrieve information

问题描述

我一直在尝试使用java代码（非android）来获取我的firebase数据库的数据。我用同样的方法，我在android应用程序中检索。但是它没有获取数据。

  Firebase firebase = new Firebase（https：//------.firebaseIO。 COM）; 
 firebase.addValueEventListener（new ValueEventListener（）{
 @Override $ b $ public void onDataChange（DataSnapshot ds）{
 long i = ds.child（Users）。getChildrenCount（） ; 
 userlist = new String [（int）i]; 
 int j = 0; 
 for（DataSnapshot each_ds：ds.getChildren（））{
 userlist [j] = （）; 
 System.out.println（userlist [j]）; 
 j ++; 
} 
} 
 $ b @Override 
 public void onCancelled（FirebaseError fe）{
 throw new UnsupportedOperationException（Not supported yet。）; //要更改生成方法的主体，请选择工具|模板。
} 
}）; 
  

解决方案

Firebase客户端连接到服务器单独的线程，并开始在那里收听数据。当没有更多的代码要执行时，程序的主线程将继续并退出，这通常发生在Firebase获取其第一个数据（可能需要几秒钟）之前。

<所以你必须等待数据回来。对于测试程序，我通常通过在程序的最后插入一个简单的 Thread.sleep（）来完成这个工作：

 的Thread.sleep（20000）; 
  

但是在真正的程序中，您可能想要找出更好的退出条件。例如，在这里我们使用一个 CountDownLatch 来让主代码等待，直到操作完成：

  final CountDownLatch sync = new CountDownLatch（1）; 
 ref.push（）。setValue（new value）
 .addOnCompleteListener（new OnCompleteListener< Void>（）{
 public void onComplete（Task< Void> task）{
 sync.countDown（）; 
} 
}）; 
 sync.await（）; 
  

在Android中不要使用这种方法，因为它会阻塞主/ UI线程并保持应用程序无响应。

I have been trying to get my data for firebase database using java code(non-android). I used same method how I retrieved in android app. But its not getting data.

    Firebase firebase = new Firebase("https://------.firebaseIO.com");
    firebase.addValueEventListener(new ValueEventListener(){
        @Override
        public void onDataChange(DataSnapshot ds) {
            long i = ds.child("Users").getChildrenCount();
            userlist = new String[(int)i];
            int j = 0;
            for( DataSnapshot each_ds : ds.getChildren() ){
                userlist[j] = each_ds.child("username").getValue().toString();
                System.out.println(userlist[j]);
                j++;
            }
        }

        @Override
        public void onCancelled(FirebaseError fe) {
            throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
        }
    });

解决方案

The Firebase client makes its connection to the server in a separate thread and starts listening for data there. The main thread of your program continues and exits when there is no more code to execute, which often happens before Firebase gets its first data back (which may take a few seconds).

So you'll have to wait for the data to come back. For test programs I usually do this by inserting a simple Thread.sleep() at the end of my program:

Thread.sleep(20000);

But in a real program you'd probably want to figure out a better exit condition. For example, here we use a CountDownLatch to make the main code wait until the operation is completed:

final CountDownLatch sync = new CountDownLatch(1);
ref.push().setValue("new value")
   .addOnCompleteListener(new OnCompleteListener<Void>() {
      public void onComplete(Task<Void> task) {
        sync.countDown();
      }
    });
sync.await();

Don't use this approach in Android by the way, as it will block the main/UI thread and leave the app unresponsive.

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