[英]Listener not working for firebase datareference in java
import com.google.auth.oauth2.GoogleCredentials;
import com.google.firebase.FirebaseApp;
import com.google.firebase.FirebaseOptions;
import com.google.firebase.database.*;
import com.google.gson.Gson;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.logging.Logger
/**
*
* @author adnan
*/
public class Json_Reader {
private final static Logger log
= Logger.getLogger(Logger.GLOBAL_LOGGER_NAME);
public static void intializeFirebase() throws FileNotFoundException, IOException {
FileInputStream serviceAccount =
new FileInputStream("/home/adnan/Downloads/cryleticstest-firebase-adminsdk-avbul-f5ea5a09ca.json");
FirebaseOptions options = new FirebaseOptions.Builder()
.setCredentials(GoogleCredentials.fromStream(serviceAccount))
.setDatabaseUrl("https://cryleticstest.firebaseio.com")
.build();
FirebaseApp.initializeApp(options);
final FirebaseDatabase database = FirebaseDatabase.getInstance();
System.out.println(FirebaseApp.getApps());
DatabaseReference ref = database.getReference();
ref.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
System.out.println(dataSnapshot.getChildrenCount());
Object object = dataSnapshot.getValue(Object.class);
String json = new Gson().toJson(object);
log.info(json);
}
@Override
public void onCancelled(DatabaseError error) {
log.info("error");
}
});
}
public static void main(String[] args) throws IOException {
intializeFirebase();
}
}
我正在尝试连接我的 firebase 数据库并从那里获取 JSON 结构。 但是我的 ref(reference variable) 中的 Listener 不起作用。 我猜该程序已连接到 Firebase 控制台,但由于侦听器无法正常工作,因此无法获取任何我认为的内容。 onDataChanged 或 onCancelled 方法均无效。
如果我没记错的话,Java 程序将退出而不等待数据加载。 您必须使用一些 Java 同步原语显式使其等待,例如:
final CountDownLatch sync = new CountDownLatch(1);
DatabaseReference ref = database.getReference();
ref.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
System.out.println(dataSnapshot.getChildrenCount());
Object object = dataSnapshot.getValue(Object.class);
String json = new Gson().toJson(object);
log.info(json);
sync.countDown();
}
@Override
public void onCancelled(DatabaseError error) {
log.info("error");
sync.countDown();
}
});
sync.await();
另见:
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.