Retrieving data from firebase

Question

I keep getting the stacktrace error below each time I implement

GenericTypeIndicator<List<String>> t = new GenericTypeIndicator<List<String>>() {
         };
         GenericTypeIndicator<List<String>> t2 = new GenericTypeIndicator<List<String>>() {};
         List<String>  namelist =  snapshot.child("Driver name").getValue(t);
         List<String> carlist =  snapshot.child("Drivers car").getValue(t2);
         if (namelist!=null & carlist!=null){


         for(int wee=0;wee<namelist.size();wee++){
             driver.add(new Driver(namelist.get(wee).toString(),carlist.get(wee).toString()));
         }

The data I sent to firebase is stored as:

"DriversList" : {
    "Driver name" : {
      "-Js6OJniEqVZAYSNhqbB" : "gvvb",
      "-Js7GjPMGNOLurrKk9rC" : "iggvv",
      "-Js7GlUlCwIoljJxpFbZ" : "iiggv",
      "-Js7GnBCRogiFUfn-ncZ" : "ihccvv",
      "-Js7GqGxH2vLYK5tsjjP" : "hhvv",
      "-Js7Gs80AoB5eeWci6jW" : "hhgc",
      "-Js7Gtm6AGh_QaTUK6fQ" : "ugghh",
      "-Js7GyomOIzjtVo3-PVg" : "tyygff",
      "-JsPxEhf4tx7O4v7JWMc" : "",
      "-JsQBoMqVBF4SzOHF3WA" : "rr",
      "-JsQC6TuGqHrBBkdalik" : "eed"
    },
    "Drivers availability" : {
      "-Js6OJozSuUvj5JnuNnW" : "No",
      "-Js7GjQ_5YgmnEYKWHrL" : "No",
      "-Js7GlVm7onoQd59Yyfq" : "No",
      "-Js7GnDPdjseoRVjgwSn" : "No",
      "-Js7GqIYy4VSEqu9qZfC" : "No",
      "-Js7Gs8VP5mp5bOR1pxR" : "No",
      "-Js7Gtmfv2M2p201k3Ra" : "No",
      "-Js7Gyvf8JkGwBlh8ZLu" : "No",
      "-JsPxEly9iGncA4VWvn2" : "No",
      "-JsQBoOE6AbGy1VMBSWp" : "No",
      "-JsQC6wGzBXBMz76IXue" : "No"
    },
    "Drivers car" : {
      "-Js6OJoyDlc4DR0IQhJr" : "gvgh",
      "-Js7GjQZ6Sb7AOooABt3" : "nbcgg",
      "-Js7GlVajAA1B5PeBnn2" : "nvvuuu",
      "-Js7GnDOCiWM874f6iL6" : "",
      "-Js7GqIYy4VSEqu9qZfB" : "nbcxx",
      "-Js7Gs8VP5mp5bOR1pxQ" : "hbccf",
      "-Js7Gtmfv2M2p201k3R_" : "hvccf",
      "-Js7Gyvf8JkGwBlh8ZLt" : "gghhhg",
      "-JsPxElx9XXm0kVLFstN" : "",
      "-JsQBoOE6AbGy1VMBSWo" : "dd",
      "-JsQC6wF0zgLApv8SwJO" : "ff"
    }

Error from stack trace:

06-30 14:35:44.918    2736-2736/com.kate.teme E/AndroidRuntime﹕ FATAL EXCEPTION: main
    com.firebase.client.FirebaseException: Failed to bounce to type
            at com.firebase.client.DataSnapshot.getValue(DataSnapshot.java:208)
            at com.kate.teme.AdminContent$2.onDataChange(AdminContent.java:105)
            at com.firebase.client.core.ValueEventRegistration.fireEvent(ValueEventRegistration.java:45)
            at com.firebase.client.core.view.DataEvent.fire(DataEvent.java:45)
            at com.firebase.client.core.view.EventRaiser$1.run(EventRaiser.java:38)
            at android.os.Handler.handleCallback(Handler.java:800)
            at android.os.Handler.dispatchMessage(Handler.java:100)
            at android.os.Looper.loop(Looper.java:194)
            at android.app.ActivityThread.main(ActivityThread.java:5371)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:525)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: com.shaded.fasterxml.jackson.databind.JsonMappingException: Can not deserialize instance of java.util.ArrayList out of START_OBJECT token
            at [Source: java.io.StringReader@42af1900; line: 1, column: 1]
            at com.shaded.fasterxml.jackson.databind.DeserializationContext.mappingException(DeserializationContext.java:575)
            at com.shaded.fasterxml.jackson.databind.DeserializationContext.mappingException(DeserializationContext.java:569)
            at com.shaded.fasterxml.jackson.databind.deser.std.StringCollectionDeserializer.handleNonArray(StringCollectionDeserializer.java:218)
            at com.shaded.fasterxml.jackson.databind.deser.std.StringCollectionDeserializer.deserialize(StringCollectionDeserializer.java:166)
            at com.shaded.fasterxml.jackson.databind.deser.std.StringCollectionDeserializer.deserialize(StringCollectionDeserializer.java:156)
            at com.shaded.fasterxml.jackson.databind.deser.std.StringCollectionDeserializer.deserialize(StringCollectionDeserializer.java:19)
            at com.shaded.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:2888)
            at com.shaded.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2041)
            at com.firebase.client.DataSnapshot.getValue(DataSnapshot.java:206)
            at com.kate.teme.AdminContent$2.onDataChange(AdminContent.java:105)
            at com.firebase.client.core.ValueEventRegistration.fireEvent(ValueEventRegistration.java:45)
            at com.firebase.client.core.view.DataEvent.fire(DataEvent.java:45)
            at com.firebase.client.core.view.EventRaiser$1.run(EventRaiser.java:38)
            at android.os.Handler.handleCallback(Handler.java:800)
            at android.os.Handler.dispatchMessage(Handler.java:100)
            at android.os.Looper.loop(Looper.java:194)
            at android.app.ActivityThread.main(ActivityThread.java:5371)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:525)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
            at dalvik.system.NativeStart.main(Native Method)

budaa huwezi appreciate msee akupa solution angalau ka-checkmark — Jack Siro
– Jack Siro, Commented Jul 28, 2017 at 7:51

Frank van Puffelen · Accepted Answer · 2015-07-02 03:52:38Z

8

Looking at your data structure:

"Driver name" : {
  "-Js6OJniEqVZAYSNhqbB" : "gvvb",
  "-Js7GjPMGNOLurrKk9rC" : "iggvv",
  "-Js7GlUlCwIoljJxpFbZ" : "iiggv",
  "-Js7GnBCRogiFUfn-ncZ" : "ihccvv",
  "-Js7GqGxH2vLYK5tsjjP" : "hhvv",
  "-Js7Gs80AoB5eeWci6jW" : "hhgc",
  "-Js7Gtm6AGh_QaTUK6fQ" : "ugghh",
  "-Js7GyomOIzjtVo3-PVg" : "tyygff",
  "-JsPxEhf4tx7O4v7JWMc" : "",
  "-JsQBoMqVBF4SzOHF3WA" : "rr",
  "-JsQC6TuGqHrBBkdalik" : "eed"
}

You try to deserialize this into a List<String>. But it actually is a Map<String,String>. So:

@Override
public void onDataChange(DataSnapshot snapshot) {
    GenericTypeIndicator<Map<String,String>> mapType = new GenericTypeIndicator<Map<String, String>>() { };
    Map<String,String>  namelist =  snapshot.child("Driver name").getValue(mapType);
    Map<String,String> carlist =  snapshot.child("Drivers car").getValue(mapType);
    if (namelist!=null & carlist!=null) {
        for (String name: namelist.values()) {
            System.out.println(name);
        }
    }
}

Note that I have no idea how you're trying to match up a driver and their car. I highly recommend that you reconsider this data structure before you continue to code.

One possible structure:

"DriversList": {
  "-Js6OJniEqVZAYSNhqbB" : {
    "name": "puf",
    "available": false,
    "car": "Toyota RAV4"
  },
  "-Js7GjPMGNOLurrKk9rC" : {
    "name": "manon",
    "available": false,
    "car": "Toyota Matrix"
  },
  ...
}

To read/write these, you'll need a Driver class:

public class Driver {
  String name;
  Boolean available;
  String car;

  public Driver() {}

  public String getName() { return name; }
  public Boolean getAvailable() { return available; }
  public String getCar() { return car; }
}

And then:

public void onDataChange(DataSnapshot snapshot) {
    GenericTypeIndicator<Map<String,Driver>> mapType = new GenericTypeIndicator<Map<String, Driver>>() { };
    Map<String,Driver> drivers = snapshot.getValue(mapType);
    if (drivers!=null) {
        for (Driver driver: drivers.values()) {
            System.out.println(driver.name);
        }
    }
}

edited Jul 2, 2015 at 3:52

answered Jun 30, 2015 at 17:57

Frank van Puffelen

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3 Comments

Irving Amukasa Anjere Over a year ago

and how do i deserialise that

Frank van Puffelen Over a year ago

I added a sample of that. Please take the time to also study this page firebase.com/docs/android/guide/saving-data.html, which we recently updated to be a better guide of how to deal with data structures such as this.

Irving Amukasa Anjere Over a year ago

thanks a lot i already had a driver class...but ive got it all sorted

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