Why do I get a \'Failed to bounce to type\' error when converting Firebase JSON to Java objects?

Why do you encounter "Failed to bounce to type" when converting JSON from Firebase to Java objects?

Firebase uses Jackson to facilitate the serialization of Java objects into JSON and their deserialization back into Java objects. This tutorial explores various approaches to using Jackson with Firebase.

Loading Complete Users

To load users from Firebase into Android, one can create a Java class mirroring the JSON structure:

private static class User {
  String handle;
  String name;
  long stackId;

  // getters and toString methods
}

This class can be used with a listener:

Firebase ref = new Firebase("https://stackoverflow.firebaseio.com/32108969/users");

ref.addListenerForSingleValueEvent(new ValueEventListener() {
  @Override
  public void onDataChange(DataSnapshot usersSnapshot) {
    for (DataSnapshot userSnapshot : usersSnapshot.getChildren()) {
      User user = userSnapshot.getValue(User.class);
      System.out.println(user.toString());
    }
  }

  @Override
  public void onCancelled(FirebaseError firebaseError) { }
});

Partially Loading Users

If only specific user properties are of interest, one can omit the unwanted properties from the Java class. However, this may result in a "failed to debounce type" exception due to Jackson's inability to recognize the omitted property.

To resolve this, the @JsonIgnoreProperties annotation can be used to instruct Jackson to ignore specific properties:

@JsonIgnoreProperties({ "stackId" })
private static class User {
  String handle;
  String name;
}

Alternatively, @JsonIgnoreProperties(ignoreUnknown=true) can be used to ignore all unknown properties.

Partially Saving Users

Convenience methods can be added to Java classes to enhance their functionality. For example, a method to get the user's display name can be added:

private static class User {
  String handle;
  String name;

  @JsonIgnore
  public String getDisplayName() {
    return getName() + " (" + getHandle() + ")";
  }
}

When saving users to Firebase, the @JsonIgnore annotation should be applied to the getDisplayName() method to prevent its inclusion in the JSON output.

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