【发布时间】：2016-03-26 03:45:21
【问题描述】：
原因：com.fasterxml.jackson.databind.JsonMappingException: Can not instantiate value of type [simple type, class net.we4x4.we4x4.userInformation] from String value;没有单字符串构造函数/工厂方法
这个错误让我很困惑，我尝试按照 firebase Docs 上提供的几条说明进行操作，例如：https://www.firebase.com/docs/android/guide/retrieving-data.html
还有一个关于查询数据的，这里还有另一个教程： https://www.simplifiedcoding.net/firebase-android-tutorial-writing-firebase-data/
我无法以适当的方式解决问题，我想做的只是从这个 JASON 获取数据：
{
"data" : {
"ratingPic" : 0,
"ratingVClip" : 36
},
"users" : {
"3c42f867-8c3a-423b-89e8-3fb777ab76f8" : {
"email" : "k@k.com",
"username" : "kkk"
},
"50347968-cedb-4648-8025-f737fea8d4c9" : {
"email" : "a@a.com",
"username" : "aaa"
}
}
}
通过 childEventListner 的 singleValueEventListner，我仍然是同样的错误，我创建了一个单独的粗略来处理从 firebase 中提取信息：
public class userInformation {
private String email;
private String username;
public userInformation(){
}
public userInformation(String username){
this.username = username;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
}
这是令人困惑的部分，正如 firebase 社区上的好 ppl 所建议的那样，我不需要 setter，但是当我不在此类中放置 setter 时，我得到了错误，我只是避免得到这个类的构造错误，它只提取一个字符串，当我添加更多字符串时，我仍然得到错误，所以当我添加时：
public userInformation(String username, String email){
this.username = username;
this.email = email;
}
我得到了错误，在下面的堆栈跟踪中？
我的主要方法是：
public void readingData() {
Firebase ref = new Firebase("https://wi4x4.firebaseio.com/users/" + UserID);
ref.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot postSnapshot: dataSnapshot.getChildren()){
userInformation userInformation = postSnapshot.getValue(userInformation.class);
String username = userInformation.getUsername();
String email = userInformation.getEmail();
usernameDisplay.setText(email);
}
}
@Override
public void onCancelled(FirebaseError firebaseError) {
firebaseError.getMessage();
}
});
}
*** addChildEventListner 产生同样的错误；
public void readingData(){
Firebase ref = new Firebase("https://wi4x4.firebaseio.com/users/" + UserID);
Query queryRef = ref.orderByChild("email");
queryRef.addChildEventListener(new ChildEventListener() {
@Override
public void onChildAdded(DataSnapshot dataSnapshot, String email) {
// Map<String, Objects> extractedEmail = (Map<String, Objects>) dataSnapshot.getValue();
userInformation userInformation = dataSnapshot.getValue(userInformation.class);
email = userInformation.getEmail();
usernameDisplay.setText(email);
}
@Override
public void onChildChanged(DataSnapshot dataSnapshot, String previousChild) {
}
@Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
}
@Override
public void onChildMoved(DataSnapshot dataSnapshot, String previousChild) {
}
@Override
public void onCancelled(FirebaseError firebaseError) {
Toast.makeText(getApplicationContext(),
"The read failed: " + firebaseError.getMessage(),
Toast.LENGTH_LONG).show();
}
});
}
我为这篇冗长的帖子道歉，但我试图提供尽可能多的信息，以便帮助理解这里的混乱。
03-26 07:30:42.654 8560-8560/net.we4x4.we4x4 E/AndroidRuntime: FATAL EXCEPTION: main
Process: net.we4x4.we4x4, PID: 8560
com.firebase.client.FirebaseException: Failed to bounce to type
at com.firebase.client.DataSnapshot.getValue(DataSnapshot.java:183)
at net.we4x4.we4x4.MainActivity$2.onDataChange(MainActivity.java:112)
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$1.run(EventRaiser.java:38)
at android.os.Handler.handleCallback(Handler.java:733)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5584)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1268)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1084)
at dalvik.system.NativeStart.main(Native Method)
Caused by: com.fasterxml.jackson.databind.JsonMappingException: Can not instantiate value of type [simple type, class net.we4x4.we4x4.userInformation] from String value; no single-String constructor/factory method
at com.fasterxml.jackson.databind.deser.std.StdValueInstantiator._createFromStringFallbacks(StdValueInstantiator.java:428)
at com.fasterxml.jackson.databind.deser.std.StdValueInstantiator.createFromString(StdValueInstantiator.java:299)
at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromString(BeanDeserializerBase.java:1056)
at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeOther(BeanDeserializer.java:136)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:123)
at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:2888)
at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2034)
at com.firebase.client.DataSnapshot.getValue(DataSnapshot.java:181)
at net.we4x4.we4x4.MainActivity$2.onDataChange(MainActivity.java:112)
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$1.run(EventRaiser.java:38)
at android.os.Handler.handleCallback(Handler.java:733)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5584)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1268)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1084)
at dalvik.system.NativeStart.main(Native Method)
【问题讨论】：
标签： android firebase firebase-realtime-database