使用gson解析json到java对象的问题 [英] Issue with parse json to java object using gson
问题描述
我想使用 google-gson 将json数据解析为java对象。
以下是我想分析的数据的一个例子：
{isBean：{userName：test，password：password112}}
IsBean.java
public interface IsBean extends Serializable，IsSerializable {
long getId（）;
$ b User.java
public class User实现IsBean，IsSerializable，Serializable {
String userName;
字符串密码;
public String getUserName（）{
return userName;
}
public void setUserName（String userName）{
this.userName = userName;
}
public String getPassword（）{
return password;
}
public void setPassword（String password）{
this.password = password;
}
@Override
public long getId（）{
return 0;
}
}
RequestObj.java
public class RequestObj实现IsBean，Serializable，IsSerializable {
IsBean isBean;
@Override
public long getId（）{
return 0;
}
public IsBean getIsBean（）{
return isBean;
}
public void setIsBean（IsBean isBean）{
this.isBean = isBean;
}
}
Test.java
public class Test {
public static void main（String [] args）{
Gson gson = new Gson（）;
User user = new User（）;
user.setPassword（password112）;
user.setUserName（test）;
RequestObj requestObj = new RequestObj（）;
requestObj.setIsBean（user）;
String jsonStr = gson.toJson（requestObj）;
System.out.println（jsonStr --->+ jsonStr）;
尝试{
RequestObj request = gson.fromJson（jsonStr，RequestObj.class）;
} catch（Exception e）{
e.printStackTrace（）;
错误：
$ / / strong>
java.lang.RuntimeException：无法为接口com.test.gson.shared调用无参数构造函数。 IsBean。用Gson注册一个InstanceCreator来解决这个问题。
at com.google.gson.internal.ConstructorConstructor $ 8.construct（ConstructorConstructor.java:167）
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory $ Adapter.read（ReflectiveTypeAdapterFactory.java:162 ）
在com.google.gson.internal.bind.ReflectiveTypeAdapterFactory $ 1.read（ReflectiveTypeAdapterFactory.java:93）
在com.google.gson.internal.bind.ReflectiveTypeAdapterFactory $ Adapter.read（ReflectiveTypeAdapterFactory。 java：172）
在com.google.gson.Gson.fromJson（Gson.java:795）
在com.google.gson.Gson.fromJson（Gson.java:761）
在com.google.gson.Gson.fromJson（Gson.java:710）
在com.google.gson.Gson.fromJson（Gson.java：682）
在com.test.gson.server .Test.main（Test.java:18）
导致：java.lang.reflect.InvocationTargetException $ b $在sun.reflect.NativeMethodAccessorImpl.invoke0（本地方法）$ b $在sun.reflect。 NativeMethodAccessorImpl.invoke（NativeMethodAccessorImpl.java:39）
at sun.reflect.De leggingMethodAccessorImpl.invoke（DelegatingMethodAccessorImpl.java:25）
at java.lang.reflect.Method.invoke（Method.java:597）
at com.google.gson.internal.UnsafeAllocator $ 1.newInstance（UnsafeAllocator .java：48）
at com.google.gson.internal.ConstructorConstructor $ 8.construct（ConstructorConstructor.java:164）
... 8 more
引起：java.lang.InstantiationException ：com.test.gson.shared.IsBean
at sun.misc.Unsafe.allocateInstance（Native Method）
... 14 more
解决方案没有看到 CommunicationObject 的代码，我不能说当然，我猜测这个类有一个类型为 IsBean 的字段，用它来保存 User >。如果是这样，问题在于GSON扫描类 CommunicationObject 的对象 obj 的字段，并根据字段定义，该字段的值（键入 IsBean ）必须被创建，因为该类型是一个接口，它不能为该字段的实例对象。 p>
换句话说，由于JSON字段没有指定对象类型，所以GSON必须依赖定义的字段类型来创建字段值的实例，这是无法完成的如果该类型是一个接口。
因此，如果对您有意义，请考虑更改该字段的类型。或着眼于创建 InstanceCreator IsBean （假设它在逻辑上是可能的）。
另请参阅：反序列化Gson中的抽象类
希望这有助于。
I want to parse json data into java object using google-gson.
Here is an example of the data I want to parse:
{"isBean":{"userName":"test","password":"password112"}}
IsBean.java
public interface IsBean extends Serializable,IsSerializable{
long getId();
}
User.java
public class User implements IsBean,IsSerializable,Serializable {
String userName;
String password;
public String getUserName() {
return userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
@Override
public long getId() {
return 0;
}
}
RequestObj.java
public class RequestObj implements IsBean, Serializable,IsSerializable{
IsBean isBean;
@Override
public long getId() {
return 0;
}
public IsBean getIsBean() {
return isBean;
}
public void setIsBean(IsBean isBean) {
this.isBean = isBean;
}
}
Test.java
public class Test {
public static void main(String[] args) {
Gson gson = new Gson();
User user=new User();
user.setPassword("password112");
user.setUserName("test");
RequestObj requestObj=new RequestObj();
requestObj.setIsBean(user);
String jsonStr=gson.toJson(requestObj);
System.out.println("jsonStr--->"+jsonStr);
try{
RequestObj request=gson.fromJson(jsonStr, RequestObj.class);
}catch (Exception e) {
e.printStackTrace();
}
}
}
Error:
java.lang.RuntimeException: Unable to invoke no-args constructor for interface com.test.gson.shared.IsBean. Register an InstanceCreator with Gson for this type may fix this problem.
at com.google.gson.internal.ConstructorConstructor$8.construct(ConstructorConstructor.java:167)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:162)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:93)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:172)
at com.google.gson.Gson.fromJson(Gson.java:795)
at com.google.gson.Gson.fromJson(Gson.java:761)
at com.google.gson.Gson.fromJson(Gson.java:710)
at com.google.gson.Gson.fromJson(Gson.java:682)
at com.test.gson.server.Test.main(Test.java:18)
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at com.google.gson.internal.UnsafeAllocator$1.newInstance(UnsafeAllocator.java:48)
at com.google.gson.internal.ConstructorConstructor$8.construct(ConstructorConstructor.java:164)
... 8 more
Caused by: java.lang.InstantiationException: com.test.gson.shared.IsBean
at sun.misc.Unsafe.allocateInstance(Native Method)
... 14 more
解决方案 Without seeing the code of CommunicationObject, I can't say for sure BUT I am guessing with confidence that the class has a field of type IsBean in which you use it to hold the User. If so, the problem is that GSON scans fields of the object obj of the class CommunicationObject and based on the field definition, the value of the field (which is typed IsBean) will have to be created BUT since the type is an interface, it can't instance object for that field.
Another words, as JSON field does not specifies the object type, GSON must relies on the defined type of the field to create the instance for the field value which can't be done if the type is an interface.
So, consider changing the type of that field if that make sense to you. OR look into creating InstanceCreator of IsBean (doute that it is logically possible).
See also: Deserializing an abstract class in Gson
Hope this helps.
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