如何解决如何从JSON正确读取此泛型？
我对我的第一个泛型容器有一定的信心，但对如何在客户端上进行强制转换表示怀疑。这是我参与学习<T>知识之前的工作方式：
CommonNounContainer typeContainer = new Json().fromJson(CommonNounContainer.class,result);
我当时正在考虑必须为每个类创建一个不同的容器，这似乎不是一个好的设计。以下是我更新后的无法正常工作的尝试，以读取我的新泛型容器：
JSONContainer<CommonNoun> typeContainer = new Json().fromJson(JSONContainer.class,result);
我的IDE对此短语不满意，请注意：
类型安全：无需检查JSONContainer类型的表达式 转换以符合JSONContainer
执行后，我的错误日志显示为：
result = {"myObject":{"cid":{"oid":129},"name":"technology","form":1},"children":[]}
com.badlogic.gdx.utils.SerializationException: Field not found: cid (java.lang.Object)
Serialization trace:
{}.myObject.cid
myObject (semanticWeb.rep.concept.JSONContainer)
at com.badlogic.gdx.utils.Json.readFields(Json.java:854)
at com.badlogic.gdx.utils.Json.readValue(Json.java:1011)
at com.badlogic.gdx.utils.Json.readFields(Json.java:863)
at com.badlogic.gdx.utils.Json.readValue(Json.java:1011)
at com.badlogic.gdx.utils.Json.fromJson(Json.java:789)
at com.b2tclient.net.Communicator$2.handleHttpResponse(Communicator.java:95)
at com.badlogic.gdx.net.NetJavaImpl$2.run(NetJavaImpl.java:224)
at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at java.base/java.lang.Thread.run(Thread.java:830)
我确定应该以某种方式在等号右边添加对CommonNoun类型的引用，但我还无法弄清楚。我该怎么做？关于泛型，转换，JSON和剥离类信息，有很多适用的文章。我尝试遵循的其中之一与上面的强制转换无关，认为在构造过程中将T类添加为容器内的私有变量：
How do I get a class instance of generic type T?
但是我遇到了类似的语法问题，试图在过程中的另一个位置正确地引用该类。我也有疑问，我可以在告诉JSON如何对文件中的信息进行分类之前从JSON文件读取此类变量。
Javadoc for the fromJson(Class<T>,String) method：
Type Parameters:
<T>
Parameters:
type May be null if the type is unknown.
json
Returns:
May be null.
我可能已经有一个由重复数据删除器提交的可行答案，但是根据要求，这是CommonNounContainer和JSONContainer类：
import java.util.ArrayList;
public class CommonNounContainer {
private CommonNoun myCommonNoun;
private ArrayList<CommonNounContainer> children;
public CommonNounContainer(CommonNoun concept) {
myCommonNoun = concept;
children = new ArrayList<CommonNounContainer>();
}
//Creates an empty shell. This would be for categories you want to group by,but not display/select in the select box.
public CommonNounContainer() {
children = new ArrayList<CommonNounContainer>();
}
public void addChildren(ArrayList<CommonNounContainer> newChildren) {
children.addAll(newChildren);
}
public void addChild(CommonNoun concept) {
children.add(new CommonNounContainer(concept));
}
public ArrayList<CommonNounContainer> getChildren() {
return children;
}
public CommonNoun getValue() {
return myCommonNoun;
}
public boolean hasChildren() {
if (children.size() > 0) return true;
else return false;
}
public String toString() {
return myCommonNoun.toString();
}
}
public class JSONContainer<T> {
private T myObject;
private ArrayList<JSONContainer<T>> children;
// public Class<T> typeParameterClass;
public JSONContainer() {
}
public JSONContainer(T anObject) {
myObject = anObject;
children = new ArrayList<JSONContainer<T>>();
}
/* public JSONContainer(T anObject,Class<T> typeParameterClass) {
myObject = anObject;
children = new ArrayList<JSONContainer<T>>();
this.typeParameterClass = typeParameterClass;
}
*/
public void addChildren(ArrayList<JSONContainer<T>> newChildren) {
children.addAll(newChildren);
}
public void addChild(T concept) {
children.add(new JSONContainer<T>(concept));
}
public ArrayList<JSONContainer<T>> getChildren() {
return children;
}
public T getValue() {
return myObject;
}
public boolean hasChildren() {
if (children.size() > 0) return true;
else return false;
}
public String toString() {
return myObject.toString();
}
}
要求的其他课程：
public class CommonNoun extends Concept {
/**
*
*/
private static final long serialVersionUID = 6444629581712454049L;
public CommonNoun() {
super();
}
public CommonNoun(String name,ConceptID cidIn) {
super(name,cidIn);
this.form = ConceptDefs.COMMON_NOUN;
}
}
public class Concept implements Serializable {
/**
*
*/
private static final long serialVersionUID = 2561549161503772431L;
private ConceptID cid = null;
private final String name;
Integer form = 0;
// ArrayList<ProperRelationship> myRelationships = null;
/* @Deprecated
public Concept(String name) {
this.name = name;
}*/
public Concept() {
name = "";
}
public Concept(String name,ConceptID cidIn) {
// this(name);
this.name = name;
cid = cidIn;
}
/*
* This should be over-ridden by any subclasses
*/
public Integer getForm() {
return form;
}
public ConceptID getID() {
return cid;
}
public void setID(ConceptID cidIn) {
cid = cidIn;
}
//this doesn't make any sense. Throw exception?
public String getName() {
return name;
}
public boolean isCommon() {
return true;
}
/**
*
* @return
*/
@Override
public String toString() {
return getName() + "(" + cid.toString() + ")";
}
public boolean equals(Concept other) {
return ((getID().equals(other.getID())));
}
}
public class ConceptID implements Serializable {
long oid;
public ConceptID() {
oid = -1;
}
public ConceptID(long oid) {
this.oid = oid;
}
public long getValue() {
return oid;
}
/**
*
* @return
*/
@Override
public String toString() {
return Long.toString(oid);
}
public Long toLong() {
return Long.valueOf(oid);
}
public boolean equals(ConceptID other) {
return (oid == other.getValue());
}
/**
* Factory model for generating ConceptIDs
*
* This one is here as a convenience as many IDs come in as a String from web POSTs
* @param idAsString
* @return
*/
static public ConceptID parseIntoID(String idAsString) {
ConceptID returnID = null;
try {
returnID = new ConceptID( Long.parseLong(idAsString) );
} catch (Exception e) {
System.err.println("Expected the string," + idAsString + ",to be Long parsable.");
e.printStackTrace();
}
return returnID;
}
解决方法
TL; DR ：
建议的修复方法...
-
System.out.println( new Json( ).toJson( new JSONContainer<>( ... ) )查看JSONContainer的 正确 字符串格式sJSON。 - 将
result的Json.fromJson(Class<T>,String)输入参数设为 确定 在1中打印的相同格式。- 例如
{myObject:{class:CommonNoun,cid:{oid:139},name:Jada Pinkett Smith,form:69},children:[{myObject:{class:CommonNoun,cid:{oid:666},name:Jaden Pinkett Smith,form:-666},children:[]},{myObject:{class:CommonNoun,cid:{oid:69},name:Willow Pinkett Smith,children:[]}]}
- 例如
详细答案 ...
„ 我的IDE对此短语不满意，请注意：“
Type safety: The expression of type JSONContainer needs unchecked conversion to conform to JSONContainer
这是编译器警告您有关heap pollution的信息。 IDE只是翻译了此编译器警告（这是您在命令行上看到的）…
...Communicator.java uses unchecked or unsafe operations.
...Recompile with -Xlint:unchecked for details.
…进入IDE向您显示的更多用户友好消息。
这只是警告；没有错误。要使该警告消失，请将以下内容： JSONContainer<CommonNoun> typeContainer = ... 更改为以下内容： JSONContainer typeContainer = ...
„ 执行后，我的错误日志显示为：“
result = {"myObject":{"cid":{"oid":129},"name":"technology","form":1},"children":[]} com.badlogic.gdx.utils.SerializationException: Field not found: cid (java.lang.Object)...
最可能导致该错误的原因是-如错误消息所述-您的 JSONContainer 类或您的 CommonNoun 类没有要尝试反序列化的 cid 字符串中的 JSON 字段。
我能够以此重现该错误……
...
private static final String JADEN_AS_JSON = "{jden:{class:CommonNoun,person:Jaden,place:Hollywood,thing:HashBeen}}";
private static final String JADEN_FAILS_AS_ACTOR = "{jden:{class:CommonNoun,thing:HasBeen,cid:{oid:129} }}";
static public void main( String ... args ){
out.printf( "%1$22s%n","foo");
JSONContainer< CommonNoun > wtf = new JSONContainer< > ( );
CommonNoun wtBrattyF = new CommonNoun( "Jaden Pinkett Smith","Hollywood","HasBeen" );
wtf.setJden( wtBrattyF );
out.printf( "%1$42s%n",wtf );
Json jden = new Json();
out.printf("%1$59s%n",jden.toJson( wtf ) );
JSONContainer wtReifiableF = jden.fromJson(JSONContainer.class,JADEN_AS_JSON); /* This is fine */
out.printf("%1$59s%n",jden.toJson( wtReifiableF ) );
JSONContainer/*< CommonNoun >*/ wtUnReifiableF = jden.fromJson( JSONContainer.class,JADEN_AS_JSON );
wtUnReifiableF = jden.fromJson( JSONContainer.class,JADEN_FAILS_AS_ACTOR ); /* This causes the error you reported */
}
...
早期成功；但后来失败了...
JSONContainer [ jden: CommonNoun [ person: Jaden Pinkett Smith,place: Hollywood,thing: HasBeen ] ]
{jden:{class:CommonNoun,person:Jaden Pinkett Smith,thing:HasBeen}}
{jden:{class:CommonNoun,thing:HashBeen}}
Exception in thread "main" com.badlogic.gdx.utils.SerializationException: Field not found: cid (CommonNoun)
Serialization trace:
{}.jden.cid
jden (JSONContainer)
at com.badlogic.gdx.utils.Json.readFields(Json.java:893)
at com.badlogic.gdx.utils.Json.readValue(Json.java:1074)
at com.badlogic.gdx.utils.Json.readFields(Json.java:902)
at com.badlogic.gdx.utils.Json.readValue(Json.java:1074)
at com.badlogic.gdx.utils.Json.fromJson(Json.java:829)
at DeduperAnswer.main(DeduperAnswer.java:33)
我现在通过实验确认，给定存在 Cid 类……
public class Cid {
int oid;
/* ... getter and setter elided ... */
}
...并且鉴于存在 CommonNoun 类，该类 HAS A Cid ...
public class CommonNoun {
Cid cid;
String name;
int form;
/* ... getters and setters elided ... */
}
…然后尝试从具有以下值的 JSONContainer 中反序列化 result ，将产生与您最初报告的完全相同的错误…
result = {"myObject":{"cid":{"oid":129},"children":[]}
如果您的实际 CommonNoun 类是像我的 stand-in 上面那样实现的（带有Cid字段 ），那么您需要使用格式如下的 json.fromJson(Class<?>,String) 字符串重试 result 呼叫
{myObject:{class:CommonNoun,children:[]}]}
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