【发布时间】：2020-12-07 06:00:07
【问题描述】：
我对我的第一个泛型容器相当有信心，但坚持在客户端如何措辞转换。这是我参与学习 <T> 之前的工作：
CommonNounContainer typeContainer = new Json().fromJson(CommonNounContainer.class, result);
我一直在考虑必须为每个类创建不同的容器，这似乎不是一个好的设计。以下是我在新的泛型容器中读取的更新但无效的尝试：
JSONContainer<CommonNoun> typeContainer = new Json().fromJson(JSONContainer.class, result);
我的 IDE 不关心这种措辞，注意：
类型安全：JSONContainer 类型的表达式需要取消选中 转换为符合 JSONContainer
执行时，我的错误日志显示：
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)
我确定有某种方法可以在等号右侧包含对 CommonNoun 类型的引用，但我无法弄清楚。我该怎么做？有很多关于泛型、强制转换、JSON 和剥离类信息的适用帖子。其中一个我试图遵循的不是关于在构造期间将 T 类作为私有变量添加到容器中的转换：
How do I get a class instance of generic type T?
但我在尝试正确引用类时遇到了类似的语法问题，只是在过程中的不同位置。我也有疑问，在告诉 JSON 如何对文件中的信息进行分类之前，我是否可以从 JSON 文件中读取此类变量。
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 deduper 提交的可行答案，但是，根据要求，这里是 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();
}
}
请求的其他课程：
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;
}
【问题讨论】：
-
由于有多个 JSON 库，最好指定您正在使用的那个。从日志看来
com.badlogic.gdx。 -
是的，就是这样。导入 com.badlogic.gdx.utils.Json;
-
我将适用的 javadoc 添加到问题的底部，以防万一。
-
可以分享
CommonNounContainer和JSONContainer的课程吗？ -
感谢分享
CommonNounContainer和JSONContainer。我能够逐字重现您的原始错误。根本原因是：原始result字符串的格式不被该 JSON 库的阅读器接受。我已经确定，只有当输入字符串采用该库的非常特定（非标准）格式时，它才能成功解析输入字符串。附言查看您的CommonNoun和Cid类如何实现的详细信息也会很有用。我用my answer 中的替身 对他们进行了疯狂的猜测。 TIA。