如何从 JSON 中正确读取此泛型？
How do I read this Generics correctly from JSON?
我对我的第一个泛型容器有相当的信心，但仍然坚持如何在客户端表达转换。这就是我参与学习 <T> 东西之前的工作方式：
CommonNounContainer typeContainer = new Json().fromJson(CommonNounContainer.class, result);
我考虑过为每个 class 创建一个不同的容器，这似乎不是一个好的设计。下面是我在新的泛型容器中读取的更新的、无效的尝试：
JSONContainer<CommonNoun> typeContainer = new Json().fromJson(JSONContainer.class, result);
我的 IDE 不关心这个措辞，注意：
Type safety: The expression of type JSONContainer needs unchecked
conversion to conform to JSONContainer
执行时，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.handleHttpResponse(Communicator.java:95)
at com.badlogic.gdx.net.NetJavaImpl.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)
我确定我应该通过某种方式在等号右侧包含对 CommonNoun 类型的引用，但我一直无法弄清楚。我该怎么做？有很多适用的帖子涉及泛型、转换、JSON 和剥离 class 信息。我试图遵循的其中一个与上面的转换无关，认为在构造期间将 T class 作为私有变量添加到容器中：
How do I get a class instance of generic type T?
但我 运行 遇到了类似的语法问题，试图正确引用 class，只是在过程中的不同位置。我也怀疑我是否可以在告诉 JSON 如何 class 验证文件中的信息之前从 JSON 文件中读取这个 class 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.
我可能已经有了 deduper 提交的可行答案，但是，根据要求，这里有 CommonNounContainer 和 JSONContainer classes:
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();
}
}
额外 class 请求：
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;
}
TL;DR:
建议修复…
System.out.println( new Json( ).toJson( new JSONContainer<>( ... ) ) 看正确的字符串格式JSONContainer的JSON.- 确保 成为
result 的 输入参数]Json.fromJson(Class<T>, String) 与 1 中打印的格式相同。
- 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,form:69},children:[]}]}
长答案…
„My IDE doesn't care for this phrasing, noting:“
Type safety: The expression of type JSONContainer needs unchecked conversion to conform to JSONContainer
这是编译器关于 heap pollution 的警告。 IDE 仅仅翻译了这个编译器警告（这是你在命令行上看到的）…
...Communicator.java uses unchecked or unsafe operations.
...Recompile with -Xlint:unchecked for details.
…进入 user-friendly 消息 IDE 给你看。
这只是一个警告；不是错误。要使该警告消失，请将此更改：JSONContainer<CommonNoun> typeContainer = ... 为：JSONContainer typeContainer = ...
„When executed, my err log reads:“
result = {"myObject":{"cid":{"oid":129},"name":"technology","form":1},"children":[]}
com.badlogic.gdx.utils.SerializationException: Field not found: cid (java.lang.Object)...
该错误最可能的原因是 — 如错误消息所述 — 您的 JSONContainer class 或您的 CommonNoun class 没有 cid 字段 JSON 您要反序列化的字符串。
我能够用这个重现该错误...
...
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,person:Jaden,place:Hollywood,thing:HasBeen, cid:{oid:129} }}";
static public void main( String ... args ){
out.printf( "%1s%n", "foo");
JSONContainer< CommonNoun > wtf = new JSONContainer< > ( );
CommonNoun wtBrattyF = new CommonNoun( "Jaden Pinkett Smith", "Hollywood", "HasBeen" );
wtf.setJden( wtBrattyF );
out.printf( "%1s%n", wtf );
Json jden = new Json();
out.printf("%1s%n", jden.toJson( wtf ) );
JSONContainer wtReifiableF = jden.fromJson(JSONContainer.class, JADEN_AS_JSON); /* This is fine */
out.printf("%1s%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,place:Hollywood,thing:HasBeen}}
{jden:{class:CommonNoun,person:Jaden,place:Hollywood,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)
现在我已经通过实验证实了给定Cidclass…
的存在
public class Cid {
int oid;
/* ... getter and setter elided ... */
}
… 并且给定 CommonNoun class 的存在 有一个 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 result 反序列化 JSONContainer，将产生与您最初报告的完全相同的错误……
result = {"myObject":{"cid":{"oid":129},"name":"technology","form":1},"children":[]}
如果你的实际 CommonNoun class 像我上面的 stand-in 那样实现（带有 Cid 字段)，那么您需要使用 [= 重试 json.fromJson(Class<?>, String) 调用22=] 字符串格式如...
{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,form:69},children:[]}]}
我对我的第一个泛型容器有相当的信心，但仍然坚持如何在客户端表达转换。这就是我参与学习 <T> 东西之前的工作方式：
CommonNounContainer typeContainer = new Json().fromJson(CommonNounContainer.class, result);
我考虑过为每个 class 创建一个不同的容器，这似乎不是一个好的设计。下面是我在新的泛型容器中读取的更新的、无效的尝试：
JSONContainer<CommonNoun> typeContainer = new Json().fromJson(JSONContainer.class, result);
我的 IDE 不关心这个措辞，注意：
Type safety: The expression of type JSONContainer needs unchecked conversion to conform to JSONContainer
执行时，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.handleHttpResponse(Communicator.java:95)
at com.badlogic.gdx.net.NetJavaImpl.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)
我确定我应该通过某种方式在等号右侧包含对 CommonNoun 类型的引用，但我一直无法弄清楚。我该怎么做？有很多适用的帖子涉及泛型、转换、JSON 和剥离 class 信息。我试图遵循的其中一个与上面的转换无关，认为在构造期间将 T class 作为私有变量添加到容器中：
How do I get a class instance of generic type T?
但我 运行 遇到了类似的语法问题，试图正确引用 class，只是在过程中的不同位置。我也怀疑我是否可以在告诉 JSON 如何 class 验证文件中的信息之前从 JSON 文件中读取这个 class 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.
我可能已经有了 deduper 提交的可行答案，但是，根据要求，这里有 CommonNounContainer 和 JSONContainer classes:
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();
}
}
额外 class 请求：
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;
}
TL;DR:
建议修复…
System.out.println( new Json( ).toJson( new JSONContainer<>( ... ) )看正确的字符串格式JSONContainer的JSON.- 确保 成为
result的 输入参数]Json.fromJson(Class<T>, String)与1中打印的格式相同。- 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,form:69},children:[]}]}
- 例如
长答案…
„My IDE doesn't care for this phrasing, noting:“
Type safety: The expression of type JSONContainer needs unchecked conversion to conform to JSONContainer
这是编译器关于 heap pollution 的警告。 IDE 仅仅翻译了这个编译器警告（这是你在命令行上看到的）…
...Communicator.java uses unchecked or unsafe operations.
...Recompile with -Xlint:unchecked for details.
…进入 user-friendly 消息 IDE 给你看。
这只是一个警告；不是错误。要使该警告消失，请将此更改：JSONContainer<CommonNoun> typeContainer = ... 为：JSONContainer typeContainer = ...
„When executed, my err log reads:“
result = {"myObject":{"cid":{"oid":129},"name":"technology","form":1},"children":[]} com.badlogic.gdx.utils.SerializationException: Field not found: cid (java.lang.Object)...
该错误最可能的原因是 — 如错误消息所述 — 您的 JSONContainer class 或您的 CommonNoun class 没有 cid 字段 JSON 您要反序列化的字符串。
我能够用这个重现该错误...
...
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,person:Jaden,place:Hollywood,thing:HasBeen, cid:{oid:129} }}";
static public void main( String ... args ){
out.printf( "%1s%n", "foo");
JSONContainer< CommonNoun > wtf = new JSONContainer< > ( );
CommonNoun wtBrattyF = new CommonNoun( "Jaden Pinkett Smith", "Hollywood", "HasBeen" );
wtf.setJden( wtBrattyF );
out.printf( "%1s%n", wtf );
Json jden = new Json();
out.printf("%1s%n", jden.toJson( wtf ) );
JSONContainer wtReifiableF = jden.fromJson(JSONContainer.class, JADEN_AS_JSON); /* This is fine */
out.printf("%1s%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,place:Hollywood,thing:HasBeen}}
{jden:{class:CommonNoun,person:Jaden,place:Hollywood,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)
现在我已经通过实验证实了给定Cidclass…
public class Cid {
int oid;
/* ... getter and setter elided ... */
}
… 并且给定 CommonNoun class 的存在 有一个 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 result 反序列化 JSONContainer，将产生与您最初报告的完全相同的错误……
result = {"myObject":{"cid":{"oid":129},"name":"technology","form":1},"children":[]}
如果你的实际 CommonNoun class 像我上面的 stand-in 那样实现（带有 Cid 字段)，那么您需要使用 [= 重试 json.fromJson(Class<?>, String) 调用22=] 字符串格式如...
{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,form:69},children:[]}]}