使用GSON解析JSON时使用Enums [英] Using Enums while parsing JSON with GSON

问题描述

这与我在前面提到的前一个问题有关

我试图解析相同的JSON，但现在我已经改变了我的类

  {
lower：20，
upper：40，
delimiter：，
scope：[$ {title}] 
} 
  

我的课目前看起来像：

  public class TruncateElement {
 
私人int较低; 
 private int upper; 
私人字符串分隔符; 
私人列表< AttributeScope>范围; 
 $ b // getters and setters 
 
 
 $ b public enum AttributeScope {
 
 TITLE（$ {title} ），
描述（$ {description}），
 
 private String scope; 
 
 AttributeScope（字符串范围）{
 this.scope = scope; 
} 
 
 public String getScope（）{
 return this.scope; 
 
 
 code $ 
 
 
 
这段代码抛出一个异常，
  com.google.gson.JsonParseException：如果给定类型com.amazon.seo，JsonDeserializer EnumTypeAdapter无法反序列化json对象$ {title} .attribute.template.parse.data.AttributeScope 
 at 
  
这个例外是可以理解的，因为根据我之前提到的问题的解决方案，GSON期望Enum对象实际上被创建为 
 
 
  $ {title}（ $ {title}），
 $ {description}（$ {description}）; 
  
但是由于这在语法上是不可能的，所以推荐的解决方案是什么？ $ b 
解决方案
 From  Gson的文档： 
 
 
 
 
 Gson提供默认序列化并为Enums反序列化...如果您希望更改默认表示形式，您可以通过GsonBuilder.registerTypeAdapter（Type，Object）注册类型适配器来完成。
 
 
以下是一种这样的方法。 
 
 
  import java.io.FileReader; 
 import java.lang.reflect.Type; 
 import java.util.List; 
 
 import com.google.gson.Gson; 
 import com.google.gson.GsonBuilder; 
 import com.google.gson.JsonDeserializationContext; 
 import com.google.gson.JsonDeserializer; 
 import com.google.gson.JsonElement; 
 import com.google.gson.JsonParseException; 
 
 public class GsonFoo 
 {
 public static void main（String [] args）throws Exception 
 {
 GsonBuilder gsonBuilder = new GsonBuilder（）; 
 gsonBuilder.registerTypeAdapter（AttributeScope.class，new AttributeScopeDeserializer（））; 
 Gson gson = gsonBuilder.create（）; 
 
 TruncateElement element = gson.fromJson（new FileReader（input.json），TruncateElement.class）; 
 
 System.out.println（element.lower）; 
 System.out.println（element.upper）; 
 System.out.println（element.delimiter）; 
 System.out.println（element.scope.get（0））; 
} 
} 
 
类AttributeScopeDeserializer实现了JsonDeserializer< AttributeScope> 
 {
 @Override 
 public AttributeScope反序列化（JsonElement json，类型typeOfT，JsonDeserializationContext上下文）
抛出JsonParseException 
 {
 AttributeScope [] scopes = AttributeScope。值（）; 
 for（AttributeScope scope：scopes）
 {
 if（scope.scope.equals（json.getAsString（）））
 return scope; 
} 
返回null; 
} 
} 
 
 class TruncateElement 
 {
 int lower; 
 int上; 
字符串分隔符; 
列表< AttributeScope>范围; 
 
 
 enum AttributeScope 
 {
 TITLE（$ {title}），DESCRIPTION（$ {description}）; 
 
字符串范围; 
 
 AttributeScope（字符串范围）
 {
 this.scope = scope; 
} 
} 
  
 
This is related to a previous question that I asked here earlier

JSON parsing using Gson

I am trying to parse the same JSON, but now I have changed my classes a little bit.
{
    "lower": 20,
    "upper": 40,
    "delimiter": " ",
    "scope": ["${title}"]
}
My class now looks like:
public class TruncateElement {

   private int lower;
   private int upper;
   private String delimiter;
   private List<AttributeScope> scope;

   // getters and setters
}


public enum AttributeScope {

    TITLE("${title}"),
    DESCRIPTION("${description}"),

    private String scope;

    AttributeScope(String scope) {
        this.scope = scope;
    }

    public String getScope() {
        return this.scope;
    }
}
This code throws an exception, 
com.google.gson.JsonParseException: The JsonDeserializer EnumTypeAdapter failed to deserialized json object "${title}" given the type class com.amazon.seo.attribute.template.parse.data.AttributeScope
at 
The exception is understandable, because as per the solution to my previous question, GSON is expecting the Enum objects to be actually be created as  
${title}("${title}"),
${description}("${description}");
But since this is syntactically impossible, what are the recommended solutions, workarounds?
解决方案
From the documentation for Gson:

  
Gson provides default serialization and deserialization for Enums... If you would prefer to change the default representation, you can do so by registering a type adapter through GsonBuilder.registerTypeAdapter(Type, Object).
Following is one such approach.
import java.io.FileReader;
import java.lang.reflect.Type;
import java.util.List;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonParseException;

public class GsonFoo
{
  public static void main(String[] args) throws Exception
  {
    GsonBuilder gsonBuilder = new GsonBuilder();
    gsonBuilder.registerTypeAdapter(AttributeScope.class, new AttributeScopeDeserializer());
    Gson gson = gsonBuilder.create();

    TruncateElement element = gson.fromJson(new FileReader("input.json"), TruncateElement.class);

    System.out.println(element.lower);
    System.out.println(element.upper);
    System.out.println(element.delimiter);
    System.out.println(element.scope.get(0));
  }
}

class AttributeScopeDeserializer implements JsonDeserializer<AttributeScope>
{
  @Override
  public AttributeScope deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context)
      throws JsonParseException
  {
    AttributeScope[] scopes = AttributeScope.values();
    for (AttributeScope scope : scopes)
    {
      if (scope.scope.equals(json.getAsString()))
        return scope;
    }
    return null;
  }
}

class TruncateElement
{
  int lower;
  int upper;
  String delimiter;
  List<AttributeScope> scope;
}

enum AttributeScope
{
  TITLE("${title}"), DESCRIPTION("${description}");

  String scope;

  AttributeScope(String scope)
  {
    this.scope = scope;
  }
}


                        
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