Question

我的json中有整数，我不希望gson将它们转换成双打。以下不起作用：

@Test
public void keepsIntsAsIs(){
    String json="[{\"id\":1,\"quantity\":2,\"name\":\"apple\"},{\"id\":3,\"quantity\":4,\"name\":\"orange\"}]";
    GsonBuilder gsonBuilder = new GsonBuilder();
    gsonBuilder.registerTypeAdapter(Double.class,  new DoubleSerializerAsInt());
    Gson gson = gsonBuilder.create();
    List<Map<String, Object>> l = gson.fromJson(json, List.class);
    for(Map<String, Object> item : l){
        System.out.println(item);
    }
}

private static class DoubleSerializerAsInt implements JsonSerializer<Double>{

    @Override
    public JsonElement serialize(Double aDouble, Type type, JsonSerializationContext jsonSerializationContext) {
        int value = (int)Math.round(aDouble);
        return new JsonPrimitive(value);
    }
}

输出不是我想要的：

{id=1.0, quantity=2.0, name=apple}
{id=3.0, quantity=4.0, name=orange}

在地图中有没有办法让整数而不是双打？

{id=1, quantity=2, name=apple}
{id=3, quantity=4, name=orange}

修改：并非所有字段都是整数。我相应地修改了我的例子。我在网上看了很多例子，包括这个网站上的一些答案，但在这个特殊情况下它不起作用。

Answer 1

1）您必须在问题中创建自定义JsonDeserializer而不是JsonSerializer。

2）我不认为这种行为来自Double反序列化程序。它更像是json对象/地图问题

此处来自source code：

case NUMBER:
      return in.nextDouble();

因此，您可以尝试使用Map<String, Object>的自定义反序列化器（如果需要，可以使用更通用的地图）：

public static class MapDeserializerDoubleAsIntFix implements JsonDeserializer<Map<String, Object>>{

    @Override  @SuppressWarnings("unchecked")
    public Map<String, Object> deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
        return (Map<String, Object>) read(json);
    }

    public Object read(JsonElement in) {

        if(in.isJsonArray()){
            List<Object> list = new ArrayList<Object>();
            JsonArray arr = in.getAsJsonArray();
            for (JsonElement anArr : arr) {
                list.add(read(anArr));
            }
            return list;
        }else if(in.isJsonObject()){
            Map<String, Object> map = new LinkedTreeMap<String, Object>();
            JsonObject obj = in.getAsJsonObject();
            Set<Map.Entry<String, JsonElement>> entitySet = obj.entrySet();
            for(Map.Entry<String, JsonElement> entry: entitySet){
                map.put(entry.getKey(), read(entry.getValue()));
            }
            return map;
        }else if( in.isJsonPrimitive()){
            JsonPrimitive prim = in.getAsJsonPrimitive();
            if(prim.isBoolean()){
                return prim.getAsBoolean();
            }else if(prim.isString()){
                return prim.getAsString();
            }else if(prim.isNumber()){
                Number num = prim.getAsNumber();
                // here you can handle double int/long values
                // and return any type you want
                // this solution will transform 3.0 float to long values
                if(Math.ceil(num.doubleValue())  == num.longValue())
                   return num.longValue();
                else{
                    return num.doubleValue();
                }
            }
        }
        return null;
    }
}

要使用它，您必须正确TypeToken到registerTypeAdapter和gson.fromJson功能：

String json="[{\"id\":1,\"quantity\":2,\"name\":\"apple\"}, {\"id\":3,\"quantity\":4,\"name\":\"orange\"}]";

GsonBuilder gsonBuilder = new GsonBuilder();

gsonBuilder.registerTypeAdapter(new TypeToken<Map <String, Object>>(){}.getType(),  new MapDeserializerDoubleAsIntFix());

Gson gson = gsonBuilder.create();
List<Map<String, Object>> l = gson.fromJson(json, new TypeToken<List<Map<String, Object>>>(){}.getType() );

for(Map<String, Object> item : l)
    System.out.println(item);

String serialized = gson.toJson(l);
System.out.println(serialized);

<强>结果：

{id=1, quantity=2, name=apple}
{id=3, quantity=4, name=orange}
Serialized back to: [{"id":1,"quantity":2,"name":"apple"},{"id":3,"quantity":4,"name":"orange"}]

PS：这是你可以尝试的另一种选择。就个人而言，我觉得为你的json而不是List<Map<String, Integer>>创建自定义对象更酷，更容易阅读

Answer 2

@ varren的流媒体版本答案：

class CustomizedObjectTypeAdapter extends TypeAdapter<Object> {

    private final TypeAdapter<Object> delegate = new Gson().getAdapter(Object.class);

    @Override
    public void write(JsonWriter out, Object value) throws IOException {
        delegate.write(out, value);
    }

    @Override
    public Object read(JsonReader in) throws IOException {
        JsonToken token = in.peek();
        switch (token) {
            case BEGIN_ARRAY:
                List<Object> list = new ArrayList<Object>();
                in.beginArray();
                while (in.hasNext()) {
                    list.add(read(in));
                }
                in.endArray();
                return list;

            case BEGIN_OBJECT:
                Map<String, Object> map = new LinkedTreeMap<String, Object>();
                in.beginObject();
                while (in.hasNext()) {
                    map.put(in.nextName(), read(in));
                }
                in.endObject();
                return map;

            case STRING:
                return in.nextString();

            case NUMBER:
                //return in.nextDouble();
                String n = in.nextString();
                if (n.indexOf('.') != -1) {
                    return Double.parseDouble(n);
                }
                return Long.parseLong(n);

            case BOOLEAN:
                return in.nextBoolean();

            case NULL:
                in.nextNull();
                return null;

            default:
                throw new IllegalStateException();
        }
    }
}

它是ObjectTypeAdapter.java的修改版本。这些原始行：

case NUMBER:
    return in.nextDouble();

被替换为：

case NUMBER:
    String n = in.nextString();
    if (n.indexOf('.') != -1) {
        return Double.parseDouble(n);
    }
    return Long.parseLong(n);

在此代码中，数字被读作字符串，数字的类型是根据点的存在选择的：数字只有在其字符串表示中有一个点时为双，否则为长。此解决方案保留源JSON的原始值。

如果您可以将其注册为Object类型但Gson阻止它，则可以将此修改后的适配器用作通用：

// built-in type adapters that cannot be overridden
factories.add(TypeAdapters.JSON_ELEMENT_FACTORY);
factories.add(ObjectTypeAdapter.FACTORY);

您必须将此类型适配器注册到您需要的类型，例如Map和List：

CustomizedObjectTypeAdapter adapter = new CustomizedObjectTypeAdapter();
Gson gson = new GsonBuilder()
        .registerTypeAdapter(Map.class, adapter)
        .registerTypeAdapter(List.class, adapter)
        .create();

现在Gson可以将数字反序列化。

Answer 3

您必须使用public T fromJson(JsonElement json, Type typeOfT)

public void keepsIntsAsIs(){
        String json="[{\"id\":1,\"quantity\":2},{\"id\":3,\"quantity\":4}]";
        GsonBuilder gsonBuilder = new GsonBuilder();
        Gson gson = gsonBuilder.create();
        Type objectListType = new TypeToken<List<Map<String, Integer>>>(){}.getType();
        List<Map<String, Integer>> l = gson.fromJson(json, objectListType);
        for(Map<String, Integer> item : l){
            System.out.println(item);
        }
    }

输出：

{id=1, quantity=2}
{id=3, quantity=4}

[编辑]

如果不是所有字段都是整数，那么解决此问题的一种方法是将json映射到对象并为该对象定义反序列化器。

以下是示例。

我将json映射到IdQuantityName，而IdQuantityDeserializer是json反序列化器。

package com.foo;



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.JsonObject;
import com.google.gson.JsonParseException;
import com.google.gson.JsonPrimitive;
import com.google.gson.JsonSerializationContext;
import com.google.gson.JsonSerializer;
import com.google.gson.reflect.TypeToken;

public class TestGSON {

public void keepsIntsAsIs(){
    String json="[{\"id\":1,\"quantity\":2,\"name\":\"apple\"},{\"id\":3,\"quantity\":4,\"name\":\"orange\"}]";
    GsonBuilder gsonBuilder = new GsonBuilder();
    gsonBuilder.registerTypeHierarchyAdapter(IdQuantityName.class, new IdQuantityDeserializer());
    gsonBuilder.registerTypeAdapter(IdQuantityName.class, new IdQuantityDeserializer());

    Gson gson = gsonBuilder.create();
    Type objectListType = new TypeToken<List<IdQuantityName>>(){}.getType();
    List<IdQuantityName> l = gson.fromJson(json,objectListType);
    for (IdQuantityName idQuantityName : l) {
        System.out.println(idQuantityName);
    }
}



class IdQuantityName{
    private int id;
    private Object quantity;
    private String name;

    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public Object getQuantity() {
        return quantity;
    }
    public void setQuantity(Object quantity) {
        this.quantity = quantity;
    }
    public Object getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    @Override
    public String toString() {
        return "IdQuantityName [id=" + id + ", quantity=" + quantity
                + ", name=" + name + "]";
    }



}
private  class IdQuantityDeserializer implements JsonDeserializer<IdQuantityName>{

    @Override
    public IdQuantityName deserialize(JsonElement json, Type typeOfT,
            JsonDeserializationContext context) throws JsonParseException {

        JsonObject jo = json.getAsJsonObject();

        IdQuantityName idq = new IdQuantityName();
        idq.setId(jo.get("id").getAsInt());
        idq.setName(jo.get("name").getAsString());

        JsonElement jsonElement = jo.get("quantity");
        if(jsonElement instanceof JsonPrimitive){
            if(((JsonPrimitive) jsonElement).isNumber()){
                idq.setQuantity(jsonElement.getAsInt());
            };
        }
        return idq;

    }
}
public static void main(String[] args) {
    new TestGSON().keepsIntsAsIs();
}
}

Answer 4

使用Jackson代替Gson，可以解决您的问题：

import com.fasterxml.jackson.databind.ObjectMapper;
import java.io.IOException;
import java.util.Map;

public class JacksonMapExample1 {

public static void main(String[] args) {

    ObjectMapper mapper = new ObjectMapper();
    String json = "{\"name\":\"mkyong\", \"age\":\"37\"}";
    try {
        // convert JSON string to Map
        Map<String, String> map = mapper.readValue(json, Map.class);
        System.out.println(map);

    } catch (IOException e) {
        e.printStackTrace();
    }

}
}

Answer 5

这对我来说很好用：

private static class DoubleSerializer implements JsonSerializer<Double> {
    @Override
    public JsonElement serialize(Double src, Type typeOfSrc, JsonSerializationContext context) {
        return src == src.longValue() ? new JsonPrimitive(src.longValue()) : new JsonPrimitive(src);
    }
}

Gson gson = new GsonBuilder().registerTypeAdapter(Double.class, new DoubleSerializer()).setPrettyPrinting().create();

Answer 6

这对我有用，我有一个“规格”字段，它是Map<String, Object>：

public class MyClass {

  public Map<String, Object> specs;

}

在修复之前，我得到以下对象列表的输出：

{  
   "hits":{  
      "content":[  
         {  
            "specs":{  
               "fiscalHorsePower":4.0,
               "nbOfDoors":5.0,
               "consumption":4.3
            }
         }
      ]
   }
}

fiscalHorsePower和nbOfDoors是整数。

这是我使用的修复程序，首先创建一个新的Adapter和一个Factory：

public class CustomizedObjectTypeAdapter extends TypeAdapter<Object> {

public static final TypeAdapterFactory FACTORY = new TypeAdapterFactory() {
    @SuppressWarnings("unchecked")
    @Override public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> type) {
        if (Map.class.isAssignableFrom(type.getRawType())) {
            return (TypeAdapter<T>) new CustomizedObjectTypeAdapter();
        }
        return null;
    }
};

private final TypeAdapter<Object> delegate = new Gson().getAdapter(Object.class);

@Override
public void write(JsonWriter out, Object value) throws IOException {
    delegate.write(out, value);
}

@Override
public Object read(JsonReader in) throws IOException {
    JsonToken token = in.peek();
    switch (token) {
        case BEGIN_ARRAY:
            List<Object> list = new ArrayList<Object>();
            in.beginArray();
            while (in.hasNext()) {
                list.add(read(in));
            }
            in.endArray();
            return list;

        case BEGIN_OBJECT:
            Map<String, Object> map = new LinkedTreeMap<String, Object>();
            in.beginObject();
            while (in.hasNext()) {
                map.put(in.nextName(), read(in));
            }
            in.endObject();
            return map;

        case STRING:
            return in.nextString();

        case NUMBER:
            //return in.nextDouble();
            String n = in.nextString();
            if (n.indexOf('.') != -1) {
                return Double.parseDouble(n);
            }
            return Long.parseLong(n);

        case BOOLEAN:
            return in.nextBoolean();

        case NULL:
            in.nextNull();
            return null;

        default:
            throw new IllegalStateException();
    }
}
}

然后注册工厂：

Gson gson = new GsonBuilder().registerTypeAdapterFactory(CustomizedObjectTypeAdapter.FACTORY);

这是修复的结果：

{  
   "hits":{  
      "content":[  
         {  
            "specs":{  
               "fiscalHorsePower":4,
               "nbOfDoors":5,
               "consumption":4.3
            }
         }
      ]
   }
}

Answer 7

这是我解决问题的解决方案。我试图尽可能干净地实现它。我没有找到更好的简单解决方案来检查数字是否为整数。

fixture `Login`    
    .httpAuth({
        username: userID,
        password: password,
    })
    .page(appUrl)

如何防止gson将整数转换为双精度数

7 个答案: