将String转换为double时，GSON中的NumberFormatException

问题描述

我正在处理格式不正确的JSON响应.所有字段都以Strings的形式返回.不幸的是，我无法控制返回数据.

I am working with a JSON response that is improperly formatted. All fields are being returned as Strings. Unfortunately, I have no control over the return data.

我正在使用Gson并尝试解析一个包含如下字段的JSON对象:

I am using Gson and attempting to parse a JSON object that includes a field like this:

{
        [...]
    "cost": "9.25"
}

显然应该将其打印为Number.当我尝试将其解析为String，Number或double时，出现NumberFormatException:

It should obviously be printed as a Number. When I try to parse this as a String, Number or double I get a NumberFormatException:

com.google.gson.JsonSyntaxException: java.lang.NumberFormatException: 
        [...]
    at com.myapp.android.LauncherActivity$1.onSuccess(LauncherActivity.java:69)
        [...]
Caused by: java.lang.NumberFormatException: 
    at org.apache.harmony.luni.util.FloatingPointParser.parseDouble(FloatingPointParser.java:267)
    at java.lang.Double.parseDouble(Double.java:285)
    at com.google.gson.stream.JsonReader.nextInt(JsonReader.java:599)
    at com.google.gson.internal.bind.TypeAdapters$7.read(TypeAdapters.java:228)
    ... 19 more

LauncherActivity第69行:

LauncherActivity Line 69:

Item item = gson.fromJson(response, Item.class);

---

所以我遵循了这类似的方法问题，并尝试创建如下的TypeAdapter:

---

So I followed this similar question and tried creating a TypeAdapter like so:

public class CostTypeAdapter implements JsonDeserializer<Double>, JsonSerializer<Double> {

    public Double deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
        Double cost;
        try {
            cost = json.getAsDouble();
        } catch (NumberFormatException e) {
            cost = 0.00d;
        }
        return cost;
    }

    public JsonElement serialize(Double src, Type typeOfSrc, 
            JsonSerializationContext context) {
        return new JsonPrimitive(src);
    }
}

并在创建GsonBuilder时注册它:

GsonBuilder builder = new GsonBuilder();
builder.registerTypeAdapter(Cost.class, new CostTypeAdapter());
Gson gson = builder.create(); 

还有我的Cost类:

public class Cost {
    private Double value;

    public Cost(Double value) {
        this.value = value;
    }

    public Double getValue() {
        return value;
    }
}

但是我得到相同的NumberFormatException.

关于这里发生的事情有什么想法吗?至少不应该在我的CostTypeAdapter.deserialize()中捕获此异常吗?

Any ideas on whats happening here? Shouldn't this exception be caught in my CostTypeAdapter.deserialize(), at the very least?

非常感谢您的帮助/指导.

Any help/guidance is greatly appreciated.

推荐答案

您还可以使用GsonBuilder的registerTypeAdapter()捕获可能的解析异常，并以所需的方式对其进行处理.

You can also use GsonBuilder's registerTypeAdapter() to catch possible parsing Exceptions and deal with them the way you want.

在解析Float并将值设置为null时捕获NumberFormatException的示例:

Example for catching NumberFormatException when parsing Float and make the value null:

    GsonBuilder gb = new GsonBuilder();
    gb.registerTypeAdapter(Float.class, new TypeAdapter<Float>() {

        @Override
        public Float read(JsonReader reader) throws IOException {
            if (reader.peek() == JsonToken.NULL) {
                reader.nextNull();
                return null;
            }
            String stringValue = reader.nextString();
            try {
                Float value = Float.valueOf(stringValue);
                return value;
            } catch (NumberFormatException e) {
                return null;
            }
        }

        @Override
        public void write(JsonWriter writer, Float value) throws IOException {
            if (value == null) {
                writer.nullValue();
                return;
            }
            writer.value(value);
        }

    });

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