背景

在使用 Gson 进行数据解析的时候，报了 Failed to parse date [“”] 错误

原代码

public void test() {
        JsonObject jsonObject = new JsonObject();
        jsonObject.addProperty("name", "小红");
        jsonObject.addProperty("birthday", "");
        Gson gson = new GsonBuilder().create();
        User user = gson.fromJson(jsonObject, new TypeToken<User>() {
        }.getType());
        System.out.println("user is:\n" + user);
    }

报错

com.google.gson.JsonSyntaxException: 
	at com.google.gson.internal.bind.DateTypeAdapter.deserializeToDate(DateTypeAdapter.java:87)
	at com.google.gson.internal.bind.DateTypeAdapter.read(DateTypeAdapter.java:75)
	at com.google.gson.internal.bind.DateTypeAdapter.read(DateTypeAdapter.java:46)
	at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:131)
	at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:222)
	at com.google.gson.Gson.fromJson(Gson.java:963)
	at com.google.gson.Gson.fromJson(Gson.java:1034)
        ...
Caused by: java.text.ParseException: Failed to parse date [""]: (java.lang.NumberFormatException)
	at com.google.gson.internal.bind.util.ISO8601Utils.parse(ISO8601Utils.java:274)
	at com.google.gson.internal.bind.DateTypeAdapter.deserializeToDate(DateTypeAdapter.java:85)
	... 34 more
Caused by: java.lang.NumberFormatException: 
	at com.google.gson.internal.bind.util.ISO8601Utils.parseInt(ISO8601Utils.java:302)
	at com.google.gson.internal.bind.util.ISO8601Utils.parse(ISO8601Utils.java:129)
	... 35 more

原因

Gson 默认的 Date 类型转换器无法处理空字符串

解决方法

通过自定义 Gson 的 Date 类型转换器来解决这个问题

Gson gson = new GsonBuilder().registerTypeAdapter(Date.class, new JsonDeserializer<Date>() {
    public Date deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
        if (json.getAsJsonPrimitive().getAsString().equals("")) {
            return null;
        }
        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        try {
            return format.parse(json.getAsJsonPrimitive().getAsString());
        } catch (ParseException e) {
            throw new JsonParseException(e);
        }
    }
}).create();

新代码

/**
 * user is:
 * User(id=null, name=小红, birthday=null)
 */
public void test() {
        JsonObject jsonObject = new JsonObject();
        jsonObject.addProperty("name", "小红");
        jsonObject.addProperty("birthday", "");
        Gson gson = new GsonBuilder().registerTypeAdapter(Date.class, new JsonDeserializer<Date>() {
            public Date deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
                if (json.getAsJsonPrimitive().getAsString().equals("")) {
                    return null;
                }
                SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
                try {
                    return format.parse(json.getAsJsonPrimitive().getAsString());
                } catch (ParseException e) {
                    throw new JsonParseException(e);
                }
            }
        }).create();
        User user = gson.fromJson(jsonObject, new TypeToken<User>() {
        }.getType());
        System.out.println("user is:\n" + user);
    }

我不是第一个踩此坑的，肯定也不会是最后一个踩此坑的，简单记录，等待有缘人