java – 如何使用GSON序列化地图的地图？

从JavaDocs：

Constructs a Gson object with default configuration. The default configuration has the following settings:

• The JSON generated by toJson methods is in compact representation. This means that all the unneeded white-space is removed. You can change this behavior with GsonBuilder.setPrettyPrinting().
• The generated JSON omits all the fields that are null. Note that nulls in arrays are kept as is since an array is an ordered list. Moreover,if a field is not null,but its generated JSON is empty,the field is kept. You can configure Gson to serialize null values by setting GsonBuilder.serializeNulls().
• Gson provides default serialization and deserialization for Enums,Map,java.net.URL,java.net.URI,java.util.Locale,java.util.Date,java.math.BigDecimal,and java.math.BigInteger classes. If you would prefer to change the default representation,you can do so by registering a type adapter through GsonBuilder.registerTypeAdapter(Type,Object).
• The default Date format is same as java.text.DateFormat.DEFAULT. This format ignores the millisecond portion of the date during serialization. You can change this by invoking GsonBuilder.setDateFormat(int) or GsonBuilder.setDateFormat(String).
• By default,Gson ignores the com.google.gson.annotations.Expose annotation. You can enable Gson to serialize/deserialize only those fields marked with this annotation through GsonBuilder.excludeFieldsWithoutExposeAnnotation().
• By default,Gson ignores the com.google.gson.annotations.Since annotation. You can enable Gson to use this annotation through GsonBuilder.setVersion(double).
• The default field naming policy for the output Json is same as in Java. So,a Java class field versionNumber will be output as “versionNumber@quot; in Json. The same rules are applied for mapping incoming Json to the Java classes. You can change this policy through GsonBuilder.setFieldNamingPolicy(FieldNamingPolicy).
• By default,Gson excludes transient or static fields from consideration for serialization and deserialization. You can change this behavior through GsonBuilder.excludeFieldsWithModifiers(int).

好的,现在我看看是什么问题.默认的Map序列化程序,如您所料,不支持嵌套映射.正如你在this source snippet from DefaultTypeAdapters中看到的那样(特别是如果你使用一个调试器),变量childGenericType被设置为java.lang.Object类型,因为一些神秘的原因,所以值的运行时类型永远不会被分析.

两个解决方案,我猜：

> Implement your own Map serializer / deserializer
>使用更复杂的方法,如下所示：

public String toJSON(){
    final Gson gson = new Gson();
    final JsonElement jsonTree = gson.toJsonTree(General,Map.class);
    final JsonObject jsonObject = new JsonObject();
    jsonObject.add("General",jsonTree);
    return jsonObject.toString();
}