Gson:有没有更简单的方法来序列化地图 [英] Gson: Is there an easier way to serialize a map
问题描述
public static class NumberTypeAdapter
实现JsonSerializer< Number> ;,JsonDeserializer< Number> ;,
InstanceCreator< Number> {
public JsonElement serialize(Number src,Type typeOfSrc,JsonSerializationContext
context){
return new JsonPrimitive(src);
$ b $ public public deserialize(JsonElement json,Type typeOfT,
JsonDeserializationContext context)
throws JsonParseException {
JsonPrimitive jsonPrimitive = json.getAsJsonPrimitive();
if(jsonPrimitive.isNumber()){
return jsonPrimitive.getAsNumber();
} else {
throw new IllegalStateException(期望的数字字段,但是是+ json);
}
}
公共数字createInstance(Type type){
return 1L;
public static void main(String [] args){
Map< String,Number> map = new HashMap< String,Number>();
map.put(int,123);
map.put(long,1234567890123456789L);
map.put(double,1234.5678D);
map.put(float,1.2345F);
类型mapType = new TypeToken< Map< String,Number>>(){} .getType();
Gson gson = new GsonBuilder()。registerTypeAdapter(Number.class,new
NumberTypeAdapter())。create();
String json = gson.toJson(map,mapType);
System.out.println(json);
地图< String,Number> deserializedMap = gson.fromJson(json,mapType);
System.out.println(deserializedMap);
$ / code>
很酷且很有效,但它看起来好像很多开销( 整个类型适配器类? )。我已经使用了其他JSON库,如JSONLib,他们让你以下面的方式构建地图:
$ b
JSONObject json = new JSONObject ); (Entry< String,Integer> entry:map.entrySet()){
json.put(entry.getKey(),entry.getValue());
}
或者如果我有一个类似下面的自定义类:
JSONObject json = new JSONObject();
for(Entry< String,MyClass> entry:map.entrySet()){
JSONObject myClassJson = JSONObject.fromObject(entry.getValue());
json.put(entry.getKey(),myClassJson);
$ / code>
这个过程比较手动,但需要的代码少一些,没有haivng为Number创建自定义类型适配器的开销,或者在大多数情况下为我自己的自定义类 创建自定义类型适配器。
这是使用Gson序列化地图的唯一方法,或者有人找到一种方法来打败Gson在以上链接中推荐的内容。
Map< String,String> myMap = new HashMap< String,String>();
myMap.put(one,hello);
myMap.put(two,world);
Gson gson = new GsonBuilder()。create();
String json = gson.toJson(myMap);
System.out.println(json);
类型typeOfHashMap = new TypeToken< Map< String,String>>(){} .getType();
Map< String,String> newMap = gson.fromJson(json,typeOfHashMap); //这个类型必须匹配TypeToken
System.out.println(newMap.get(one));
System.out.println(newMap.get(two));
输出:
{two:world,one:hello}
hello
world
This link from the Gson project seems to indicate that I would have to do something like the following for serializing a typed Map to JSON:
public static class NumberTypeAdapter
implements JsonSerializer<Number>, JsonDeserializer<Number>,
InstanceCreator<Number> {
public JsonElement serialize(Number src, Type typeOfSrc, JsonSerializationContext
context) {
return new JsonPrimitive(src);
}
public Number deserialize(JsonElement json, Type typeOfT,
JsonDeserializationContext context)
throws JsonParseException {
JsonPrimitive jsonPrimitive = json.getAsJsonPrimitive();
if (jsonPrimitive.isNumber()) {
return jsonPrimitive.getAsNumber();
} else {
throw new IllegalStateException("Expected a number field, but was " + json);
}
}
public Number createInstance(Type type) {
return 1L;
}
}
public static void main(String[] args) {
Map<String, Number> map = new HashMap<String, Number>();
map.put("int", 123);
map.put("long", 1234567890123456789L);
map.put("double", 1234.5678D);
map.put("float", 1.2345F);
Type mapType = new TypeToken<Map<String, Number>>() {}.getType();
Gson gson = new GsonBuilder().registerTypeAdapter(Number.class, new
NumberTypeAdapter()).create();
String json = gson.toJson(map, mapType);
System.out.println(json);
Map<String, Number> deserializedMap = gson.fromJson(json, mapType);
System.out.println(deserializedMap);
}
Cool and that works, but it seems like so much overhead (a whole Type Adapter class?). I have used other JSON libraries like JSONLib and they let you build a map in the following way:
JSONObject json = new JSONObject();
for(Entry<String,Integer> entry : map.entrySet()){
json.put(entry.getKey(), entry.getValue());
}
Or if I have a custom class something like the following:
JSONObject json = new JSONObject();
for(Entry<String,MyClass> entry : map.entrySet()){
JSONObject myClassJson = JSONObject.fromObject(entry.getValue());
json.put(entry.getKey(), myClassJson);
}
The process is more manual, but requires way less code and doesn't have the overhead of haivng to create a custom Type Adapter for Number or in most cases for my own custom class.
Is this the only way to serialize a map with Gson, or has anyone found a way that beats out what Gson recommends in the link above.
Only the TypeToken part is neccesary (when there are Generics involved).
Map<String, String> myMap = new HashMap<String, String>();
myMap.put("one", "hello");
myMap.put("two", "world");
Gson gson = new GsonBuilder().create();
String json = gson.toJson(myMap);
System.out.println(json);
Type typeOfHashMap = new TypeToken<Map<String, String>>() { }.getType();
Map<String, String> newMap = gson.fromJson(json, typeOfHashMap); // This type must match TypeToken
System.out.println(newMap.get("one"));
System.out.println(newMap.get("two"));
Output:
{"two":"world","one":"hello"}
hello
world
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