I have a problem trying to deserialize a gson LocalDate.
I have the next 2 adaptors:
public class LocalDateSerializer implements JsonSerializer < LocalDate > {
private static final DateTimeFormatter formatter = DateTimeFormatter.ofPattern("d-MMM-yyyy");
#Override
public JsonElement serialize(LocalDate localDate, Type srcType, JsonSerializationContext context) {
return new JsonPrimitive(formatter.format(localDate));
}
}
and
public class LocalDateDeserializer implements JsonDeserializer < LocalDate > {
#Override
public LocalDate deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context)
throws JsonParseException {
return LocalDate.parse(json.getAsString(),
DateTimeFormatter.ofPattern("d-MMM-yyyy").withLocale(Locale.ENGLISH));
}
}
I try to make a simple Serialization of an object "Task" which have a field starttime of LocalDate type.
GsonBuilder gsonBuilder = new GsonBuilder();
gsonBuilder.registerTypeAdapter(LocalDate.class, new LocalDateSerializer());
gsonBuilder.registerTypeAdapter(LocalDate.class, new LocalDateDeserializer());
Gson gson = gsonBuilder.setPrettyPrinting().create();
LocalDate now=LocalDate.now();
Task task=new Task();
task.setID(1);
task.setDuration(2);
task.setID_Proiect(1);
task.setStarttime(now);
JSONObject json=new JSONObject(task);
String aux1=gson.toJson(json);
System.out.println(aux1);
Task t2=gson.fromJson(aux1,Task.class);
I receive the error
Failed making field 'java.time.LocalDateTime#date' accessible; either
change its visibility or write a custom TypeAdapter for its declaring
type
Can you tell me what is wrong with this code? I know it is probably a noobie question but i rly need help to improve my skills. Ty
Related
I've got a json file which has got a Date field. I'm transforming this to a required Date format(dd/MM/yyyy) using JsonDeserializer and registering the class as a TypeAdapter in GsonBuilder. Now, I want to transform this field to different date formats(say ISO8601) for different use cases. Instead of creating new JsonDeserializer's for different date formats, Is there anyway I can pass date format as one of the parameters to JsonSerializer class to make it extensible.
Deserializer class:
public class DateDeserializer implements JsonDeserializer<Date> {
private static final SimpleDateFormat DATE_FORMAT = new SimpleDateFormat("dd/MM/yyyy");
#Override
public Date deserialize(JsonElement jsonElement, Type type, JsonDeserializationContext jsonDeserializationContext) {
String dateString = jsonElement.getAsString();
if (!StringUtils.isEmpty(dateString)) {
try {
return DATE_FORMAT.parse(dateString);
} catch (ParseException e) {
}
}
}
GsonBuilder:
public static final Gson GSON = new GsonBuilder()
.registerTypeAdapter(Date.class, new DateDeserializer())
.serializeNulls()
.create();
For example
public class HistoryRecordDeserializer implements JsonDeserializer<HistoryRecord> {
private LocalDateTimeConverter dateTimeConverter = new LocalDateTimeConverter();
#Override
public HistoryRecord deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
User user = new User();
user.setId(UUUID.fromString(json.get("user").get("id").getAsString()));
OtherData data = new OtherData();
data.setData(json.get("otherData").getAsLong());
return UserAndData(user, otherData);
}
As you can see, I instantiate User and OtherData manually, but I think there is a better solution. What is the best way to deserialize user with fromJson(...)? Should I pass Gson instance to HistoryRecordDeserializer? Should I create new one?
My problem was solved by using JsonDeserializationContext.
#Override
public HistoryRecord deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
JsonObject object = json.getAsJsonObject();
JsonObject extras = object.get("extraData").getAsJsonObject();
HistoryRecord hr = object.context.deserialize(object.get("data"), HistoryRecord.class);
hr.appendExtraData(extras, HistoryRecordExtraData.class);
...
}
As #varren sad:
If you Gson can deserialize this, then context will be also able to do this.
So, you can even apply another custom type adapter(LocalDateTimeConverter):
gson = new GsonBuilder()
.registerTypeAdapter(LocalDateTime.class, new LocalDateTimeConverter())
.registerTypeHierarchyAdapter(HistoryRecord.class, new HistoryRecordDeserializer())
.create();
and use it inside HistoryRecordDeserializer:
LocalDateTime localDateTime = context.deserialize(object.get("dateTime"), LocalDateTime.class);
I have one class User, I received JSON (for User class) from system1 and I should read info , validate then forward to system2, I can't touch these 2 systems, the problem is the names of keys are different, I want to differentiate between deserialized and serialized name
received JSON is :
{"userId":"user1","pwd":"123456","country":"US"}
"{"username":"user1","password":"123456","country":"US"}"
But the sent should be like this
I am using Gson lib, and this is my code:
User class:
class User implements Cloneable {
#SerializedName("username")
private String username ;
#SerializedName("password")
private String password ;
#SerializedName("country")
private String country ;
}
TestJson class
class TestJson {
private static GsonBuilder gsonBuilder;
private static Gson gson;
public static Object fromJson(String json, Class clz) {
gson = new Gson();
return gson.fromJson(json, clz);
}
public static String toJson(Object obj) {
gsonBuilder = new GsonBuilder();
gson = gsonBuilder.create();
String json = gson.toJson(obj);
return json;
}
public static void main(String[] args) {
String json2 = "{\"userId\":\"user1\",\"pwd\":\"123456\",\"country\":\"US\"}";
User user = (User) TestJson.fromJson(json2, User.class);
System.out.println(user.getPassword());
User u = new User("user1","123456","US");
String json1 = TestJson.toJson(u);
System.out.println(json1);
}
}
If there are alternative names of field just use alternate param of #SerializedName
public class User {
#SerializedName(value="username", alternate={"userId", "useriD"})
private String username ;
...
}
You can create custom serializer/deserializer for this purpose.
Serializer:
public class UserSerializer implements JsonSerializer<User> {
#Override public JsonElement serialize(User obj, Type type, JsonSerializationContext jsonSerializationContext) {
..........
}
}
Deserializer:
public class UserDeserializer implements JsonDeserializer<User> {
#Override public User deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
...........
}
}
and to create Gson instance:
GsonBuilder gsonBuilder = new GsonBuilder();
gsonBuilder.registerTypeAdapter(User.class, new UserSerializer());
gsonBuilder.registerTypeAdapter(User.class, new UserDeserializer());
Gson gson = gsonBuilder.create();
Example
Edit: this is an example of a custom deserializer which might fit into your need. We don't need a custom serializer in this case.
Add this UserDeserializer.java:
public class UserDeserializer implements JsonDeserializer<User> {
#Override
public User deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
JsonObject obj = json.getAsJsonObject();
User user = new User(obj.get("userId").getAsString(), obj.get("pwd").getAsString(), obj.get("country").getAsString());
return user;
}
}
Replace your fromJson implementation with this (I use generic to avoid the need for casting when calling fromJson):
public static <T> T fromJson(String json, Class<T> clz) {
gsonBuilder = new GsonBuilder();
gsonBuilder.registerTypeAdapter(User.class, new UserDeserializer());
gson = gsonBuilder.create();
return gson.fromJson(json, clz);
}
The only way I can think of would be to have a custom Adapter or deser to a JsonObject and then map it to your User.
With Genson you can create two instances of Genson, one for deserialization and another one for serializaiton. The one used in deserialization could be configured with renamed properties like that.
// you can also precise that you want to rename only the properties from User class
Genson genson = new GensonBuilder()
.rename("username", "userId")
.rename("password", "pwd")
.create();
User user = genson.deserialize(json, User.class);
What pattern should I use for date format 1418805300000-0100 ? (Timestamp and timezone)
GsonBuilder().setDateFormat("?????????????-Z")
Solution:
create new GSON with adapters
private static Gson createGson(){
return new GsonBuilder().disableHtmlEscaping()
.registerTypeHierarchyAdapter(Date.class, new DateTimeSerializer())
.registerTypeHierarchyAdapter(Date.class, new DateTimeDeserializer())
.create();
}
public static MyClass fromJson(String json) {
return createGson().fromJson(json, MyClass.class);
}
public String toJson() {
return createGson().toJson(this);
}
JSON Serializer
private static class DateTimeSerializer implements JsonSerializer<Date> {
#Override
public JsonElement serialize(Date src, Type typeOfSrc, JsonSerializationContext context) {
// hodgie code
return new JsonPrimitive(src.getTime() + new SimpleDateFormat("Z").format(src));
}
}
Deserializer
private static class DateTimeDeserializer implements JsonDeserializer<Date> {
#Override
public Date deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
// hodgie code
return new Date(Long.valueOf((json).getAsString().substring(0, 13)));
}
}
GsonBuilder#setDateFormat(String) uses the String provided as an argument for creating SimpleDateFormat instances. SimpleDateFormat does not provide any patterns for generating a timestamp. You won't be able to achieve what you want with setDateFormat. A custom TypeAdapter seems appropriate.
I have a json response that looks like this:
{
"id":"001",
"name":"Name",
"param_distance":"10",
"param_sampling":"2"
}
And I have two classes: Teste and Parameters
public class Test {
private int id;
private String name;
private Parameters params;
}
public class Parameters {
private double distance;
private int sampling;
}
My question is: is there a way to make Gson understand that some of the json attributes should go to the Parameters class, or the only way is to "manually" parse this ?
EDIT
Well, just to make my comment in #MikO's answer more readable:
I'll add a list of an object to the json output, so json response should look like this:
{
"id":"001",
"name":"Name",
"param_distance":"10",
"param_sampling":"2",
"events":[
{
"id":"01",
"value":"22.5"
},
{
"id":"02",
"value":"31.0"
}
]
}
And the Deserializer class would look like this:
public class TestDeserializer implements JsonDeserializer<Test> {
#Override
public Test deserialize(JsonElement json, Type type,
JsonDeserializationContext context) throws JsonParseException {
JsonObject obj = json.getAsJsonObject();
Test test = new Test();
test.setId(obj.get("id").getAsInt());
test.setName(obj.get("name").getAsString());
Parameters params = new Parameters();
params.setDistance(obj.get("param_distance").getAsDouble());
params.setSampling(obj.get("param_sampling").getAsInt());
test.setParameters(params);
Gson eventGson = new Gson();
Type eventsType = new TypeToken<List<Event>>(){}.getType();
List<Event> eventList = eventGson.fromJson(obj.get("events"), eventsType);
test.setEvents(eventList);
return test;
}
}
And doing:
GsonBuilder gBuilder = new GsonBuilder();
gBuilder.registerTypeAdapter(Test.class, new TestDeserializer());
Gson gson = gBuilder.create();
Test test = gson.fromJson(reader, Test.class);
Gives me the test object the way I wanted.
The way to make Gson understand it is to write a custom deserializer by creating a TypeAdapter for your Test class. You can find information in Gson's User Guide. It is not exactly a manual parsing, but it is not that different, since you have to tell Gson how to deal with each JSON value...
It should be something like this:
private class TestDeserializer implements JsonDeserializer<Test> {
public Test deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context)
throws JsonParseException {
JsonObject obj = json.getAsJsonObject();
int id = obj.get("id").getAsInt();
String name = obj.get("name").getAsString();
double distance = obj.get("param_distance").getAsDouble();
int sampling = obj.get("param_sampling").getAsInt();
//assuming you have suitable constructors...
Test test = new Test(id, name, new Parameters(distance, sampling));
return test;
}
}
Then you have to register the TypeAdapter with:
GsonBuilder gson = new GsonBuilder();
gson.registerTypeAdapter(Test.class, new TestDeserializer());
And finally you just have to parse your JSON as usual, with:
gson.fromJson(yourJsonString, Test.class);
Gson will automatically use your custom deserializer to parse your JSON into your Test class.