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Jackson Vs. Gson [closed]

After searching through some existing libraries for JSON, I have finally ended up with these two:

• Jackson
• Google GSon

I am a bit partial towards GSON, but word on the net is that GSon suffers from a certain celestial performance issue (as of Sept 2009).

I am continuing my comparison; in the meantime, I'm looking for help to make up my mind.

How to deserialize JS date using Jackson?

I'm getting a date string from ExtJS in the format:

"2011-04-08T09:00:00"

when i try to deserialize this date, it changes the timezone to Indian Standard Time (adds +5:30 to the time) . This is how i'm deserializing the date:

SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss");
getObjectMapper().getDeserializationConfig().setDateFormat(dateFormat);

Doing this also doesn't change the timezone. I still get the date in IST:

SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss");
dateFormat.setTimeZone(TimeZone.getTimeZone("GMT"));
getObjectMapper().getDeserializationConfig().setDateFormat(dateFormat);

How do I deserialize the date in the way in which it is coming without the hassles of Timezone?

Convert Java Object to JsonNode in Jackson [duplicate]

Is it possible to directly convert a Java Object to an JsonNode-Object?

The only way I found to solve this is to convert the Java Object to String and then to JsonNode:

ObjectMapper mapper = new ObjectMapper(); 
String json = mapper.writeValueAsString(object);
JsonNode jsonNode = mapper.readTree(json);

Jackson enum Serializing and DeSerializer

I'm using JAVA 1.6 and Jackson 1.9.9 I've got an enum

public enum Event {
    FORGOT_PASSWORD("forgot password");

    private final String value;

    private Event(final String description) {
        this.value = description;
    }

    @JsonValue
    final String value() {
        return this.value;
    }
}

I've added a @JsonValue, this seems to do the job it serializes the object into:

{"event":"forgot password"}

but when I try to deserialize I get a

Caused by: org.codehaus.jackson.map.JsonMappingException: Can not construct instance of com.globalrelay.gas.appsjson.authportal.Event from String value 'forgot password': value not one of declared Enum instance names

What am I missing here?

How do I use a custom Serializer with Jackson?

I have two Java classes that I want to serialize to JSON using Jackson:

public class User {
    public final int id;
    public final String name;

    public User(int id, String name) {
        this.id = id;
        this.name = name;
    }
}

public class Item {
    public final int id;
    public final String itemNr;
    public final User createdBy;

    public Item(int id, String itemNr, User createdBy) {
        this.id = id;
        this.itemNr = itemNr;
        this.createdBy = createdBy;
    }
}

I want to serialize an Item to this JSON:

{"id":7, "itemNr":"TEST", "createdBy":3}

with User serialized to only include the id. I will also be able to serilize all user objects to JSON like:

{"id":3, "name": "Jonas", "email": "jonas@example.com"}

So I guess that I need to write a custom serializer for Item and tried with this:

public class ItemSerializer extends JsonSerializer<Item> {

@Override
public void serialize(Item value, JsonGenerator jgen,
        SerializerProvider provider) throws IOException,
        JsonProcessingException {
    jgen.writeStartObject();
    jgen.writeNumberField("id", value.id);
    jgen.writeNumberField("itemNr", value.itemNr);
    jgen.writeNumberField("createdBy", value.user.id);
    jgen.writeEndObject();
}

}

I serialize the JSON with this code from Jackson How-to: Custom Serializers:

ObjectMapper mapper = new ObjectMapper();
SimpleModule simpleModule = new SimpleModule("SimpleModule", 
                                              new Version(1,0,0,null));
simpleModule.addSerializer(new ItemSerializer());
mapper.registerModule(simpleModule);
StringWriter writer = new StringWriter();
try {
    mapper.writeValue(writer, myItem);
} catch (JsonGenerationException e) {
    e.printStackTrace();
} catch (JsonMappingException e) {
    e.printStackTrace();
} catch (IOException e) {
    e.printStackTrace();
}

But I get this error:

Exception in thread "main" java.lang.IllegalArgumentException: JsonSerializer of type com.example.ItemSerializer does not define valid handledType() (use alternative registration method?)
    at org.codehaus.jackson.map.module.SimpleSerializers.addSerializer(SimpleSerializers.java:62)
    at org.codehaus.jackson.map.module.SimpleModule.addSerializer(SimpleModule.java:54)
    at com.example.JsonTest.main(JsonTest.java:54)

How can I use a custom Serializer with Jackson?

This is how I would do it with Gson:

public class UserAdapter implements JsonSerializer<User> {

    @Override 
    public JsonElement serialize(User src, java.lang.reflect.Type typeOfSrc,
            JsonSerializationContext context) {
        return new JsonPrimitive(src.id);
    }
}

    GsonBuilder builder = new GsonBuilder();
    builder.registerTypeAdapter(User.class, new UserAdapter());
    Gson gson = builder.create();
    String json = gson.toJson(myItem);
    System.out.println("JSON: "+json);

But I need to do it with Jackson now, since Gson doesn't have support for interfaces.

Converting Java objects to JSON with Jackson

I want my JSON to look like this:

{
    "information": [{
        "timestamp": "xxxx",
        "feature": "xxxx",
        "ean": 1234,
        "data": "xxxx"
    }, {
        "timestamp": "yyy",
        "feature": "yyy",
        "ean": 12345,
        "data": "yyy"
    }]
}

Code so far:

import java.util.List;

public class ValueData {

    private List<ValueItems> information;

    public ValueData(){

    }

    public List<ValueItems> getInformation() {
        return information;
    }

    public void setInformation(List<ValueItems> information) {
        this.information = information;
    }

    @Override
    public String toString() {
        return String.format("{information:%s}", information);
    }

}

and

public class ValueItems {

    private String timestamp;
    private String feature;
    private int ean;
    private String data;


    public ValueItems(){

    }

    public ValueItems(String timestamp, String feature, int ean, String data){
        this.timestamp = timestamp;
        this.feature = feature;
        this.ean = ean;
        this.data = data;
    }

    public String getTimestamp() {
        return timestamp;
    }

    public void setTimestamp(String timestamp) {
        this.timestamp = timestamp;
    }

    public String getFeature() {
        return feature;
    }

    public void setFeature(String feature) {
        this.feature = feature;
    }

    public int getEan() {
        return ean;
    }

    public void setEan(int ean) {
        this.ean = ean;
    }

    public String getData() {
        return data;
    }

    public void setData(String data) {
        this.data = data;
    }

    @Override
    public String toString() {
        return String.format("{timestamp:%s,feature:%s,ean:%s,data:%s}", timestamp, feature, ean, data);
    }
}

I just missing the part how I can convert the Java object to JSON with Jackson:

public static void main(String[] args) {
   // CONVERT THE JAVA OBJECT TO JSON HERE
    System.out.println(json);
}

My Question is: Are my classes correct? Which instance do I have to call and how that I can achieve this JSON output?

Representing null in JSON

What is the preferred method for returning null values in JSON? Is there a different preference for primitives?

For example, if my object on the server has an Integer called "myCount" with no value, the most correct JSON for that value would be:

{}

or

{
    "myCount": null
}

or

{
    "myCount": 0
}

Same question for Strings - if I have a null string "myString" on the server, is the best JSON:

{}

or

{
    "myString": null
}

or

{
    "myStrung": ""
}

or (lord help me)

{
    "myString": "null"
}

I like the convention for collections to be represented in the JSON as an empty collection http://jtechies.blogspot.nl/2012/07/item-43-return-empty-arrays-or.html

An empty Array would be represented:

{
    "myArray": []
}

EDIT Summary

The 'personal preference' argument seems realistic, but short sited in that, as a community will be consuming greater numbers of disparate services/sources. Conventions for JSON structure would help normalize consumption and reuse of said services. As far as establishing a standard, I would suggest adopting most of the Jackson conventions with a few exceptions:

• Objects are preferred over primitives.
• Empty collections are preferred over null.
• Objects with no value are represented as null.
• Primitives return their value.

If you are returning a JSON object with mostly null values, you may have a candidate for refactoring into multiple services.

{

    "value1": null,

    "value2": null,

    "text1": null,

    "text2": "hello",

    "intValue": 0, //use primitive only if you are absolutely sure the answer is 0

    "myList": [],

    "myEmptyList": null, //NOT BEST PRACTICE - return [] instead

    "boolean1": null, //use primitive only if you are absolutely sure the answer is true/false

    "littleboolean": false

}

The above JSON was generated from the following Java class.

package jackson;

import java.util.ArrayList;
import java.util.List;

import com.fasterxml.jackson.databind.ObjectMapper;

public class JacksonApp {

    public static class Data {

        public Integer value1;

        public Integer value2;

        public String text1;

        public String text2 = "hello";

        public int intValue;

        public List<Object> myList = new ArrayList<Object>();

        public List<Object> myEmptyList;

        public Boolean boolean1;

        public boolean littleboolean;

    }

    public static void main(String[] args) throws Exception {
        ObjectMapper mapper = new ObjectMapper();
        System.out.println(mapper.writeValueAsString(new Data()));
    }
}

Maven dependency:

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-core</artifactId>
    <version>2.3.0</version>
</dependency>

How to convert a JSON string to a Map with Jackson JSON

This is my first time trying to do something useful with Java.. I'm trying to do something like this but it doesn't work:

Map<String, String> propertyMap = new HashMap<String, String>();

propertyMap = JacksonUtils.fromJSON(properties, Map.class);

But the IDE says: 'Unchecked assignment Map to Map<String,String>'

What's the right way to do this? I'm only using Jackson because that's what is already available in the project, is there a native Java way of converting to/from JSON?

In PHP I would simply json_decode($str) and I'd get back an array. I need basically the same thing here.

Thanks!

Serializing enums with Jackson

I have an Enum desrcibed below:

public enum OrderType {

  UNKNOWN(0, "Undefined"),
  TYPEA(1, "Type A"),
  TYPEB(2, "Type B"),
  TYPEC(3, "Type C");

  private Integer id;
  private String name;

  private WorkOrderType(Integer id, String name) {
    this.id = id;
    this.name = name;
  }

  //Setters, getters....
}

I return enum array with my controller ( new OrderType[] {UNKNOWN,TYPEA,TYPEB,TYPEC};), and Spring serializes it into the following json string:

["UNKNOWN", "TYPEA", "TYPEB", "TYPEC"] 

What is the best approach to force Jackson to serialize enums just like POJOs? E.g.:

[
  {"id": 1, "name": "Undefined"},
  {"id": 2, "name": "Type A"},
  {"id": 3, "name": "Type B"},
  {"id": 4, "name": "Type C"}
]

I played with different annotations but couldn't manage to get such result.

Only using @JsonIgnore during serialization, but not deserialization

I have a user object that is sent to and from the server. When I send out the user object I don't want to send the hashed password to the client. So I added @JsonIgnore on the password property, but this also blocks it from being deserialized into the password which makes it hard to sign up users when they ain't got a password.

How can I only get @JsonIgnore to apply to serialization and not deserialization? I'm using Spring JSONView so I don't have a ton of control over the ObjectMapper.

Things I've tried:

1. Add @JsonIgnore to the property
2. Add @JsonIgnore on the getter method only

downloading jackson.codehaus.org jar

I need to download a json parser so I go to the jackson.codehaus.org website. Instead of a convenient link to click and download the jar/jars, they have me going in circles. Does anyone know where the jars are -- exactly?

Jackson: how to prevent field serialization

I have an entity class with a password field:

class User {
    private String password;

    //setter, getter..
}

I want this field to be skipped during serialization. But it should still be able to DEserialize. This is needed, so that the client can send me a new password, but is not able to read the current one.

How do I accomplish this with Jackson?

how to specify jackson to only use fields - preferably globally

Default jackon behaviour seems to use both properties (getters and setters) and fields to serialize and deserialize to json.

I would like to use the fields as the canonical source of serialization config and thus don't want jackson to look at properties at all.

I can do this on an individual class basis with the annotation:

 @JsonAutoDetect(fieldVisibility = Visibility.ANY, getterVisibility = Visibility.NONE, setterVisibility = Visibility.NONE)

But I don't want to have to put this on every single class...

Is it possible to configure this globally? Like add some to the Object Mapper?

How to serialize Joda DateTime with Jackson JSON processer?

How do I get Jackson to serialize my Joda DateTime object according to a simple pattern (like "dd-MM-yyyy"?

I've tried:

@JsonSerialize(using=DateTimeSerializer.class)
private final DateTime date;

I've tried:

ObjectMapper mapper = new ObjectMapper()
    .getSerializationConfig()
    .setDateFormat(df);

Thanks!

Serializing with Jackson (JSON) - getting "No serializer found"?

I get the an exception when trying to serialize a very simple object using Jackson. The error:

org.codehaus.jackson.map.JsonMappingException: No serializer found for class MyPackage.TestA and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationConfig.Feature.FAIL_ON_EMPTY_BEANS) )

Below is the simple class and code to serialize.

Can anyone tell my why I get this error?

public class TestA {
    String SomeString = "asd";
}

TestA testA = new TestA();
ObjectMapper om = new ObjectMapper();
try {
    String testAString = om.writeValueAsString(testA); // error here!

    TestA newTestA = om.readValue(testAString, TestA.class);
} catch (JsonGenerationException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
} catch (JsonMappingException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
} catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
}