I've started using Jackson as a JSON generator, as an alternative to google GSON. I've run into an issue where Jackson is generating object: null if the object is indeed null. GSON on the other hand generates NO entry in JSON, which is the behavior I want. Is there a way to stop Jackson from generating null object/value when an object is missing?
Jackson
ObjectMapper mapper = new ObjectMapper();
StringWriter sw = new StringWriter();
mapper.writeValue(sw, some_complex_object);
String jackson = sw.getBuffer().toString();
System.out.println("********************* START JACKSON JSON ****************************");
System.out.println(jackson);
System.out.println("********************* END JACKSON JSON ****************************");
generates this:
{"eatwithrustyspoon":{"urlList":null,"device":"iPad","os":"iPhone OS","peer_id":
and GSON looks like this:
Gson gson = new Gson();
String json = gson.toJson(some_complex_object);
System.out.println("********************* START GSON JSON ****************************");
System.out.println(json);
System.out.println("********************* END GSON JSON ****************************");
and it generates this (which is what I want - note that "urlList":null was not generated) :
{"eatwithrustyspoon":{"device":"iPad","os":"iPhone OS","peer_id"
From the Jackson FAQ:
Can I omit writing of Bean properties with null value? ("how to prevent writing of null properties", "how to suppress null values")
Yes. As per JacksonAnnotationSerializeNulls, you can use:
objectMapper.setSerializationInclusion(JsonSerialize.Inclusion.NON_NULL);
// or (for older versions):
objectMapper.configure(SerializationConfig.WRITE_NULL_PROPERTIES, false);
and voila, no more null values. Note that you MUST configure mapper before beans are serialized, since this setting may be cached along with serializers. So setting it too late might prevent change from taking effect.
my issue was bit different actually i was getting Null values for the properties of POJO class.
however i solved the problem by giving mapping to properties in my pojo class like this :
#JsonProperty("PROPERTY_NAME")
thought it may help someone :)
The following solution saved me.
objectMapper.setSerializationInclusion(Include.NON_NULL);
Related
I am working on a project, where the Json contract may change overtime, If they had new property to the response Json, I might get a exception when deserializing into java object, How to ignore the new properties and only deserialize elements which are present in java Object, I am using Jackson 1.9.13, Does this version have feature which could ignore the Json element?
You can do this in 2 ways:
Add annotation to class:
#JsonIgnoreProperties(ignoreUnknown = true)
class <class_name>{
....
....
}
Configure ObjectMapper:
objectMapper.configure(Feature.FAIL_ON_UNKNOWN_PROPERTIES, false);
I'm looking to replace Jackson deserialization with Boon to test the differences in deserialization speeds. I am reading JSON from a file (which can be in the millions of lines long), consisting of multiple blocks that will each represent a POJO instance (MyPojo.java)and storing these instances in a Collection. I also have a custom deserializer that will omit the creation of certain POJOs. At the minute I have the following in Jackson:
public Collection<MyPojo> load()
{
ObjectMapper mapper = new ObjectMapper().registerModule(new MyCustomDeserializer());
return mapper.readValue(jsonFile, new TypeReference<Collection<MyPojo>>(){});
}
I know that the Boon API mimics Jacksons so I tried:
ObjectMapper boonMapper = JsonFactory.create();
return boonMapper.readValue(jsonFile, new TypeReference<Collection<MyPojo>>(){});
...but it doesn't seem to like this, it can't find the method that accepts these types.
Forgetting the registering the custom deserializer for now (that'll be my next problem), is this type of deserialization, straight to a Collection, supported in Boon?
Do the following;
return boonMapper.readValue(jsonFile, List.class, MyPojo.class);
I'm trying to generate a JSON string from a complex java object (using Jackson API). While parsing a field I see ClassCastException. The Java objects are not owned by my project so cannot change and fix the issue. Is there any easy way to fix this?
Please note, my code deals with any kind of Java object and doesn't this Java object in particular so I'm looking for something generic where if a field is not parsed successful, just ignore and move to the next one.
ObjectMapper mapper = new ObjectMapper();
CustomModule module = new CustomModule();
mapper.registerModule(module);
ObjectWriter ow = mapper.writer().withDefaultPrettyPrinter();
ow.writeValueAsString(value)
You can globally disable checking for instance :
objectMapper.configure(DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES, false);
By default Jackson throws an exception, if it encounters a JSON property that it can not bind to object property.
Good Day,
Hi All,
I'm trying to configure the Jackson Object Mapper to de-serialize any json String to my domain specific objects.
I've configured the Object Mapper as below
ObjectMapper mapper = new ObjectMapper();
mapper.configure(Feature.FAIL_ON_UNKNOWN_PROPERTIES, false);
mapper.enableDefaultTypingAsProperty(DefaultTyping.NON_FINAL, "remoteClass");
In my domain, any json string should contain a remoteClass property which denotes the actual JAVA POJO (canonical name) that it corresponds to. The above configuration helps resolve abstract types
However with the above, now java.util.Lists are not getting properly deserialized, since they are abstract types.
I get the following error
Unexpected token (START_OBJECT), expected VALUE_STRING: need JSON String that contains type id (for subtype of java.util.List)
Object Mapper in this case is not resorting to the default collectionFallBacks
I tried other configuration to overcome the issue such as
SimpleModule module = new SimpleModule("test", Version.unknownVersion());
module.addAbstractTypeMapping(List.class, ArrayList.class);
mapper.registerModule(module);
However these lead to other problems.
Can someone please help me with the same. I've spent days on this now. This seems like a limitation in Jackson. Correct me if I'm wrong
I faced this problem recently. Try this, in your POJO, instead of defining property as
List<SimpleModule>
define it as
List<Object>.
I have a restful web service(JAVA) which has to accept JSON requests. I have to first validate this JSON against a JSON schema that I have.
I'm not sure what is the best JAVA library to validate JSON again JSON schemas.
I have used json-schema-validator-2.1.7 library but it has not been very helpful. Even thought my JSON is not a valid JSON I do not get any errors.
Here is the code I use for json-schema-validator-2.1.7
InputStream jsonSchemaInputStream = Assessment.class.getClassLoader().getResourceAsStream("Schemas/AssessmentMetrics.json");
ObjectMapper mapper = new ObjectMapper();
// Allows to retrieve a JSONSchema object on various sources
// supported by the ObjectMapper provided
JSONSchemaProvider schemaProvider = new JacksonSchemaProvider(mapper);
// Retrieves a JSON Schema object based on a file
JSONSchema schema = schemaProvider.getSchema(jsonSchemaInputStream);
// Validates a JSON Instance object stored in a file
List<String> errors = schema.validate(contents);
Projects worth exploring:
https://github.com/java-json-tools/json-schema-validator
https://github.com/everit-org/json-schema
https://github.com/networknt/json-schema-validator
Here is a nice list.
Here is an online sandbox.
I'm biased with jackson for all things JSON.
https://github.com/FasterXML/jackson-module-jsonSchema