Jackson: Serialize only 10 Properties out of 100 - jackson

Jackson by default includes all public getters. But if I have hundreds of getters and I want to serialize just few of them, how can I achieve this?
I don't want to use #JsonIgnore annotation to specify all others hundred properties.

You can use Jackson's views or filters to select the serialization form of your object. Here is an example using the filter which picks up the properties with the given names:
public class JacksonFilter {
#JsonFilter("filter")
public static class Bean {
private final String field1;
private final String field12;
private final String field10;
private final String field100;
public Bean(String field1, String field12, String field10, String field100) {
this.field1 = field1;
this.field12 = field12;
this.field10 = field10;
this.field100 = field100;
}
public String getField1() {
return field1;
}
public String getField12() {
return field12;
}
public String getField10() {
return field10;
}
public String getField100() {
return field100;
}
}
public static void main(String[] args) throws JsonProcessingException {
ObjectMapper mapper = new ObjectMapper();
SimpleFilterProvider filters = new SimpleFilterProvider();
filters.addFilter("filter",
SimpleBeanPropertyFilter.serializeAllExcept("field12", "field100"));
mapper.setFilters(filters);
Bean bean = new Bean("A", "B", "C", "D");
System.out.println(mapper.writerWithDefaultPrettyPrinter().writeValueAsString(bean));
}
}
Output:
{
"field1" : "A",
"field10" : "C"
}

Related

Jackson Serialization Problems

I am having some trouble serializing/deserializing my classes below.
My Data class holds a list of other classes.
When I call the serialize/deserialize methods in the Data class, I get the following error:
Caused by: com.fasterxml.jackson.databind.JsonMappingException: Can not construct instance of com.amazon.rancor.storage.types.ChildData: no suitable constructor found, can not deserialize from Object value (missing default constructor or creator, or perhaps need to add/enable type information?)
The error comes from the deserialize method. But I also believe the serialization is not working properly. This is what the serialized Data object looks like:
{childData:[{zipCode:{present:true},countryCode:"US"}]
The Optional field is not being serialized properly even though I have set the objectMapper.registerModule(new Jdk8Module()); field
I can't seem to figure out what I am doing wrong. Maybe I need to change something in ChildData and ChildDataV2 class. But I am not sure what.
Any pointers would be appreciated!
public class Data {
private List<ChildData> childData;
private List<ChildDataV2> childDataV2;
private static ObjectMapper objectMapper;
static {
objectMapper = new ObjectMapper();
objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
objectMapper.registerModule(new Jdk8Module());
}
public Data() { }
#JsonCreator
public Data(#JsonProperty("childData") final List<ChildData> childData,
#JsonProperty("childDataV2") final List<ChildDataV2> childDataV2) {
this.childData = childData;
this.childDataV2 = childDataV2;
}
public List<ChildData> getChildData() {
return childData;
}
public void setChildData(final List<ChildData> childData) {
this.childData = childData;
}
public List<ChildDataV2> getChildDataV2() {
return childDataV2;
}
public void setChildDataV2(final List<ChildDataV2> childDataV2) {
this.childDataV2 = childDataV2;
}
public String serialize() {
try {
return objectMapper.writeValueAsString(this);
} catch (JsonProcessingException e) {
throw new RuntimeException("Failed to serialize. Data: " + this, e);
}
}
public Data deSerialize(final String data) {
try {
return objectMapper.readValue(data, Data.class);
} catch (IOException e) {
throw new RuntimeException("Failed to deserialize. Data" + data, e);
}
}
}
public class ChildData {
private final String countryCode;
private final Optional<String> zipCode;
public ChildData(final String countryCode, final Optional<String> zipCode) {
this.countryCode = countryCode;
this.zipCode = zipCode;
}
public Optional<String> getZipCode() {
return zipCode;
}
public String getCountryCode() {
return countryCode;
}
}
public class ChildDataV2 extends ChildData {
private final Object struct;
public ChildDataV2(final String cc, final Optional<String> postalCode,
final Object struct) {
super(cc, postalcode);
this.struct = struct;
}
}
The exception is quite clear right? You need to add a default constructor for ChildData or annotate the existing constructor like this:
#JsonCreator
public ChildData(#JsonProperty("countryCode") String countryCode, #JsonProperty("zipCode") Optional<String> zipCode) {
this.countryCode = countryCode;
this.zipCode = zipCode;
}

Mapping DTO with final members in MapStruct

is there a way to map a DTO using MatStruct which have a few final data members as well and cannot have a default constructor , like :
public class TestDto {
private final String testName;
private int id;
private String testCase;
public TestDto(String testName) {
this.testName = testName;
}
public String getTestName() {
return testName;
}
public int getId() {
return id;
}
public String getTestCase() {
return testCase;
}
public void setId(int id) {
this.id = id;
}
public void setTestCase(String testCase) {
this.testCase = testCase;
}
}
please suggest how could this DTO be mapped using MapStruct.
You can use #ObjectFactory that would construct an instance of your DTO.
For example:
#Mapper
public interface MyMapper {
#ObjectFactory
default TestDto create() {
return new TestDto("My Test Name");
}
//the rest of the mappings
}
You can also enhance the #ObjectFactory to accept the source parameter, that you can use to construct the TestDto. You can even use a #Context as an Object Factory.
NB: You don't have to put the #ObjectFactory method in the same Mapper, or even a MapStruct #Mapper. You can put it in any class (or make it static) and then #Mapper(uses = MyFactory.class)

Deserializing a list results in duplicates

I have a simple pojo where i have one list of strings and default get/set, i have another get so that in json i get 2 different fields
my pojo and test code snippet are below
public static class TestClass{
public ArrayList<String> names = null;
public ArrayList<String> getNames() {
if(null == names) names = new ArrayList<>();
return names;
}
public void setNames(ArrayList<String> names) {
this.names = names;
}
public ArrayList<String> getNames_r() {
return getNames();
}
#Override
public String toString() {
return "TestClass [names=" + names + "]";
}
}
#Test
public void testDeSerializationSimple() throws JsonParseException, JsonMappingException, IOException{
String justSchool = "{\"names\":[\"second\",\"one\",\"two\",\"three\"],\"names_r\":[\"second\",\"one\",\"two\",\"three\"]}";
ObjectMapper myDefaultMapper= new ObjectMapper();
myDefaultMapper.setDateFormat(CoreUtils.COMMON_SIMPLE_DATE_FORMAT)
.setTimeZone(TimeZone.getTimeZone("UTC"))
.enable(SerializationFeature.INDENT_OUTPUT)
.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
TestClass testReadDummy = myDefaultMapper.readValue(justSchool, TestClass.class);
System.out.println(" mapper test read = "+testReadDummy);
//assertEquals(testRead.getListString().size(),4);
System.out.println("list = "+testReadDummy);
assertEquals(testReadDummy.names.size(), 4);
}
Try using the #JsonIgnore annotation in the duplicate of your list so it doesn't get serialized, it would look something like:
#JsonIgnore
public ArrayList<String> getNames_r() {
return getNames();
}
That should get rid of your duplicate field in you serialized JSON.
Hope it helps,
Jose Luis
configuring the mapper to not use getters as setters using
MAPPER.configure(MapperFeature.USE_GETTERS_AS_SETTERS, false);
solved this

Deserialize JSON array into Map using Jackson in Java

I'm using fasterXML's Jackson (v2.3.3) library to deserialize and serialize a custom class. The class is defined as following:
public class Person {
private String name;
private Map<String, Person> children;
// lots of other fields of different types with no issues
}
the keys of map children are the name fields. I receive data in JSON with each person object structured as following (I have omitted the other fields):
{"name":"Bob", "children":[{"name":"Jimmmy"},{"name":"Judy"}]}
(Many Fields such as children are optional and aren't serialized when null)
I have been storing children in a List<Person> so far with no issues, but many new use cases need to have access to the set of names or to a specific Person using his name as key. This is why I have decided to store them using a Map.
After some research, I think the best way is to use Annotations #JsonDeserialize and #JsonSerialize with a JsonDeserializer and JsonSerializer as parameter respectively for the field children:
public class Person {
private String id;
#JsonSerialize(using=MySerializer.class)
#JsonDeserialize(using=MyDeserializer.class)
private Map<String, Person> friends;
// lots of other fields
}
My question is: Does such a JsonSerializer/JsonDeserializer exist and if not, how do I define one?
edit: I have started implementing a custom Deserializer, but I get this exception:
com.fasterxml.jackson.databind.JsonMappingException: Class has no default (no arg) constructor
which is weird because I have defined a default constructor. Here is my custom Deserializer:
public class MyDeserializer extends JsonDeserializer<Map<String, Person>> {
public MyDeserializer() {
}
#Override
public Map<String, Person> deserialize(JsonParser jp, DeserializationContext ctxt)
throws IOException, JsonProcessingException {
JsonNode personsNodeArray = jp.getCodec().readTree(jp);
Map<String, Person> newChildren = null;
if (personsNodeArray.isArray() && personsNodeArray.size() > 0) {
newChildren = new HashMap<String, Person>();
for (JsonNode personNode : personsNodeArray) {
String id = personNode.get("name").asText();
// jsonMapper is a default ObjectMapper
newChildren.put(id, jsonMapper.readValue(personNode.toString(), Person.class));
}
}
return newChildren;
}
}
You can also consider reading children information as a collection of persons with subsequent conversion into a map. You can define a setter method (or a constructor parameter) to accept a List<Person> and then put each element into the Map<String, Person> children field. That would avoid unnecessary complexity of custom serialisation.
Here is an example:
public class JacksonChildren {
public static final String JSON = "{\"name\":\"Bob\", \"children\":[{\"name\":\"Jimmmy\"}," +
"{\"name\":\"Judy\"}]}";
public static class Person {
public String name;
private Map<String, Person> children = new HashMap<>();
public void setChildren(final List<Person> children) {
for (Person p : children) {
this.children.put(p.name, p);
}
}
#Override
public String toString() {
return "Person{" +
"name='" + name + '\'' +
", children=" + children +
'}';
}
}
public static void main(String[] args) throws IOException {
ObjectMapper mapper = new ObjectMapper();
System.out.println(mapper.readValue(JSON, Person.class));
}
}
Output:
Person{name='Bob', children={Judy=Person{name='Judy', children={}}, Jimmmy=Person{name='Jimmmy', children={}}}}

Jackson configuration to write enum as object

When I try to serialize and deserialize a Set<ClassA<?>> of generic objects that look as follows:
public class ClassA<T> {
private ClassB datum;
private T value;
...
}
If that T happens to be an enum, it gets written as a String value. This is fine for serialization, but when I deserialize, it's not possible to know if the String value is an enum or not. Jackson then turns the resulting object into a String and you get a ClassA<String> instead of ClassA<SomeEnumType>.
Is there a configuration in Jackson to have it create some hints that the value is an enum? Or perhaps turn the enum into a JSON object rather then a string value?
Is there a configuration in Jackson to have it create some hints that the value is an enum?
It's possible to deserialize to an enum instance from a matching JSON string value. Or is this somehow not applicable to your situation?
Here is an example.
import java.util.Set;
import java.util.TreeSet;
import org.codehaus.jackson.annotate.JsonAutoDetect.Visibility;
import org.codehaus.jackson.annotate.JsonMethod;
import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.map.type.TypeFactory;
public class JacksonFoo
{
public static void main(String[] args) throws Exception
{
ObjectMapper mapper = new ObjectMapper().setVisibility(JsonMethod.FIELD, Visibility.ANY);
String myEnumJson = mapper.writeValueAsString(MyEnum.MyEnum1);
System.out.println(myEnumJson);
MyEnum myEnum = mapper.readValue(myEnumJson, MyEnum.class);
System.out.println(myEnum);
Set<ClassA<MyEnum>> set = new TreeSet<ClassA<MyEnum>>();
set.add(new ClassA<MyEnum>(new ClassB("bValue7"), MyEnum.MyEnum1));
set.add(new ClassA<MyEnum>(new ClassB("bValue8"), MyEnum.MyEnum2));
String setJson = mapper.writeValueAsString(set);
System.out.println(setJson);
TypeFactory typeFactory = TypeFactory.defaultInstance();
Set<ClassA<MyEnum>> setCopy = mapper.readValue(setJson,
typeFactory.constructCollectionType(Set.class,
typeFactory.constructParametricType(ClassA.class, MyEnum.class)));
System.out.println(setCopy);
}
}
class ClassA<T> implements Comparable<ClassA<T>>
{
ClassB datum;
T value;
ClassA()
{
}
ClassA(ClassB datum, T value)
{
this.datum = datum;
this.value = value;
}
#Override
public int compareTo(ClassA<T> o)
{
return 42;
}
#Override
public String toString()
{
return String.format("ClassA: datum=%s, value=%s", datum, value);
}
}
class ClassB
{
String bValue;
ClassB()
{
}
ClassB(String bValue)
{
this.bValue = bValue;
}
#Override
public String toString()
{
return String.format("ClassB: bValue=%s", bValue);
}
}
enum MyEnum
{
MyEnum1("myEnum1", 1), MyEnum2("myEnum2", 2);
String name;
int id;
MyEnum(String name, int id)
{
this.name = name;
this.id = id;
}
}
Output:
"MyEnum1"
MyEnum1
[{"datum":{"bValue":"bValue7"},"value":"MyEnum1"},{"datum":{"bValue":"bValue8"},"value":"MyEnum2"}]
[ClassA: datum=ClassB: bValue=bValue7, value=MyEnum1, ClassA: datum=ClassB: bValue=bValue8, value=MyEnum2]
If for some reason it's necessary to have enums serialized as POJOs, then it appears custom serialization processing is required. Serializing enums with Jackson