I want to serialize and deserialize an immutable object using com.fasterxml.jackson.databind.ObjectMapper.
The immutable class looks like this (just 3 internal attributes, getters and constructors):
JavaScript
x
public final class ImportResultItemImpl implements ImportResultItem {
private final ImportResultItemType resultType;
private final String message;
private final String name;
public ImportResultItemImpl(String name, ImportResultItemType resultType, String message) {
super();
this.resultType = resultType;
this.message = message;
this.name = name;
}
public ImportResultItemImpl(String name, ImportResultItemType resultType) {
super();
this.resultType = resultType;
this.name = name;
this.message = null;
}
@Override
public ImportResultItemType getResultType() {
return this.resultType;
}
@Override
public String getMessage() {
return this.message;
}
@Override
public String getName() {
return this.name;
}
}
However when I run this unit test:
JavaScript
@Test
public void testObjectMapper() throws Exception {
ImportResultItemImpl originalItem = new ImportResultItemImpl("Name1", ImportResultItemType.SUCCESS);
String serialized = new ObjectMapper().writeValueAsString((ImportResultItemImpl) originalItem);
System.out.println("serialized: " + serialized);
//this line will throw exception
ImportResultItemImpl deserialized = new ObjectMapper().readValue(serialized, ImportResultItemImpl.class);
}
I get this exception:
JavaScript
com.fasterxml.jackson.databind.JsonMappingException: No suitable constructor found for type [simple type, class eu.ibacz.pdkd.core.service.importcommon.ImportResultItemImpl]: can not instantiate from JSON object (missing default constructor or creator, or perhaps need to add/enable type information?)
at [Source: {"resultType":"SUCCESS","message":null,"name":"Name1"}; line: 1, column: 2]
at
nothing interesting here
This exception asks me to create a default constructor, but this is an immutable object, so I don’t want to have it. How would it set the internal attributes? It would totally confuse the user of the API.
So my question is: Can I somehow de/serialize immutable objects without default constructor?
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Answer
To let Jackson know how to create an object for deserialization, use the @JsonCreator
and @JsonProperty
annotations for your constructors, like this:
JavaScript
@JsonCreator
public ImportResultItemImpl(@JsonProperty("name") String name,
@JsonProperty("resultType") ImportResultItemType resultType,
@JsonProperty("message") String message) {
super();
this.resultType = resultType;
this.message = message;
this.name = name;
}