Deserializing "Unwrapped" Json Arrays to POJO - jackson

Question

Half of my problem is not knowing the exact terms to search for an answer. I believe I'm dealing with what's called a "flat" or "unwrapped" json array with the underlying "members" node in that this would work if there was a "member:" element for each of the "members" underlying property nodes, but there isn't.
I receive json (I can't control format) that looks like this:
{
"id" : "1",
"context" :
{
"id" : "123,
"title" : "My Title"
},
"members": [
{
"prop1" : { },
"prop2" : "123",
"propArray1" : [ "Value1", "Value2" ],
"prop3" : "xyz",
"prop4" : "123"
},
{
"prop1" : { },
"prop2" : "456",
"propArray1" : [ "Value1", "Value2" ],
"prop3" : "abc",
"prop4" : "456"
}
] }
My POJO (minus the simple gets/sets):
#JsonAutoDetect
public class MyPojo {
#JsonProperty
private String id;
#JsonProperty
private Context context;
#JsonProperty("members")
private List<Member> members = new ArrayList<>();
#JsonAutoDetect
public class Context {
public Context() {}
#JsonProperty
private String id;
#JsonProperty
private String title;
}
#JsonAutoDetect
public class Member {
public Member() {}
#JsonProperty
private String prop1;
#JsonProperty
private String prop2;
#JsonProperty
private List<String> propArray1 = new ArrayList<>();
#JsonProperty
private String prop3;
#JsonProperty
private String prop4;
#JsonProperty
private String prop5;
}
public List<Member> getMembers() {
return members;
}
public void setMembers(List<Member> members) {
this.members = members;
}
}
I've tried GSON:
new Gson().fromJson(jsonEntity, MyPojo.class);
returns:
java.lang.IllegalStateException: Expected a string but was BEGIN_OBJECT
I've tried Jackson:
new ObjectMapper().readValue(jsonEntity, MyPojo.class);
throws:
org.codehaus.jackson.map.JsonMappingException: No suitable constructor found for type [simple type, class MyPojo$Member]: can not instantiate from JSON object (need to add/enable type information?)
at [Source: java.io.StringReader#5c6e5b53; line: 10, column: 3] (through reference chain: MyPojo["members"])
I don't think "add/enable" type information is a relevant warning and I do have the default constructor.
I've searched dozens of json deserialization posts and this one seems similar to this but I have to get the entire Json object not just a piece of it...and I tried it just to extract members array and it didn't work.
Cannot deserialize JSON to POJO

Answer 1

there are some issues here:
the JSON testdata is not valid (missing closing " at second id). corrected version:
{
"id" : "1",
"context" :
{
"id" : "123",
"title" : "My Title"
},
"members": [
{
"prop1" : { },
"prop2" : "123",
"propArray1" : [ "Value1", "Value2" ],
"prop3" : "xyz",
"prop4" : "123"
},
{
"prop1" : { },
"prop2" : "456",
"propArray1" : [ "Value1", "Value2" ],
"prop3" : "abc",
"prop4" : "456"
}
] }
second issue: nested classes by default have a reference to the enclosing class. one consequence of this is that they cannot be created without an instance of the enclosing class. Jackson i get this exception:
Cannot construct instance of `foo.MyPojo$Member` (although at least one Creator exists)
fix this by converting the nested classes to static inner classes:
public static class Context {
...
}
third issue: the mapping does not match the JSON.
Cannot deserialize instance of `java.lang.String` out of START_OBJECT token
...
(through reference chain: foo.MyPojo["members"]->java.util.ArrayList[0]->foo.MyPojo$Member["prop1"])
fix this by changing the mapping. e.g:
#JsonAutoDetect
public static class Member {
public Member() {}
#JsonProperty
private Map<String, String> prop1;
...
}
Using this 3 changes its possible to deserialize the JSON using Jackson.