Converting BSON Type ObjectId to JSON (Storing in Mongodb) -Java -

new gson().tojson(new objectid())

when above, output

"_id" : { "_time" : 1374347520 , "_machine" : -1025067326 , "_inc" : 585905201 , "_new" : false}

but want

"_id":{"$oid":51eae100c2e6b6c222ec3431}

which usual mongodb id format. preferable method in java this?

update:

my value object

import com.google.gson.annotations.serializedname; import org.bson.types.objectid;  public class taskobject {      @serializedname("_id")     private objectid _id;      @serializedname("revno")     private int revno; } 

i trying store mongodb custom _id

taskobject taskobject = new taskobject(); taskobject.set_id(new objectid()); taskmongodbclient.getinstance().         persistnewtaskdata(new gson().tojson(taskobject)); 

what stored in mongodb looks this.

_id: { "_time" : 1397464341 , "_machine" : 1441187434 , "_inc" : -1687457948 , "_new" : true}

instead of _id:{"$oid": xxxx} can query using oid value.

what doing wrong here? please help.

thanks

there @ least 2 possible ways this. correct way use gson typeadapter configure how objectid written (and read from) json. need create implements typeadapter , register gsonbuilder, way gson knows there's special way handle objectids.

i've written small test prove works, using use case , example object (but omitted revno field brevity):

@test public void shouldwritecorrectjson() {     // given     taskobject taskobject = new taskobject();     taskobject._id = new objectid("51eae100c2e6b6c222ec3431");      gson gson = new gsonbuilder().registertypeadapter(objectid.class, new objectidtypeadapter()).create();      // when     string gsonstring = gson.tojson(taskobject);      //     assertthat(gsonstring, is("{\"_id\":{\"$oid\":\"51eae100c2e6b6c222ec3431\"}}")); }  private class objectidtypeadapter extends typeadapter<objectid> {     @override     public void write(final jsonwriter out, final objectid value) throws ioexception {         out.beginobject()            .name("$oid")            .value(value.tostring())            .endobject();     }      @override     public objectid read(final jsonreader in) throws ioexception {         in.beginobject();         assert "$oid".equals(in.nextname());         string objectid = in.nextstring();         in.endobject();         return new objectid(objectid);     } } 

note test asserts json looks way want to, , had create objectidtypeadapter knows field name of objectid "$oid" , value string value of objectid, , not serialise of fields individually.

note if change way object written json, need change way it's read. i've implemented read check field name correct 1 (you should throw exception here instead of using simple assert if it's not correct), , read value , create objectid string value.

in real life, want check null values in both of cases too.

because i'm responsible coder, wrote test show reading case works too:

@test public void shouldreadfromjson() {     // given     gson gson = new gsonbuilder().registertypeadapter(objectid.class, new objectidtypeadapter()).create();      // when     taskobject actualtaskobject = gson.fromjson("{\"_id\":{\"$oid\":\"51eae100c2e6b6c222ec3431\"}}", taskobject.class);      //     taskobject taskobject = new taskobject();     taskobject._id = new objectid("51eae100c2e6b6c222ec3431");     assertthat(actualtaskobject._id, is(taskobject._id)); } 

further reading:

• typeadapter
• gsonbuilder.registertypeadapter
• jsonreader , jsonwriter