How to use Jackson to deserialise an array of objects

Question

The Jackson data binding documentation indicates that Jackson supports deserialising   Arrays of all supported types  but I can t figure out the exact syntax for this   For a single object I would do this     json input        id     junk        stuff     things       Java MyClass instance   objectMapper readValue json  MyClass class     Now for an array I want to do this     json input         id     junk        stuff     things            id     spam        stuff     eggs        Java List lt MyClass gt  entries       Anyone know if there is a magic missing command  If not then what is the solution

User · Answer

you could also create a class which extends ArrayList:

public static class MyList extends ArrayList<Myclass> {}

and then use it like:

List<MyClass> list = objectMapper.readValue(json, MyList.class);

User · Answer

I was unable to use this answer because my linter won t allow unchecked casts   Here is an alternative you can use  I feel it is actually a cleaner solution   public  lt T gt  List lt T gt  parseJsonArray String json  Class lt T gt  clazz  throws JsonProcessingException     var tree   objectMapper readTree json     var list   new ArrayList lt T gt       for  JsonNode jsonNode   tree        list add objectMapper treeToValue jsonNode  clazz          return list

User · Answer

First create an instance of ObjectReader which is thread-safe   ObjectMapper objectMapper   new ObjectMapper    ObjectReader objectReader   objectMapper reader   forType new TypeReference lt List lt MyClass gt  gt          Then use it    List lt MyClass gt  result   objectReader readValue inputStream

User · Answer

here is an utility which is up to transform json2object  or   Object2json  whatever your pojo  entity T    import java io IOException  import java io StringWriter  import java util List   import com fasterxml jackson core JsonGenerationException  import com fasterxml jackson core JsonParseException  import com fasterxml jackson core type TypeReference  import com fasterxml jackson databind DeserializationFeature  import com fasterxml jackson databind JsonMappingException  import com fasterxml jackson databind ObjectMapper  import com fasterxml jackson databind SerializationFeature               author TIAGO MEDICI         public class JsonUtils        public static boolean isJSONValid String jsonInString            try               final ObjectMapper mapper   new ObjectMapper                mapper readTree jsonInString               return true            catch  IOException e                return false                       public static String serializeAsJsonString Object object  throws JsonGenerationException  JsonMappingException  IOException           ObjectMapper objMapper   new ObjectMapper            objMapper enable SerializationFeature INDENT OUTPUT           objMapper disable SerializationFeature FAIL ON EMPTY BEANS           StringWriter sw   new StringWriter            objMapper writeValue sw  object           return sw toString               public static String serializeAsJsonString Object object  boolean indent  throws JsonGenerationException  JsonMappingException  IOException           ObjectMapper objMapper   new ObjectMapper            if  indent    true                objMapper enable SerializationFeature INDENT OUTPUT               objMapper disable SerializationFeature FAIL ON EMPTY BEANS                      StringWriter stringWriter   new StringWriter            objMapper writeValue stringWriter  object           return stringWriter toString               public static  lt T gt  T jsonStringToObject String content  Class lt T gt  clazz  throws JsonParseException  JsonMappingException  IOException           T obj   null          ObjectMapper objMapper   new ObjectMapper            obj   objMapper readValue content  clazz           return obj              SuppressWarnings  rawtypes       public static  lt T gt  T jsonStringToObjectArray String content  throws JsonParseException  JsonMappingException  IOException           T obj   null          ObjectMapper mapper   new ObjectMapper            obj   mapper readValue content  new TypeReference lt List gt                          return obj             public static  lt T gt  T jsonStringToObjectArray String content  Class lt T gt  clazz  throws JsonParseException  JsonMappingException  IOException           T obj   null          ObjectMapper mapper   new ObjectMapper            mapper   new ObjectMapper   configure DeserializationFeature ACCEPT SINGLE VALUE AS ARRAY  true           obj   mapper readValue content  mapper getTypeFactory   constructCollectionType List class  clazz            return obj

User · Answer

try       ObjectMapper mapper   new ObjectMapper        JsonFactory f   new JsonFactory        List lt User gt  lstUser   null      JsonParser jp   f createJsonParser new File  C   maven  user json         TypeReference lt List lt User gt  gt  tRef   new TypeReference lt List lt User gt  gt            lstUser   mapper readValue jp  tRef       for  User user   lstUser            System out println user toString              catch  JsonGenerationException e        e printStackTrace      catch  JsonMappingException e        e printStackTrace      catch  IOException e        e printStackTrace

User · Answer

From Eugene Tskhovrebov List lt MyClass gt  myObjects   Arrays asList mapper readValue json  MyClass   class    This solution seems to be the best for me

User · Answer

First create a mapper    import com fasterxml jackson databind ObjectMapper    in play 2 3 ObjectMapper mapper   new ObjectMapper      As Array   MyClass   myObjects   mapper readValue json  MyClass   class     As List   List lt MyClass gt  myObjects   mapper readValue jsonInput  new TypeReference lt List lt MyClass gt  gt          Another way to specify the List type   List lt MyClass gt  myObjects   mapper readValue jsonInput  mapper getTypeFactory   constructCollectionType List class  MyClass class

User · Answer

For Generic Implementation   public static  lt T gt  List lt T gt  parseJsonArray String json                                           Class lt T gt  classOnWhichArrayIsDefined                                            throws IOException  ClassNotFoundException      ObjectMapper mapper   new ObjectMapper       Class lt T   gt  arrayClass    Class lt T   gt   Class forName   L    classOnWhichArrayIsDefined getName              T   objects   mapper readValue json  arrayClass      return Arrays asList objects

[java] How to use Jackson to deserialise an array of objects

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