How to convert JSON string into List of Java object

Question

This is my JSON Array   -                     firstName     abc            lastName     xyz                         firstName     pqr            lastName     str             I have this in my String object  Now I want to convert it into Java object and store it in List of java object  e g  In Student object  I am using below code to convert it into List of Java object   -   ObjectMapper mapper   new ObjectMapper    StudentList studentList   mapper readValue jsonString  StudentList class     My List class is -   public class StudentList        private List lt Student gt  participantList   new ArrayList lt Student gt            getters and setters     My Student object is  -  class Student        String firstName      String lastName         getters and setters     Am I missing something here  I am getting below exception  -  Exception   com fasterxml jackson databind JsonMappingException  Can not deserialize instance of com aa Student out of START ARRAY token

User · Answer

You can use below class to read list of objects. It contains static method to read a list with some specific object type. It is included Jdk8Module changes which provide new time class supports too. It is a clean and generic class.

List<Student> students = JsonMapper.readList(jsonString, Student.class);

Generic JsonMapper class:

import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.datatype.jdk8.Jdk8Module;
import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;

import java.io.IOException;
import java.util.*;

import java.util.Collection;

public class JsonMapper {

    public static <T> List<T> readList(String str, Class<T> type) {
        return readList(str, ArrayList.class, type);
    }

    public static <T> List<T> readList(String str, Class<? extends Collection> type, Class<T> elementType) {
        final ObjectMapper mapper = newMapper();
        try {
            return mapper.readValue(str, mapper.getTypeFactory().constructCollectionType(type, elementType));
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    private static ObjectMapper newMapper() {
        final ObjectMapper mapper = new ObjectMapper();
        mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
        mapper.registerModule(new JavaTimeModule());
        mapper.registerModule(new Jdk8Module());
        return mapper;
    }
}

User · Answer

Try this  It works with me  Hope you too    x000D   x000D  List lt YOUR OBJECT gt  testList   new ArrayList lt  gt     x000D  testList add test1   x000D   x000D  Gson gson   new Gson    x000D   x000D  String json   gson toJson testList   x000D   x000D  Type type   new TypeToken lt ArrayList lt YOUR OBJECT gt  gt      getType    x000D   x000D  ArrayList lt YOUR OBJECT gt  array   gson fromJson json  type   x000D   x000D   x000D

User · Answer

I made a method to do this below called jsonArrayToObjectList  Its a handy static class that will take a filename and the file contains an array in JSON form    List lt Items gt  items   jsonArrayToObjectList               domain ItemsArray json    Item class        public static  lt T gt  List lt T gt  jsonArrayToObjectList String jsonFileName  Class lt T gt  tClass  throws IOException           ObjectMapper mapper   new ObjectMapper            final File file   ResourceUtils getFile  classpath     jsonFileName           CollectionType listType   mapper getTypeFactory                constructCollectionType ArrayList class  tClass           List lt T gt  ts   mapper readValue file  listType           return ts

User · Answer

use below simple code  no need to use any library  String list    your json string   Gson gson   new Gson                             Type listType   new TypeToken lt ArrayList lt YourClassObject gt  gt       getType    ArrayList lt YourClassObject gt  users   new Gson   fromJson list   listType

User · Answer

You can also use Gson for this scenario   Gson gson   new Gson    NameList nameList   gson fromJson data  NameList class    List lt Name gt  list   nameList getList      Your NameList class could look like   class NameList   List lt Name gt  list     getter and setter

User · Answer

StudentList studentList   mapper readValue jsonString StudentList class     Change this to this one  StudentList studentList   mapper readValue jsonString  new TypeReference lt List lt Student gt  gt

User · Answer

I have resolved this one by creating the POJO class  Student class  of the JSON and Main Class is used for read the values from the JSON in the problem        Main Class        public static void main String   args  throws JsonParseException          JsonMappingException  IOException        String jsonStr       r n           r n               firstName       abc    r n                           lastName       xyz   r n             r n           r n                           firstName       pqr    r n               lastName       str   r n            r n              ObjectMapper mapper   new ObjectMapper         List lt Student gt  details   mapper readValue jsonStr  new        TypeReference lt List lt Student gt  gt                    for  Student itr   details             System out println  Value for getFirstName is                         itr getFirstName             System out println  Value for getLastName  is                        itr getLastName                RESULT             Value for getFirstName is  abc          Value for getLastName  is  xyz          Value for getFirstName is  pqr          Value for getLastName  is  str      Student class     public class Student   private String lastName   private String firstName   public String getLastName         return lastName     public String getFirstName         return firstName

User · Answer

For any one who looks for answer yet  1 Add jackson-databind library to your build tools like Gradle or Maven 2 in your Code  ObjectMapper mapper   new ObjectMapper     List lt Student gt  studentList   new ArrayList lt  gt      studentList   Arrays asList mapper readValue jsonStringArray  Student   class

User · Answer

You are asking Jackson to parse a StudentList  Tell it to parse a List  of students  instead  Since List is generic you will typically use a TypeReference  List lt Student gt  participantJsonList   mapper readValue jsonString  new TypeReference lt List lt Student gt  gt

[java] How to convert JSON string into List of Java object?

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