jackson deserialization json to java-objects

Question

Here is my Java code which is used for the de-serialization   i am trying to convert json string into java object  In doing so i have used the following code   package ex1jackson  import com fasterxml jackson core JsonGenerationException  import com fasterxml jackson databind JsonMappingException  import com fasterxml jackson databind ObjectMapper  import java io IOException  public class Ex1jackson   public static void main String   args       ObjectMapper mapper   new ObjectMapper    try           String userDataJSON        id     value11     name      value12     qty     value13                                          id      value21     name     value22     qty      value23               product userFromJSON   mapper readValue userDataJSON  product class           System out println userFromJSON         catch  JsonGenerationException e            System out println e             catch  JsonMappingException e           System out println e         catch  IOException e        System out println e                and my product java class  package ex1jackson  public class product    private String id  private String name   private String qty     Override public String toString         return  Product  id     id     name      name   qty   qty            i am getting the following error   com fasterxml jackson databind exc UnrecognizedPropertyException   Unrecognized field  id   class ex1jackson product   not marked as ignorable  0 known properties     at   Source  java io StringReader 16f76a8  line  1  column  8   through reference chain  ex1jackson product  id     BUILD SUCCESSFUL  total time  0 seconds    help me to solve this

User · Accepted Answer

It looks like you are trying to read an object from JSON that actually describes an array. Java objects are mapped to JSON objects with curly braces {} but your JSON actually starts with square brackets [] designating an array.

What you actually have is a List<product> To describe generic types, due to Java's type erasure, you must use a TypeReference. Your deserialization could read: myProduct = objectMapper.readValue(productJson, new TypeReference<List<product>>() {});

A couple of other notes: your classes should always be PascalCased. Your main method can just be public static void main(String[] args) throws Exception which saves you all the useless catch blocks.

User · Answer

Your product class needs a parameterless constructor  You can make it private  but Jackson needs the constructor   As a side note  You should use Pascal casing for your class names  That is Product  and not product

User · Answer

You have to change the line  product userFromJSON   mapper readValue userDataJSON  product class     to  product   userFromJSON   mapper readValue userDataJSON  product   class     since you are deserializing an array  btw  you should start your class names with upper case letters as mentioned earlier   Additionally you have to create setter methods for your fields or mark them as public in order to make this work   Edit  You can also go with Steven Schlansker s suggestion and use  List lt product gt  userFromJSON           mapper readValue userDataJSON  new TypeReference lt List lt product gt  gt           instead if you want to avoid arrays

User · Answer

JsonNode node   mapper readValue      id     value11     name      value12     qty     value13        System out println  id     node findValues  id   get 0  asText       this also done the trick

[java] jackson deserialization json to java-objects

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