JsonMappingException: Can not deserialize instance of java.lang.String out of START_OBJECT token 1

问题

I'm trying to parse a JSON to an object in java, the JSON is something like that

{"usage":{"text_characters":22,"features":1,"text_units":1},"entities":[{"count":1,"text":"pisos","disambiguation":{"subtype":["NONE"]},"type":"Producto"},{"count":1,"text":"No hay","disambiguation":{"subtype":["NONE"]},"type":"Quiebre_Stock"},{"count":1,"text":"madera","disambiguation":{"subtype":["NONE"]},"type":"Producto"}],"language":"es"}

I'm trying to mapping with this method

parsedJsonObj = mapper.readValue(result, NLUEntitiesRelations.class);

and NLUEntitiesRelations.class is like that

public class NLUEntitiesRelations {
    private UsageNLU usage;
    private List<EntityNLU> entities;
    private String language;

    //getter and setter
}

public class UsageNLU {
    private int text_characters;
    private int features;
    private int text_units;
    //getersand setter
}

public class EntityNLU {
    private int count;
    private String text;
    private DisambiguationNLU disambiguation;
    private String type;
    //getter and setter
}

public class DisambiguationNLU {
    private List<String> subtype;
    //getter and setter
}

but when executing it I am given the following error, and I was careful to create a new class when it was a JSON within JSON as in usagenlu

Error: com.fasterxml.jackson.databind.JsonMappingException: Can not deserialize instance of java.lang.String out of START_OBJECT token at [Source: { "usage": { "text_units": 1, "text_characters": 22, "features": 1 }, "language": "es", "entities": [ { "type": "Producto", "text": "pisos", "disambiguation": { "subtype": [ "NONE" ] }, "count": 1 }, { "type": "Quiebre_Stock", "text": "no hay", "disambiguation": { "subtype": [ "NONE" ] }, "count": 1 }, { "type": "Producto", "text": "madera", "disambiguation": { "subtype": [ "NONE" ] }, "count": 1 } ] } ; line: 2, column: 12] (through reference chain: cl.sodimac.watson.alchemy.json.NLUEntitiesRelations["usage"])

回答1:

In the entity parts of your JSON there are things like this:

"disambiguation": {
    "subtype": [
        "NONE"
    ]
}

That means there are 2 issues with your Java classes making them incompatible with your JSON content:

In your class EntityNLU
it should be private DisambiguationNLU disambiguation; (without List<>)
instead of private List<DisambiguationNLU> disambiguation;
In your class DisambiguationNLU
it should be private List<String> subtype; (wth lower-case t)
instead of private List<String> subType;

回答2:

Your field

private List<DisambiguationNLU> disambiguation;

should be

private DisambiguationNLU disambiguation;

It's an object, not array

回答3:

Resolved this problem and it's working fine for me. Have used Jackson lib and Sharing my code snippets.

   **MainClass** 


     public class MainClass {

     public static void main(String[] args) throws JsonParseException, 
     JsonMappingException, IOException {

    String jsonStr = "{\r\n" + "    \"usage\": {\r\n" + "       \"text_characters\": 22,\r\n"
            + "     \"features\": 1,\r\n" + "       \"text_units\": 1\r\n" + "  },\r\n" + " \"entities\": [{\r\n"
            + "     \"count\": 1,\r\n" + "      \"text\": \"pisos\",\r\n" + "       \"disambiguation\": {\r\n"
            + "         \"subtype\": [\"NONE\"]\r\n" + "        },\r\n" + "     \"type\": \"Producto\"\r\n"
            + " }, {\r\n" + "       \"count\": 1,\r\n" + "      \"text\": \"No hay\",\r\n"
            + "     \"disambiguation\": {\r\n" + "          \"subtype\": [\"NONE\"]\r\n" + "        },\r\n"
            + "     \"type\": \"Quiebre_Stock\"\r\n" + "    }, {\r\n" + "       \"count\": 1,\r\n"
            + "     \"text\": \"madera\",\r\n" + "      \"disambiguation\": {\r\n"
            + "         \"subtype\": [\"NONE\"]\r\n" + "        },\r\n" + "     \"type\": \"Producto\"\r\n"
            + " }],\r\n" + "    \"language\": \"es\"\r\n" + "}";

    ObjectMapper mapper = new ObjectMapper();

    MyPojo details = mapper.readValue(jsonStr, MyPojo.class);

    System.out.println("Value for getText_characters is: " + details.getUsage().getText_characters());
    System.out.println("Value for getFeatures is: " + details.getUsage().getFeatures());
    System.out.println("Value for getLanguage is: " + details.getLanguage().toString() + "\n");

    for (Entities itr : details.getEntities()) {

        System.out.println("Value for getCount is: " + itr.getCount());
        System.out.println("Value for getText is: " + itr.getText());
        System.out.println("Value for getText is: " + itr.getType() + "\n");

        for (String itrs : itr.getDisambiguation().getSubtype()) {

            System.out.println("Value for getSubtype is: " + itrs + "\n");

        }       }   } }



    **MyPojo.java**

import java.util.ArrayList;

public class MyPojo {
private Usage usage;

private String language;

private ArrayList<Entities> entities;

public Usage getUsage() {
    return usage;
}

public void setUsage(Usage usage) {
    this.usage = usage;
}

public String getLanguage() {
    return language;
}

public void setLanguage(String language) {
    this.language = language;
}

public ArrayList<Entities> getEntities() {
    return entities;
}

public void setEntities(ArrayList<Entities> entities) {
    this.entities = entities;
} }

 **Entities class**

      public class Entities {
private Disambiguation disambiguation;

private String text;

private String count;

private String type;

public Disambiguation getDisambiguation() {
    return disambiguation;
}

public void setDisambiguation(Disambiguation disambiguation) {
    this.disambiguation = disambiguation;
}

public String getText() {
    return text;
}

public void setText(String text) {
    this.text = text;
}

public String getCount() {
    return count;
}

public void setCount(String count) {
    this.count = count;
}

public String getType() {
    return type;
}

public void setType(String type) {
    this.type = type;
} }

   **Disambiguation** 

  public class Disambiguation {
  private String[] subtype;

 public String[] getSubtype() {
    return subtype;
}

public void setSubtype(String[] subtype) {
    this.subtype = subtype;
} }

 **Usage.java**


   public class Usage {
private String features;

private String text_characters;

private String text_units;

public String getFeatures() {
    return features;
}

public void setFeatures(String features) {
    this.features = features;
}

public String getText_characters() {
    return text_characters;
}

public void setText_characters(String text_characters) {
    this.text_characters = text_characters;
}

public String getText_units() {
    return text_units;
}

public void setText_units(String text_units) {
    this.text_units = text_units;
} }


   **RESULTS**:
     Value for getText_characters is: 22
     Value for getFeatures is: 1
     Value for getLanguage is: es

        Value for getCount is: 1
        Value for getText is: pisos
        Value for getText is: Producto

       Value for getSubtype is: NONE

        Value for getCount is: 1
        Value for getText is: No hay
        Value for getText is: Quiebre_Stock

        Value for getSubtype is: NONE

        Value for getCount is: 1
        Value for getText is: madera
        Value for getText is: Producto

       Value for getSubtype is: NONE

来源：https://stackoverflow.com/questions/50202876/jsonmappingexception-can-not-deserialize-instance-of-java-lang-string-out-of-st

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