json object deserialization/unmarshalling to java object(mainly array/list) with Jackson

jackson_templates.java

//jackson mapper.readValue - json to java object
@RequestMapping(value="/newPost", method = RequestMethod.POST, produces="application/json", consumes = "application/json")
@ResponseBody
public ResponseEntity newPost(@RequestBody String body) throws Exception {
    ObjectMapper mapper = new ObjectMapper();
    TypeReference<HashMap<String,Object>> typeRef = new TypeReference<HashMap<String,Object>>() {};
    HashMap<String,Object> map = mapper.readValue(body, typeRef);
}

//jackson - json to object
ObjectMapper mapper = new ObjectMapper();
//JSON file to Java object
Staff obj = mapper.readValue(new File("c:\\test\\staff.json"), Staff.class);
//JSON URL to Java object
Staff obj = mapper.readValue(new URL("http://some-domains/api/name.json"), Staff.class);
//JSON string to Java Object
Staff obj = mapper.readValue("{'name' : 'mkyong'}", Staff.class);


//jackson serializing/marshalling - java object to json
ObjectMapper mapper = new ObjectMapper();
// Java object to JSON file
mapper.writeValue(new File("c:\\test\\staff.json"), new Staff());
// Java object to JSON string
String jsonString = mapper.writeValueAsString(object);
//pretty print
String jsonInString2 = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(staff);

//setting an object
private static Staff createStaff() {
  Staff staff = new Staff();

  staff.setName("mkyong");
  staff.setAge(38);
  staff.setPosition(new String[]{"Founder", "CTO", "Writer"});
  Map<String, BigDecimal> salary = new HashMap() {{
      put("2010", new BigDecimal(10000));
      put("2012", new BigDecimal(12000));
      put("2018", new BigDecimal(14000));
  }};
  staff.setSalary(salary);
  staff.setSkills(Arrays.asList("java", "python", "node", "kotlin"));

  return staff;
}


//a JSON can be parsed into a JsonNode object and used to retrieve data from a specific node:
String json = "{ \"color\" : \"Black\", \"type\" : \"FIAT\" }";
JsonNode jsonNode = objectMapper.readTree(json);
String color = jsonNode.get("color").asText();
// Output: color -> Black


//customizable serialization and deserialization process.
//custom serializer
public class CustomCarSerializer extends StdSerializer<Car> {
     
    public CustomCarSerializer() {
        this(null);
    }
 
    public CustomCarSerializer(Class<Car> t) {
        super(t);
    }
 
    @Override
    public void serialize(
      Car car, JsonGenerator jsonGenerator, SerializerProvider serializer) {
        jsonGenerator.writeStartObject();
        jsonGenerator.writeStringField("car_brand", car.getType());
        jsonGenerator.writeEndObject();
    }
}
//invocation
ObjectMapper mapper = new ObjectMapper();
SimpleModule module = new SimpleModule("CustomCarSerializer", new Version(1, 0, 0, null, null, null));
module.addSerializer(Car.class, new CustomCarSerializer());
mapper.registerModule(module);
Car car = new Car("yellow", "renault");
String carJson = mapper.writeValueAsString(car);

//custom deserializer
public class CustomCarDeserializer extends StdDeserializer<Car> {
     
    public CustomCarDeserializer() {
        this(null);
    }
 
    public CustomCarDeserializer(Class<?> vc) {
        super(vc);
    }
 
    @Override
    public Car deserialize(JsonParser parser, DeserializationContext deserializer) {
        Car car = new Car();
        ObjectCodec codec = parser.getCodec();
        JsonNode node = codec.readTree(parser);
         
        // try catch block
        JsonNode colorNode = node.get("color");
        String color = colorNode.asText();
        car.setColor(color);
        return car;
    }
}

//invocation
String json = "{ \"color\" : \"Black\", \"type\" : \"BMW\" }";
ObjectMapper mapper = new ObjectMapper();
SimpleModule module =
  new SimpleModule("CustomCarDeserializer", new Version(1, 0, 0, null, null, null));
module.addDeserializer(Car.class, new CustomCarDeserializer());
mapper.registerModule(module);
Car car = mapper.readValue(json, Car.class);

//handle data formats
ObjectMapper objectMapper = new ObjectMapper();
DateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm a z");
objectMapper.setDateFormat(df);
String carAsString = objectMapper.writeValueAsString(request);
// output: {"car":{"color":"yellow","type":"renault"},"datePurchased":"2016-07-03 11:43 AM CEST"}


//handle dynamic JSON objects, which have unknown properties
class Product {
 
    // common fields
 
    JsonNode details;
 
    // standard getters and setters
}

//invocation
String json = "<json object>";
Product product = objectMapper.readValue(json, Product.class);
assertThat(product.getName()).isEqualTo("Pear yPhone 72");
assertThat(product.getDetails().get("audioConnector").asText()).isEqualTo("none");

//or without jackson dependency in pojo
class Product {
 
    // common fields
 
    Map<String, Object> details;
 
    // standard getters and setters
}

//when having fixed and dynamic properties mixed in a single JSON object
class Product {
 
    // common fields
 
    Map<String, Object> details = new LinkedHashMap<>();
 
    @JsonAnySetter
    void setDetail(String key, Object value) {
        details.put(key, value);
    }
 
    // standard getters and setters
}

//@RequestBody Spring MVC annotation to deserialize/un-marshall JSON string to Java object
@RestController
public class CustomerController {
    //@Autowired CustomerService customerService;

    @RequestMapping(path="/customers", method= RequestMethod.POST)
    @ResponseStatus(HttpStatus.CREATED)
    public Customer postCustomer(@RequestBody Customer customer){
        //return customerService.createCustomer(customer);
    }
}

//BU GEREKLİ Mİ? - Annotate your entities member elements with @JsonProperty with corresponding json field names.
public class Customer {
    @JsonProperty("customer_id")
    private long customerId;
    @JsonProperty("first_name")
    private String firstName;
    @JsonProperty("last_name")
    private String lastName;
    @JsonProperty("town")
    private String town;
}

//if your objects have some common properties, as well as some optional ones
@JsonIgnore
private Map<String, Object> additionalProperties = new HashMap<String, Object>();

@JsonAnyGetter
public Map<String, Object> getAdditionalProperties() {
return this.additionalProperties;
}

@JsonAnySetter
public void setAdditionalProperty(String name, Object value) {
this.additionalProperties.put(name, value);
}

//The way I understand it, your objects have some common properties, as well as some optional ones. You can model the optional properties using @JsonAnyGetter and @JsonAnySetter:

class Data {
    @JsonProperty
    private Long created;
    @JsonProperty
    private String id;
    @JsonProperty
    private String type;
    private Map<String, Object> optional = new HashMap<>();
    public Data() { // empty public constructor is required
    }
    // getters/setters for all properties omitted for brevity
    @JsonAnySetter
    public void addOptional(String name, Object value) {
        optional.put(name, value);
    }
    @JsonAnyGetter
    public Object getOptional(String name) {
        return optional.get(name);
    }
}
//Then you can deserialize your objects using

ObjectMapper objectMapper = new ObjectMapper();
Data data = objectMapper.readValue(j, Data.class);
//or, if you've got an array of your Data objects as input,

Data[] data = objectMapper.readValue(j, Data[].class);
//All properties except created, id and type will be placed in the optional map.

//creating a custom pojo
package com.stackoverflow.question;

import com.fasterxml.jackson.annotation.*;

import java.util.HashMap;
import java.util.Map;

@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonPropertyOrder({
        "userId",
        "postBody",
        "postTitle",
        "created",
        "tagList"
})
public class MyRequest {

    @JsonProperty("userId")
    private int userId;
    @JsonProperty("postBody")
    private String postBody;
    @JsonProperty("postTitle")
    private String postTitle;
    @JsonProperty("created")
    private Object created;
    @JsonProperty("tagList")
    private String[] tagList = null;
    @JsonIgnore
    private Map<String, Object> additionalProperties = new HashMap<String, Object>();

    @JsonProperty("userId")
    public int getUserId() {
        return userId;
    }

    @JsonProperty("userId")
    public void setUserId(int userId) {
        this.userId = userId;
    }

    @JsonProperty("postBody")
    public String getPostBody() {
        return postBody;
    }

    @JsonProperty("postBody")
    public void setPostBody(String postBody) {
        this.postBody = postBody;
    }

    @JsonProperty("postTitle")
    public String getPostTitle() {
        return postTitle;
    }

    @JsonProperty("postTitle")
    public void setPostTitle(String postTitle) {
        this.postTitle = postTitle;
    }

    @JsonProperty("created")
    public Object getCreated() {
        return created;
    }

    @JsonProperty("created")
    public void setCreated(Object created) {
        this.created = created;
    }

    @JsonProperty("tagList")
    public String[] getTagList() {
        return tagList;
    }

    @JsonProperty("tagList")
    public void setTagList(String[] tagList) {
        this.tagList = tagList;
    }

    @JsonAnyGetter
    public Map<String, Object> getAdditionalProperties() {
        return this.additionalProperties;
    }

    @JsonAnySetter
    public void setAdditionalProperty(String name, Object value) {
        this.additionalProperties.put(name, value);
    }
}