Object Mapping - Jackson

Two popular libraries to map JSON data with Java objects.

Jackson

Dependency

   <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.11.0</version>
    </dependency>

Anotation

    @JsonIgnoreProperties(ignoreUnknown = true)  // ignore properties that not defined in the class
    @JsonInclude(JsonInclude.Include.NON_NULL)   // null value shoudn't be read in

    @JsonProperty("titile")   //match title with the class variable 
    public String getTitle() {
        return title;
    }

Mapper Usage

  1. Mapping from JSON file directly, i.e., JSON is flat data that includes the object data.
    ObjectMapper mapper = new ObjectMapper();
    Item item = mapper.readValue(entity.getContent(), Item.class); // to single object
    Item[] times = mapper.readValue(entity.getContent(), Item[].class); // to object array
  1. Mapping from nested array of object using JsonNode.
    ObjectMapper mapper = new ObjectMapper();
    JsonNode jsonNode = mapper.readTree(entity.getContent()); // read content to JsonNode
    JsonNode jobs = jsonNode.get("jobs");  // get a value from the key jobs
    List<Item> items = new ArrayList(Arrays.asList(mapper.readValue(jobs.toString(), Item[].class))); // mapper them to an array of Items.
Written on May 13, 2021