How to Convert JSON to Java Objects Using Jackson?

How to Convert JSON to Java Objects Using Jackson

In this guide, we aim to transform a JSON string into a Java object, allowing for convenient access to its properties. This example showcases a JSON string containing a library with multiple music tracks, demonstrating how to use both Jackson's mapping methods and custom Java classes to achieve this conversion.

Using Jackson's Map-Based deserialization:

<code class="java">ObjectMapper mapper = new ObjectMapper();
Map<String, Object> map = mapper.readValue(json, Map.class);</code>

This approach creates a plain Java Map where each JSON key is mapped to an Object value. However, it lacks the structure and type-safety of custom Java classes.

Using Jackson's JSON Tree:

<code class="java">JsonNode rootNode = mapper.readTree(json);</code>

This method returns a JSON Tree, a hierarchical representation of the JSON string that provides better flexibility than a plain Map. It allows for dynamic exploration and traversal of the JSON data.

Creating Custom Java Classes:

For a more structured and type-safe representation, we can define custom Java classes:

<code class="java">public class Library {
  @JsonProperty("libraryname")
  public String name;

  @JsonProperty("mymusic")
  public List<Song> songs;
}
public class Song {
  @JsonProperty("Artist Name") public String artistName;
  @JsonProperty("Song Name") public String songName;
}</code>

Using these classes, we can deserialize the JSON string as follows:

<code class="java">Library lib = mapper.readValue(jsonString, Library.class);</code>

Now, we can access the library and its tracks conveniently:

<code class="java">String libraryName = lib.name;
Song firstTrack = lib.songs.get(0);
String artistName = firstTrack.artistName;</code>

This approach provides a more intuitive and object-oriented way of manipulating the JSON data compared to using plain Maps or JSON Trees.

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