Deserialize complex Json with Jackson

Question

I ran into an issue with a "complex" json :

{
  "Books": [
    {
      "title": "Java",
      "instructions": [],
      "links": {
        "EJB": {
          "href": "www.java.com/EJB"
        }
      }
    },
    {
      "title": "C#",
      "instructions": [],
      "links": {
        "SOAP": {
          "href": "www.C#.com/SOAP"
        }
      }
    }]
}

Can someone tell me how to deserialize this kind of JSON to get a list of POJO please ?

The POJO has to be a "Book" with 3 fields : title , instructions and the links

thank you.

Answer 1

Your POJO classes could look like this:

class Books {

    @JsonProperty("Books")
    private List<Book> books;

    public List<Book> getBooks() {
        return books;
    }

    public void setBooks(List<Book> books) {
        this.books = books;
    }

    @Override
    public String toString() {
        return "Books [books=" + books + "]";
    }
}

class Book {

    private String title;
    private List<String> instructions;
    private Map<String, Link> links;

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public List<String> getInstructions() {
        return instructions;
    }

    public void setInstructions(List<String> instructions) {
        this.instructions = instructions;
    }

    public Map<String, Link> getLinks() {
        return links;
    }

    public void setLinks(Map<String, Link> links) {
        this.links = links;
    }

    @Override
    public String toString() {
        return "Book [title=" + title + ", instructions=" + instructions + ", links=" + links + "]";
    }
}

class Link {

    private String href;

    public String getHref() {
        return href;
    }

    public void setHref(String href) {
        this.href = href;
    }

    @Override
    public String toString() {
        return href;
    }
}

Simple usage:

ObjectMapper mapper = new ObjectMapper();

System.out.println(mapper.readValue(json, Books.class));

Above program prints:

Books [books=[Book [title=Java, instructions=[], links={EJB=www.java.com/EJB}], Book [title=C#, instructions=[], links={SOAP=www.C#.com/SOAP}]]]

Answer 2

You have a fundamental problem with your JSON for starters; you have duplicate member names.

And in this case, the behaviour of the parser is undefined (RFC 7159, section 4). Since jsonschema2pojo uses Jackson, this means you will get the last defined value for each duplicate member.

Use an array:

[
{
  "title":"Title 1",
  "instructions" : [],
  "links": {
    "link 1": {
      "href": "The link 1"
    }
  }
},
{
   "title":"Title 2",
   "instructions" : [],
   "links": {
    "link 2": {
      "href": "The link 2"
    }
  }
}
]

Then, jsonschema2pojo will not really deserialize to a POJO; what you really want is to define class MyClass for an array element (ie, one object) and use Jackson's ObjectMapper to deserialize:

final TypeReference<List<MyClass>> typeref
    = new TypeReference<List<MyClass>>() {};

final ObjectMapper mapper = new ObjectMapper();

final List<MyClass> list = mapper.readValue(whatever, typeref);