Transform JSON-LD in Java Transform JSON-LD in Java

Ashish Lahoti
Java
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In this tutorial, we’ll learn how to transform a Java Object to JSON-LD and vice versa. Also learn how to verify the schema of JSON-LD.

JSON-LD

JSON-LD is a JSON-based format which is used to represent structured data and linked data. Schema of JSON-LD can be found in documentation of schema.org.

JSON-LD is widely used in websites to markup the schema of website pages. This helps website indexers (such as Google) to understand the website better and boost SEO. Though the JSON-LD usage are not limited to websites, also used in REST Web services, and unstructured databases such as Apache CouchDB and MongoDB.

Transform Java Object to JSON-LD

Let’s transform the Java object to JSON-LD using jackson-jsonld which is a Jackson module that provides the annotation to generate JSON-LD documents.

Add Maven Dependency

If you are using maven, add jackson-jsonld dependency in your pom.xml

<dependency>
  <groupId>com.io-informatics.oss</groupId>
  <artifactId>jackson-jsonld</artifactId>
  <version>0.1.1</version>
</dependency>

Transform Java Object to JSON-LD

Next, We create a Person class and annotate it with json-ld annotations.

package com.cnc;

import ioinformarics.oss.jackson.module.jsonld.annotation.JsonldId;
import ioinformarics.oss.jackson.module.jsonld.annotation.JsonldProperty;
import ioinformarics.oss.jackson.module.jsonld.annotation.JsonldType;

@JsonldType("http://schema.org/Person")
public class Person {
    @JsonldId
    public  String id;
    @JsonldProperty("http://schema.org/name")
    public String name;
    @JsonldProperty("http://schema.org/jobTitle")
    public String jobtitle;
    @JsonldProperty("http://schema.org/url")
    public String url;
}

Finally, we create a Person object instance and transform it in JSON-LD

// Register Jsonld Module with Jackson
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.configure(SerializationFeature.INDENT_OUTPUT, true);
objectMapper.registerModule(new JsonldModule(() -> objectMapper.createObjectNode()));

// Create Person Instance
Person person = new Person();
person.id = "mailto:lahoti.ashish20@gmail.com";
person.name = "Ashish Lahoti";
person.jobtitle = "Software Developer";
person.url = "https://codingnconcepts.com";

// Transform to JSON-LD
String personJsonLd = objectMapper.writer().writeValueAsString(JsonldResource.Builder.create().build(person));
System.out.println(personJsonLd);

Output

{
  "@context" : {
    "jobtitle" : "http://schema.org/jobTitle",
    "name" : "http://schema.org/name",
    "url" : "http://schema.org/url"
  },
  "@type" : "http://schema.org/Person",
  "name" : "Ashish Lahoti",
  "jobtitle" : "Software Developer",
  "url" : "https://codingnconcepts.com",
  "@id" : "mailto:lahoti.ashish20@gmail.com"
}

Transform Nested Java Object to JSON-LD

We can also transform nested java objects to complex JSON-LD. Let’s annotate Organization and Location classes with json-ld annotations.

@JsonldType("http://schema.org/Organization")
public class Organization {
	@JsonldId
	public Integer id;
	@JsonldProperty("http://schema.org/url")
	public String url;
	@JsonldProperty("http://schema.org/name")
	public String name;
	@JsonldProperty("http://schema.org/location")
	public Location location;
}

@JsonldType("http://schema.org/PostalAddress")
public class Location {
	@JsonldProperty("http://schema.org/streetAddress")
	public String address;
	@JsonldProperty("http://schema.org/addressLocality")
	public String city;
	@JsonldProperty("http://schema.org/addressRegion")
	public String state;
	@JsonldProperty("http://schema.org/addressCountry")
	public String country;
	@JsonldProperty("http://schema.org/postalCode")
	public String zipcode;
}

Now, create an instance of Organization which also have a Location property and transform the instance to JSON-LD

// Register Jsonld Module with Jackson
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.configure(SerializationFeature.INDENT_OUTPUT, true);
objectMapper.registerModule(new JsonldModule(() -> objectMapper.createObjectNode()));

// Create Organization and Location Instances
Organization org = new Organization();
org.id = 12345;
org.url = "https://codingnconcepts.com";
org.name = "CodingNConcepts";

Location location = new Location();
location.address = "7 S. Broadway";
location.city = "Denver";
location.state = "CO";
location.country = "USA";
location.zipcode = "80209";
org.location = location;

// Transform to JSON-LD
String orgJsonLd = objectMapper.writer().writeValueAsString(JsonldResource.Builder.create().build(org));
System.out.println(orgJsonLd);

Output

{
  "@context" : {
    "name" : "http://schema.org/name",
    "location" : "http://schema.org/location",
    "url" : "http://schema.org/url"
  },
  "@type" : "http://schema.org/Organization",
  "url" : "https://codingnconcepts.com",
  "name" : "CodingNConcepts",
  "location" : {
    "@type" : "http://schema.org/PostalAddress",
    "@context" : {
      "zipcode" : "http://schema.org/postalCode",
      "country" : "http://schema.org/addressCountry",
      "address" : "http://schema.org/streetAddress",
      "city" : "http://schema.org/addressLocality",
      "state" : "http://schema.org/addressRegion"
    },
    "address" : "7 S. Broadway",
    "city" : "Denver",
    "state" : "CO",
    "country" : "USA",
    "zipcode" : "80209"
  },
  "@id" : 12345
}

Transform JSON-LD to Java Object

We can also transform the JSON-LD document to a plain JSON object and further transform the JSON to Java Object using Jackson Object Mapper. Let’s use jsonld-java which is a Java implementation of the JSON-LD 1.0 specification.

Add Maven Dependency

If you are using maven, add jsonld-java dependency in your pom.xml

<dependency>
    <groupId>com.github.jsonld-java</groupId>
    <artifactId>jsonld-java</artifactId>
    <version>0.13.0</version>
</dependency>

Transform JSON-LD to JSON

Let’s user the Person JSON-LD and save it in a file input.json

input.json

{
  "@context" : {
    "jobtitle" : "http://schema.org/jobTitle",
    "name" : "http://schema.org/name",
    "url" : "http://schema.org/url"
  },
  "@type" : "http://schema.org/Person",
  "name" : "Ashish Lahoti",
  "jobtitle" : "Software Developer",
  "url" : "https://codingnconcepts.com",
  "@id" : "mailto:lahoti.ashish20@gmail.com"
}

Next, read from this file and transform to a simple JSON string

// Read from JSON-LD file
InputStream inputStream = new FileInputStream("input.json");
Object jsonObject = JsonUtils.fromInputStream(inputStream);

// Transform to Simple JSON compact object
Object compact = JsonLdProcessor.compact(jsonObject, new HashMap<>(), new JsonLdOptions());

// Convert JSON to String
String compactContent = JsonUtils.toPrettyString(compact);
System.out.println(compactContent);

Output

{
  "@id" : "mailto:lahoti.ashish20@gmail.com",
  "@type" : "http://schema.org/Person",
  "http://schema.org/jobTitle" : "Software Developer",
  "http://schema.org/name" : "Ashish Lahoti",
  "http://schema.org/url" : "https://codingnconcepts.com"
}

Transform JSON to Java Object

We can further map this JSON string to a PersonJson POJO using Jackson ObjectMapper

@JsonIgnoreProperties(ignoreUnknown = true)
public class PersonJson {
    @JsonProperty("@id")
    private String id;
    @JsonProperty("@type")
    private String type;
    @JsonProperty("http://schema.org/name")
    private String name;
    @JsonProperty("http://schema.org/url")
    private String url;
    @JsonProperty("http://schema.org/jobTitle")
    private String jobtitle;
}

// Map JSON to POJO
ObjectMapper objectMapper = new ObjectMapper();
PersonJson person = objectMapper.readValue(compactContent, PersonJson.class);
System.out.println(person);

Verify Transformed JSON-LD

You can verify the schema of transformed JSON-LD using Structured Data Testing Tool.

Click on the link and select “CODE SNIPPET” tab. Then copy paste the generated JSON-LD. Click “Run Test”. It tells if the schema of generated JSON-LD is correct and show errors if any.


The full source code of this tutorial is available on GitHub.