JSON P JsonArrayBuilder Java Example

JSR 354 addresses the standard Java API for JSON processing(JSON-P) and shipped as part of JEE 7. The Java API for JSON Processing provides portable APIs to parse, generate, transform, and query JSON using the streaming API or the object model API.

The code example is available at my Github repository.

Check out complete JSON-P tutorial at Java JSON Processing Tutorial.

JSON-P Object model API provides below important classes and interfaces:

• Json - Contains static methods to create JSON parsers, generators, and their factories.
• JsonObjectBuilder - Creates an object model in memory by adding values from application code.
• JsonArrayBuilder - Creates an array model in memory by adding values from application code.
• JsonReader - Reads a JsonObject or a JsonArray from an input source.
• JsonWriter - Writes a JsonObject or a JsonArray to an output source.

In this example, we use a JsonArrayBuilder for creating and modifying JsonArray objects.

Java JSON-P JsonArrayBuilder Example

In this example, we create a list of post objects and transform them into a JsonArray and we write this JSON to console.

package net.javaguides.jsonp.examples;

import java.io.StringWriter;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import javax.json.Json;
import javax.json.JsonArray;
import javax.json.JsonArrayBuilder;
import javax.json.JsonObject;
import javax.json.JsonWriter;
import javax.json.JsonWriterFactory;
import javax.json.stream.JsonGenerator;

import net.javaguides.jsonp.tutorial.Post;

/**
 * The class to demonstrate the usage of JsonArrayBuilder interface.
 * @author Ramesh Fadatare
 *
 */
public class JsonArrayBuilderExample {
    public static void main(String[] args) {

        JsonArrayBuilder jsonArrayBuilder = Json.createArrayBuilder();

        List < Post > posts = createPosts();

        posts.forEach(post - > {

            JsonObject json = Json.createObjectBuilder()
            .add("id", post.getId())
            .add("title", post.getTitle())
            .add("description", post.getDescription())
            .add("content", post.getContent()).build();

            jsonArrayBuilder.add(json);
        });


        JsonArray jsonArray = jsonArrayBuilder.build();

        Map < String, Boolean > config = new HashMap < String, Boolean > ();
        config.put(JsonGenerator.PRETTY_PRINTING, true);

        JsonWriterFactory jwf = Json.createWriterFactory(config);
        StringWriter sw = new StringWriter();

        try (JsonWriter jsonWriter = jwf.createWriter(sw)) {

            jsonWriter.writeArray(jsonArray);

            System.out.println(sw);
        }
    }

    public static List < Post > createPosts() {

        List < Post > posts = new ArrayList < > ();
        // create a post
        Post post = new Post();
        post.setTitle("JSONP Tutorial");
        post.setId(100);
        post.setDescription("Post about JSONP");
        post.setContent("HTML content here");

        String[] tags = {
            "Java",
            "JSON"
        };
        // create some predefined tags
        post.setTags(tags);


        // create a post
        Post post1 = new Post();
        post1.setTitle("Jackson Tutorial");
        post1.setId(100);
        post1.setDescription("Post about Jackson API");
        post1.setContent("HTML content here");
        // create some predefined tags
        post1.setTags(new String[] {
            "Java",
            "JSON",
            "Jackson"
        });

        // create a post
        Post post2 = new Post();
        post2.setTitle("Google Gson Tutorial");
        post2.setId(100);
        post2.setDescription("Post about Google Gson");
        post2.setContent("HTML content here");

        // create some predefined tags
        post2.setTags(new String[] {
            "Java",
            "JSON",
            "Gson"
        });

        posts.add(post);
        posts.add(post1);
        posts.add(post2);
        return posts;
    }
}

Output:

[
    {
        "id": 100,
        "title": "JSONP Tutorial",
        "description": "Post about JSONP",
        "content": "HTML content here"
    },
    {
        "id": 100,
        "title": "Jackson Tutorial",
        "description": "Post about Jackson API",
        "content": "HTML content here"
    },
    {
        "id": 100,
        "title": "Google Gson Tutorial",
        "description": "Post about Google Gson",
        "content": "HTML content here"
    }
]

Let's understand the above example.

A JsonArrayBuilder is created with createArrayBuilder():

JsonArrayBuilder jsonArrayBuilder = Json.createArrayBuilder();

In this for loop, we create JSON objects and add them to the builder:

posts.forEach(post -> {

	JsonObject json = Json.createObjectBuilder()
			.add("id", post.getId())
			.add("title", post.getTitle())
			.add("description", post.getDescription())
			.add("content", post.getContent()).build();

	jsonArrayBuilder.add(json);
});

The build() method creates a JsonArray from the builder:

JsonArray jsonArray = jsonArrayBuilder.build();

The JsonArray is written to the writer:

jsonWriter.writeArray(jsonArray);

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