Read JSON Java Example - JSON Processing API

In this example, we will see a quick example to read a JSON file with JSON-P library.

The code example is available at my Github repository.

• Check out complete JSON-P tutorial at Java JSON Processing Tutorial.
• Check out the Jackson JSON tutorial at https://www.javaguides.net/p/java-jackson-json-tutorial-with-examples.html.
• Check out google GSON tutorial at Google GSON Tutorial.

JSON-P

JSON Processing (JSON-P) is a Java API to process (for e.g. parse, generate, transform and query) JSON messages. It produces and consumes JSON text in a streaming fashion (similar to StAX API for XML) and allows to build a Java object model for JSON text using API classes (similar to DOM API for XML).

Read more about JSON-P at official documentation - https://javaee.github.io/jsonp.

Add Dependencies

JSON-P is the reference implementation for Java JSON Processing API. We can use this in maven project by adding the following dependencies:

<dependency>
    <groupId>javax.json</groupId>
    <artifactId>javax.json-api</artifactId>
    <version>1.1</version>
</dependency>

<dependency>
    <groupId>org.glassfish</groupId>
    <artifactId>javax.json</artifactId>
    <version>1.1</version>
</dependency>

Let's create a JSON file named "posts.json":

{
    "id": 100,
    "title": "JSONP Tutorial",
    "description": "Post about JSONP",
     "content": "HTML content here",
    "tags": [
        "Java",
        "JSON"
    ]
}

We have Java bean classes that represent above JSON format as:

package net.javaguides.jsonp.tutorial;

import java.util.Arrays;

public class Post {
    private int id;
    private String title;
    private String description;
    private String content;
    private String[] tags;

    public Post() {

    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getTitle() {
        return title;
    }

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

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    public String getContent() {
        return content;
    }

    public void setContent(String content) {
        this.content = content;
    }

    public String[] getTags() {
        return tags;
    }

    public void setTags(String[] tags) {
        this.tags = tags;
    }

    @Override
    public String toString() {
        return "Post [id=" + id + ", title=" + title + ", description=" + description + ", content=" + content +
            ", tags=" + Arrays.toString(tags) + "]";
    }
}

Java JSON Read Example

In this example, we are reading above "posts.json" file. We use JsonReader and JsonObject interfaces to read and extract fields and display.

Here is complete source code:

package net.javaguides.jsonp.tutorial;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;

import javax.json.Json;
import javax.json.JsonArray;
import javax.json.JsonObject;
import javax.json.JsonReader;
import javax.json.JsonValue;

/**
 * Class to read json from a posts.json file.
 * @author Ramesh fadatare
 *
 */
public class ReadJSON {

    public static void main(String[] args) throws IOException {
        InputStream fis = new FileInputStream("posts.json");

        // create JsonReader object
        JsonReader jsonReader = Json.createReader(fis);

        // get JsonObject from JsonReader
        JsonObject jsonObject = jsonReader.readObject();

        // we can close IO resource and JsonReader now
        jsonReader.close();
        fis.close();

        // Retrieve data from JsonObject and create Post bean
        Post post = new Post();
        post.setId(jsonObject.getInt("id"));
        post.setTitle(jsonObject.getString("title"));
        post.setDescription(jsonObject.getString("description"));
        post.setContent(jsonObject.getString("content"));

        // reading arrays from json
        JsonArray jsonArray = jsonObject.getJsonArray("tags");
        String[] tags = new String[jsonArray.size()];
        int index = 0;
        for (JsonValue value: jsonArray) {
            tags[index++] = value.toString();
        }
        post.setTags(tags);
        // print post object
        System.out.println(post.toString());
    }
}

Output:

Post [id=100, title=JSONP Tutorial, description=Post about JSONP, 
content=HTML content here, tags=["Java", "JSON"]]

The code example is available at my Github repository.

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

• Check out the Jackson JSON tutorial at https://www.javaguides.net/p/java-jackson-json-tutorial-with-examples.html.

• Check out google GSON tutorial at Google GSON Tutorial.