Parsing JSON in Spring Boot using JsonParser

In this tutorial we will learn how to parse JSON data in Spring Boot using the org.springframework.boot.json.JsonParser.

Overview of JSON Parsing

The simplest way to parse JSON Strings in Spring Boot is by means of the org.springframework.boot.json API which is native in Spring Boot. Let’s see a concrete example. Consider the following REST Service: https://jsonplaceholder.typicode.com/todos/1

Here is the above JSON:

{
  "userId": 1,
  "id": 1,
  "title": "delectus aut autem",
  "completed": false
}

In order to parse it, we can simply use the RestTemplate and request an Object for that URL. The JsonParser, in turn, will convert the JSON Document into a Map (Key,Value):

package com.example.parsejson;

import java.util.Map;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.json.JsonParser;
import org.springframework.boot.json.JsonParserFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;

@SpringBootApplication
public class ParsejsonApplication {

  public static void main(String[] args) {
    SpringApplication.run(ParsejsonApplication.class, args);
  }

  @Bean
  public CommandLineRunner commandLineRunner(ApplicationContext ctx) {
    return args -> {

      String url = "https://jsonplaceholder.typicode.com/todos/1";
      RestTemplate restTemplate = new RestTemplate();
      String resp = restTemplate.getForObject(url, String.class);
      JsonParser springParser = JsonParserFactory.getJsonParser();
      Map < String, Object > map = springParser.parseMap(resp);
      String mapArray[] = new String[map.size()];
      System.out.println("Items found: " + mapArray.length);

      int i = 0;

      for (Map.Entry < String, Object > entry: map.entrySet()) {
        System.out.println(entry.getKey() + " = " + entry.getValue());
        i++;
      }

    };
  }

}

And here’s the output when running the above piece of code:

Items found: 4
userId = 1
id = 1
title = delectus aut autem
completed = false

To run the above example, you don’t need any extra dependency to parse the JSON File. Just include the web starter:

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-web</artifactId>
</dependency>

Parsing an array of JSON Documents:

A more complex example consists in parsing a set of JSON items. For example: https://jsonplaceholder.typicode.com/todos/

The above REST Service returns an array of items. In order to parse them we will use the parseList method of the JsonParser as follows:

String url = "https://jsonplaceholder.typicode.com/todos/";
RestTemplate restTemplate = new RestTemplate();
String resp = restTemplate.getForObject(url, String.class);
JsonParser springParser = JsonParserFactory.getJsonParser();
List < Object > list = springParser.parseList(resp);
for (Object o: list) {
  if (o instanceof Map) {
    Map < String, Object > map = (Map < String, Object > ) o;
    System.out.println("Items found: " + map.size());
    int i = 0;
    for (Map.Entry < String, Object > entry: map.entrySet()) {
      System.out.println(entry.getKey() + " = " + entry.getValue());
      i++;
    }
  }
}