Using RestTemplate in Spring boot

problem

You wish to quickly send an Http Request, for example to an API and get back its response. In this post we’re gonna use the https://www.themealdb.com/ API for testing purposes and because I like it.

SOLUTION

Using the RestTemplate object.

In Spring boot, we can autowire the RestTemplate and perform http requests by using an endpoint.

First, let’s create a @Bean configuration for the RestTemplate as follows:

				
					@Bean
public RestTemplate restTemplate(RestTemplateBuilder builder) {
    return builder.build();
}

I placed that in the main class that runs the Spring Boot application, for example:

ResttemplateApplication.java

				
					package com.programmerabroad.resttemplate;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.client.RestTemplateBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;

@SpringBootApplication
public class ResttemplateApplication {

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

    @Bean
    public RestTemplate restTemplate(RestTemplateBuilder builder) {
        return builder.build();
    }
}

Setting the Api url in the application properties and later loading it using the @Value annotation.

application.properties

				
					spring.application.name=resttemplate
themealdb.url=https://www.themealdb.com/api/json/v1/1/search.php?s=

I’m using the RestTemplate to send the HttpRequest to the API:

ResttemplateApplication.java

				
					String url = this.apiUrl + search;
ResponseEntity<String> forEntity = restTemplate.getForEntity(url, String.class);
return forEntity.getBody();

Simply the getForEntity() method is doing all the job in one line.

Then I get the response which is a JSON object. The full code as follows:

ResttemplateApplication.java

				
					package com.programmerabroad.resttemplate;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;
import org.springframework.web.client.RestTemplate;

@RestController
public class ApiController {

    @Autowired
    private RestTemplate restTemplate;

    @Value("${themealdb.url}")
    private String apiUrl;

    @GetMapping(value = "/", produces = MediaType.APPLICATION_JSON_VALUE)
    public String index(@RequestParam(name = "search") String search) {

        String url = this.apiUrl + search;

        ResponseEntity<String> forEntity = restTemplate.getForEntity(url, String.class);

        return forEntity.getBody();
    }
}

Search by parameter To make things a little bit more exciting I pass the search term via a @RequestParam parameter as shown in the GetMapping method.

output

Mapping the JSON response to an object - DTO

We can create a DTO – Data Transfer Object that will be responsible for representing the JSON from the API into an object in the Java world. It’s simply a class that contains all the fields according to the keys in the JSON.

Productivity Tip I used an online web app to make things easier and faster. In this case, the json2csharp website that can be found here. Just paste the JSON and it will generate the Java class for you.

For example:

MealDto.java

				
					package com.programmerabroad.resttemplate;

import java.io.Serializable;

public class MealDto implements Serializable {
    public String idMeal;
    public String strMeal;
    public Object strMealAlternate;
    public String strCategory;
    public String strArea;
    public String strInstructions;
    public String strMealThumb;
    public String strTags;
    public String strYoutube;
    public String strIngredient1;
    public String strIngredient2;
    public String strIngredient3;
    public String strIngredient4;
    public String strIngredient5;
    public String strIngredient6;
    public String strIngredient7;
    public String strIngredient8;
    public String strIngredient9;
    public String strIngredient10;
    public String strIngredient11;
    public String strIngredient12;
    public String strIngredient13;
    public String strIngredient14;
    public String strIngredient15;
    public String strIngredient16;
    public String strIngredient17;
    public String strIngredient18;
    public String strIngredient19;
    public String strIngredient20;
    public String strMeasure1;
    public String strMeasure2;
    public String strMeasure3;
    public String strMeasure4;
    public String strMeasure5;
    public String strMeasure6;
    public String strMeasure7;
    public String strMeasure8;
    public String strMeasure9;
    public String strMeasure10;
    public String strMeasure11;
    public String strMeasure12;
    public String strMeasure13;
    public String strMeasure14;
    public String strMeasure15;
    public String strMeasure16;
    public String strMeasure17;
    public String strMeasure18;
    public String strMeasure19;
    public String strMeasure20;
    public String strSource;
    public Object strImageSource;
    public Object strCreativeCommonsConfirmed;
    public Object dateModified;
}

Because our search result in the API can return more than one results (meals) we need another one DTO class to hold a list of the meals.

For example:

RootDto.java

				
					package com.programmerabroad.resttemplate;

import java.io.Serializable;
import java.util.ArrayList;

public class RootDto implements Serializable {
    public ArrayList<MealDto> meals;
}

Change the controller to adopt the change:

ApiController.java

				
					  @GetMapping(value = "/", produces = MediaType.APPLICATION_JSON_VALUE)
    public ResponseEntity<RootDto> index(@RequestParam(name = "search") String search) {

        String url = this.apiUrl + search;

        ResponseEntity<RootDto> forEntity = restTemplate.getForEntity(url, RootDto.class);

        return forEntity;
    }

Note Now, the method returns a ResponseEntity with a RootDto. So we’re dealing with an object that has organised information and not just a raw JSON in a String.

For example, we can retrieve only the instructions of making a meal, e.g. pasta.

				
					forEntity.body.meals.get(0).strInstructions

Simply by accessing the field strInstructions above we can see the instructions as String.

output

Important The DTO/ POJO class defined above by the generator is using public fields. This is considered a bad practice when it comes to Java coding and OOP. But for the sake of simplicity, it was left as is from the code generator. Otherwise, I would have applied the Immutable Design Pattern by using private final fields and more.

conclusion

In this post we saw how to use the RestTemplate object given by Spring Boot and how to hit the API of themealdb.com and get a JSON response to our web browser. Also, we saw how to easily map the JSON response to a Java object POJO/ DTO for more organized information.

Share it!

Ellion

Professional IT consultant, writer, programmer enthusiast interested in all sorts of coding.
Eats all cookies 🍪

Tagged Spring Boot