How To Eat Json From Restful Spider Web Service As Well As Convert To Coffee Object - Jump Resttemplate Example

So far, I stimulate got non written much virtually REST together with RESTful spider web service barring simply about interview questions e.g. REST vs SOAP, which is thankfully really much appreciated past times my readers together with simply about full general suggestions virtually best books to acquire REST inwards past, but today I am going to write something virtually RESTTemplate cast from Spring MVC framework. Like its predecessors JdbcTemplate together with JmsTemplate, the RestTemplate is simply about other useful utility cast which allows you lot to interact amongst RESTful spider web services from a Java application built using Spring framework. It's a characteristic rich together with supports almost all REST methods e.g. GET, POST, HEAD, PUT or DELETE, though we'll solely job the GET method inwards this article to eat a RESTful Web Service together with convert the JSON reply to Java objects. It's 1 of the basic but interesting examples, given you lot volition oft notice scenarios to eat a RESTful spider web service from Java program.

I am too using Spring Boot to run my programme every bit a main() method instead of edifice a WAR file together with deploying inwards tomcat together with and so writing Servlet together with JSP to demonstrate the example. I actually notice the convenience offered past times Spring kick keen every bit it embeds Tomcat servlet container every bit the HTTP runtime, which is plenty to run this program.

Free RESTful Web Services on the Internet for Testing

In firm to exercise a RESTful client, you lot postulate to stimulate got a RESTful spider web service which tin render JSON content you lot desire to consume. Though you lot tin develop a RESTful customer inwards Spring framework itself, for testing role its amend to job the existing costless RESTful spider web service on the network e.g. http://jsonplaceholder.typicode.com has several useful RESTful API to render comments together with posts related information e.g. http://jsonplaceholder.typicode.com/posts/1 volition render ship information amongst id= 1, which looks something similar this:

{ "userId": 1, "Id": 1, "Title": "a championship " "Body": "the trunk of the content" }

Though, I stimulate got used simply about other costless REStful spider web service which returns Country's advert together with their ii together with iii missive of the alphabet ISO codes every bit shown below:

{   "RestResponse" : {     "messages" : [ "More webservices are available at http://www.groupkt.com/post/f2129b88/services.htm",      "Country works life matching code [IN]." ],     "result" : {       "name" : "India",       "alpha2_code" : "IN",       "alpha3_code" : "IND"     }   } } 

You tin job whatsoever of these spider web services to construct a RESTful client for testing. Though your domain cast volition alter depending upon which RESTful spider web service you lot are consuming.


Here is the screenshot of this RESTful spider web service reply inwards my browser:

Spring framework together with RestTemplate class. This programme has 4 Java files :  App.java, Response.java, RestResponse.java, together with Result.java. The outset cast is the principal cast which drives this application together with others are classes corresponding to JSON response nosotros acquire from this RESTful API.

App.java
This is our principal cast which drives this RESTful Spring application. It uses Spring kick to setup together with runs the program. The cast App implements CommandLineRunner together with calls the SpringApplication.run() method past times passing this instance of cast i.e. App.class. This will, inwards turn, telephone telephone the run method, where nosotros stimulate got code to telephone telephone a RESTful Web Service together with eat JSON reply using RestTemplate cast of Spring framework.

Just similar it's predecessor or closed cousins e.g. JmsTemplate together with JdbcTemplate, the RestTemplate cast too does everything for you.  All you lot postulate to say is the advert of the cast you lot desire to map the incoming JSON response.

We stimulate got outset created an instance of RestTemplate cast together with and so called the getForObject() method. This accepts ii parameters, first, a String URL to telephone telephone the RESTful Web Service together with minute the advert of the cast it should render amongst the response.  So, inwards simply 1 business of code, it calls the RESTful spider web service, parse the JSON reply together with render the Java object to you.

If you lot are curious to acquire to a greater extent than virtually RestTemplate cast together with so you lot tin too read Spring REST book. It explains all nitty gritty of developing RESTful spider web services inwards Spring framework.

Here are the Java classes required to telephone telephone a RESTful Web Service from Java Program using Spring together with RestTemplate utility:

package rest;  import org.slf4j.Logger; import org.slf4j.LoggerFactory; import org.springframework.boot.CommandLineRunner; import org.springframework.boot.SpringApplication; import org.springframework.web.client.RestTemplate;  public class App implements CommandLineRunner {    private static terminal Logger log = LoggerFactory.getLogger(App.class);    public static void main(String args[]) {     SpringApplication.run(App.class);   }     public void run(String... args) throws Exception {     RestTemplate restTemplate = new RestTemplate();     Response response = restTemplate.getForObject(                            "http://services.groupkt.com/country/get/iso2code/IN",                             Response.class);     log.info("==== RESTful API Response using Spring RESTTemplate START =======");     log.info(response.toString());     log.info("==== RESTful API Response using Spring RESTTemplate END =======");   } }

Response.java
This is the top-level cast to convert JSON reply to Java object you lot have past times consuming the RESTful spider web service response. I stimulate got use @JSonProperty to annotate the RestResponse patch to say the Jackson that this is the cardinal patch inwards the JSON document.

package rest;  import com.fasterxml.jackson.annotation.JsonProperty;  public class Response {    @JsonProperty   private RestResponse RestResponse;      public RestResponse getRestResponse() {     return RestResponse;   }    public void setRestResponse(RestResponse restResponse) {     RestResponse = restResponse;   }    public Response(){        }    @Override   public String toString() {     return "Response [RestResponse=" + RestResponse + "]";   }  }

RestResponse.java
This cast contains ii fields corresponding to RestResponse department of JSON reply nosotros received from RESTful Web service. The outset patch is a String array, messages together with Jackson volition parse the JSON array to String array together with shop the output for that belongings inwards this field. The minute field, the effect is in 1 trial to a greater extent than a custom type Java object to shop the information nosotros postulate i.e. advert together with ISO code of the country.

package rest;  import java.util.Arrays;  import com.fasterxml.jackson.annotation.JsonIgnoreProperties;   public class RestResponse {     private String[] messages;   private Result result;      public RestResponse(){       }      public String[] getMessages() {     return messages;   }   public void setMessages(String[] messages) {     this.messages = messages;   }   public Result getResult() {     return result;   }   public void setResult(Result result) {     this.result = result;   }    @Override   public String toString() {     return "RestResponse [messages=" + Arrays.toString(messages) + ", result=" + result + "]";   }   }

Result.java
This cast has 3 fields, corresponding to 3 properties for effect department inwards JSON response. All iii fields are String, first, the name is the advert of the country, second, alpha2_code is the two-digit ISO code for the dry reason together with third, alpha3_code is the three-digit ISO code of the country.

package rest;  import com.fasterxml.jackson.annotation.JsonIgnoreProperties;  @JsonIgnoreProperties(ignoreUnknown = true) public class Result {    private String name;   private String alpha2_code;   private String alpah3_code;    public Result() {    }    public String getName() {     return name;   }    public void setName(String name) {     this.name = name;   }    public String getAlpha2_code() {     return alpha2_code;   }    public void setAlpha2_code(String alpha2_code) {     this.alpha2_code = alpha2_code;   }    public String getAlpah3_code() {     return alpah3_code;   }    public void setAlpah3_code(String alpah3_code) {     this.alpah3_code = alpah3_code;   }    @Override   public String toString() {     return "Result [name=" + name + ", alpha2_code=" + alpha2_code         + ", alpah3_code=" + alpah3_code + "]";   }  }

Here is how our projection setup looks similar inwards Eclipse IDE, you lot tin encounter all the classes along amongst Maven dependencies together with JARs:

RESTful Web Services:

    <dependencies>         <dependency>             <groupId>junit</groupId>             <artifactId>junit</artifactId>             <version>3.8.1</version>             <scope>test</scope>         </dependency>         <dependency>             <groupId>org.springframework.boot</groupId>             <artifactId>spring-boot-starter</artifactId>             <version>1.2.7.RELEASE</version>         </dependency>         <dependency>             <groupId>com.fasterxml.jackson.core</groupId>             <artifactId>jackson-databind</artifactId>             <version>2.2.3</version>         </dependency>         <dependency>             <groupId>org.springframework</groupId>             <artifactId>spring-web</artifactId>             <version>4.0.0.RELEASE</version>         </dependency>      </dependencies> 

JARs

Here is the listing of JAR files used past times this application, I stimulate got conduct copied it from Maven Dependencies referenced inwards Eclipse.

C:\.m2\org\springframework\boot\spring-boot-starter\1.2.7.RELEASE\spring-boot-starter-1.2.7.RELEASE.jar
C:\.m2\org\springframework\boot\spring-boot\1.2.7.RELEASE\spring-boot-1.2.7.RELEASE.jar
C:\.m2\org\springframework\boot\spring-boot-autoconfigure\1.2.7.RELEASE\spring-boot-autoconfigure-1.2.7.RELEASE.jar
C:\.m2\org\springframework\boot\spring-boot-starter-logging\1.2.7.RELEASE\spring-boot-starter-logging-1.2.7.RELEASE.jar
C:\.m2\org\slf4j\jcl-over-slf4j\1.7.12\jcl-over-slf4j-1.7.12.jar
C:\.m2\org\slf4j\slf4j-api\1.7.12\slf4j-api-1.7.12.jar
C:\.m2\org\slf4j\jul-to-slf4j\1.7.12\jul-to-slf4j-1.7.12.jar
C:\.m2\org\slf4j\log4j-over-slf4j\1.7.12\log4j-over-slf4j-1.7.12.jar
C:\.m2\ch\qos\logback\logback-classic\1.1.3\logback-classic-1.1.3.jar
C:\.m2\ch\qos\logback\logback-core\1.1.3\logback-core-1.1.3.jar
C:\.m2\org\springframework\spring-core\4.1.8.RELEASE\spring-core-4.1.8.RELEASE.jar
C:\.m2\org\yaml\snakeyaml\1.14\snakeyaml-1.14.jar
C:\.m2\com\fasterxml\jackson\core\jackson-databind\2.2.3\jackson-databind-2.2.3.jar
C:\.m2\com\fasterxml\jackson\core\jackson-annotations\2.2.3\jackson-annotations-2.2.3.jar
C:\.m2\com\fasterxml\jackson\core\jackson-core\2.2.3\jackson-core-2.2.3.jar
C:\.m2\org\springframework\spring-web\4.0.0.RELEASE\spring-web-4.0.0.RELEASE.jar
C:\.m2\aopalliance\aopalliance\1.0\aopalliance-1.0.jar
C:\.m2\org\springframework\spring-aop\4.0.0.RELEASE\spring-aop-4.0.0.RELEASE.jar
C:\.m2\org\springframework\spring-beans\4.0.0.RELEASE\spring-beans-4.0.0.RELEASE.jar
C:\.m2\org\springframework\spring-context\4.0.0.RELEASE\spring-context-4.0.0.RELEASE.jar
C:\.m2\org\springframework\spring-expression\4.0.0.RELEASE\spring-expression-4.0.0.RELEASE.jar

Here is the response, you lot volition encounter inwards Eclipse's console when you lot run this programme past times right clicking on App cast together with choosing "Run every bit Java Application"

You tin encounter that reply is correctly received together with parsed from JSON to Java object past times Jackson API automatically.

Important points

Here are a twain of of import points you lot should recollect or acquire past times writing together with running this Java programme to telephone telephone a RESTful Web service using Spring Boot together with RestTemplate

1. Since nosotros are using Jackson library inwards our CLASSPATH, RestTemplate cast volition job it (via a message converter e.g. HttpMessageConverter to convert the incoming JSON reply into a Result object.

2. We stimulate got used @JsonIgnoreProperties from the Jackson,  a JSON processing library to dot that whatsoever properties non saltation inwards whatsoever of model classes e.g. RestResponse or Result should survive ignored.

3. In firm to conduct bind your information from JSON reply to your custom Java class, you lot postulate to specify the patch advert inwards the Java cast just same every bit the cardinal inwards the JSON reply returned from the RESTful API.

4. If patch advert inwards the Java cast together with cardinal inwards JSON reply are non matching, together with so you lot postulate to job the @JsonProperty notation to specify the exact cardinal of JSON document. You tin encounter nosotros stimulate got used this notation to map RestResponse cardinal to RestResponse patch inwards our Response class.

4. Sometimes, when you lot run the application together with you lot encounter solely nulls inwards the response, you lot tin withdraw the @JsonIgnoreProperties to banking concern check what's happening behind the scene. In my case, the RestResponse patch was non mapping correctly due to advert mismatch together with that was revealed past times the next exception when I removed the @JsonIgnoreProperties annotation. This is quite useful for debugging together with troubleshooting.

Caused by: org.springframework.http.converter.HttpMessageNotReadableException: Could non read JSON: Unrecognized patch "RestResponse" (class rest.example.SpringJSONRestTest.Response), non marked every bit ignorable (one known property: "restResponse"])
 at [Source: sun.net.www.protocol.http.HttpURLConnection$HttpInputStream@45af76e7; line: 2, column: 21] (through reference chain: rest.example.SpringJSONRestTest.Response["RestResponse"]); nested exception is com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized patch "RestResponse" (class rest.example.SpringJSONRestTest.Response), non marked every bit ignorable (one known property: "restResponse"])
 at [Source: sun.net.www.protocol.http.HttpURLConnection$HttpInputStream@45af76e7; line: 2, column: 21] (through reference chain: rest.example.SpringJSONRestTest.Response["RestResponse"])
at org.springframework.http.converter.json.MappingJackson2HttpMessageConverter.readJavaType(MappingJackson2HttpMessageConverter.java:185)
at org.springframework.http.converter.json.MappingJackson2HttpMessageConverter.read(MappingJackson2HttpMessageConverter.java:177)
at org.springframework.web.client.HttpMessageConverterExtractor.extractData(HttpMessageConverterExtractor.java:95)
at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:535)
at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:489)
at org.springframework.web.client.RestTemplate.getForObject(RestTemplate.java:226)
at rest.example.SpringJSONRestTest.App.run(App.java:20)
at org.springframework.boot.SpringApplication.runCommandLineRunners(SpringApplication.java:674)

5.  When you lot job the Spring, you lot acquire the embedded Tomcat to run your Java application every bit plainly erstwhile Java application past times running the principal class. It uses Tomcat internally to brand HTTP cast together with parse HTTP response.

That's all virtually how to eat JSON information from a RESTful spider web service inwards Java using Spring's RestTemplate class. This cast is super useful together with allows you lot to perform whatsoever REST operations. In this example, nosotros stimulate got solely used RestTemplate to brand an HTTP GET request, but you lot tin too job RestTemplate to execute HTTP POST, PUT or DELETE method.

Further Learning
Spring Framework 5: Beginner to Guru
RESTFul Services inwards Java using Jersey
Spring Master Class - Beginner to Expert

Btw, If you lot are mortal who prefers preparation courses together with coaching classes than books, together with so you lot tin too banking concern check out Eugen's REST amongst Spring course, it's currently 1 of the best courses to acquire RESTful spider web services evolution using Spring framework. The class expects candidates to know Java together with Spring, hence, it's ideal for intermediate together with experienced Java together with Web developers.

Eugen has severals options on his courses suited for unlike sense grade together with needs e.g. REST amongst Spring: The Intermediate cast is skillful for essential noesis piece REST amongst Spring: The Masterclass is to a greater extent than especial oriented. You tin banking concern check out all his class options here.