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

So far, I get got non written much almost REST in addition to RESTful spider web service barring or so interview questions e.g. REST vs SOAP, which is thankfully really much appreciated yesteryear my readers in addition to or so full general suggestions almost best books to larn REST inwards past, but today I am going to write something almost RESTTemplate flat from Spring MVC framework. Like its predecessors JdbcTemplate in addition to JmsTemplate, the RestTemplate is or so other useful utility flat which allows y'all to interact amongst RESTful spider web services from a Java application built using Spring framework. It's a characteristic rich in addition to supports almost all REST methods e.g. GET, POST, HEAD, PUT or DELETE, though we'll alone usage the GET method inwards this article to eat a RESTful Web Service in addition to convert the JSON reply to Java objects. It's 1 of the basic but interesting examples, given y'all volition frequently abide by 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 in addition to deploying inwards tomcat in addition to and so writing Servlet in addition to JSP to demonstrate the example. I actually abide by the convenience offered yesteryear Spring kicking 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 companionship to exercise a RESTful client, y'all postulate to get got a RESTful spider web service which tin terminate furnish JSON content y'all desire to consume. Though y'all tin terminate develop a RESTful customer inwards Spring framework itself, for testing piece of job its amend to usage the existing gratuitous RESTful spider web service on the meshwork e.g. http://jsonplaceholder.typicode.com has several useful RESTful API to render comments in addition to posts related information e.g. http://jsonplaceholder.typicode.com/posts/1 volition render postal service information amongst id= 1, which looks something similar this:

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

Though, I get got used or so other gratuitous REStful spider web service which returns Country's cite in addition to their 2 in addition to 3 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 constitute matching code [IN]." ],     "result" : {       "name" : "India",       "alpha2_code" : "IN",       "alpha3_code" : "IND"     }   } } 

You tin terminate usage whatsoever of these spider web services to prepare a RESTful client for testing. Though your domain flat volition alter depending upon which RESTful spider web service y'all are consuming.


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

Spring framework in addition to RestTemplate class. This programme has iv Java files :  App.java, Response.java, RestResponse.java, in addition to Result.java. The showtime flat is the principal flat which drives this application in addition to others are classes corresponding to JSON response nosotros acquire from this RESTful API.

App.java
This is our principal flat which drives this RESTful Spring application. It uses Spring kicking to setup in addition to runs the program. The flat App implements CommandLineRunner in addition to calls the SpringApplication.run() method yesteryear passing this instance of flat i.e. App.class. This will, inwards turn, telephone phone the run method, where nosotros get got code to telephone phone a RESTful Web Service in addition to eat JSON reply using RestTemplate flat of Spring framework.

Just similar it's predecessor or unopen cousins e.g. JmsTemplate in addition to JdbcTemplate, the RestTemplate flat too does everything for you.  All y'all postulate to say is the cite of the flat y'all desire to map the incoming JSON response.

We get got showtime created an instance of RestTemplate flat in addition to and so called the getForObject() method. This accepts 2 parameters, first, a String URL to telephone phone the RESTful Web Service in addition to instant the cite of the flat it should render amongst the response.  So, inwards simply 1 draw of piece of job of code, it calls the RESTful spider web service, parse the JSON reply in addition to render the Java object to you.

If y'all are curious to larn to a greater extent than almost RestTemplate flat in addition to so y'all tin terminate 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 phone a RESTful Web Service from Java Program using Spring in addition to 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 in conclusion 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 flat to convert JSON reply to Java object y'all have yesteryear consuming the RESTful spider web service response. I get got use @JSonProperty to annotate the RestResponse land to say the Jackson that this is the fundamental land 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 flat contains 2 fields corresponding to RestResponse department of JSON reply nosotros received from RESTful Web service. The showtime land is a String array, messages in addition to Jackson volition parse the JSON array to String array in addition to shop the output for that belongings inwards this field. The instant field, the lawsuit is 1 time again a custom type Java object to shop the information nosotros postulate i.e. cite in addition to 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 flat has 3 fields, corresponding to 3 properties for lawsuit department inwards JSON response. All 3 fields are String, first, the name is the cite of the country, second, alpha2_code is the two-digit ISO code for the province in addition to 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, y'all tin terminate encounter all the classes along amongst Maven dependencies in addition to 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 yesteryear this application, I get 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, y'all volition encounter inwards Eclipse's console when y'all run this programme yesteryear right clicking on App flat in addition to choosing "Run every bit Java Application"

You tin terminate encounter that reply is correctly received in addition to parsed from JSON to Java object yesteryear Jackson API automatically.

Important points

Here are a dyad of of import points y'all should retrieve or larn yesteryear writing in addition to running this Java programme to telephone phone a RESTful Web service using Spring Boot in addition to RestTemplate

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

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

3. In companionship to conduct bind your information from JSON reply to your custom Java class, y'all postulate to specify the land cite inwards the Java flat precisely same every bit the fundamental inwards the JSON reply returned from the RESTful API.

4. If land cite inwards the Java flat in addition to fundamental inwards JSON reply are non matching, in addition to so y'all postulate to usage the @JsonProperty musical note to specify the exact fundamental of JSON document. You tin terminate encounter nosotros get got used this musical note to map RestResponse fundamental to RestResponse land inwards our Response class.

4. Sometimes, when y'all run the application in addition to y'all encounter alone nulls inwards the response, y'all tin terminate take the @JsonIgnoreProperties to cheque what's happening behind the scene. In my case, the RestResponse land was non mapping correctly due to cite mismatch in addition to that was revealed yesteryear the next exception when I removed the @JsonIgnoreProperties annotation. This is quite useful for debugging in addition to troubleshooting.

Caused by: org.springframework.http.converter.HttpMessageNotReadableException: Could non read JSON: Unrecognized land "RestResponse" (class rest.example.SpringJSONRestTest.Response), non marked every bit ignorable (one known property: "restResponse"])
 at [Source: sun.net.www.protocol.http.HttpURLConnection$HttpInputStream@45af76e7; line: 2, column: 21] (through reference chain: rest.example.SpringJSONRestTest.Response["RestResponse"]); nested exception is com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized land "RestResponse" (class rest.example.SpringJSONRestTest.Response), non marked every bit ignorable (one known property: "restResponse"])
 at [Source: sun.net.www.protocol.http.HttpURLConnection$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 y'all usage the Spring, y'all acquire the embedded Tomcat to run your Java application every bit evidently onetime Java application yesteryear running the principal class. It uses Tomcat internally to brand HTTP flat in addition to parse HTTP response.

That's all almost how to eat JSON information from a RESTful spider web service inwards Java using Spring's RestTemplate class. This flat is super useful in addition to allows y'all to perform whatsoever REST operations. In this example, nosotros get got alone used RestTemplate to brand an HTTP GET request, but y'all tin terminate too usage 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 y'all are soul who prefers grooming courses in addition to coaching classes than books, in addition to so y'all tin terminate too cheque out Eugen's REST amongst Spring course, it's currently 1 of the best courses to larn RESTful spider web services evolution using Spring framework. The course of report expects candidates to know Java in addition to Spring, hence, it's ideal for intermediate in addition to experienced Java in addition to Web developers.

Eugen has severals options on his courses suited for unlike sense flat in addition to needs e.g. REST amongst Spring: The Intermediate flat is expert for essential noesis patch REST amongst Spring: The Masterclass is to a greater extent than special oriented. You tin terminate cheque out all his course of report options here.

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