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What You Will Learn during this Step:

  • Create a REST Service for Retrieving all questions for a survey
  • Autowire SurveyService
  • Create @GetMapping("/surveys/{surveyId}/questions")
  • Use @PathVariable String surveyId
  • http://localhost:8080/surveys/Survey1/questions/
  • How does the Bean get converted to a JSON?
  • Auto Configuration : If Jackson jar is on the class path, message converters are auto created! (Search in log :Creating shared instance of singleton bean 'mappingJackson2HttpMessageConverter')

Some Theory

  • What is REST?
  • Architectural style for the web. REST specifies a set of constraints.
    • Client - Server : Server (service provider) should be different from a client (service consumer).
      • Enables loose coupling and independent evolution of server and client as new technologies emerge.
    • Each service should be stateless.
    • Each Resource has a resource identifier.
    • It should be possible to cache response.
    • Consumer of the service may not have a direct connection to the Service Provider. Response might be sent from a middle layer cache.
    • A resource can have multiple representations. Resource can modified through a message in any of the these representations.

Useful Snippets and References

@RestController
class SurveyController {
    @Autowired
    private SurveyService surveyService;

    @GetMapping("/surveys/{surveyId}/questions")
    public List<Question> retrieveQuestions(@PathVariable String surveyId) {
        return surveyService.retrieveQuestions(surveyId);
    }
}

Exercise

  • Try to think about how the URI for retrieving the details of a specific question should be!

Files List

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>com.in28minutes.springboot</groupId>
	<artifactId>first-springboot-project</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>1.4.0.RELEASE</version>
	</parent>

	<properties>
		<java.version>1.8</java.version>
	</properties>

	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>
		
		<dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <optional>true</optional>
        </dependency>
	</dependencies>

	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>
</project>

src/main/java/com/in28minutes/springboot/Application.java

package com.in28minutes.springboot;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;

@SpringBootApplication
public class Application {

	public static void main(String[] args) {
		ApplicationContext ctx = SpringApplication.run(Application.class, args);

	}

}

src/main/java/com/in28minutes/springboot/controller/SurveyController.java

package com.in28minutes.springboot.controller;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;

import com.in28minutes.springboot.model.Question;
import com.in28minutes.springboot.service.SurveyService;

@RestController
class SurveyController {
	@Autowired
	private SurveyService surveyService;

	@GetMapping("/surveys/{surveyId}/questions")
	public List<Question> retrieveQuestions(@PathVariable String surveyId) {
		return surveyService.retrieveQuestions(surveyId);
	}
}

src/main/java/com/in28minutes/springboot/model/Question.java

package com.in28minutes.springboot.model;

import java.util.List;

public class Question {
	private String id;
	private String description;
	private String correctAnswer;
	private List<String> options;

	// Needed by Caused by: com.fasterxml.jackson.databind.JsonMappingException:
	// Can not construct instance of com.in28minutes.springboot.model.Question:
	// no suitable constructor found, can not deserialize from Object value
	// (missing default constructor or creator, or perhaps need to add/enable
	// type information?)
	public Question() {

	}

	public Question(String id, String description, String correctAnswer,
			List<String> options) {
		super();
		this.id = id;
		this.description = description;
		this.correctAnswer = correctAnswer;
		this.options = options;
	}

	public String getId() {
		return id;
	}

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

	public String getDescription() {
		return description;
	}

	public String getCorrectAnswer() {
		return correctAnswer;
	}

	public List<String> getOptions() {
		return options;
	}

	@Override
	public String toString() {
		return String
				.format("Question [id=%s, description=%s, correctAnswer=%s, options=%s]",
						id, description, correctAnswer, options);
	}

	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + ((id == null) ? 0 : id.hashCode());
		return result;
	}

	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		Question other = (Question) obj;
		if (id == null) {
			if (other.id != null)
				return false;
		} else if (!id.equals(other.id))
			return false;
		return true;
	}

}

src/main/java/com/in28minutes/springboot/model/Survey.java

package com.in28minutes.springboot.model;

import java.util.List;

public class Survey {
	private String id;
	private String title;
	private String description;
	private List<Question> questions;

	public Survey(String id, String title, String description,
			List<Question> questions) {
		super();
		this.id = id;
		this.title = title;
		this.description = description;
		this.questions = questions;
	}

	public String getId() {
		return id;
	}

	public void setId(String 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 List<Question> getQuestions() {
		return questions;
	}

	public void setQuestions(List<Question> questions) {
		this.questions = questions;
	}

	@Override
	public String toString() {
		return "Survey [id=" + id + ", title=" + title + ", description="
				+ description + ", questions=" + questions + "]";
	}

}

src/main/java/com/in28minutes/springboot/service/SurveyService.java

package com.in28minutes.springboot.service;

import java.math.BigInteger;
import java.security.SecureRandom;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import org.springframework.stereotype.Component;

import com.in28minutes.springboot.model.Question;
import com.in28minutes.springboot.model.Survey;

@Component
public class SurveyService {
	private static List<Survey> surveys = new ArrayList<>();
	static {
		Question question1 = new Question("Question1",
				"Largest Country in the World", "Russia", Arrays.asList(
						"India", "Russia", "United States", "China"));
		Question question2 = new Question("Question2",
				"Most Populus Country in the World", "China", Arrays.asList(
						"India", "Russia", "United States", "China"));
		Question question3 = new Question("Question3",
				"Highest GDP in the World", "United States", Arrays.asList(
						"India", "Russia", "United States", "China"));
		Question question4 = new Question("Question4",
				"Second largest english speaking country", "India", Arrays
						.asList("India", "Russia", "United States", "China"));

		List<Question> questions = new ArrayList<>(Arrays.asList(question1,
				question2, question3, question4));

		Survey survey = new Survey("Survey1", "My Favorite Survey",
				"Description of the Survey", questions);

		surveys.add(survey);
	}

	public List<Survey> retrieveAllSurveys() {
		return surveys;
	}

	public Survey retrieveSurvey(String surveyId) {
		for (Survey survey : surveys) {
			if (survey.getId().equals(surveyId)) {
				return survey;
			}
		}
		return null;
	}

	public List<Question> retrieveQuestions(String surveyId) {
		Survey survey = retrieveSurvey(surveyId);

		if (survey == null) {
			return null;
		}

		return survey.getQuestions();
	}

	public Question retrieveQuestion(String surveyId, String questionId) {
		Survey survey = retrieveSurvey(surveyId);

		if (survey == null) {
			return null;
		}

		for (Question question : survey.getQuestions()) {
			if (question.getId().equals(questionId)) {
				return question;
			}
		}

		return null;
	}

	private SecureRandom random = new SecureRandom();

	public Question addQuestion(String surveyId, Question question) {
		Survey survey = retrieveSurvey(surveyId);

		if (survey == null) {
			return null;
		}

		String randomId = new BigInteger(130, random).toString(32);
		question.setId(randomId);

		survey.getQuestions().add(question);

		return question;
	}
}

src/main/java/com/in28minutes/springboot/WelcomeController.java

package com.in28minutes.springboot;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class WelcomeController {

	//Auto wiring
	@Autowired
	private WelcomeService service;

	@RequestMapping("/welcome")
	public String welcome() {
		return service.retrieveWelcomeMessage();
	}
}

src/main/java/com/in28minutes/springboot/WelcomeService.java

package com.in28minutes.springboot;

import org.springframework.stereotype.Component;

@Component
public class WelcomeService {

	public String retrieveWelcomeMessage() {
		//Complex Method
		return "Good Morning updated";
	}
}

src/main/resources/application.properties

logging.level.org.springframework: DEBUG