Spring RestTemplate Example

Filed Under: Spring

Spring RestTemplate provides a convenient way to test RESTful web services.

Spring RestTemplate

  • Spring RestTemplate class is part of spring-web, introduced in Spring 3.
  • We can use RestTemplate to test HTTP based restful web services, it doesn’t support HTTPS protocol.
  • RestTemplate class provides overloaded methods for different HTTP methods, such as GET, POST, PUT, DELETE etc.

Spring RestTemplate Example

Let’s look at Spring RestTemplate example where we will test REST web services created in Spring Data JPA article. Below table illustrates the URIs supported by this rest web service.

URI HTTP Method Description
/springData/person GET Get all persons from database
/springData/person/{id} GET Get person by id
/springData/person POST Add person to database
/springData/person PUT Update person
/springData/person/{id} DELETE Delete person by id

Let’s start creating our Rest client project to test these web services.

Below image shows our final Spring RestTemplate example project.

Spring RestTemplate Example

Spring RestTemplate Maven Dependencies

We need spring-core, spring-context dependencies for spring framework. Then we need spring-web artefact that contains RestTemplate class. We also need jackson-mapper-asl for Spring JSON support through Jackson API.


<?xml version="1.0" encoding="UTF-8"?>
<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.journaldev.spring</groupId>
	<artifactId>SpringRestTemplate</artifactId>
	<version>1.0-SNAPSHOT</version>
	<properties>
		<spring.framework>4.3.0.RELEASE</spring.framework>
		<spring.web>3.0.2.RELEASE</spring.web>
		<serializer.version>2.8.1</serializer.version>
	</properties>
	<dependencies>
		<dependency>
			<groupId>org.springframework</groupId>
			<artifactId>spring-core</artifactId>
			<version>${spring.framework}</version>
		</dependency>
		<dependency>
			<groupId>org.springframework</groupId>
			<artifactId>spring-context</artifactId>
			<version>${spring.framework}</version>
		</dependency>
		<dependency>
			<groupId>org.codehaus.jackson</groupId>
			<artifactId>jackson-mapper-asl</artifactId>
			<version>1.9.4</version>
		</dependency>
		<dependency>
			<groupId>org.springframework</groupId>
			<artifactId>spring-web</artifactId>
			<version>${spring.web}</version>
		</dependency>
	</dependencies>
</project>

Spring Configuration Class

We have to define a spring bean for RestTemplate class, that’s done in AppConfig class.


package com.journaldev.spring.config;

import org.codehaus.jackson.map.ObjectMapper;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.converter.json.MappingJacksonHttpMessageConverter;
import org.springframework.web.client.RestTemplate;

@Configuration
@ComponentScan("com.journaldev.spring")
public class AppConfig {

	@Bean
	RestTemplate restTemplate() {
		RestTemplate restTemplate = new RestTemplate();
		MappingJacksonHttpMessageConverter converter = new MappingJacksonHttpMessageConverter();
		converter.setObjectMapper(new ObjectMapper());
		restTemplate.getMessageConverters().add(converter);
		return restTemplate;
	}
}

Note that RestTamplate uses MessageConverter and we need to set this property in the RestTemplate bean. In our example we are using MappingJacksonHttpMessageConverter for fetching data from JSON format.

Model Class

Since we are trying to convert JSON returned by our web service to a java object using jackson mapper, we have to create the model class for this. Note that this model class will be very similar to the model class used in the web service, except that here we don’t need JPA annotations.


package com.journaldev.spring.model;

public class Person {

	private Long id;

	private Integer age;

	private String firstName;

	private String lastName;

	public Person() {
	}

	public Long getId() {
		return id;
	}

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

	public Integer getAge() {
		return age;
	}

	public void setAge(Integer age) {
		this.age = age;
	}

	public String getFirstName() {
		return firstName;
	}

	public void setFirstName(String firstName) {
		this.firstName = firstName;
	}

	public String getLastName() {
		return lastName;
	}

	public void setLastName(String lastName) {
		this.lastName = lastName;
	}

	@Override
	public String toString() {
		return "Person{" + "id=" + id + ", age=" + age + ", firstName='" + firstName + '\'' + ", lastName='" + lastName
				+ '\'' + '}';
	}
}

Spring RestTemplate Client Class

Final step is to create the client classes that will use RestTemplate bean defined above.


package com.journaldev.spring.config;

import java.util.List;

import org.springframework.http.HttpStatus;

import com.journaldev.spring.model.Person;

public interface PersonClient {
	List<Person> getAllPerson();

	Person getById(Long id);

	HttpStatus addPerson(Person person);

	void updatePerson(Person person);

	void deletePerson(Long id);
}

package com.journaldev.spring.config;

import java.util.Arrays;
import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.stereotype.Service;
import org.springframework.web.client.RestTemplate;

import com.journaldev.spring.model.Person;

@Service
public class PersonClientImpl implements PersonClient {

	@Autowired
	RestTemplate restTemplate;

	final String ROOT_URI = "http://localhost:8080/springData/person";

	public List<Person> getAllPerson() {
		ResponseEntity<Person[]> response = restTemplate.getForEntity(ROOT_URI, Person[].class);
		return Arrays.asList(response.getBody());

	}

	public Person getById(Long id) {
		ResponseEntity<Person> response = restTemplate.getForEntity(ROOT_URI + "/"+id, Person.class);
		return response.getBody();
	}

	public HttpStatus addPerson(Person person) {
		ResponseEntity<HttpStatus> response = restTemplate.postForEntity(ROOT_URI, person, HttpStatus.class);
		return response.getBody();
	}

	public void updatePerson(Person person) {
		restTemplate.put(ROOT_URI, person);
	}

	public void deletePerson(Long id) {
		restTemplate.delete(ROOT_URI + id);

	}
}

The code is self understood, we are calling RestTemplate methods based on the URI and the HTTP method and by passing appropriate request object if needed.

Spring RestTemplate Test Class

It’s time to test our Spring RestTemplate example project, below class shows how to use RestTemplate methods in Spring way.


package com.journaldev.spring;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.http.HttpStatus;

import com.journaldev.spring.config.AppConfig;
import com.journaldev.spring.config.PersonClient;
import com.journaldev.spring.model.Person;

public class Main {

	public static void main(String[] args) {
		AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(AppConfig.class);

		PersonClient client = applicationContext.getBean(PersonClient.class);

		System.out.println("Getting list of all people:");

		for (Person p : client.getAllPerson()) {
			System.out.println(p);
		}

		System.out.println("\nGetting person with ID 2");

		Person personById = client.getById(2L);

		System.out.println(personById);

		System.out.println("Adding a Person");
		Person p = new Person();
		p.setAge(50);
		p.setFirstName("David");
		p.setLastName("Blain");
		HttpStatus status = client.addPerson(p);
		System.out.println("Add Person Response = " + status);

		applicationContext.close();
	}
}

When I run above program against my local setup, I get following output.


Getting list of all people:
Person{id=2, age=30, firstName='Oksi', lastName=' Bahatskaya'}
Person{id=1, age=30, firstName='Vlad', lastName='Mateo'}

Getting person with ID 2
Person{id=2, age=30, firstName='Oksi', lastName=' Bahatskaya'}
Adding a Person
Add Person Response = 201

Below image shows the web service database table data before and after executing above program.

Spring RestTemplate

As you can see that the program output matches with the sample table data. That’s all for Spring RestTemplate example, you can download the project from below link.

Reference: API Doc

Comments

  1. rohit verma says:

    Thanks for explanation.
    Can you suggest best way to make 100-1000 post request to any rest URL.
    I am worried about connection establishment/closer for each request, although I don’t have to write code for same.

  2. priyanka says:

    How to run this app? I am getting below error:
    INFO: Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@2ff4f00f: startup date [Wed Nov 14 10:40:41 IST 2018]; root of context hierarchy
    Getting list of all people:
    Exception in thread “main” org.springframework.web.client.ResourceAccessException: I/O error: Connection refused: connect; nested exception is java.net.ConnectException: Connection refused: connect
    at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:453)
    at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:401)
    at org.springframework.web.client.RestTemplate.getForEntity(RestTemplate.java:221)
    at com.journaldev.spring.config.PersonClientImpl.getAllPerson(PersonClientImpl.java:23)
    at com.journaldev.spring.Main.main(Main.java:19)
    Caused by: java.net.ConnectException: Connection refused: connect
    at java.net.DualStackPlainSocketImpl.connect0(Native Method)
    at java.net.DualStackPlainSocketImpl.socketConnect(Unknown Source)
    at java.net.AbstractPlainSocketImpl.doConnect(Unknown Source)
    at java.net.AbstractPlainSocketImpl.connectToAddress(Unknown Source)
    at java.net.AbstractPlainSocketImpl.connect(Unknown Source)

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