Rapid development of REST webservices with persistence

Development of modern business applications, has to become faster and easier, if we are to meet business delivery demands, spanning over ever shorter cycles. Also we are now required to deliver softwares continuosly and incrementally, in an agile manner.

Jump-starting the development process with the right tools and technolgies is the need of the hour.

Rapid development, using currently popular technology, has always been in vogue. Right now exposing middle tier services as REST APIs is all the rage. So how do we develop REST services with persistence, in a rapid manner, with least effort?

I had written an earlier post on grails 2_3 providing out of box support for REST CRUD , writing only a simple java bean (DTO), using the grails framework. But that would mean using an entirely new framework like grails only to exploit its REST CRUD functionality. The engineer in me, thought that was an unoptimized use of grails. Why shoudlnt we have this, out of box REST CRUD using spring, hibernate the technologies that we know best already :-)

Well more recently, advancements made in the Spring Data JPA framework, makes it very very easy to develop CRUD REST services out of the box, writing only the entity classes with JPA annotations.
Well here is how...

Effectively, we will see, how to write only a simple java bean, annotated with JPA annotations for persistence and using spring data jpa and spring boot, we can automatically generate REST CRUD services for our bean / entity. All this using very little code :-)



Create a typical maven java project (not a web project) 
eg. using maven-archetype-quickstart

We will use spring boot based spring data jpa and spring data rest

Use a pom.xml similar to below

https://github.com/ganeshghag/RestSpringDataJpa/blob/master/pom.xml



As per spring data jpa, create persistent entity class say Person as a POJO and annotate it with JPA annotations

package com.ghag.rnd.rest.domain;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@Entity
public class Person {

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private long id;

private String firstName;
private String lastName;
private String email;
private String address;
private String mobile;
private Integer employeeId;

//getters and setters go here
}

Again as per spring data jpa framework, create an interface which will tell the spring data jpa framework, to create hibernate jpa based CRUD functionality with respect to the entity class Person we defined above

package com.ghag.rnd.rest.repository;

import java.util.List;
import org.springframework.data.repository.PagingAndSortingRepository;
import org.springframework.data.repository.query.Param;
import org.springframework.data.rest.core.annotation.RepositoryRestResource;
import com.ghag.rnd.rest.domain.Person;


@RepositoryRestResource(collectionResourceRel = "people", path = "people")
public interface PersonRepository extends PagingAndSortingRepository<Person, Long> {

List<Person> findByLastName(@Param("name") String name);

}

The methods in the interface like findByLastName, impart filtering capability on the the entity queries by entity attributes like lastName.


The annotation below
@RepositoryRestResource(collectionResourceRel = "people", path = "people")
ensures that, the CRUD rest services for the Person entity are auto-magically generated for us. This is the main fetaure, I wanted to publicize in this article.


Thats it, now using Spring Boot and its default sensible configurations, you can just right a class similar to below and you should be able to start up the applicatoin with an embedded tomcat server.

package com.ghag.rnd.rest;


import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;
import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
import org.springframework.data.rest.webmvc.config.RepositoryRestMvcConfiguration;

@Configuration
@EnableJpaRepositories
@Import(RepositoryRestMvcConfiguration.class)
@EnableAutoConfiguration
@ComponentScan  //important and required
public class Application {

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


The application will expose the CRUD REST services for persistent entity Person at
http://server:port/people

you can easily test the services using curl commands like following:
curl -i -X POST -H "Content-Type:application/json" -d @insert.cmd http://localhost:8080/people
where file insert.cmd contains json for the Person object like thus:
{
"firstName" : "Ganesh",
"lastName" : "Ghag",
"email":"some@some.com",
"address":"flower valley, thane",
"mobile":"3662626262",
"employeeId":8373
}

In order to customize the application, writing custom REST controllers is as easy as writing below POJO

package com.ghag.rnd.rest.controllers;

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

import com.ghag.rnd.rest.repository.PersonRepository;


@RestController
@RequestMapping("/custom")
public class MyCustomController {

@Autowired
PersonRepository personRepository;

@RequestMapping(value="/sayHello/{input}", method=RequestMethod.GET)
public String sayHello(@PathVariable String input){

System.out.println("findall="+personRepository.findAll());
personRepository.deleteAll();
return "Hello!"+input;
}
}

To further enhance the CRUD application, we can easily

• use above application as a microservice, using spring boot as is
• export above application as a war and deploy it on traditional app server
• use various logging for debugging
• use spring based validations
• use spring security
• switch CRUD database from current default H2 to any of our choice using spring boot config file application.properties

Please refer spring boot documentation for accomplishing the above mentioned enhancments.
http://docs.spring.io/spring-boot/docs/current/reference/htmlsingle/
http://docs.spring.io/spring-data/jpa/docs/current/reference/html/


By using hibernate tools reverse engineering, given an existing database, auto-generating JPA annotated entities is a no-brainer and with the above knowledge of generating REST CRUD services, it means, you can expose a database, as  REST services, with less than a days work.