[JAVA] [Beginner] Let's write REST API of Todo application with Spring Boot

Postscript

• Fixed part of Controller code was cut off
• Added because the story around the Controller annotation was missing.

Contents

• Java beginners study Spring during summer vacation
• Spring Framework seems to have a high hurdle, so for the time being from Spring Boot
• The theme is the REST API of the Todo app that beginners often do.

Do not touch in detail

• Around gradle
• Around Database
  • JPA
  • H2 Database

Main story

• Development uses ʻIntelliJ IDEA`
• Leave the build and application startup to us

Creating a template

• Created at https://start.spring.io/
  • Project: Gradle Project
  • Language: Java
  • Spring Boot: 2.1.8
  • Project Metadaba:
    • Group: com.example
    • Artifact: todoapp
• Options: As is
  • Dependencies:
    • Spring Web
    • Spring Data JPA
    • H2 Database
    • Lombok
• Start from unzipping the downloaded zip file and opening it in IntelliJ

Package configuration

• Arrange the following directly under com.example.todoapp
  • controllers
  • repositories
  • models
• There may be services, but this time it is omitted

code

models

• Task.java

package com.example.todoapp.models;

import lombok.Data;

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

@Data
@Entity
public class Task {

    @Id
    @GeneratedValue
    private Long id;
    private String summary;
    private Boolean done = false;

    public Task(){}
}

• About each annotation
  • @Data
• Defines setters and getters for each field
• Defines toString () method and hashCode () method
  • @Entity
• Indicates that it is an entity.
• A table with fields of this class will be created in the DB
  • @Id
• Specify the field of the entity's primary key
  • @GeneratedValue
• Specifies how to generate primary key values
• It seems that you can change the behavior by specifying strategy or generator (I have not tried it)

repositories

• TaskRepository.java

package com.example.todoapp.repositories;

import com.example.todoapp.models.Task;
import org.springframework.data.jpa.repository.JpaRepository;

public interface TaskRepository extends JpaRepository<Task, Long> {
}

• Define an interface that inherits JpaRepository
• The CrudRepository interface, which is an ancestor of JpaRepository, defines an interface such as findById.
• Is the implementation SimpleJpaRepository?
• JpaRepository specifies the target entity class and its primary key type
• The primary key type specified here is used as the argument type for findById and deleteById.
• Since the primary key of the Task entity created this time is of type Long, specify Long here.

controllers

• ApiController.java

package com.example.todoapp.controllers;

import com.example.todoapp.models.Task;
import com.example.todoapp.repositories.TaskRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;

import java.util.List;
import java.util.Optional;

@RestController
@RequestMapping(value = "/api")
public class ApiController {

    @Autowired
    TaskRepository taskrepo;

    @GetMapping(value = "/todos")
    public List<Task> tasklist(){
        return taskrepo.findAll();
    }

    @GetMapping(value = "todo/{id}")
    public Optional<Task> retrieve(@PathVariable Long id){
        return taskrepo.findById(id);
    }

    @PostMapping(value = "/todo")
    public ResponseEntity<Task> newTask(@RequestBody Task task){
        Task result = taskrepo.save(task);
        return new ResponseEntity<Task> (result, HttpStatus.CREATED);
    }

    @PutMapping(value = "/todo/{id}")
    public Task update(@PathVariable Long id, @RequestBody Task task){
        task.setId(id);
        return taskrepo.save(task);
    }

    @DeleteMapping(value = "/todo/{id}")
    @ResponseStatus(HttpStatus.NO_CONTENT)
    public void delete(@PathVariable Long id){
        taskrepo.deleteById(id);
    }
}

• About each annotation
  • @RestController
• The return value of each method becomes the response body as it is
• When using @Controller, it seems that the return value of the method is made into a String and embedded in the template.
  • @RequestMapping
• You can specify the path, method and query parameters of the request accepted by this controller.
  • @Autowired
• Associate with registered Bean with @Component annotation
• Classes with @ Repository and @ Service also have @Component added internally.
• Here, the classes that satisfy the TaskRepository interface are automatically stored in taskrepo.
  • @GetMapping, @PostMapping, @PutMapping, @DeleteMapping
• Fixed method of @RequestMapping
• For @GetMapping, equivalent to@RequestMapping (method = RequestMethod.GET)
  • @ResponseStatus
• Specify the default status code
• Use when you want to return something other than 200?

Operation check

sign up

$ curl http://localhost:8080/api/todo -XPOST -H 'Content-Type: application/json' -d '{"summary": "my first task"}' | jq .
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100    75    0    47  100    28    170    101 --:--:-- --:--:-- --:--:--   170
{
  "id": 1,
  "summary": "my first task",
  "done": false
}

Get list

$ curl http://localhost:8080/api/todos | jq .
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100    49    0    49    0     0    285      0 --:--:-- --:--:-- --:--:--   286
[
  {
    "id": 1,
    "summary": "my first task",
    "done": false
  }
]

Get 1

$ curl http://localhost:8080/api/todo/1 | jq .
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100    47    0    47    0     0   2045      0 --:--:-- --:--:-- --:--:--  2136
{
  "id": 1,
  "summary": "my first task",
  "done": false
}

update

$ curl http://localhost:8080/api/todo/1 -XPUT -H 'Content-Type: application/json' -d '{"summary": "updated my task", "done": true}' | jq .
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100    92    0    48  100    44   2632   2412 --:--:-- --:--:-- --:--:--  2666
{
  "id": 1,
  "summary": "updated my task",
  "done": true
}

Delete (Check with Status Code because there is no response body)

$ curl http://localhost:8080/api/todo/1 -XDELETE -v
*   Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 8080 (#0)
> DELETE /api/todo/1 HTTP/1.1
> Host: localhost:8080
> User-Agent: curl/7.54.0
> Accept: */*
>
< HTTP/1.1 204
< Date: Wed, 25 Sep 2019 15:29:37 GMT
<
* Connection #0 to host localhost left intact

Summary

• It was very easy to move what I wanted to move
• There are too many types of annotations and I don't know what to use
• For the time being, I want to keep at least the one I used this time
• After that, it would be nice if you could check it every time you do something