CPIT-251 | Working With Frameworks in Java: The Spring Framework

The Spring framework is an open-source application framework for the Java programming language. It provides a set of classes and libraries to build flexible and scalable enterprise grade web applications.

Spring boot is a module or an extension built on top of the Spring framework to speed up the development process of building Spring applications.

For a complete description of Spring boot and how its relate to the Spring framework, refer to the links above or to this article “What is Java Spring Boot?” by Microsoft.

Building a REST API for a ToDo app

We’re going to build a simple ToDo list API using Spring boot, which is an extension of the Spring framework. The API will have three endpoints:

HTTP GET method that returns a todo item by its Id.
```
GET /todos/{id}
```
HTTP POST method that creates a new todo item.
```
POST /todos/
```
HTTP DELETE method that deletes a todo item by its Id.
```
DELETE /todos/{id}
```

Step 1: Generate the starter project using Spring Initializr

Go to https://start.spring.io. This service allows you to add all the dependencies you need for an application to start up your Spring Boot project.
Choose Maven and Java and complete the project metadata.
Click Add Dependencies and select Spring Web.
Click Generate to download the resulting ZIP file, which is an archive of the Spring web application.

Spring initializer

Step 2: Import the project into your IDE and write the code

Unzip the downloaded project and open it up in Intellij IDEA.
Open the pom.xml file. If you see an error message that says the spring-boot-maven-plugin can not be found, then add the version to this plugin as highlighted below:

<plugin>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-maven-plugin</artifactId>
	<version>${project.parent.version}</version>
</plugin>

Open the main class under src/main/java/<your-project-id> and add the following to the main method:

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

Create the Controller class TodoController.java next to the main class (under src/main/java/<your-project-id>)
Add the API end points to the controller as shown below.
- Note that this class will make use of features such as streams and collection, which are available in Java 8 and above, to find, add, and delete a ToDo item.

import org.springframework.web.bind.annotation.*;
import java.util.ArrayList;
import java.util.List;


@RestController
@RequestMapping("todos")
@CrossOrigin(origins ="*", allowedHeaders = "*")
public class TodoController {

    List<ToDo> todoList = new ArrayList<ToDo>();

    // HTTP GET method that returns a todo item by its Id.
    @GetMapping(value="/{id}", produces = "application/json")
    public @ResponseBody ToDo getToDo(@PathVariable String id) {
        System.out.println("Finding a todo item with id " + id);
        return findToDoById(id);
    }

    // HTTP POST method that creates a new todo item.
    @PostMapping(value="/", consumes = "application/json", produces = "application/json")
    public @ResponseBody boolean createToDo(@RequestBody ToDo todo) {
        System.out.println("Adding a todo item  " + todo);
        return addToDoItem(todo);
    }

    // HTTP DELETE method that deletes a todo item by its Id.
    @DeleteMapping(value="/{id}", produces = "application/json")
    public @ResponseBody boolean deleteToDo(@PathVariable String id) {
        System.out.println("Deleting a todo item with id " + id);
        return deleteToDoById(id);
    }

    private ToDo findToDoById(String id) {
        return todoList.stream().filter(todo -> id.equals(todo.getId())).findFirst().orElse(null);
    }

    private boolean addToDoItem(ToDo todo) {
        return todoList.add(todo);
    }

    private boolean deleteToDoById(String id) {
        return todoList.removeIf(todoItem -> todoItem.getId().equals(id));
    }
}

Create a class for the ToDo item named ToDo.java

import java.util.UUID;

public class ToDo {
    private String name;
    private String id;
    private boolean isComplete;

    public ToDo(){
        this.isComplete = false;
        this.id = UUID.randomUUID().toString();
    }

    public ToDo(String name) {
        this.name = name;
        this.isComplete = false;
        this.id = UUID.randomUUID().toString();
    }

    public String getId() {
        return this.id;
    }

    public String getName() {
        return this.name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public boolean isComplete() {
        return this.isComplete;
    }

    public void setComplete(boolean isComplete) {
        this.isComplete = isComplete;
    }

    public String toString() {
        return "ToDo: id: " + this.id + "\nName: " + this.name + "\nDone: " + (this.isComplete ? "Yes" : "No");
    }
}

Running the application

You can run the application from either the IDE or the Terminal.

Running the app from the Intellij IDEA IDE

Go to the maven window
Expand the project lifecycle and select package.
Click on Run
Run the jar file from the Terminal window in Intellij using java -jar target/<your-project-id-version.jar>

Running the app from the Terminal

On the Windows environment, open your Terminal application, cd to the project directory and run:

mvnw.cmd spring-boot:run

On macOS or Linux environment, open your Terminal application, cd to the project directory and run:

./mvnw spring-boot:run

Step 4: Using the API

You may use the command line tool curl to send requests to the API or use a desktop HTTP client app like Postman.

Using the command line tool curl:

Add a todo list item

curl -X POST "http://localhost:8080/todos/" -H 'Content-Type: application/json' -d '{"name":"Buy Milk"}'

true

Find a todo list Item

curl http://localhost:8080/todos/5a3c41e0-0fcb-439e-91f1-3c9b0862b016

{"name":"Buy Milk","id":"5a3c41e0-0fcb-439e-91f1-3c9b0862b016","complete":false}

Delete a todo item

curl -X DELETE http://localhost:8080/todos/5a3c41e0-0fcb-439e-91f1-3c9b0862b016

true

Using Postman

Add a todo list item
Find a todo list Item
Delete a todo item