TIL: Spring Boot, pt4

Looks like there’ll be about one more day of working through this tutorial series. There as a lot of info covered today, and rather than trying to force myself to finish, I’m just going to call it quits at a good stopping point.

On top of all of the notes down below from today’s work, I also have a few other topics that I need to do some more reading on:

1. method references
2. lambda expressions
3. the Optional Type

Anyways, here’s today’s notes.

Other Ways of Starting a Spring Boot App

• There are other ways of starting a new Spring Boot app aside from the Maven method above

Spring Initializer

• Located on the spring website: https://start.spring.io
• Lets you select the type of project, as well as the version of spring boot that you want to use
• Lets you supply the Group and Artifact for the project
• Finally, allows you to supply the list of dependencies you want to add to the application
  • There’s a full list you can expand and select from, or type them in manually
• Finally you can hit generate project, and it will create a link for you to download the generated project

Spring Boot CLI

• Look on google for install link
• Allows you to bootstrap a project from a Groovy template script
• This is pretty much only used for quick prototyping, this isn’t something that you would use in a production environment.
• Here’s a sample example of a hello-world rest api:

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@RestController
class ApplCtrl {

    @GetMapping("/")
    String app() {
        "Hello World"
    }
}

• By running ./spring run hello.groovy, the CLI will create an entire application from it (will be up and running)

Via Spring Tool Suite IDE

• IDE has an option to create a new Spring starter project
• Gives you all of the same options that the initializer gives you
• Will actually download the zip file from the start website and then import it for you automatically (just saves you one step of importing the project)

Customizing Spring Boot

• This is when you need to change some parameters that aren’t satisfied by the default installation
• This is done via a property file (the “easiest way”), which is spring related
  • application.properties
• For example, let’s look at changing the default port that comes up at run time
• Create the new file under the /src/main/resources directory
• Inside the file, add server.port=8081
• When you run the app again, it will start up on port 8081 instead
• The properties that can go in this file can be found here

Connecting to a DB

• This is done through the Spring JPA
  • Java Persistence API
  • Allows for Object - Relational Mapping

Setting up the Project

• Create a new project using the initializr tool
  • Need the following dependencies: Web, JPA, Apache Derby (embedded db instance for prototyping)
• In Intellij, go back to the main screen and click on import and then select the pom file
• It will pull in the project and download everything that it needs

Switching from Static Data to DB

• We first need to tell JPA that we have a data model that needs to be converted to a DB record
  • This is done by using the @Entity annotation on the model class
• Need to give the JPA the primary key
  • Field level annotation @Id
• Need to update our service so that it will connect over to the database instead of our premade data
• This is handled by a new interface file which will allow us to extend a bunch of built in functionality from the CrudRepository class
  • Your basic get, post, update, delete functionality is already baked in, there’s no need to write these database calls yourself
  • Any calls that require more work (filtering) would just plug into the file

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package io.springboot.topic;

import org.springframework.data.repository.CrudRepository;

public interface TopicRepository extends CrudRepository<Topic, String> {

}

• Then in order to access this baked in functionality, we’ll wire in an instance of that interface file which will give us our functionality calls

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@Autowired
private TopicRepository topicRepository;

Get All

• In order to get all of the records from the database for the specific resource, we can run a .findAll() on the instance of our interface
  • Note that the findAll() will return an iterable

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public List<Topic> getAllTopics() {
   List<Topic> topics = new ArrayList<>();
   topicRepository.findAll()
       .forEach(topics::add);
   return topics;
}

Add

• In order to add a record we can use the save method.

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public void addTopic(Topic topic) {
   topicRepository.save(topic);
}

Get One

• The sample tutorial uses a method that’s now deprecated in later releases
• To get a single record, you can use findById, but you also need to extend it with a orElse method, as it returns back an Optional

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public Topic getTopic(String id) {
   return topicRepository.findById(id).orElse(null);
}

Update

• Just need to use the save method again. No difference between add and update

Delete

• Use the deleteById method (video says delete, but that’s deprecated)

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public void deleteTopic(String id) {
   topicRepository.deleteById(id);
}

💚