Spring Boot Tutorials Part #1

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Spring Boot Tutorials Part #1

Introduction

Hi there, welcome to my blog on Spring Boot Tutorials. In this blog, I will show you how to use Spring Boot, a powerful and flexible framework that makes Java development easier and faster. Spring Boot is an extension of the Spring framework that provides many features, such as quick and safe environment configuration, reduced code length, simplified dependency management, production-ready features, and easy testing. 

Spring Boot also supports multiple programming languages and integrates with various tools and libraries. Spring Boot is a great choice for building modern and scalable web applications that can meet the changing business needs. 

In this blog, I will cover the following topics: how to get started with Spring Boot, how to use Spring Boot annotations, how to configure Spring Boot properties, how to use Spring Boot starters, how to use Spring Boot actuator, and how to test Spring Boot applications. I hope you will find this blog useful and informative. Let’s get started!

Spring Initializr

I will show you how to get started with Spring Boot. Spring Boot makes it easy to create a simple Spring Boot application using Spring Initializr, Maven, or Gradle. 

Spring Initializr is a web tool that helps you generate a basic Spring Boot project with the dependencies you need. 

Maven and Gradle are build tools that help you manage your project dependencies and packaging. You can use them to create a Spring Boot project from scratch or from an existing template. 

To create a Spring Boot project using Spring Initializr, you need to follow these steps: 

1.  Go to 1 and choose your project type (Maven or Gradle), language (Java, Kotlin, or Groovy), Spring Boot version, group ID, artifact ID, name, description, package name, and packaging (Jar or War). 

2. Add the dependencies you want for your project. For example, if you want to create a web application, you can add the “web” dependency. You can search for and add other dependencies as well.

3. Click on the “Generate” button and download the zip file containing your project.

4. Unzip the file and open it in your favorite IDE or code editor. You can also import it as an existing Maven or Gradle project.

5. Run the main class (Application.java by default) or use the Maven or Gradle command to run your application. You should see a message like “Tomcat started on port(s): 8080” in the console. 

6. Open your browser and go to http://localhost:8080. You should see a blank page with the title “Welcome”. Congratulations! You have created your first Spring Boot application using Spring Initializr.

Spring Boot Annotations

In this section, I will explain some of the common annotations used in Spring Boot applications. Annotations are a way of adding metadata to your code that can be used by Spring to configure your beans and components. 

Spring Boot provides many annotations that can help you simplify your code and reduce boilerplate. Here are some of the annotations that you will encounter frequently: 

- @SpringBootApplication: This annotation is usually placed on the main class of your application. It enables auto-configuration, component scanning, and other features that make your application ready to run. It is equivalent to using @Configuration, @EnableAutoConfiguration, and @ComponentScan together. 

For example: 

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

- @RestController: This annotation is used to mark a class as a controller that can handle web requests. It combines @Controller and @ResponseBody annotations, which means that the methods in the class will return data rather than a view. You can use @RequestMapping or its variants (@GetMapping, @PostMapping, etc.) to map the methods to specific URLs. 

For example: 

@RestController
public class GreetingController {
     @GetMapping("/greeting")
     public String greeting() {
         return "Hello, World!";
     }
}

- @Autowired: This annotation is used to inject dependencies into your beans. It means that Spring will automatically provide an instance of the required bean and assign it to the annotated field or constructor parameter. You don’t need to write any code to create or wire the beans. 

For example: 

@Service
public class BookService {
     @Autowired
     private BookRepository
      bookRepository;
    // … 
}

- @RequestMapping: This annotation is used to map web requests to specific handler methods or classes. It can take various attributes, such as value (the URL path), method (the HTTP method), produces (the media type of the response), consumes (the media type of the request), etc. You can also use shortcut annotations, such as @GetMapping, @PostMapping, @PutMapping, etc., which are composed of @RequestMapping with a specific method attribute. 

For example: 

@RequestMapping("/books")
public class BookController {
     @GetMapping("/{id}")
     public Book
      getBookById(@PathVariable Long id) {
         // …
     }
 
     @PostMapping 
     public Book
      createBook(@RequestBody Book book) { 
         // … 
     } 
     // …

}

These are some of the basic annotations that you will use in your Spring Boot applications. There are many more annotations that you can explore in the official documentation. Annotations can make your code more concise and expressive, but they also hide some details behind the scenes. It is important to understand how they work and what they do under the hood.

Spring Boot Properties

Properties files are simple text files that contain key-value pairs. They are useful for storing configuration values that can vary depending on the environment or the deployment. Spring Boot supports two types of properties files: application.properties and application.yml. 

The former uses the traditional.properties format, while the latter uses YAML syntax. You can choose either format based on your preference. By default, Spring Boot looks for these files in the following locations: 

- The classpath root 

- The classpath /config package 

- The current directory 

- The /config subdirectory of the current directory You can also specify a custom location for these files using the spring.config.location property. 

For example: 

  java -jar myapp.jar
  --spring.config.location=classpath:/custom.properties,file:/opt/app/config.properties 

You can also use spring.config.additional-location to add additional locations that do not replace the default ones. 

For example: 

  java -jar myapp.jar
  --spring.config.additional-location=file:/opt/app/config.properties 

In both cases, you can use comma-separated values to specify multiple locations. Spring Boot loads the properties from these locations in a specific order, so that the properties in later locations override the ones in earlier locations. 

For example, if you have a property foo=bar in application.properties and foo=baz in custom.properties, the final value of foo will be baz. 

You can use properties files to configure various aspects of your Spring Boot applications, such as logging, data sources, security, web server, etc. 

You can also define your own custom properties and use them in your code. To access the properties values in your code, you have two options: 

- Use the @Value annotation to inject a property value into a field or a constructor parameter. 

For example: 

@Value("${app.name}")
private String appName;

- Use the @ConfigurationProperties annotation to bind a group of properties to a bean. 

For example: 

@ConfigurationProperties(prefix = "app")
public class AppProperties {
     private String name;
     private String version;
     // getters and setters }
}

You can also use @ConfigurationProperties with @EnableConfigurationProperties or @Component to register the bean with Spring. 

For example: 

@Component 
@ConfigurationProperties(prefix="app") 
public class AppProperties { 
     //… 
     } 
}

To learn more about properties and configuration in Spring Boot, you can refer to the official documentation. Properties files are a convenient way to externalize your configuration and make your applications more flexible and adaptable.

Spring Boot Starters

Now I will explain Spring Boot Starters and how they simplify dependency management. Dependency management is a critical aspect of any complex project. It involves adding the required libraries and frameworks to your project and keeping them up to date. 

Doing this manually can be tedious and error-prone. You have to hunt for the right versions of the dependencies, avoid conflicts and compatibility issues, and update them regularly. Spring Boot starters can help you avoid these problems by providing a set of convenient dependency descriptors that you can include in your project. 

A starter is a Maven artifact that contains a list of dependencies that are needed for a specific functionality or feature. 

For example, if you want to create a web application with Spring Boot, you can simply add the spring-boot-starter-web dependency to your pom.xml file and it will bring all the necessary dependencies for web development, such as Spring MVC, Tomcat, Jackson, etc. You don’t have to specify the versions of these dependencies, as Spring Boot will figure them out for you based on the version of Spring Boot that you are using. 

This way, you can focus more on your business logic and less on your infrastructure. Spring Boot provides more than 30 starters for various purposes, such as data access, security, testing, actuator, etc. You can find the complete list of starters in the official documentation. You can also create your own custom starters if you need to group some common dependencies for your own projects or share them with others. 

To use a starter, you just need to add it as a dependency in your pom.xml file. 

For example: 

  
<dependency>
     <groupId>org.springframework.boot</groupId>
     <artifactId>spring-boot-starter-web</artifactId>
</dependency>

You can also use multiple starters together if you need more features. 

For example:

  
<dependency>
     <groupId>org.springframework.boot</groupId>
     <artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
     <groupId>org.springframework.boot</groupId>
     <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>

This will add all the dependencies for web development and data access with JPA. Spring Boot starters are a great way to simplify your dependency management and make your project more consistent and maintainable. They also help you keep up with the latest versions of Spring Boot and its related technologies without much hassle.

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