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Spring Boot

  • Make it easy to start a Spring project
  • Minimize the amount of manual configuration
  • Provides an embedded HTTP server (tomcat, jetty, undertow, ...)
  • But you can also deploy the war file to an external server
  • Spring Initializr creates a spring project boilerplate
  • https://start.spring.io/
  • jar: do not use src/main/webapp folder
  • war: use src/main/webapp

Project Structure

  • src/main/java: source code
  • src/main/resources: properties and config files

  • src/test/java: unit tests

  • Maven Wrapper Files

  • mvnw & mvnw.cmd
    • script to run maven commands with no need to have maven installed.
    • E.g., ./mvnw clean compile test
    • These files can be safely removed

Starter Parent

  • Special starter that provides Maven defaults
<parent>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-parent</artifactId>
  <version>2.5.3</version>
  <relativePath/> <!-- lookup parent from repository -->
</parent>
  • There's no need to list the spring-boot-starter versions
  • They are all inherited by the spring-boot-starter-parent version
  • Ensures that all versions are compatible

Dependencies (Starters)

  • spring-boot-starter-web
  • spring-web
  • spring-webmvc
  • spring-boot-starter
  • spring-boot-starter-tomcat
  • spring-boot-starter-json
<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-web</artifactId>
</dependency>
  • spring-boot-starter-security: security support and login forms
<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-security</artifactId>
</dependency>
  • spring-boot-devtools: Automatically restarts the app on code change
<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-devtools</artifactId>
  <scope>runtime</scope>
</dependency>
  • spring-boot-starter-actuator
  • Exposes endpoints to monitor and manager your application
  • Rest endpoints are automatically added to the app
  • /actuator/health, /actuator/info, /actuator/auditevents, /actuator/beans, /actuator/mappings
<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-actuator</artifactId>
</dependency>
  • spring-boot-starter-data-jpa:
  • JPA (Java Persistence API) and hibernate
  • JPA is an standard API for ORM (a set of interfaces)
  • Hibernate implements the JPA interfaces
  • Hibernate is the default implementation of JPA on Spring Boot
  • EntityManager is a wrapper on the hibernate session (wraps the SessionFactory)
<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
  • spring-boot-starter-data-rest
  • Generate REST API automatically from an Entity
<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-data-rest</artifactId>
</dependency>
  • spring-boot-starter-thymeleaf
<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-thymeleaf</artifactId>
</dependency>

Maven Plugin

<build>
  <plugins>
    <plugin>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-maven-plugin</artifactId>

      <!-- Container image build configuration -->
      <configuration>
        <image>
          <name>hvitoi/ms-${project.artifactId}:${project.version}</name>
        </image>
        <pullPolicy>IF_NOT_PRESENT</pullPolicy>
      </configuration>

    </plugin>
  </plugins>
</build>

# Build (generate jar)
mvn package

# Run app
java -jar "demo-0.0.1-SNAPSHOT.jar"
mvn spring-boot:run

# Build container image for the app
mvn spring-boot:build-image

Application

  • @SpringBootApplication
  • @EnableAutoConfiguration: auto-configuration support
  • @ComponentScan: scan components to register beans
  • @Configuration: register extra beans
  • SpringApplication.run(DemoApplication.class, args)
  • Creates the application context and register all beans
  • Starts the embedded server
  • Place your Application.java in the root package
  • Implicitly defines the base search package (component scanning)
  • You can also explicitly base package with scanBasePackages parameter
@SpringBootApplication(scanBasePackages={"com.hvitoi.demo", "org.acme.iot.utils"})
public class DemoApplication {

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

}

Properties

server.port=8585
coach.name=Mickey Mouse
team.name=The Mouse Crew

@RestController
public class FunRestController {
  @Value("${coach.name}")
  private String coachName

  @Value("${team.name}")
  private String teamName
}
  • src/main/resources/static: html, css, js, images, etc

Spring Data JPA

  • Generate DAO API from an Entity and Primary Key
  • Expose methods to manipulate database information automatically
package com.hvitoi.demo.dao;

import org.springframework.data.jpa.repository.JpaRepository;
import com.hvitoi.demo.entity.Employee;

public interface EmployeeRepository extends JpaRepository<Employee, Integer> {
}
  • Expose many methods such as
  • findAll
  • findById
  • save
  • deleteById

Spring Data Rest

  • Generate a REST API from a Repository
  • Expose REST endpoints for entities automatically
  • Simply add the dependency
<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-data-rest</artifactId>
</dependency>

Spring Data JPA & Spring Data REST

  • Spring Data REST endpoints are HATEOAS compliant

  • Hypermedia as the Engine of Application State (HATEOS)

  • Hypermedia-driven sites provide information to access REST interfaces (Metadata of REST data)
  • HATEOS uses Hypertext Application Language (HAL) data format (format of the json)
  • Offer pagination, sorting, searching, etc

  • Offer Query Domain Specific Language (Query DSL)

  • @RepositoryRestResource(path = "employees"): modifies the path (case the word has a complex plural)

@RepositoryRestResource(path = "employees") // if not specified "employee + s" will be used
public interface EmployeeRepository extends JpaRepository<Employee, Integer> {
  // Give "Entity Type" and "Primary Key" and receive a funcional DAO
  // There is no implementation, just the interface
}
  • Example: GET /employees
  • For collections, medata includes page size, total elements, pages, etc
{
  "_embedded": {
    "employees": [
      {
        "firstName": "Leslie",
        "lastName": "Andrews",
        "email": "[email protected]",
        "_links": {
          "self": {
            "href": "http://localhost:8080/magic-api/employees/1"
          },
          "employee": {
            "href": "http://localhost:8080/magic-api/employees/1"
          }
        }
      },
      {
        "firstName": "Emma",
        "lastName": "Baumgarten",
        "email": "[email protected]",
        "_links": {
          "self": {
            "href": "http://localhost:8080/magic-api/employees/2"
          },
          "employee": {
            "href": "http://localhost:8080/magic-api/employees/2"
          }
        }
      }
    ]
  },
  "_links": {
    "self": {
      "href": "http://localhost:8080/magic-api/employees"
    },
    "profile": {
      "href": "http://localhost:8080/magic-api/profile/employees"
    }
  },
  "page": {
    "size": 20,
    "totalElements": 2,
    "totalPages": 1,
    "number": 0
  }
}
  • Example: GET /employees/1
{
  "firstName": "Leslie",
  "lastName": "Andrews",
  "email": "[email protected]",
  "_links": {
    "self": {
      "href": "http://localhost:8080/magic-api/employees/1"
    },
    "employee": {
      "href": "http://localhost:8080/magic-api/employees/1"
    }
  }
}
  • Other queries
  • /employees?page=1
  • /employees?page=1
  • /employees?sort=lastName
  • /employees?sort=lastName,desc
  • /employees?sort=lastName,firstName,asc