Un confronto tra Spring e Spring Boot

1. Panoramica

In questo articolo, esamineremo le differenze tra i framework Spring standard e Spring Boot.

Ci concentreremo su e discuteremo su come i moduli di Spring, come MVC e Security, differiscono quando utilizzati nel core Spring rispetto a quando utilizzati con Boot.

2. Cos'è la primavera?

In poche parole, il framework Spring fornisce un supporto infrastrutturale completo per lo sviluppo di applicazioni Java .

È ricco di alcune funzionalità interessanti come Dependency Injection e moduli pronti all'uso come:

  • Spring JDBC
  • Spring MVC
  • Spring Security
  • Primavera AOP
  • ORM di primavera
  • Test di primavera

Questi moduli possono ridurre drasticamente i tempi di sviluppo di un'applicazione.

Ad esempio, all'inizio dello sviluppo web Java, avevamo bisogno di scrivere molto codice boilerplate per inserire un record in un'origine dati. Ma utilizzando il JDBCTemplate del modulo Spring JDBC possiamo ridurlo a poche righe di codice con solo poche configurazioni.

3. Cos'è Spring Boot?

Spring Boot è fondamentalmente un'estensione del framework Spring che ha eliminato le configurazioni standard richieste per l'impostazione di un'applicazione Spring.

Assume una visione ostinata della piattaforma Spring che ha aperto la strada a un ecosistema di sviluppo più rapido ed efficiente .

Di seguito sono riportate solo alcune delle funzionalità di Spring Boot:

  • Dipendenze "iniziali" per semplificare la compilazione e la configurazione dell'applicazione
  • Server incorporato per evitare complessità nella distribuzione delle applicazioni
  • Metriche, controllo dello stato e configurazione esternalizzata
  • Configurazione automatica per la funzionalità Spring, quando possibile

Acquisiamo familiarità con entrambi questi framework passo dopo passo.

4. Dipendenze di Maven

Prima di tutto, diamo un'occhiata alle dipendenze minime richieste per creare un'applicazione web utilizzando Spring:

 org.springframework spring-web 5.2.9.RELEASE   org.springframework spring-webmvc 5.2.9.RELEASE 

A differenza di Spring, Spring Boot richiede solo una dipendenza per far funzionare un'applicazione web:

 org.springframework.boot spring-boot-starter-web 2.3.4.RELEASE 

Tutte le altre dipendenze vengono aggiunte automaticamente all'archivio finale durante la fase di compilazione.

Un altro buon esempio è il test delle librerie. Di solito usiamo il set di librerie Spring Test, JUnit, Hamcrest e Mockito. In un progetto Spring, dovremmo aggiungere tutte queste librerie come dipendenze.

Ma in Spring Boot, abbiamo solo bisogno della dipendenza starter per i test per includere automaticamente queste librerie.

Spring Boot fornisce una serie di dipendenze iniziali per diversi moduli Spring. Alcuni di quelli più comunemente usati sono:

  • spring-boot-starter-data-jpa
  • Spring-boot-starter-security
  • test di avviamento a molla
  • spring-boot-starter-web
  • primavera-boot-starter-thymeleaf

Per l'elenco completo degli antipasti, controlla anche la documentazione di Spring.

5. Configurazione MVC

Esploriamo la configurazione richiesta per creare un'applicazione Web JSP utilizzando sia Spring che Spring Boot.

Spring richiede la definizione del servlet del dispatcher, dei mapping e di altre configurazioni di supporto. Possiamo farlo utilizzando il file web.xml o una classe Initializer :

public class MyWebAppInitializer implements WebApplicationInitializer { @Override public void onStartup(ServletContext container) { AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext(); context.setConfigLocation("com.baeldung"); container.addListener(new ContextLoaderListener(context)); ServletRegistration.Dynamic dispatcher = container .addServlet("dispatcher", new DispatcherServlet(context)); dispatcher.setLoadOnStartup(1); dispatcher.addMapping("/"); } }

We also need to add the @EnableWebMvc annotation to a @Configuration class and define a view-resolver to resolve the views returned from the controllers:

@EnableWebMvc @Configuration public class ClientWebConfig implements WebMvcConfigurer { @Bean public ViewResolver viewResolver() { InternalResourceViewResolver bean = new InternalResourceViewResolver(); bean.setViewClass(JstlView.class); bean.setPrefix("/WEB-INF/view/"); bean.setSuffix(".jsp"); return bean; } }

By comparison to all this, Spring Boot only needs a couple of properties to make things work, once we've added the web starter:

spring.mvc.view.prefix=/WEB-INF/jsp/ spring.mvc.view.suffix=.jsp

All the Spring configuration above is automatically included by adding the Boot web starter, through a process called auto-configuration.

What this means is that Spring Boot will look at the dependencies, properties, and beans that exist in the application and enable configuration based on these.

Of course, if we want to add our own custom configuration, then the Spring Boot auto-configuration will back away.

5.1. Configuring Template Engine

Let's now learn how to configure a Thymeleaf template engine in both Spring and Spring Boot.

In Spring we need to add the thymeleaf-spring5 dependency and some configurations for the view resolver:

@Configuration @EnableWebMvc public class MvcWebConfig implements WebMvcConfigurer { @Autowired private ApplicationContext applicationContext; @Bean public SpringResourceTemplateResolver templateResolver() { SpringResourceTemplateResolver templateResolver = new SpringResourceTemplateResolver(); templateResolver.setApplicationContext(applicationContext); templateResolver.setPrefix("/WEB-INF/views/"); templateResolver.setSuffix(".html"); return templateResolver; } @Bean public SpringTemplateEngine templateEngine() { SpringTemplateEngine templateEngine = new SpringTemplateEngine(); templateEngine.setTemplateResolver(templateResolver()); templateEngine.setEnableSpringELCompiler(true); return templateEngine; } @Override public void configureViewResolvers(ViewResolverRegistry registry) { ThymeleafViewResolver resolver = new ThymeleafViewResolver(); resolver.setTemplateEngine(templateEngine()); registry.viewResolver(resolver); } }

Spring Boot 1 required only the dependency of spring-boot-starter-thymeleaf to enable Thymeleaf support in a web application. But because of the new features in Thymeleaf3.0, we have to add thymeleaf-layout-dialect also as a dependency in a Spring Boot 2 web application. Alternatively, we can choose to add a spring-boot-starter-thymeleaf dependency that'll take care of all this for us.

Once the dependencies are in place, we can add the templates to the src/main/resources/templates folder and the Spring Boot will display them automatically.

6. Spring Security Configuration

For the sake of simplicity, we'll see how the default HTTP Basic authentication is enabled using these frameworks.

Let's start by looking at the dependencies and configuration we need to enable Security using Spring.

Spring requires both the standard spring-security-web and spring-security-config dependencies to set up Security in an application.

Next, we need to add a class that extends the WebSecurityConfigurerAdapter and makes use of the @EnableWebSecurity annotation:

@Configuration @EnableWebSecurity public class CustomWebSecurityConfigurerAdapter extends WebSecurityConfigurerAdapter { @Autowired public void configureGlobal(AuthenticationManagerBuilder auth) throws Exception { auth.inMemoryAuthentication() .withUser("user1") .password(passwordEncoder() .encode("user1Pass")) .authorities("ROLE_USER"); } @Override protected void configure(HttpSecurity http) throws Exception { http.authorizeRequests() .anyRequest().authenticated() .and() .httpBasic(); } @Bean public PasswordEncoder passwordEncoder() { return new BCryptPasswordEncoder(); } }

Here we're using inMemoryAuthentication to set up the authentication.

Similarly, Spring Boot also requires these dependencies to make it work. But we need to define only the dependency ofspring-boot-starter-security as this will automatically add all the relevant dependencies to the classpath.

The security configuration in Spring Boot is the same as the one above.

If you need to know how the JPA configuration can be achieved in both Spring and Spring Boot, then check out our article A Guide to JPA with Spring.

7. Application Bootstrap

The basic difference in bootstrapping of an application in Spring and Spring Boot lies with the servlet. Spring uses either the web.xml or SpringServletContainerInitializer as its bootstrap entry point.

On the other hand, Spring Boot uses only Servlet 3 features to bootstrap an application. Let's talk about this in detail.

7.1. How Spring Bootstraps?

Spring supports both the legacy web.xml way of bootstrapping as well as the latest Servlet 3+ method.

Let's see the web.xml approach in steps:

  1. Servlet container (the server) reads web.xml
  2. The DispatcherServlet defined in the web.xml is instantiated by the container
  3. DispatcherServlet creates WebApplicationContext by reading WEB-INF/{servletName}-servlet.xml
  4. Finally, the DispatcherServlet registers the beans defined in the application context

Here's how Spring bootstraps using Servlet 3+ approach:

  1. The container searches for classes implementing ServletContainerInitializer and executes
  2. The SpringServletContainerInitializer finds all classes implementing WebApplicationInitializer
  3. The WebApplicationInitializer creates the context with XML or @Configuration classes
  4. The WebApplicationInitializer creates the DispatcherServlet with the previously created context.

7.2. How Spring Boot Bootstraps?

The entry point of a Spring Boot application is the class which is annotated with @SpringBootApplication:

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

By default, Spring Boot uses an embedded container to run the application. In this case, Spring Boot uses the public static void main entry-point to launch an embedded web server.

Also, it takes care of the binding of the Servlet, Filter, and ServletContextInitializer beans from the application context to the embedded servlet container.

Another feature of Spring Boot is that it automatically scans all the classes in the same package or sub packages of the Main-class for components.

Spring Boot provides the option of deploying it as a web archive in an external container as well. In this case, we have to extend the SpringBootServletInitializer:

@SpringBootApplication public class Application extends SpringBootServletInitializer { // ... }

Here the external servlet container looks for the Main-class defined in the META-INF file of the web archive and the SpringBootServletInitializer will take care of binding the Servlet, Filter, and ServletContextInitializer.

8. Packaging and Deployment

Finally, let's see how an application can be packaged and deployed. Both of these frameworks support the common package managing technologies like Maven and Gradle. But when it comes to deployment, these frameworks differ a lot.

For instance, the Spring Boot Maven Plugin provides Spring Boot support in Maven. It also allows packaging executable jar or war archives and running an application “in-place”.

Some of the advantages of Spring Boot over Spring in the context of deployment include:

  • Provides embedded container support
  • Provision to run the jars independently using the command java -jar
  • Option to exclude dependencies to avoid potential jar conflicts when deploying in an external container
  • Option to specify active profiles when deploying
  • Random port generation for integration tests

9. Conclusion

In questo tutorial, abbiamo appreso le differenze tra Spring e Spring Boot.

In poche parole, possiamo dire che Spring Boot è semplicemente un'estensione di Spring stesso per rendere più convenienti lo sviluppo, il test e la distribuzione.