What does spring-boot-starter-parent exactly do in pom file?

Question

I'm developing a project which is not Spring boot but also spring mvc. I mean I don't have this class for example in my project:

@SpringBootApplication
public class Application extends SpringBootServletInitializer {

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

I have these three classes for configuration file of spring mvc:

@Import(WebSocketConfig.class)
@Configuration
@EnableWebMvc
@ComponentScan(basePackages = "......")

public class MainConfiguration extends WebMvcConfigurerAdapter {
    @Override
    public void addResourceHandlers(ResourceHandlerRegistry registry) {
        registry.addResourceHandler("/Content/**")
                .addResourceLocations("/Content/");
        registry.addResourceHandler("/Scripts/**")
                .addResourceLocations("/Scripts/");


    }

    @Bean
    public InternalResourceViewResolver viewResolver() {
        InternalResourceViewResolver viewResolver
                = new InternalResourceViewResolver();
        viewResolver.setPrefix("/");
        viewResolver.setSuffix(".jsp");
        return viewResolver;
    }

}

Second:

public class MainInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {
    public static HashMap<String, String> response_code = new HashMap<String, String>();


    @Override
    protected Class<?>[] getRootConfigClasses() {
        return new Class[] { MainConfiguration.class,
        WebSocketConfig.class};
    }

    @Override
    protected Class<?>[] getServletConfigClasses() {
        return null;
    }

    @Override
    protected String[] getServletMappings() {
        return new String[] { "/" };
    }

    @Override
    public void onStartup(ServletContext servletContext) throws ServletException {
        super.onStartup(servletContext);
        Security.addProvider(new BouncyCastleProvider());
        servletContext.addListener(new MainContextListener());
        System.out.println("MainInitializer.onStartup()");
}}

Third,

public class MainContextListener implements ServletContextListener {

    public void contextInitialized(ServletContextEvent servletContextEvent) {
        System.out.println("Context Initialized");
        Security.addProvider(new BouncyCastleProvider());
    }

    public void contextDestroyed(ServletContextEvent servletContextEvent) {
        System.out.println("Shutting down!");
    }
}

There is a controller and jsp file and I've configured it to run on tomcat webserver, something is strange for me is that when I add this snippet of code to my pom, index.jsp will appear in browser exactly but when I remove it , it gives 404 not found url for my controller. why is it that even my project is not a spring boot project need spring boot starter parent? I thought below code is related to spring boot and since my project is not spring boot but spring mvc, doesn't need it. but it has problem without this code added in pom:

<parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.1.RELEASE</version>
    </parent>

Answer 1

It provides place for common configuration for CHILD POM s. for eg

Dependencies & Properties

For eg Here is the parent POM configuration 1.4.2.RELEASE spring-boot-dependencies which is parent of spring-boot-starter-parent

<properties>
    <activemq.version>5.13.4</activemq.version>
    <antlr2.version>2.7.7</antlr2.version>
    <appengine.version>1.9.44</appengine.version>
    <artemis.version>1.3.0</artemis.version>
    <aspectj.version>1.8.9</aspectj.version>
    <assertj.version>2.5.0</assertj.version>
    <atomikos.version>3.9.3</atomikos.version>
    <bitronix.version>2.1.4</bitronix.version>
    <caffeine.version>2.3.4</caffeine.version>

common properties for child POM s

<dependencyManagement>
    <dependencies>
        <!-- Spring Boot -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot</artifactId>
            <version>1.4.2.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot</artifactId>
            <type>test-jar</type>
            <version>1.4.2.RELEASE</version>
        </dependency>
        <dependency>

common dependencies for childs

Answer 2

If you can provide more informations, like your pom integrality, we can look futher to inderstand and help you more.

In the other hand, the parent pom spring-boot-starter-parent, contains the full dependencies(mvc, cache, jpa) and commons properties to maintain dependencies versions in a good consistency, to be used in your project or/and submodules.

Basically, you can add some starters in your pom.xml depending on your need (web, jpa, batch....) For your example, you can just add a starter mvc to your pom.xml without adding other dependencies, so your pom.xml can just be like that :

 <parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>1.5.9.RELEASE</version>
</parent>

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

<properties>
    <java.version>1.8</java.version>
</properties>


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

Answer 3

Spring Boot provides a number of “Starters” that let you add jars to your classpath. For ex. spring-boot-starter-security,spring-boot-starter-web etc. The "spring-boot-starter-parent" is a special starter that provides useful Maven defaults ie it adds all the required jars and other things automatically. It also provides a dependency-management section so that you can omit version tags for dependencies you are using in pom.xml. For ex. suppose you want to create web application with spring boot so you need to add the following.

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

Now note here that tag is omitted. So ultimately the "spring-boot-starter-parent" adds so many things by default so we no need to worry about those things.