Interview for Santander UK

What is springboot?

Technically speaking, according to Pivotal's engineers:

Spring Boot is just pairs of @Configurations and @Conditions classes, which will create @Beans classes for us if those @Conditions are met.

Three of the most important conditions are:

    @ConditionsOnClass. It will check if the dependencies or rather specific classes of dependencies are loaded in the classpath (think: Tomcat, HikariCP, etc).

    ConditionOnProperty. Is that property described in any property file?

    Conditional on the missing sibling. If the user has already specified his own, for example, DataSource, then Spring Boot will not attempt to create its auto-configuration.

Not so technically speaking It can be seen as a set of classes or beans, defined by dependencies in the pom.xml, stable to each other, which are going to be loaded in the context of spring 
provided that a number of conditions are met.

What are those conditions?

Those expressed by the label @Conditionals. 

Basically spring-boot is a configuration of a shared spring context with a bunch of @Conditionals tags.
A tag of this type will return a true or false depending on the code you wanted to use, for example, 

Given the following code, you can see that a @IsRelationalDatabaseCondition tag implements something like this:

import org.springframework.context.annotation.condition;
import org.springframework.context.annotation.conditionContext;
import org.springframework.core.type.AnnotatedTypeMetadata;

public class IsRelationalDatabaseCondition implements Condition {

    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) { // (1)
        return oracleJdbcDriverOnClassPath() && databaseUrlSet(context); // (2)

    private boolean databaseUrlSet(ConditionContext context) { // (3)
        return context.getEnvironment().containsProperty("spring.datasource.url");

    private boolean oracleJdbcDriverOnClassPath() { // (4)
        try {
            return true;
        } catch (ClassNotFoundException e) {
            return false;

And we can use it in such a way:

public class ReallyBigCompanySharedContextConfiguration {

    Conditional(IsRelationalDatabaseCondition.class) // (1)
    public ReallyBigCompanyProprietaryFlywayClone flywayClone() {
        return new ReallyBigCompanyProprietaryFlywayClone();


Spring-boot is going to add a lot of @Conditional labels for us to make our life easier.


Software engineer. Eternal learner.

Laniakea, Cúmulo de Virgo, Grupo Local, Vía Lactea, Sistema Solar, Tierra, Badajoz

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