fix: EXPOSED-714 [exposed-spring-boot-starter] Fix NPE from DatabaseInitializer when non-object Table is defined

[PeraSite]

Description

If spring.exposed.generate-ddl option is enabled, DatabaseInitializer discover exposed tables using following function.

fun discoverExposedTables(applicationContext: ApplicationContext, excludedPackages: List<String>): List<Table> {
    val provider = ClassPathScanningCandidateComponentProvider(false)
    provider.addIncludeFilter(AssignableTypeFilter(Table::class.java))
    excludedPackages.forEach { provider.addExcludeFilter(RegexPatternTypeFilter(Pattern.compile(it.replace(".", "\\.") + ".*"))) }
    val packages = AutoConfigurationPackages.get(applicationContext)
    val components = packages.map { provider.findCandidateComponents(it) }.flatten()
    return components.map { Class.forName(it.beanClassName).kotlin.objectInstance as Table }
    //                                                                             ^ Here
}

The discoverExposedTables function finds that

1. Class that assignable from Table type
2. Not in the excludedPackages package that cames from Spring property

And directly cast bean's objectInstance to Table.

The problem is that found bean can be a normal class not singleton object. For example, If I created open class like this

open class BaseTable() : Table()

and getting objectInstance of BaseTable class returns null.

Casting null to Table throws NPE like this.

java.lang.NullPointerException: null cannot be cast to non-null type org.jetbrains.exposed.sql.Table
	at org.jetbrains.exposed.spring.DatabaseInitializerKt.discoverExposedTables(DatabaseInitializer.kt:56) ~[exposed-spring-boot-starter-0.58.0.jar:na]

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Type of Change

• Bug fix

Affected databases:

• All

Checklist

• Unit tests are in place
• The build is green (including the Detekt check)
• All public methods affected by my PR has up to date API docs
• Documentation for my change is up to date

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Related Issues

EXPOSED-714 Throws NullPointerException when Table class isn't object

[bog-walk]

Thanks for reporting this issue & working on a fix so quickly @PeraSite !