Resource Iterator

A simple kotlin library providing ResourceIterator, which is an extended kotlin.collections.Iterator implementing AutoCloseable interface:

interface ResourceIterator<out X> : Iterator<X>, AutoCloseable {
    ...
}

The standard kotlin-stdlib does not contain Sequence or Iterator which implement AutoCloseable interface (e.g., see open discussion: KT-34719).

This library complements the standard kotlin functionality with an extended iterator as well as various utility methods such as flatMap, filter, etc., similar to Sequence methods. Each of these methods produces a subsequent ResourceIterator, closing which also closes the source iterator. The ResourceIterator extends Iterator, not Sequence, since it is hard to control every standard method-extension of Sequence.

Known alternatives:

• JDK java.util.stream.Stream
• Apache Jena org.apache.jena.util.iterator.ExtendedIterator
• Apache Kafka org.apache.kafka.common.utils.CloseableIterator

When to use:

If you have some resources which need to be closed after or during iteration, and you don't want to use JDK or some external heavy library. For example, ResourceIterator is used by textfile-utils (see cc.datafabric.textfileutils.files.LineReade.kt).

Examples of use:

// with standard collections:
listOf<Long>(1, 2).asResourceIterator { println("close outer") }
    .flatMap { x ->
        resourceIteratorOf(21 * x, 42 * x) { println("close inner for $x") }
    }
    .filter { it > 0 }
    .use {
        println("it = ${it.firstOrNull()}")
    }

// with jdbc:
fun <X> Connection.executeQuery(
    query: String,
    extractor: (ResultSet) -> X,
    exec: PreparedStatement.() -> ResultSet
): ResourceIterator<X> {
    val statement = prepareStatement(query)
    val rs = statement.exec()
    return generateResourceIterator({ if (rs.next()) extractor(rs) else null }) { statement.close() }
}

Available via maven-central:

dependencies {
    implementation("io.github.datafabricrus:resource-iterator-jvm:{{latest_version}}")
}

Apache License Version 2.0