---

id: 41

slug: "stream-mapmulti"

title: "Stream.mapMulti()"

category: "streams"

difficulty: "intermediate"

jdkVersion: "16"

oldLabel: "Java 8"

modernLabel: "Java 16+"

oldApproach: "flatMap + List"

modernApproach: "mapMulti()"

oldCode: |-

stream.flatMap(order ->

order.items().stream()

.map(item -> new OrderItem(

order.id(), item)

)

);

modernCode: |-

stream.<OrderItem>mapMulti(

(order, downstream) -> {

for (var item : order.items())

downstream.accept(

new OrderItem(order.id(), item));

}

);

summary: "Emit zero or more elements per input without creating intermediate streams."

explanation: "mapMulti() is an imperative alternative to flatMap that avoids creating\

\ intermediate Stream objects for each element. It's more efficient when the mapping\

\ produces a small number of elements."

whyModernWins:

- icon: "⚡"

title: "Less allocation"

desc: "No intermediate Stream created per element."

- icon: "🎯"

title: "Imperative style"

desc: "Use loops and conditionals directly."

- icon: "📐"

title: "Flexible"

desc: "Emit zero, one, or many elements with full control."

support:

state: "available"

description: "Widely available since JDK 16 (March 2021)"

prev: "streams/stream-tolist"

next: "streams/stream-gatherers"

related:

- "streams/stream-iterate-predicate"

- "streams/stream-of-nullable"

- "streams/stream-gatherers"

docs:

- title: "Stream.mapMulti()"

href: "https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/util/stream/Stream.html#mapMulti(java.util.function.BiConsumer)"