CODEWITHSUNDEEP
unit-testingjava-8stream
evgeniy44
evgeniy44

Reputation: 3162

How to check if a Java 8 Stream is closed?

I have a java 8 stream with underlying IOStream and I want to make sure that my method closes that stream.

Is there any way to check it with unit test?

Upvotes: 3

Views: 2411

Answers (2)

Austin
Austin

Reputation: 185

I think providing a handler to Stream's onClose method is the easiest way to do this.

AtomicBoolean wasClosed = new AtomicBoolean(false);
Stream<> stream = Stream.of(foo, bar).onClose(() -> wasClosed.set(true));

// ...code under test that uses the stream

assertThat(wasClosed.get()).isTrue();

For what it's worth, I legitimately needed to test this, as we make Streams from JDBC ResultSets, and the actual Stream relies on onClose to close the ResultSet.

Upvotes: 3

Jocke
Jocke

Reputation: 2284

Streams have a BaseStream.close() method and implement AutoCloseable, but nearly all stream instances do not actually need to be closed after use. Generally, only streams whose source is an IO channel (such as those returned by Files.lines(Path, Charset)) will require closing. Most streams are backed by collections, arrays, or generating functions, which require no special resource management. (If a stream does require closing, it can be declared as a resource in a try-with-resources statement.)

https://docs.oracle.com/javase/8/docs/api/java/util/stream/Stream.html

Upvotes: -1

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