Does below code need to be wrapped in try-with-resources to make sure underlying file is closed?
List<String> rows = Files.lines(inputFilePath).collect(Collectors.toList());
Does below code need to be wrapped in try-with-resources to make sure underlying file is closed?
List<String> rows = Files.lines(inputFilePath).collect(Collectors.toList());
As the javadoc of the overloaded Files#lines(Path, Charset)
method states
The returned stream encapsulates a
Reader
. If timely disposal of file system resources is required, thetry-with-resources
construct should be used to ensure that the stream's close method is invoked after the stream operations are completed.
So yes, wrap the Stream
returned by lines
in a try-with-resources
statement. (Or close it appropriately.)
There is a trick to make the Stream
implementation calling close()
after the terminal operation:
List<String> rows = Stream.of(Files.lines(inputFilePath)).flatMap(s->s)
.collect(Collectors.toList());
It simply creates a stream encapsulating the stream of lines as a single item and uses flatMap
with an identity function (Function.identity()
would work as well) to turn it into a stream of lines again.
The interesting point is a property of Stream.flatMap(…)
:
Each mapped stream is closed after its contents have been placed into this stream.
So the code above will close the stream of lines. While it looks more concise it has the disadvantage over try with resources that current implementation of flatMap
lacks lazy evaluation which is not relevant here as you are collecting all lines into a list anyway. But it’s something to keep in mind when using this trick in other scenarios.
For the question’s code as-is there is an even simpler solution:
List<String> rows = Files.readAllLines(inputFilePath);
Reads all lines and closes all resources…