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RxIo

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The AsyncFiles class allows JVM applications to easily read/write files asynchronously with non-blocking IO. AsyncFiles take advantage of Java AsynchronousFileChannel to perform asynchronous I/O operations.

AsyncFiles provides equivalent operations to the standard JDK Files class but using non-blocking IO and an asynchronous API with different asynchronous idioms, namely: CompletableFuture, jayield AsyncQuery, reactive-streams Publisher, Kotlin coroutines and Kotlin Asynchronous Flow.

In section Usage we present some examples using the AsyncFiles class side by side with the corresponding blocking version of Files.

Installation

First, in order to include it to your project, simply add this dependency:

Maven Gradle 
<dependency> 
    <groupId>com.github.javasync</groupId>
    <artifactId>RxIo</artifactId>
    <version>1.2.5</version>
</dependency>
 
implementation 'com.github.javasync:RxIo:1.2.5'

Usage

Kotlin examples:

suspend fun copyNio(from: String, to: String) {
  val data = Path(from).readText() // suspension point
  Path(to).writeText(data)         // suspension point
}
 
fun copy(from: String, to: String) {
    val data = File(from).readText()
    File(to).writeText(data)
}
 
Path("input.txt")
  .lines()   // Flow<String>
  .onEach(::println)
  .collect() // block if you want to wait for completion
 
Path("input.txt")
  .readLines() // List<String>
  .forEach(::println)

Java examples:

AsyncFiles
  .readAllBytes("input.txt")
  .thenCompose(bytes -> AsyncFiles.writeBytes("output.txt", bytes))
  .join(); // block if you want to wait for completion
 
Path in = Paths.get("input.txt");
Path out = Paths.get("output.txt");
byte[] bytes = Files.readAllBytes(in);
Files.write(out, bytes);
 
AsyncFiles
  .asyncQuery("input.txt")
  .onNext((line, err) -> out.println(line)) // lack check err
  .blockingSubscribe(); // block if you want to wait for completion
 
Path path = Paths.get("input.txt");
Files
  .lines(path)
  .forEach(out::println)
 
List<String> data = asList("super", "brave", "isel", "gain");
AsyncFiles
  .write("output.txt", data) // writing lines to output.txt
  .join(); // block if you want to wait for completion
 
List<String> data = asList("super", "brave", "isel", "gain");
Path path = Paths.get("output.txt")
Files.write(path, data);

The AsyncFiles::lines() returns a reactive Publisher which is compatible with Reactor or RxJava streams. Thus we can use the utility methods of Reactor Flux to easily operate on the result of AsyncFiles::lines(). In the following example we show how to print all words of a gutenberg.org file content without repetitions:

Flux
    .from(AsyncFiles.lines(file))
    .filter(line -> !line.isEmpty())                   // Skip empty lines
    .skip(14)                                          // Skip gutenberg header
    .takeWhile(line -> !line.contains("*** END OF "))  // Skip gutenberg footnote
    .flatMap(line -> Flux.fromArray(line.split("\\W+")))
    .distinct()
    .doOnNext(out::println)
    .doOnError(Throwable::printStackTrace)
    .blockLast(); // block if you want to wait for completion

Alternatively, the AsyncFiles::asyncQuery() returns an AsyncQuery that allows asynchronous subscription and chaining intermediate operations such as filter, map and others. We can rewrite the previous sample as:

AsyncFiles
    .asyncQuery(file)
    .filter(line -> !line.isEmpty())                   // Skip empty lines
    .skip(14)                                          // Skip gutenberg header
    .takeWhile(line -> !line.contains("*** END OF "))  // Skip gutenberg footnote
    .flatMapMerge(line -> AsyncQuery.of(line.split("\\W+")))
    .distinct()
    .subscribe((word, err) -> {
        if(err != null) err.printStackTrace();
        else out.println(word);
    })
    .join(); // block if you want to wait for completion