Scala-IO Core: Unmanaged Resources

The main design of Scala-IO is around automatic closing of resources each time a resource is accessed in order to ensure that a programmer cannot unintentionally leave resources open in the face of exceptions or other unexpected situations. However, there are cases where the Scala-IO API is desired but the resource management is undesired. The classic case is of reading or writing to System.in and out. Thus Unmanaged resources exist to satisfy this use-case. 

Since unmanaged resources is a less common use-case there is not a factory object like there is for normal managed Resources.  Instead certain objects can be converted to unmanaged resources using the JavaConverters implicit methods as follows:

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// JavaConverters implicit methods are required to create the // unmanaged resources scala> import scalax.io.JavaConverters._ import scalax.io.JavaConverters._   // now that JavaConverters are in scope we can convert // System.out to a Output object and use it as any normal // output object except that the stream will not be closed // WriteableByteChannels can also be converted scala> System.out.asUnmanagedOutput.write("Not closing right?") Not closing right?   // See, still not closed scala> System.out.asUnmanagedOutput.write("Still not closed?") Still not closed?   scala> import java.io._ import java.io._   // another demonstration of converting an output stream to a // unmanaged Output object.  This is frowned upon unless // unavoidable. scala> val fout = new FileOutputStream("somefile.txt") fout: java.io.FileOutputStream = java.io.FileOutputStream@23987721   scala> val foutOutput = fout.asUnmanagedOutput foutOutput: scalax.io.Output = scalax.io.unmanaged.WritableByteChannelResource@36b54a77   scala> foutOutput.write("Hello ")   scala> foutOutput.write("World!")   scala> fout.close   // see the output object is broken now because the stream is closed scala> foutOutput.write("boom") No Main Exception --- class java.nio.channels.ClosedChannelException(null) ...   // The mirror image is converting an input stream to an Input object scala> val fin = new FileInputStream("somefile.txt") fin: java.io.FileInputStream = java.io.FileInputStream@4fcbc4de   scala> val chars = fin.asUnmanagedInput.chars chars: scalax.io.LongTraversable[Char] = LongTraversable(...)   // normally a LongTraversable will close the resource // but this LongTraversable is obtained from a unmanagedInput // so can be used multiple times without closing the resource scala> chars.head res19: Char = H   scala> chars.head res20: Char = e   scala> chars.head res21: Char = l   scala> chars.head res22: Char = l   // don't forget to close scala> fin.close   // quick demo of using channels // the following is a major anti-pattern and is // here mainly for completeness scala> val fchannel = new RandomAccessFile("somefile.txt", "rw").getChannel fchannel: java.nio.channels.FileChannel = sun.nio.ch.FileChannelImpl@1e10cb60   scala> val fInput2 = fchannel.asUnmanagedInput fInput2: scalax.io.Input = scalax.io.unmanaged.ReadableByteChannelResource@679a339e   scala> println(fInput2.string) Hello World!   scala> fchannel.isOpen res13: Boolean = true   scala> val fOutput = fchannel.asUnmanagedOutput fOutput: scalax.io.Output = scalax.io.unmanaged.WritableByteChannelResource@9cc8b91   scala> fOutput.write("hi there")   scala> println(fInput2.string) hi thererld!   // don't forget to close scala> fchannel.close