Java: a fluent I/O API (2/4)

This is the second post about my experiments with a fluent I/O API. This post covers how to extend the API.

Doctoring streams

Let's look at some of the API's Doctor implementations. The code uses some static imports to keep things clean:

import static demo.fluentio.Closers.closer; import static demo.fluentio.Doctors.DETECT_BOM; import static demo.fluentio.Doctors.bom; import static demo.fluentio.Drains.drain;

This code writes UTF-8 character data, prefixing the stream with a Unicode byte-order-mark:

private void save(File output, String data) throws IOException {     Closer closer = closer();     try {       Writer writer = IO.open(closer, output)                         .utf8()                         .doctor(bom())                         .die();       writer.write(data);     } finally {       closer.close();     }   }

This code detects the encoding of a text file by inspecting the byte-order-mark:

private String load(File input) throws IOException {     Closer closer = closer();     try {       InputStreamReader reader = IO.access(closer, input)                                    .doctor(DETECT_BOM)                                    .die();       return drain(reader, new StringBuilder()).toString();     } finally {       closer.close();     }   }

Extending the API

You can add support for other stream types by implementing your own Doctor implementations. This Doctor decorates a stream with a filter class (elided) that turns characters into upper case:

public class ShoutyDoctor implements     Doctor<WriterDie<ShoutyWriter>, Die<Writer>> {   public static ShoutyDoctor INSTANCE = new ShoutyDoctor();   private ShoutyDoctor() {}   @Override   public WriterDie<ShoutyWriter> op(Die<Writer> f) throws IOException {     Writer decorated = f.die();     ShoutyWriter writer = new ShoutyWriter(decorated);     return IO.writing(f.getCloser(), writer);   } }

This code prints out WOULD YOU LIKE TO PLAY A GAME?:

PrintWriter shouter = IO.out(SHUT, System.out)         .encode(defaultCharset())         .operate(SHOUTY)         .printer()         .die();     shouter.println("Would you like to play a game?");     shouter.flush();

Doctoring streams

Adding decorators isn't the only thing you can do with a Doctor implementation. This code creates one to perform a byte copy operation:

private static void copy(File src, File dest) throws IOException {     CoupledCloser closer = coupledCloser();     try {       Doctor<OutputStream, ?> drainBytesOp = access(closer.in(), src).drain();       open(closer.out(), dest).doctor(drainBytesOp);     } finally {       closer.close();     }   }

Related posts

• Part 1: introduction
• Part 2: extending the API
• Part 3: error handling
• Part 4: conclusions and downloads

Comments & criticism are welcome.