package com.mindprod.example;

import java.io.FileInputStream;
import java.io.IOException;
import java.nio.Buffer;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;

/**
 * Example  use of java.nio to read a file.
 * Requires a test file of approximately 29K called E:\temp\tempin.txt
 * <p/>
 * composed with IntelliJ IDEA
 *
 * @author Roedy Green, Canadian Mind Products
 * @version 1.0
 */
public class TestNioRead
    {
    // -------------------------- STATIC METHODS --------------------------

    /**
     * read some raw bytes from a file
     *
     * @throws IOException if problems with read
     */
    @SuppressWarnings( { "UnusedAssignment" } )
    private static void readRawBytes() throws IOException
        {
        final FileInputStream fis = new FileInputStream( "E:/temp/tempin.txt" );

        // allocate a channel to read that file
        FileChannel fc = fis.getChannel();

        // allocate a buffer, as big a chunk as we are willing to handle at a pop.
        ByteBuffer buffer = ByteBuffer.allocate( 1024 * 15 );
        showStats( "newly allocated read", fc, buffer );

        // read a chunk of raw bytes, up to 15K bytes long
        // -1 means eof.
        int bytesRead = fc.read( buffer );
        showStats( "after first read", fc, buffer );

        // flip from filling to emptying
        showStats( "before flip", fc, buffer );
        buffer.flip();
        showStats( "after flip", fc, buffer );

        byte[] receive = new byte[1024];
        buffer.get( receive );
        showStats( "after first get", fc, buffer );

        buffer.get( receive );
        showStats( "after second get", fc, buffer );

        // empty buffer to fill with more data.
        buffer.clear();
        showStats( "after clear", fc, buffer );

        bytesRead = fc.read( buffer );
        showStats( "after second read", fc, buffer );

        // flip from filling to emptying
        showStats( "before flip", fc, buffer );
        buffer.flip();
        showStats( "after flip", fc, buffer );

        fc.close();
        }

    /**
     * Display state of channel/buffer.
     *
     * @param where description of where we are in the program to label the state snapzhot
     * @param fc    FileChannel reading/writing.
     * @param b     Buffer to display state of:
     * @throws IOException if i/o problems.
     */
    private static void showStats( String where, FileChannel fc, Buffer b ) throws IOException
        {
        System.out
                .println( where +
                          " channelPosition: " +
                          fc.position() +
                          " bufferPosition: " +
                          b.position() +
                          " limit: " +
                          b.limit() +
                          " remaining: " +
                          b.remaining() +
                          " capacity: " +
                          b.capacity() );
        }

    // --------------------------- main() method ---------------------------

    /**
     * test harness
     *
     * @param args not used
     * @throws IOException if problems reading.
     */
    public static void main( String[] args ) throws IOException
        {
        readRawBytes();
        }
    }