File Gotchas

From:

Roedy Green <see_website@mindprod.com.invalid>

Newsgroups:

comp.lang.java.help

Date:

Sat, 16 Mar 2013 20:16:03 -0700

Message-ID:

<t9cak8lc0kuljdsgges7rkpl98hrj5bt8b@4ax.com>

/*
* [TestFileCombine.java]
*
* Summary: combining two filenames with java.io.File
*
* Copyright: (c) 2013 Roedy Green, Canadian Mind Products,
http://mindprod.com
*
* Licence: This software may be copied and used freely for any
purpose but military.
* http://mindprod.com/contact/nonmil.html
*
* Requires: JDK 1.7+
*
* Created with: JetBrains IntelliJ IDEA IDE
http://www.jetbrains.com/idea/
*
* Version History:
* 1.0 2013-03-16 initial version
*/
package com.mindprod.example;

import com.mindprod.common11.Misc;

import java.io.File;
import java.io.IOException;

import static java.lang.System.out;

/**
* combining two filenames with java.io.File
*
* @author Roedy Green, Canadian Mind Products
* @version 1.0 2013-03-16 initial version
* @since 2013-03-16
*/
public final class TestFileCombine
    {

    /**
     * Experiment with various ways of combining file names
     *
     * @param args not used
     *
     * @throws java.io.IOException on I/O failure.
     */
    public static void main( String[] args ) throws IOException
        {

        // file is not suitable for resolving relative or absolute
offsets from a base filename.
        File root = new File( "E:/mindprod" );
        File o1 = new File( root, "index.html" );
        out.println( Misc.getCanOrAbsPath( o1 ) );
        // prints: E:/mindprod/index.html (actually with backslashes)

        File o2 = new File( root, "/index.html" );
        out.println( Misc.getCanOrAbsPath( o2 ) );
        // prints: E:/mindprod/index.html

        File base = new File( "E:/mindprod/jgloss/encoding" );
        File o3 = new File( base, "pad.html" );
        out.println( Misc.getCanOrAbsPath( o3 ) );
        // prints: E:\mindprod\jgloss\encoding\pad.html

        File o4 = new File( base, "../pad.html" );
        out.println( Misc.getCanOrAbsPath( o4 ) );
        // prints: E:\mindprod\jgloss\pad.html

        File o5 = new File( base, "/jgloss/pad.html" );
        out.println( Misc.getCanOrAbsPath( o5 ) );
        // prints:E:\mindprod\jgloss\encoding\jgloss\pad.html (ouch)
        // You might have naively hoped for:
E:/mindprod/jgloss/pad.html
        // However, File has no idea that / on your website refers to
E:/mindprod.

        File base2 = new File( "E:/mindprod/jgloss/encoding/utf8.html"
);
        File o6 = new File( base2, "pad.html" );
        out.println( Misc.getCanOrAbsPath( o6 ) );
        // prints: E:\mindprod\jgloss\encoding\utf8.html\pad.html
(ouch)
        // You might have hoped for:
E:\mindprod\jgloss\encoding\pad.html

        File o7 = new File( base2, "../pad.html" );
        out.println( Misc.getCanOrAbsPath( o7 ) );
        // prints: E:\mindprod\jgloss\encoding\pad.html (ouch)
        // You might have hoped for: E:\mindprod\jgloss\pad.html

        File o8 = new File( base2, "/jgloss/pad.html" );
        out.println( Misc.getCanOrAbsPath( o8 ) );
        // prints:
E:\mindprod\jgloss\encoding\utf8.html\jgloss\pad.html (ouch)
        // You might have naively hoped for:
E:/mindprod/jgloss/pad.html
        // However, File has no idea that / on your website refers to
E:/mindprod.
        }

    }
--
Roedy Green Canadian Mind Products http://mindprod.com
The computer programmer is a creator of universes for which he alone
is the lawgiver. No playwright, no stage director, no emperor, however
powerful, has ever exercised such absolute authority to arrange a stage
or a field of battle and to command such unswervingly dutiful actors or
troops.
~ Joseph Weizenbaum (born: 1923-01-08 died: 2008-03-05 at age: 85)