Java Path Create Canonical canonicalPath(String path)

Description

Convert a path to a cananonical form.

License

Open Source License

Parameter

Parameter	Description
path	a parameter

Return

path or null.

Declaration

public static String canonicalPath(String path) 

Method Source Code

//package com.java2s;
//  are made available under the terms of the Eclipse Public License v1.0

public class Main {
    /**/*from w  w w.  j ava2  s . c o  m*/
     * Convert a path to a cananonical form. All instances of "." and ".." are factored out. Null is returned if the path tries to .. above its root.
     * 
     * @param path
     * @return path or null.
     */
    public static String canonicalPath(String path) {
        if (path == null || path.length() == 0)
            return path;

        int end = path.length();
        int start = path.lastIndexOf('/', end);

        search: while (end > 0) {
            switch (end - start) {
            case 2: // possible single dot
                if (path.charAt(start + 1) != '.')
                    break;
                break search;
            case 3: // possible double dot
                if (path.charAt(start + 1) != '.' || path.charAt(start + 2) != '.')
                    break;
                break search;
            }

            end = start;
            start = path.lastIndexOf('/', end - 1);
        }

        // If we have checked the entire string
        if (start >= end)
            return path;

        StringBuilder buf = new StringBuilder(path);
        int delStart = -1;
        int delEnd = -1;
        int skip = 0;

        while (end > 0) {
            switch (end - start) {
            case 2: // possible single dot
                if (buf.charAt(start + 1) != '.') {
                    if (skip > 0 && --skip == 0) {
                        delStart = start >= 0 ? start : 0;
                        if (delStart > 0 && delEnd == buf.length() && buf.charAt(delEnd - 1) == '.')
                            delStart++;
                    }
                    break;
                }

                if (start < 0 && buf.length() > 2 && buf.charAt(1) == '/' && buf.charAt(2) == '/')
                    break;
                if (delEnd < 0)
                    delEnd = end;
                delStart = start;
                if (delStart < 0 || delStart == 0 && buf.charAt(delStart) == '/') {
                    delStart++;
                    if (delEnd < buf.length() && buf.charAt(delEnd) == '/')
                        delEnd++;
                    break;
                }
                if (end == buf.length())
                    delStart++;

                end = start--;
                while (start >= 0 && buf.charAt(start) != '/')
                    start--;
                continue;

            case 3: // possible double dot
                if (buf.charAt(start + 1) != '.' || buf.charAt(start + 2) != '.') {
                    if (skip > 0 && --skip == 0) {
                        delStart = start >= 0 ? start : 0;
                        if (delStart > 0 && delEnd == buf.length() && buf.charAt(delEnd - 1) == '.')
                            delStart++;
                    }
                    break;
                }

                delStart = start;
                if (delEnd < 0)
                    delEnd = end;

                skip++;
                end = start--;
                while (start >= 0 && buf.charAt(start) != '/')
                    start--;
                continue;

            default:
                if (skip > 0 && --skip == 0) {
                    delStart = start >= 0 ? start : 0;
                    if (delEnd == buf.length() && buf.charAt(delEnd - 1) == '.')
                        delStart++;
                }
            }

            // Do the delete
            if (skip <= 0 && delStart >= 0 && delEnd >= delStart) {
                buf.delete(delStart, delEnd);
                delStart = delEnd = -1;
                if (skip > 0)
                    delEnd = end;
            }

            end = start--;
            while (start >= 0 && buf.charAt(start) != '/')
                start--;
        }

        // Too many ..
        if (skip > 0)
            return null;

        // Do the delete
        if (delEnd >= 0)
            buf.delete(delStart, delEnd);

        return buf.toString();
    }
}

Related

1. canonicalPath(String orig)
2. canonicalpath(String path)
3. canonicalpath(String path, boolean relative)