Java example source code file (AbstractFileTypeDetector.java)

This example Java source code file (AbstractFileTypeDetector.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

abstractfiletypedetector, ioexception, nullpointerexception, override, string, stringbuilder, tspecials, util

The AbstractFileTypeDetector.java Java example source code

/*
 * Copyright (c) 2008, 2011, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package sun.nio.fs;

import java.nio.file.Path;
import java.nio.file.spi.FileTypeDetector;
import java.util.Locale;
import java.io.IOException;

/**
 * Base implementation of FileTypeDetector
 */

public abstract class AbstractFileTypeDetector
    extends FileTypeDetector
{
    protected AbstractFileTypeDetector() {
        super();
    }

    /**
     * Invokes the appropriate probe method to guess a file's content type,
     * and checks that the content type's syntax is valid.
     */
    @Override
    public final String probeContentType(Path file) throws IOException {
        if (file == null)
            throw new NullPointerException("'file' is null");
        String result = implProbeContentType(file);
        return (result == null) ? null : parse(result);
    }

    /**
     * Probes the given file to guess its content type.
     */
    protected abstract String implProbeContentType(Path file)
        throws IOException;

    /**
     * Parses a candidate content type into its type and subtype, returning
     * null if either token is invalid.
     */
    private static String parse(String s) {
        int slash = s.indexOf('/');
        int semicolon = s.indexOf(';');
        if (slash < 0)
            return null;  // no subtype
        String type = s.substring(0, slash).trim().toLowerCase(Locale.ENGLISH);
        if (!isValidToken(type))
            return null;  // invalid type
        String subtype = (semicolon < 0) ? s.substring(slash + 1) :
            s.substring(slash + 1, semicolon);
        subtype = subtype.trim().toLowerCase(Locale.ENGLISH);
        if (!isValidToken(subtype))
            return null;  // invalid subtype
        StringBuilder sb = new StringBuilder(type.length() + subtype.length() + 1);
        sb.append(type);
        sb.append('/');
        sb.append(subtype);
        return sb.toString();
    }

    /**
     * Special characters
     */
    private static final String TSPECIALS = "()<>@,;:/[]?=\\\"";

    /**
     * Returns true if the character is a valid token character.
     */
    private static boolean isTokenChar(char c) {
        return (c > 040) && (c < 0177) && (TSPECIALS.indexOf(c) < 0);
    }

    /**
     * Returns true if the given string is a legal type or subtype.
     */
    private static boolean isValidToken(String s) {
        int len = s.length();
        if (len == 0)
            return false;
        for (int i = 0; i < len; i++) {
            if (!isTokenChar(s.charAt(i)))
                return false;
        }
        return true;
    }
}