Java example source code file (URLEncoder.java)

This example Java source code file (URLEncoder.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

bitset, chararraywriter, charset, deprecated, getpropertyaction, illegalcharsetnameexception, nullpointerexception, security, string, stringbuffer, unsupportedcharsetexception, unsupportedencodingexception, urlencoder, util

The URLEncoder.java Java example source code

/*
 * Copyright (c) 1995, 2013, 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 java.net;

import java.io.ByteArrayOutputStream;
import java.io.BufferedWriter;
import java.io.OutputStreamWriter;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.io.CharArrayWriter;
import java.nio.charset.Charset;
import java.nio.charset.IllegalCharsetNameException;
import java.nio.charset.UnsupportedCharsetException ;
import java.util.BitSet;
import java.security.AccessController;
import java.security.PrivilegedAction;
import sun.security.action.GetBooleanAction;
import sun.security.action.GetPropertyAction;

/**
 * Utility class for HTML form encoding. This class contains static methods
 * for converting a String to the <CODE>application/x-www-form-urlencoded MIME
 * format. For more information about HTML form encoding, consult the HTML
 * <A HREF="http://www.w3.org/TR/html4/">specification.
 *
 * <p>
 * When encoding a String, the following rules apply:
 *
 * <ul>
 * <li>The alphanumeric characters "{@code a}" through
 *     "{@code z}", "{@code A}" through
 *     "{@code Z}" and "{@code 0}"
 *     through "{@code 9}" remain the same.
 * <li>The special characters "{@code .}",
 *     "{@code -}", "{@code *}", and
 *     "{@code _}" remain the same.
 * <li>The space character "   " is
 *     converted into a plus sign "{@code +}".
 * <li>All other characters are unsafe and are first converted into
 *     one or more bytes using some encoding scheme. Then each byte is
 *     represented by the 3-character string
 *     "<i>{@code %xy}", where xy is the
 *     two-digit hexadecimal representation of the byte.
 *     The recommended encoding scheme to use is UTF-8. However,
 *     for compatibility reasons, if an encoding is not specified,
 *     then the default encoding of the platform is used.
 * </ul>
 *
 * <p>
 * For example using UTF-8 as the encoding scheme the string "The
 * string ü@foo-bar" would get converted to
 * "The+string+%C3%BC%40foo-bar" because in UTF-8 the character
 * ü is encoded as two bytes C3 (hex) and BC (hex), and the
 * character @ is encoded as one byte 40 (hex).
 *
 * @author  Herb Jellinek
 * @since   JDK1.0
 */
public class URLEncoder {
    static BitSet dontNeedEncoding;
    static final int caseDiff = ('a' - 'A');
    static String dfltEncName = null;

    static {

        /* The list of characters that are not encoded has been
         * determined as follows:
         *
         * RFC 2396 states:
         * -----
         * Data characters that are allowed in a URI but do not have a
         * reserved purpose are called unreserved.  These include upper
         * and lower case letters, decimal digits, and a limited set of
         * punctuation marks and symbols.
         *
         * unreserved  = alphanum | mark
         *
         * mark        = "-" | "_" | "." | "!" | "~" | "*" | "'" | "(" | ")"
         *
         * Unreserved characters can be escaped without changing the
         * semantics of the URI, but this should not be done unless the
         * URI is being used in a context that does not allow the
         * unescaped character to appear.
         * -----
         *
         * It appears that both Netscape and Internet Explorer escape
         * all special characters from this list with the exception
         * of "-", "_", ".", "*". While it is not clear why they are
         * escaping the other characters, perhaps it is safest to
         * assume that there might be contexts in which the others
         * are unsafe if not escaped. Therefore, we will use the same
         * list. It is also noteworthy that this is consistent with
         * O'Reilly's "HTML: The Definitive Guide" (page 164).
         *
         * As a last note, Intenet Explorer does not encode the "@"
         * character which is clearly not unreserved according to the
         * RFC. We are being consistent with the RFC in this matter,
         * as is Netscape.
         *
         */

        dontNeedEncoding = new BitSet(256);
        int i;
        for (i = 'a'; i <= 'z'; i++) {
            dontNeedEncoding.set(i);
        }
        for (i = 'A'; i <= 'Z'; i++) {
            dontNeedEncoding.set(i);
        }
        for (i = '0'; i <= '9'; i++) {
            dontNeedEncoding.set(i);
        }
        dontNeedEncoding.set(' '); /* encoding a space to a + is done
                                    * in the encode() method */
        dontNeedEncoding.set('-');
        dontNeedEncoding.set('_');
        dontNeedEncoding.set('.');
        dontNeedEncoding.set('*');

        dfltEncName = AccessController.doPrivileged(
            new GetPropertyAction("file.encoding")
        );
    }

    /**
     * You can't call the constructor.
     */
    private URLEncoder() { }

    /**
     * Translates a string into {@code x-www-form-urlencoded}
     * format. This method uses the platform's default encoding
     * as the encoding scheme to obtain the bytes for unsafe characters.
     *
     * @param   s   {@code String} to be translated.
     * @deprecated The resulting string may vary depending on the platform's
     *             default encoding. Instead, use the encode(String,String)
     *             method to specify the encoding.
     * @return  the translated {@code String}.
     */
    @Deprecated
    public static String encode(String s) {

        String str = null;

        try {
            str = encode(s, dfltEncName);
        } catch (UnsupportedEncodingException e) {
            // The system should always have the platform default
        }

        return str;
    }

    /**
     * Translates a string into {@code application/x-www-form-urlencoded}
     * format using a specific encoding scheme. This method uses the
     * supplied encoding scheme to obtain the bytes for unsafe
     * characters.
     * <p>
     * <em>Note: The  4) & 0xF, 16);
                    // converting to use uppercase letter as part of
                    // the hex value if ch is a letter.
                    if (Character.isLetter(ch)) {
                        ch -= caseDiff;
                    }
                    out.append(ch);
                    ch = Character.forDigit(ba[j] & 0xF, 16);
                    if (Character.isLetter(ch)) {
                        ch -= caseDiff;
                    }
                    out.append(ch);
                }
                charArrayWriter.reset();
                needToChange = true;
            }
        }

        return (needToChange? out.toString() : s);
    }
}