URLEncoder原码

/* * Copyright (c) 1995, 2013, Oracle and/or its affiliates. All rights reserved. * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. * * * * * * * * * * * * * * * * * * * * */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</CODE> MIME * format. For more information about HTML form encoding, consult the HTML * <A HREF="http://www.w3.org/TR/html4/">specification</A>. * * <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}</i>", where <i>xy</i> 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><strong>Note:</strong> The <a href=     * "http://www.w3.org/TR/html40/appendix/notes.html#non-ascii-chars">     * World Wide Web Consortium Recommendation</a> states that     * UTF-8 should be used. Not doing so may introduce     * incompatibilities.</em>     *     * @param   s   {@code String} to be translated.     * @param   enc   The name of a supported     *    <a href="../lang/package-summary.html#charenc">character     *    encoding</a>.     * @return  the translated {@code String}.     * @exception  UnsupportedEncodingException     *             If the named encoding is not supported     * @see URLDecoder#decode(java.lang.String, java.lang.String)     * @since 1.4     */    public static String encode(String s, String enc)        throws UnsupportedEncodingException {        boolean needToChange = false;        StringBuffer out = new StringBuffer(s.length());        Charset charset;        CharArrayWriter charArrayWriter = new CharArrayWriter();        if (enc == null)            throw new NullPointerException("charsetName");        try {            charset = Charset.forName(enc);        } catch (IllegalCharsetNameException e) {            throw new UnsupportedEncodingException(enc);        } catch (UnsupportedCharsetException e) {            throw new UnsupportedEncodingException(enc);        }        for (int i = 0; i < s.length();) {            int c = (int) s.charAt(i);            //System.out.println("Examining character: " + c);            if (dontNeedEncoding.get(c)) {                if (c == ' ') {                    c = '+';                    needToChange = true;                }                //System.out.println("Storing: " + c);                out.append((char)c);                i++;            } else {                // convert to external encoding before hex conversion                do {                    charArrayWriter.write(c);                    /*                     * If this character represents the start of a Unicode                     * surrogate pair, then pass in two characters. It's not                     * clear what should be done if a bytes reserved in the                     * surrogate pairs range occurs outside of a legal                     * surrogate pair. For now, just treat it as if it were                     * any other character.                     */                    if (c >= 0xD800 && c <= 0xDBFF) {                        /*                          System.out.println(Integer.toHexString(c)                          + " is high surrogate");                        */                        if ( (i+1) < s.length()) {                            int d = (int) s.charAt(i+1);                            /*                              System.out.println("\tExamining "                              + Integer.toHexString(d));                            */                            if (d >= 0xDC00 && d <= 0xDFFF) {                                /*                                  System.out.println("\t"                                  + Integer.toHexString(d)                                  + " is low surrogate");                                */                                charArrayWriter.write(d);                                i++;                            }                        }                    }                    i++;                } while (i < s.length() && !dontNeedEncoding.get((c = (int) s.charAt(i))));                charArrayWriter.flush();                String str = new String(charArrayWriter.toCharArray());                byte[] ba = str.getBytes(charset);                for (int j = 0; j < ba.length; j++) {                    out.append('%');                    char ch = Character.forDigit((ba[j] >> 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);    }}