Java tutorial
/* * Copyright (C) 2008 The Guava Authors * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.google.common.net; import static com.google.common.base.Preconditions.checkNotNull; import com.google.common.annotations.Beta; import com.google.common.annotations.GwtCompatible; import com.google.common.escape.UnicodeEscaper; /** * A {@code UnicodeEscaper} that escapes some set of Java characters using a * UTF-8 based percent encoding scheme. The set of safe characters (those which * remain unescaped) can be specified on construction. * * <p>This class is primarily used for creating URI escapers in {@link * UrlEscapers} but can be used directly if required. While URI escapers impose * specific semantics on which characters are considered 'safe', this class has * a minimal set of restrictions. * * <p>When escaping a String, the following rules apply: * <ul> * <li>All specified safe characters remain unchanged. * <li>If {@code plusForSpace} was specified, the space character " " is * converted into a plus sign {@code "+"}. * <li>All other characters are converted into one or more bytes using UTF-8 * encoding and each byte is then represented by the 3-character string * "%XX", where "XX" is the two-digit, uppercase, hexadecimal representation * of the byte value. * </ul> * * <p>For performance reasons the only currently supported character encoding of * this class is UTF-8. * * <p><b>Note:</b> This escaper produces uppercase hexadecimal sequences. From * <a href="http://www.ietf.org/rfc/rfc3986.txt">RFC 3986</a>:<br> * <i>"URI producers and normalizers should use uppercase hexadecimal digits * for all percent-encodings."</i> * * @author David Beaumont * @since 15.0 */ @Beta @GwtCompatible public final class PercentEscaper extends UnicodeEscaper { // In some escapers spaces are escaped to '+' private static final char[] PLUS_SIGN = { '+' }; // Percent escapers output upper case hex digits (uri escapers require this). private static final char[] UPPER_HEX_DIGITS = "0123456789ABCDEF".toCharArray(); /** * If true we should convert space to the {@code +} character. */ private final boolean plusForSpace; /** * An array of flags where for any {@code char c} if {@code safeOctets[c]} is * true then {@code c} should remain unmodified in the output. If * {@code c > safeOctets.length} then it should be escaped. */ private final boolean[] safeOctets; /** * Constructs a percent escaper with the specified safe characters and * optional handling of the space character. * * <p>Not that it is allowed, but not necessarily desirable to specify {@code %} * as a safe character. This has the effect of creating an escaper which has no * well defined inverse but it can be useful when escaping additional characters. * * @param safeChars a non null string specifying additional safe characters * for this escaper (the ranges 0..9, a..z and A..Z are always safe and * should not be specified here) * @param plusForSpace true if ASCII space should be escaped to {@code +} * rather than {@code %20} * @throws IllegalArgumentException if any of the parameters were invalid */ public PercentEscaper(String safeChars, boolean plusForSpace) { // TODO(user): Switch to static factory methods for creation now that class is final. // TODO(user): Support escapers where alphanumeric chars are not safe. checkNotNull(safeChars); // eager for GWT. // Avoid any misunderstandings about the behavior of this escaper if (safeChars.matches(".*[0-9A-Za-z].*")) { throw new IllegalArgumentException( "Alphanumeric characters are always 'safe' and should not be " + "explicitly specified"); } safeChars += "abcdefghijklmnopqrstuvwxyz" + "ABCDEFGHIJKLMNOPQRSTUVWXYZ" + "0123456789"; // Avoid ambiguous parameters. Safe characters are never modified so if // space is a safe character then setting plusForSpace is meaningless. if (plusForSpace && safeChars.contains(" ")) { throw new IllegalArgumentException("plusForSpace cannot be specified when space is a 'safe' character"); } this.plusForSpace = plusForSpace; this.safeOctets = createSafeOctets(safeChars); } /** * Creates a boolean array with entries corresponding to the character values * specified in safeChars set to true. The array is as small as is required to * hold the given character information. */ private static boolean[] createSafeOctets(String safeChars) { int maxChar = -1; char[] safeCharArray = safeChars.toCharArray(); for (char c : safeCharArray) { maxChar = Math.max(c, maxChar); } boolean[] octets = new boolean[maxChar + 1]; for (char c : safeCharArray) { octets[c] = true; } return octets; } /* * Overridden for performance. For unescaped strings this improved the * performance of the uri escaper from ~760ns to ~400ns as measured by * {@link CharEscapersBenchmark}. */ @Override protected int nextEscapeIndex(CharSequence csq, int index, int end) { checkNotNull(csq); for (; index < end; index++) { char c = csq.charAt(index); if (c >= safeOctets.length || !safeOctets[c]) { break; } } return index; } /* * Overridden for performance. For unescaped strings this improved the * performance of the uri escaper from ~400ns to ~170ns as measured by * {@link CharEscapersBenchmark}. */ @Override public String escape(String s) { checkNotNull(s); int slen = s.length(); for (int index = 0; index < slen; index++) { char c = s.charAt(index); if (c >= safeOctets.length || !safeOctets[c]) { return escapeSlow(s, index); } } return s; } /** * Escapes the given Unicode code point in UTF-8. */ @Override protected char[] escape(int cp) { // We should never get negative values here but if we do it will throw an // IndexOutOfBoundsException, so at least it will get spotted. if (cp < safeOctets.length && safeOctets[cp]) { return null; } else if (cp == ' ' && plusForSpace) { return PLUS_SIGN; } else if (cp <= 0x7F) { // Single byte UTF-8 characters // Start with "%--" and fill in the blanks char[] dest = new char[3]; dest[0] = '%'; dest[2] = UPPER_HEX_DIGITS[cp & 0xF]; dest[1] = UPPER_HEX_DIGITS[cp >>> 4]; return dest; } else if (cp <= 0x7ff) { // Two byte UTF-8 characters [cp >= 0x80 && cp <= 0x7ff] // Start with "%--%--" and fill in the blanks char[] dest = new char[6]; dest[0] = '%'; dest[3] = '%'; dest[5] = UPPER_HEX_DIGITS[cp & 0xF]; cp >>>= 4; dest[4] = UPPER_HEX_DIGITS[0x8 | (cp & 0x3)]; cp >>>= 2; dest[2] = UPPER_HEX_DIGITS[cp & 0xF]; cp >>>= 4; dest[1] = UPPER_HEX_DIGITS[0xC | cp]; return dest; } else if (cp <= 0xffff) { // Three byte UTF-8 characters [cp >= 0x800 && cp <= 0xffff] // Start with "%E-%--%--" and fill in the blanks char[] dest = new char[9]; dest[0] = '%'; dest[1] = 'E'; dest[3] = '%'; dest[6] = '%'; dest[8] = UPPER_HEX_DIGITS[cp & 0xF]; cp >>>= 4; dest[7] = UPPER_HEX_DIGITS[0x8 | (cp & 0x3)]; cp >>>= 2; dest[5] = UPPER_HEX_DIGITS[cp & 0xF]; cp >>>= 4; dest[4] = UPPER_HEX_DIGITS[0x8 | (cp & 0x3)]; cp >>>= 2; dest[2] = UPPER_HEX_DIGITS[cp]; return dest; } else if (cp <= 0x10ffff) { char[] dest = new char[12]; // Four byte UTF-8 characters [cp >= 0xffff && cp <= 0x10ffff] // Start with "%F-%--%--%--" and fill in the blanks dest[0] = '%'; dest[1] = 'F'; dest[3] = '%'; dest[6] = '%'; dest[9] = '%'; dest[11] = UPPER_HEX_DIGITS[cp & 0xF]; cp >>>= 4; dest[10] = UPPER_HEX_DIGITS[0x8 | (cp & 0x3)]; cp >>>= 2; dest[8] = UPPER_HEX_DIGITS[cp & 0xF]; cp >>>= 4; dest[7] = UPPER_HEX_DIGITS[0x8 | (cp & 0x3)]; cp >>>= 2; dest[5] = UPPER_HEX_DIGITS[cp & 0xF]; cp >>>= 4; dest[4] = UPPER_HEX_DIGITS[0x8 | (cp & 0x3)]; cp >>>= 2; dest[2] = UPPER_HEX_DIGITS[cp & 0x7]; return dest; } else { // If this ever happens it is due to bug in UnicodeEscaper, not bad input. throw new IllegalArgumentException("Invalid unicode character value " + cp); } } }