1 /*
2 * Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.nio.charset;
27
28 import java.nio.ByteBuffer;
29 import java.nio.CharBuffer;
30 import java.nio.charset.spi.CharsetProvider;
31 import java.security.AccessController;
32 import java.security.PrivilegedAction;
33 import java.util.Arrays;
34 import java.util.Collections;
35 import java.util.HashSet;
36 import java.util.Iterator;
37 import java.util.Locale;
38 import java.util.Map;
39 import java.util.NoSuchElementException;
40 import java.util.Objects;
41 import java.util.Set;
42 import java.util.ServiceLoader;
43 import java.util.ServiceConfigurationError;
44 import java.util.SortedMap;
45 import java.util.TreeMap;
46 import jdk.internal.misc.VM;
47 import sun.misc.ASCIICaseInsensitiveComparator;
48 import sun.nio.cs.StandardCharsets;
49 import sun.nio.cs.ThreadLocalCoders;
50 import sun.security.action.GetPropertyAction;
51
52
53 /**
54 * A named mapping between sequences of sixteen-bit Unicode <a
55 * href="../../lang/Character.html#unicode">code units</a> and sequences of
56 * bytes. This class defines methods for creating decoders and encoders and
57 * for retrieving the various names associated with a charset. Instances of
58 * this class are immutable.
59 *
60 * <p> This class also defines static methods for testing whether a particular
61 * charset is supported, for locating charset instances by name, and for
62 * constructing a map that contains every charset for which support is
63 * available in the current Java virtual machine. Support for new charsets can
64 * be added via the service-provider interface defined in the {@link
65 * java.nio.charset.spi.CharsetProvider} class.
66 *
67 * <p> All of the methods defined in this class are safe for use by multiple
68 * concurrent threads.
69 *
70 *
71 * <a name="names"></a><a name="charenc"></a>
72 * <h2>Charset names</h2>
73 *
74 * <p> Charsets are named by strings composed of the following characters:
75 *
76 * <ul>
77 *
78 * <li> The uppercase letters {@code 'A'} through {@code 'Z'}
79 * (<code>'\u0041'</code> through <code>'\u005a'</code>),
80 *
81 * <li> The lowercase letters {@code 'a'} through {@code 'z'}
82 * (<code>'\u0061'</code> through <code>'\u007a'</code>),
83 *
84 * <li> The digits {@code '0'} through {@code '9'}
85 * (<code>'\u0030'</code> through <code>'\u0039'</code>),
86 *
87 * <li> The dash character {@code '-'}
88 * (<code>'\u002d'</code>, <small>HYPHEN-MINUS</small>),
89 *
90 * <li> The plus character {@code '+'}
91 * (<code>'\u002b'</code>, <small>PLUS SIGN</small>),
92 *
93 * <li> The period character {@code '.'}
94 * (<code>'\u002e'</code>, <small>FULL STOP</small>),
95 *
96 * <li> The colon character {@code ':'}
97 * (<code>'\u003a'</code>, <small>COLON</small>), and
98 *
99 * <li> The underscore character {@code '_'}
100 * (<code>'\u005f'</code>, <small>LOW LINE</small>).
101 *
102 * </ul>
103 *
104 * A charset name must begin with either a letter or a digit. The empty string
105 * is not a legal charset name. Charset names are not case-sensitive; that is,
106 * case is always ignored when comparing charset names. Charset names
107 * generally follow the conventions documented in <a
108 * href="http://www.ietf.org/rfc/rfc2278.txt"><i>RFC 2278: IANA Charset
109 * Registration Procedures</i></a>.
110 *
111 * <p> Every charset has a <i>canonical name</i> and may also have one or more
112 * <i>aliases</i>. The canonical name is returned by the {@link #name() name} method
113 * of this class. Canonical names are, by convention, usually in upper case.
114 * The aliases of a charset are returned by the {@link #aliases() aliases}
115 * method.
116 *
117 * <p><a name="hn">Some charsets have an <i>historical name</i> that is defined for
118 * compatibility with previous versions of the Java platform.</a> A charset's
119 * historical name is either its canonical name or one of its aliases. The
120 * historical name is returned by the {@code getEncoding()} methods of the
121 * {@link java.io.InputStreamReader#getEncoding InputStreamReader} and {@link
122 * java.io.OutputStreamWriter#getEncoding OutputStreamWriter} classes.
123 *
124 * <p><a name="iana"> </a>If a charset listed in the <a
125 * href="http://www.iana.org/assignments/character-sets"><i>IANA Charset
126 * Registry</i></a> is supported by an implementation of the Java platform then
127 * its canonical name must be the name listed in the registry. Many charsets
128 * are given more than one name in the registry, in which case the registry
129 * identifies one of the names as <i>MIME-preferred</i>. If a charset has more
130 * than one registry name then its canonical name must be the MIME-preferred
131 * name and the other names in the registry must be valid aliases. If a
132 * supported charset is not listed in the IANA registry then its canonical name
133 * must begin with one of the strings {@code "X-"} or {@code "x-"}.
134 *
135 * <p> The IANA charset registry does change over time, and so the canonical
136 * name and the aliases of a particular charset may also change over time. To
137 * ensure compatibility it is recommended that no alias ever be removed from a
138 * charset, and that if the canonical name of a charset is changed then its
139 * previous canonical name be made into an alias.
140 *
141 *
142 * <h2>Standard charsets</h2>
143 *
144 *
145 *
146 * <p><a name="standard">Every implementation of the Java platform is required to support the
147 * following standard charsets.</a> Consult the release documentation for your
148 * implementation to see if any other charsets are supported. The behavior
149 * of such optional charsets may differ between implementations.
150 *
151 * <blockquote><table width="80%" summary="Description of standard charsets">
152 * <tr><th align="left">Charset</th><th align="left">Description</th></tr>
153 * <tr><td valign=top>{@code US-ASCII}</td>
154 * <td>Seven-bit ASCII, a.k.a. {@code ISO646-US},
155 * a.k.a. the Basic Latin block of the Unicode character set</td></tr>
156 * <tr><td valign=top><code>ISO-8859-1 </code></td>
157 * <td>ISO Latin Alphabet No. 1, a.k.a. {@code ISO-LATIN-1}</td></tr>
158 * <tr><td valign=top>{@code UTF-8}</td>
159 * <td>Eight-bit UCS Transformation Format</td></tr>
160 * <tr><td valign=top>{@code UTF-16BE}</td>
161 * <td>Sixteen-bit UCS Transformation Format,
162 * big-endian byte order</td></tr>
163 * <tr><td valign=top>{@code UTF-16LE}</td>
164 * <td>Sixteen-bit UCS Transformation Format,
165 * little-endian byte order</td></tr>
166 * <tr><td valign=top>{@code UTF-16}</td>
167 * <td>Sixteen-bit UCS Transformation Format,
168 * byte order identified by an optional byte-order mark</td></tr>
169 * </table></blockquote>
170 *
171 * <p> The {@code UTF-8} charset is specified by <a
172 * href="http://www.ietf.org/rfc/rfc2279.txt"><i>RFC 2279</i></a>; the
173 * transformation format upon which it is based is specified in
174 * Amendment 2 of ISO 10646-1 and is also described in the <a
175 * href="http://www.unicode.org/unicode/standard/standard.html"><i>Unicode
176 * Standard</i></a>.
177 *
178 * <p> The {@code UTF-16} charsets are specified by <a
179 * href="http://www.ietf.org/rfc/rfc2781.txt"><i>RFC 2781</i></a>; the
180 * transformation formats upon which they are based are specified in
181 * Amendment 1 of ISO 10646-1 and are also described in the <a
182 * href="http://www.unicode.org/unicode/standard/standard.html"><i>Unicode
183 * Standard</i></a>.
184 *
185 * <p> The {@code UTF-16} charsets use sixteen-bit quantities and are
186 * therefore sensitive to byte order. In these encodings the byte order of a
187 * stream may be indicated by an initial <i>byte-order mark</i> represented by
188 * the Unicode character <code>'\uFEFF'</code>. Byte-order marks are handled
189 * as follows:
190 *
191 * <ul>
192 *
193 * <li><p> When decoding, the {@code UTF-16BE} and {@code UTF-16LE}
194 * charsets interpret the initial byte-order marks as a <small>ZERO-WIDTH
195 * NON-BREAKING SPACE</small>; when encoding, they do not write
196 * byte-order marks. </p></li>
197
198 *
199 * <li><p> When decoding, the {@code UTF-16} charset interprets the
200 * byte-order mark at the beginning of the input stream to indicate the
201 * byte-order of the stream but defaults to big-endian if there is no
202 * byte-order mark; when encoding, it uses big-endian byte order and writes
203 * a big-endian byte-order mark. </p></li>
204 *
205 * </ul>
206 *
207 * In any case, byte order marks occurring after the first element of an
208 * input sequence are not omitted since the same code is used to represent
209 * <small>ZERO-WIDTH NON-BREAKING SPACE</small>.
210 *
211 * <p> Every instance of the Java virtual machine has a default charset, which
212 * may or may not be one of the standard charsets. The default charset is
213 * determined during virtual-machine startup and typically depends upon the
214 * locale and charset being used by the underlying operating system. </p>
215 *
216 * <p>The {@link StandardCharsets} class defines constants for each of the
217 * standard charsets.
218 *
219 * <h2>Terminology</h2>
220 *
221 * <p> The name of this class is taken from the terms used in
222 * <a href="http://www.ietf.org/rfc/rfc2278.txt"><i>RFC 2278</i></a>.
223 * In that document a <i>charset</i> is defined as the combination of
224 * one or more coded character sets and a character-encoding scheme.
225 * (This definition is confusing; some other software systems define
226 * <i>charset</i> as a synonym for <i>coded character set</i>.)
227 *
228 * <p> A <i>coded character set</i> is a mapping between a set of abstract
229 * characters and a set of integers. US-ASCII, ISO 8859-1,
230 * JIS X 0201, and Unicode are examples of coded character sets.
231 *
232 * <p> Some standards have defined a <i>character set</i> to be simply a
233 * set of abstract characters without an associated assigned numbering.
234 * An alphabet is an example of such a character set. However, the subtle
235 * distinction between <i>character set</i> and <i>coded character set</i>
236 * is rarely used in practice; the former has become a short form for the
237 * latter, including in the Java API specification.
238 *
239 * <p> A <i>character-encoding scheme</i> is a mapping between one or more
240 * coded character sets and a set of octet (eight-bit byte) sequences.
241 * UTF-8, UTF-16, ISO 2022, and EUC are examples of
242 * character-encoding schemes. Encoding schemes are often associated with
243 * a particular coded character set; UTF-8, for example, is used only to
244 * encode Unicode. Some schemes, however, are associated with multiple
245 * coded character sets; EUC, for example, can be used to encode
246 * characters in a variety of Asian coded character sets.
247 *
248 * <p> When a coded character set is used exclusively with a single
249 * character-encoding scheme then the corresponding charset is usually
250 * named for the coded character set; otherwise a charset is usually named
251 * for the encoding scheme and, possibly, the locale of the coded
252 * character sets that it supports. Hence {@code US-ASCII} is both the
253 * name of a coded character set and of the charset that encodes it, while
254 * {@code EUC-JP} is the name of the charset that encodes the
255 * JIS X 0201, JIS X 0208, and JIS X 0212
256 * coded character sets for the Japanese language.
257 *
258 * <p> The native character encoding of the Java programming language is
259 * UTF-16. A charset in the Java platform therefore defines a mapping
260 * between sequences of sixteen-bit UTF-16 code units (that is, sequences
261 * of chars) and sequences of bytes. </p>
262 *
263 *
264 * @author Mark Reinhold
265 * @author JSR-51 Expert Group
266 * @since 1.4
267 *
268 * @see CharsetDecoder
269 * @see CharsetEncoder
270 * @see java.nio.charset.spi.CharsetProvider
271 * @see java.lang.Character
272 */
273
274 public abstract class Charset
275 implements Comparable<Charset>
276 {
277
278 /* -- Static methods -- */
279
280 private static volatile String bugLevel;
281
282 static boolean atBugLevel(String bl) { // package-private
283 String level = bugLevel;
284 if (level == null) {
285 if (!VM.isBooted())
286 return false;
287 bugLevel = level = AccessController.doPrivileged(
288 new GetPropertyAction("sun.nio.cs.bugLevel", ""));
289 }
290 return level.equals(bl);
291 }
292
293 /**
294 * Checks that the given string is a legal charset name. </p>
295 *
296 * @param s
297 * A purported charset name
298 *
299 * @throws IllegalCharsetNameException
300 * If the given name is not a legal charset name
301 */
302 private static void checkName(String s) {
303 int n = s.length();
304 if (!atBugLevel("1.4")) {
305 if (n == 0)
306 throw new IllegalCharsetNameException(s);
307 }
308 for (int i = 0; i < n; i++) {
309 char c = s.charAt(i);
310 if (c >= 'A' && c <= 'Z') continue;
311 if (c >= 'a' && c <= 'z') continue;
312 if (c >= '0' && c <= '9') continue;
313 if (c == '-' && i != 0) continue;
314 if (c == '+' && i != 0) continue;
315 if (c == ':' && i != 0) continue;
316 if (c == '_' && i != 0) continue;
317 if (c == '.' && i != 0) continue;
318 throw new IllegalCharsetNameException(s);
319 }
320 }
321
322 /* The standard set of charsets */
323 private static CharsetProvider standardProvider = new StandardCharsets();
324
325 // Cache of the most-recently-returned charsets,
326 // along with the names that were used to find them
327 //
328 private static volatile Object[] cache1; // "Level 1" cache
329 private static volatile Object[] cache2; // "Level 2" cache
330
331 private static void cache(String charsetName, Charset cs) {
332 cache2 = cache1;
333 cache1 = new Object[] { charsetName, cs };
334 }
335
336 // Creates an iterator that walks over the available providers, ignoring
337 // those whose lookup or instantiation causes a security exception to be
338 // thrown. Should be invoked with full privileges.
339 //
340 private static Iterator<CharsetProvider> providers() {
341 return new Iterator<>() {
342 ClassLoader cl = ClassLoader.getSystemClassLoader();
343 ServiceLoader<CharsetProvider> sl =
344 ServiceLoader.load(CharsetProvider.class, cl);
345 Iterator<CharsetProvider> i = sl.iterator();
346 CharsetProvider next = null;
347
348 private boolean getNext() {
349 while (next == null) {
350 try {
351 if (!i.hasNext())
352 return false;
353 next = i.next();
354 } catch (ServiceConfigurationError sce) {
355 if (sce.getCause() instanceof SecurityException) {
356 // Ignore security exceptions
357 continue;
358 }
359 throw sce;
360 }
361 }
362 return true;
363 }
364
365 public boolean hasNext() {
366 return getNext();
367 }
368
369 public CharsetProvider next() {
370 if (!getNext())
371 throw new NoSuchElementException();
372 CharsetProvider n = next;
373 next = null;
374 return n;
375 }
376
377 public void remove() {
378 throw new UnsupportedOperationException();
379 }
380
381 };
382 }
383
384 // Thread-local gate to prevent recursive provider lookups
385 private static ThreadLocal<ThreadLocal<?>> gate =
386 new ThreadLocal<ThreadLocal<?>>();
387
388 private static Charset lookupViaProviders(final String charsetName) {
389
390 // The runtime startup sequence looks up standard charsets as a
391 // consequence of the VM's invocation of System.initializeSystemClass
392 // in order to, e.g., set system properties and encode filenames. At
393 // that point the application class loader has not been initialized,
394 // however, so we can't look for providers because doing so will cause
395 // that loader to be prematurely initialized with incomplete
396 // information.
397 //
398 if (!VM.isBooted())
399 return null;
400
401 if (gate.get() != null)
402 // Avoid recursive provider lookups
403 return null;
404 try {
405 gate.set(gate);
406
407 return AccessController.doPrivileged(
408 new PrivilegedAction<>() {
409 public Charset run() {
410 for (Iterator<CharsetProvider> i = providers();
411 i.hasNext();) {
412 CharsetProvider cp = i.next();
413 Charset cs = cp.charsetForName(charsetName);
414 if (cs != null)
415 return cs;
416 }
417 return null;
418 }
419 });
420
421 } finally {
422 gate.set(null);
423 }
424 }
425
426 /* The extended set of charsets */
427 private static class ExtendedProviderHolder {
428 static final CharsetProvider[] extendedProviders = extendedProviders();
429 // returns ExtendedProvider, if installed
430 private static CharsetProvider[] extendedProviders() {
431 return AccessController.doPrivileged(new PrivilegedAction<>() {
432 public CharsetProvider[] run() {
433 CharsetProvider[] cps = new CharsetProvider[1];
434 int n = 0;
435 ServiceLoader<CharsetProvider> sl =
436 ServiceLoader.loadInstalled(CharsetProvider.class);
437 for (CharsetProvider cp : sl) {
438 if (n + 1 > cps.length) {
439 cps = Arrays.copyOf(cps, cps.length << 1);
440 }
441 cps[n++] = cp;
442 }
443 return n == cps.length ? cps : Arrays.copyOf(cps, n);
444 }});
445 }
446 }
447
448 private static Charset lookupExtendedCharset(String charsetName) {
449 if (!VM.isBooted()) // see lookupViaProviders()
450 return null;
451 CharsetProvider[] ecps = ExtendedProviderHolder.extendedProviders;
452 for (CharsetProvider cp : ecps) {
453 Charset cs = cp.charsetForName(charsetName);
454 if (cs != null)
455 return cs;
456 }
457 return null;
458 }
459
460 private static Charset lookup(String charsetName) {
461 if (charsetName == null)
462 throw new IllegalArgumentException("Null charset name");
463 Object[] a;
464 if ((a = cache1) != null && charsetName.equals(a[0]))
465 return (Charset)a[1];
466 // We expect most programs to use one Charset repeatedly.
467 // We convey a hint to this effect to the VM by putting the
468 // level 1 cache miss code in a separate method.
469 return lookup2(charsetName);
470 }
471
472 private static Charset lookup2(String charsetName) {
473 Object[] a;
474 if ((a = cache2) != null && charsetName.equals(a[0])) {
475 cache2 = cache1;
476 cache1 = a;
477 return (Charset)a[1];
478 }
479 Charset cs;
480 if ((cs = standardProvider.charsetForName(charsetName)) != null ||
481 (cs = lookupExtendedCharset(charsetName)) != null ||
482 (cs = lookupViaProviders(charsetName)) != null)
483 {
484 cache(charsetName, cs);
485 return cs;
486 }
487
488 /* Only need to check the name if we didn't find a charset for it */
489 checkName(charsetName);
490 return null;
491 }
492
493 /**
494 * Tells whether the named charset is supported.
495 *
496 * @param charsetName
497 * The name of the requested charset; may be either
498 * a canonical name or an alias
499 *
500 * @return {@code true} if, and only if, support for the named charset
501 * is available in the current Java virtual machine
502 *
503 * @throws IllegalCharsetNameException
504 * If the given charset name is illegal
505 *
506 * @throws IllegalArgumentException
507 * If the given {@code charsetName} is null
508 */
509 public static boolean isSupported(String charsetName) {
510 return (lookup(charsetName) != null);
511 }
512
513 /**
514 * Returns a charset object for the named charset.
515 *
516 * @param charsetName
517 * The name of the requested charset; may be either
518 * a canonical name or an alias
519 *
520 * @return A charset object for the named charset
521 *
522 * @throws IllegalCharsetNameException
523 * If the given charset name is illegal
524 *
525 * @throws IllegalArgumentException
526 * If the given {@code charsetName} is null
527 *
528 * @throws UnsupportedCharsetException
529 * If no support for the named charset is available
530 * in this instance of the Java virtual machine
531 */
532 public static Charset forName(String charsetName) {
533 Charset cs = lookup(charsetName);
534 if (cs != null)
535 return cs;
536 throw new UnsupportedCharsetException(charsetName);
537 }
538
539 // Fold charsets from the given iterator into the given map, ignoring
540 // charsets whose names already have entries in the map.
541 //
542 private static void put(Iterator<Charset> i, Map<String,Charset> m) {
543 while (i.hasNext()) {
544 Charset cs = i.next();
545 if (!m.containsKey(cs.name()))
546 m.put(cs.name(), cs);
547 }
548 }
549
550 /**
551 * Constructs a sorted map from canonical charset names to charset objects.
552 *
553 * <p> The map returned by this method will have one entry for each charset
554 * for which support is available in the current Java virtual machine. If
555 * two or more supported charsets have the same canonical name then the
556 * resulting map will contain just one of them; which one it will contain
557 * is not specified. </p>
558 *
559 * <p> The invocation of this method, and the subsequent use of the
560 * resulting map, may cause time-consuming disk or network I/O operations
561 * to occur. This method is provided for applications that need to
562 * enumerate all of the available charsets, for example to allow user
563 * charset selection. This method is not used by the {@link #forName
564 * forName} method, which instead employs an efficient incremental lookup
565 * algorithm.
566 *
567 * <p> This method may return different results at different times if new
568 * charset providers are dynamically made available to the current Java
569 * virtual machine. In the absence of such changes, the charsets returned
570 * by this method are exactly those that can be retrieved via the {@link
571 * #forName forName} method. </p>
572 *
573 * @return An immutable, case-insensitive map from canonical charset names
574 * to charset objects
575 */
576 public static SortedMap<String,Charset> availableCharsets() {
577 return AccessController.doPrivileged(
578 new PrivilegedAction<>() {
579 public SortedMap<String,Charset> run() {
580 TreeMap<String,Charset> m =
581 new TreeMap<>(
582 ASCIICaseInsensitiveComparator.CASE_INSENSITIVE_ORDER);
583 put(standardProvider.charsets(), m);
584 CharsetProvider[] ecps = ExtendedProviderHolder.extendedProviders;
585 for (CharsetProvider ecp :ecps) {
586 put(ecp.charsets(), m);
587 }
588 for (Iterator<CharsetProvider> i = providers(); i.hasNext();) {
589 CharsetProvider cp = i.next();
590 put(cp.charsets(), m);
591 }
592 return Collections.unmodifiableSortedMap(m);
593 }
594 });
595 }
596
597 private static volatile Charset defaultCharset;
598
599 /**
600 * Returns the default charset of this Java virtual machine.
601 *
602 * <p> The default charset is determined during virtual-machine startup and
603 * typically depends upon the locale and charset of the underlying
604 * operating system.
605 *
606 * @return A charset object for the default charset
607 *
608 * @since 1.5
609 */
610 public static Charset defaultCharset() {
611 if (defaultCharset == null) {
612 synchronized (Charset.class) {
613 String csn = AccessController.doPrivileged(
614 new GetPropertyAction("file.encoding"));
615 Charset cs = lookup(csn);
616 if (cs != null)
617 defaultCharset = cs;
618 else
619 defaultCharset = forName("UTF-8");
620 }
621 }
622 return defaultCharset;
623 }
624
625
626 /* -- Instance fields and methods -- */
627
628 private final String name; // tickles a bug in oldjavac
629 private final String[] aliases; // tickles a bug in oldjavac
630 private final String[] zeroAliases = new String[0];
631 private Set<String> aliasSet = null;
632
633 /**
634 * Initializes a new charset with the given canonical name and alias
635 * set.
636 *
637 * @param canonicalName
638 * The canonical name of this charset
639 *
640 * @param aliases
641 * An array of this charset's aliases, or null if it has no aliases
642 *
643 * @throws IllegalCharsetNameException
644 * If the canonical name or any of the aliases are illegal
645 */
646 protected Charset(String canonicalName, String[] aliases) {
647 checkName(canonicalName);
648 String[] as = Objects.requireNonNullElse(aliases, zeroAliases);
649 for (int i = 0; i < as.length; i++)
650 checkName(as[i]);
651 this.name = canonicalName;
652 this.aliases = as;
653 }
654
655 /**
656 * Returns this charset's canonical name.
657 *
658 * @return The canonical name of this charset
659 */
660 public final String name() {
661 return name;
662 }
663
664 /**
665 * Returns a set containing this charset's aliases.
666 *
667 * @return An immutable set of this charset's aliases
668 */
669 public final Set<String> aliases() {
670 if (aliasSet != null)
671 return aliasSet;
672 int n = aliases.length;
673 HashSet<String> hs = new HashSet<>(n);
674 for (int i = 0; i < n; i++)
675 hs.add(aliases[i]);
676 aliasSet = Collections.unmodifiableSet(hs);
677 return aliasSet;
678 }
679
680 /**
681 * Returns this charset's human-readable name for the default locale.
682 *
683 * <p> The default implementation of this method simply returns this
684 * charset's canonical name. Concrete subclasses of this class may
685 * override this method in order to provide a localized display name. </p>
686 *
687 * @return The display name of this charset in the default locale
688 */
689 public String displayName() {
690 return name;
691 }
692
693 /**
694 * Tells whether or not this charset is registered in the <a
695 * href="http://www.iana.org/assignments/character-sets">IANA Charset
696 * Registry</a>.
697 *
698 * @return {@code true} if, and only if, this charset is known by its
699 * implementor to be registered with the IANA
700 */
701 public final boolean isRegistered() {
702 return !name.startsWith("X-") && !name.startsWith("x-");
703 }
704
705 /**
706 * Returns this charset's human-readable name for the given locale.
707 *
708 * <p> The default implementation of this method simply returns this
709 * charset's canonical name. Concrete subclasses of this class may
710 * override this method in order to provide a localized display name. </p>
711 *
712 * @param locale
713 * The locale for which the display name is to be retrieved
714 *
715 * @return The display name of this charset in the given locale
716 */
717 public String displayName(Locale locale) {
718 return name;
719 }
720
721 /**
722 * Tells whether or not this charset contains the given charset.
723 *
724 * <p> A charset <i>C</i> is said to <i>contain</i> a charset <i>D</i> if,
725 * and only if, every character representable in <i>D</i> is also
726 * representable in <i>C</i>. If this relationship holds then it is
727 * guaranteed that every string that can be encoded in <i>D</i> can also be
728 * encoded in <i>C</i> without performing any replacements.
729 *
730 * <p> That <i>C</i> contains <i>D</i> does not imply that each character
731 * representable in <i>C</i> by a particular byte sequence is represented
732 * in <i>D</i> by the same byte sequence, although sometimes this is the
733 * case.
734 *
735 * <p> Every charset contains itself.
736 *
737 * <p> This method computes an approximation of the containment relation:
738 * If it returns {@code true} then the given charset is known to be
739 * contained by this charset; if it returns {@code false}, however, then
740 * it is not necessarily the case that the given charset is not contained
741 * in this charset.
742 *
743 * @param cs
744 * The given charset
745 *
746 * @return {@code true} if the given charset is contained in this charset
747 */
748 public abstract boolean contains(Charset cs);
749
750 /**
751 * Constructs a new decoder for this charset.
752 *
753 * @return A new decoder for this charset
754 */
755 public abstract CharsetDecoder newDecoder();
756
757 /**
758 * Constructs a new encoder for this charset.
759 *
760 * @return A new encoder for this charset
761 *
762 * @throws UnsupportedOperationException
763 * If this charset does not support encoding
764 */
765 public abstract CharsetEncoder newEncoder();
766
767 /**
768 * Tells whether or not this charset supports encoding.
769 *
770 * <p> Nearly all charsets support encoding. The primary exceptions are
771 * special-purpose <i>auto-detect</i> charsets whose decoders can determine
772 * which of several possible encoding schemes is in use by examining the
773 * input byte sequence. Such charsets do not support encoding because
774 * there is no way to determine which encoding should be used on output.
775 * Implementations of such charsets should override this method to return
776 * {@code false}. </p>
777 *
778 * @return {@code true} if, and only if, this charset supports encoding
779 */
780 public boolean canEncode() {
781 return true;
782 }
783
784 /**
785 * Convenience method that decodes bytes in this charset into Unicode
786 * characters.
787 *
788 * <p> An invocation of this method upon a charset {@code cs} returns the
789 * same result as the expression
790 *
791 * <pre>
792 * cs.newDecoder()
793 * .onMalformedInput(CodingErrorAction.REPLACE)
794 * .onUnmappableCharacter(CodingErrorAction.REPLACE)
795 * .decode(bb); </pre>
796 *
797 * except that it is potentially more efficient because it can cache
798 * decoders between successive invocations.
799 *
800 * <p> This method always replaces malformed-input and unmappable-character
801 * sequences with this charset's default replacement byte array. In order
802 * to detect such sequences, use the {@link
803 * CharsetDecoder#decode(java.nio.ByteBuffer)} method directly. </p>
804 *
805 * @param bb The byte buffer to be decoded
806 *
807 * @return A char buffer containing the decoded characters
808 */
809 public final CharBuffer decode(ByteBuffer bb) {
810 try {
811 return ThreadLocalCoders.decoderFor(this)
812 .onMalformedInput(CodingErrorAction.REPLACE)
813 .onUnmappableCharacter(CodingErrorAction.REPLACE)
814 .decode(bb);
815 } catch (CharacterCodingException x) {
816 throw new Error(x); // Can't happen
817 }
818 }
819
820 /**
821 * Convenience method that encodes Unicode characters into bytes in this
822 * charset.
823 *
824 * <p> An invocation of this method upon a charset {@code cs} returns the
825 * same result as the expression
826 *
827 * <pre>
828 * cs.newEncoder()
829 * .onMalformedInput(CodingErrorAction.REPLACE)
830 * .onUnmappableCharacter(CodingErrorAction.REPLACE)
831 * .encode(bb); </pre>
832 *
833 * except that it is potentially more efficient because it can cache
834 * encoders between successive invocations.
835 *
836 * <p> This method always replaces malformed-input and unmappable-character
837 * sequences with this charset's default replacement string. In order to
838 * detect such sequences, use the {@link
839 * CharsetEncoder#encode(java.nio.CharBuffer)} method directly. </p>
840 *
841 * @param cb The char buffer to be encoded
842 *
843 * @return A byte buffer containing the encoded characters
844 */
845 public final ByteBuffer encode(CharBuffer cb) {
846 try {
847 return ThreadLocalCoders.encoderFor(this)
848 .onMalformedInput(CodingErrorAction.REPLACE)
849 .onUnmappableCharacter(CodingErrorAction.REPLACE)
850 .encode(cb);
851 } catch (CharacterCodingException x) {
852 throw new Error(x); // Can't happen
853 }
854 }
855
856 /**
857 * Convenience method that encodes a string into bytes in this charset.
858 *
859 * <p> An invocation of this method upon a charset {@code cs} returns the
860 * same result as the expression
861 *
862 * <pre>
863 * cs.encode(CharBuffer.wrap(s)); </pre>
864 *
865 * @param str The string to be encoded
866 *
867 * @return A byte buffer containing the encoded characters
868 */
869 public final ByteBuffer encode(String str) {
870 return encode(CharBuffer.wrap(str));
871 }
872
873 /**
874 * Compares this charset to another.
875 *
876 * <p> Charsets are ordered by their canonical names, without regard to
877 * case. </p>
878 *
879 * @param that
880 * The charset to which this charset is to be compared
881 *
882 * @return A negative integer, zero, or a positive integer as this charset
883 * is less than, equal to, or greater than the specified charset
884 */
885 public final int compareTo(Charset that) {
886 return (name().compareToIgnoreCase(that.name()));
887 }
888
889 /**
890 * Computes a hashcode for this charset.
891 *
892 * @return An integer hashcode
893 */
894 public final int hashCode() {
895 return name().hashCode();
896 }
897
898 /**
899 * Tells whether or not this object is equal to another.
900 *
901 * <p> Two charsets are equal if, and only if, they have the same canonical
902 * names. A charset is never equal to any other type of object. </p>
903 *
904 * @return {@code true} if, and only if, this charset is equal to the
905 * given object
906 */
907 public final boolean equals(Object ob) {
908 if (!(ob instanceof Charset))
909 return false;
910 if (this == ob)
911 return true;
912 return name.equals(((Charset)ob).name());
913 }
914
915 /**
916 * Returns a string describing this charset.
917 *
918 * @return A string describing this charset
919 */
920 public final String toString() {
921 return name();
922 }
923
924 }