1 /*
2 * Copyright (c) 2000, 2017, 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 jdk.internal.misc.VM;
29 import sun.nio.cs.ThreadLocalCoders;
30 import sun.security.action.GetPropertyAction;
31
32 import java.nio.ByteBuffer;
33 import java.nio.CharBuffer;
34 import java.nio.charset.spi.CharsetProvider;
35 import java.security.AccessController;
36 import java.security.PrivilegedAction;
37 import java.util.Arrays;
38 import java.util.Collections;
39 import java.util.HashSet;
40 import java.util.Iterator;
41 import java.util.Locale;
42 import java.util.Map;
43 import java.util.NoSuchElementException;
44 import java.util.Objects;
45 import java.util.ServiceConfigurationError;
46 import java.util.ServiceLoader;
47 import java.util.Set;
48 import java.util.SortedMap;
49 import java.util.TreeMap;
50
51
52 /**
53 * A named mapping between sequences of sixteen-bit Unicode <a
54 * href="../../lang/Character.html#unicode">code units</a> and sequences of
55 * bytes. This class defines methods for creating decoders and encoders and
56 * for retrieving the various names associated with a charset. Instances of
57 * this class are immutable.
58 *
59 * <p> This class also defines static methods for testing whether a particular
60 * charset is supported, for locating charset instances by name, and for
61 * constructing a map that contains every charset for which support is
62 * available in the current Java virtual machine. Support for new charsets can
63 * be added via the service-provider interface defined in the {@link
64 * java.nio.charset.spi.CharsetProvider} class.
65 *
66 * <p> All of the methods defined in this class are safe for use by multiple
67 * concurrent threads.
68 *
69 *
70 * <a id="names"></a><a id="charenc"></a>
71 * <h2>Charset names</h2>
72 *
73 * <p> Charsets are named by strings composed of the following characters:
74 *
75 * <ul>
76 *
77 * <li> The uppercase letters {@code 'A'} through {@code 'Z'}
78 * (<code>'\u0041'</code> through <code>'\u005a'</code>),
79 *
80 * <li> The lowercase letters {@code 'a'} through {@code 'z'}
81 * (<code>'\u0061'</code> through <code>'\u007a'</code>),
82 *
83 * <li> The digits {@code '0'} through {@code '9'}
84 * (<code>'\u0030'</code> through <code>'\u0039'</code>),
85 *
86 * <li> The dash character {@code '-'}
87 * (<code>'\u002d'</code>, <small>HYPHEN-MINUS</small>),
88 *
89 * <li> The plus character {@code '+'}
90 * (<code>'\u002b'</code>, <small>PLUS SIGN</small>),
91 *
92 * <li> The period character {@code '.'}
93 * (<code>'\u002e'</code>, <small>FULL STOP</small>),
94 *
95 * <li> The colon character {@code ':'}
96 * (<code>'\u003a'</code>, <small>COLON</small>), and
97 *
98 * <li> The underscore character {@code '_'}
99 * (<code>'\u005f'</code>, <small>LOW LINE</small>).
100 *
101 * </ul>
102 *
103 * A charset name must begin with either a letter or a digit. The empty string
104 * is not a legal charset name. Charset names are not case-sensitive; that is,
105 * case is always ignored when comparing charset names. Charset names
106 * generally follow the conventions documented in <a
107 * href="http://www.ietf.org/rfc/rfc2278.txt"><i>RFC 2278: IANA Charset
108 * Registration Procedures</i></a>.
109 *
110 * <p> Every charset has a <i>canonical name</i> and may also have one or more
111 * <i>aliases</i>. The canonical name is returned by the {@link #name() name} method
112 * of this class. Canonical names are, by convention, usually in upper case.
113 * The aliases of a charset are returned by the {@link #aliases() aliases}
114 * method.
115 *
116 * <p><a id="hn">Some charsets have an <i>historical name</i> that is defined for
117 * compatibility with previous versions of the Java platform.</a> A charset's
118 * historical name is either its canonical name or one of its aliases. The
119 * historical name is returned by the {@code getEncoding()} methods of the
120 * {@link java.io.InputStreamReader#getEncoding InputStreamReader} and {@link
121 * java.io.OutputStreamWriter#getEncoding OutputStreamWriter} classes.
122 *
123 * <p><a id="iana"> </a>If a charset listed in the <a
124 * href="http://www.iana.org/assignments/character-sets"><i>IANA Charset
125 * Registry</i></a> is supported by an implementation of the Java platform then
126 * its canonical name must be the name listed in the registry. Many charsets
127 * are given more than one name in the registry, in which case the registry
128 * identifies one of the names as <i>MIME-preferred</i>. If a charset has more
129 * than one registry name then its canonical name must be the MIME-preferred
130 * name and the other names in the registry must be valid aliases. If a
131 * supported charset is not listed in the IANA registry then its canonical name
132 * must begin with one of the strings {@code "X-"} or {@code "x-"}.
133 *
134 * <p> The IANA charset registry does change over time, and so the canonical
135 * name and the aliases of a particular charset may also change over time. To
136 * ensure compatibility it is recommended that no alias ever be removed from a
137 * charset, and that if the canonical name of a charset is changed then its
138 * previous canonical name be made into an alias.
139 *
140 *
141 * <h2>Standard charsets</h2>
142 *
143 *
144 *
145 * <p><a id="standard">Every implementation of the Java platform is required to support the
146 * following standard charsets.</a> Consult the release documentation for your
147 * implementation to see if any other charsets are supported. The behavior
148 * of such optional charsets may differ between implementations.
149 *
150 * <blockquote><table class="striped" style="width:80%">
151 * <caption style="display:none">Description of standard charsets</caption>
152 * <thead>
153 * <tr><th scope="col" style="text-align:left">Charset</th><th scope="col" style="text-align:left">Description</th></tr>
154 * </thead>
155 * <tbody>
156 * <tr><th scope="row" style="vertical-align:top">{@code US-ASCII}</th>
157 * <td>Seven-bit ASCII, a.k.a. {@code ISO646-US},
158 * a.k.a. the Basic Latin block of the Unicode character set</td></tr>
159 * <tr><th scope="row" style="vertical-align:top"><code>ISO-8859-1 </code></th>
160 * <td>ISO Latin Alphabet No. 1, a.k.a. {@code ISO-LATIN-1}</td></tr>
161 * <tr><th scope="row" style="vertical-align:top">{@code UTF-8}</th>
162 * <td>Eight-bit UCS Transformation Format</td></tr>
163 * <tr><th scope="row" style="vertical-align:top">{@code UTF-16BE}</th>
164 * <td>Sixteen-bit UCS Transformation Format,
165 * big-endian byte order</td></tr>
166 * <tr><th scope="row" style="vertical-align:top">{@code UTF-16LE}</th>
167 * <td>Sixteen-bit UCS Transformation Format,
168 * little-endian byte order</td></tr>
169 * <tr><th scope="row" style="vertical-align:top">{@code UTF-16}</th>
170 * <td>Sixteen-bit UCS Transformation Format,
171 * byte order identified by an optional byte-order mark</td></tr>
172 * </tbody>
173 * </table></blockquote>
174 *
175 * <p> The {@code UTF-8} charset is specified by <a
176 * href="http://www.ietf.org/rfc/rfc2279.txt"><i>RFC 2279</i></a>; the
177 * transformation format upon which it is based is specified in
178 * Amendment 2 of ISO 10646-1 and is also described in the <a
179 * href="http://www.unicode.org/unicode/standard/standard.html"><i>Unicode
180 * Standard</i></a>.
181 *
182 * <p> The {@code UTF-16} charsets are specified by <a
183 * href="http://www.ietf.org/rfc/rfc2781.txt"><i>RFC 2781</i></a>; the
184 * transformation formats upon which they are based are specified in
185 * Amendment 1 of ISO 10646-1 and are also described in the <a
186 * href="http://www.unicode.org/unicode/standard/standard.html"><i>Unicode
187 * Standard</i></a>.
188 *
189 * <p> The {@code UTF-16} charsets use sixteen-bit quantities and are
190 * therefore sensitive to byte order. In these encodings the byte order of a
191 * stream may be indicated by an initial <i>byte-order mark</i> represented by
192 * the Unicode character <code>'\uFEFF'</code>. Byte-order marks are handled
193 * as follows:
194 *
195 * <ul>
196 *
197 * <li><p> When decoding, the {@code UTF-16BE} and {@code UTF-16LE}
198 * charsets interpret the initial byte-order marks as a <small>ZERO-WIDTH
199 * NON-BREAKING SPACE</small>; when encoding, they do not write
200 * byte-order marks. </p></li>
201
202 *
203 * <li><p> When decoding, the {@code UTF-16} charset interprets the
204 * byte-order mark at the beginning of the input stream to indicate the
205 * byte-order of the stream but defaults to big-endian if there is no
206 * byte-order mark; when encoding, it uses big-endian byte order and writes
207 * a big-endian byte-order mark. </p></li>
208 *
209 * </ul>
210 *
211 * In any case, byte order marks occurring after the first element of an
212 * input sequence are not omitted since the same code is used to represent
213 * <small>ZERO-WIDTH NON-BREAKING SPACE</small>.
214 *
215 * <p> Every instance of the Java virtual machine has a default charset, which
216 * may or may not be one of the standard charsets. The default charset is
217 * determined during virtual-machine startup and typically depends upon the
218 * locale and charset being used by the underlying operating system. </p>
219 *
220 * <p>The {@link StandardCharsets} class defines constants for each of the
221 * standard charsets.
222 *
223 * <h2>Terminology</h2>
224 *
225 * <p> The name of this class is taken from the terms used in
226 * <a href="http://www.ietf.org/rfc/rfc2278.txt"><i>RFC 2278</i></a>.
227 * In that document a <i>charset</i> is defined as the combination of
228 * one or more coded character sets and a character-encoding scheme.
229 * (This definition is confusing; some other software systems define
230 * <i>charset</i> as a synonym for <i>coded character set</i>.)
231 *
232 * <p> A <i>coded character set</i> is a mapping between a set of abstract
233 * characters and a set of integers. US-ASCII, ISO 8859-1,
234 * JIS X 0201, and Unicode are examples of coded character sets.
235 *
236 * <p> Some standards have defined a <i>character set</i> to be simply a
237 * set of abstract characters without an associated assigned numbering.
238 * An alphabet is an example of such a character set. However, the subtle
239 * distinction between <i>character set</i> and <i>coded character set</i>
240 * is rarely used in practice; the former has become a short form for the
241 * latter, including in the Java API specification.
242 *
243 * <p> A <i>character-encoding scheme</i> is a mapping between one or more
244 * coded character sets and a set of octet (eight-bit byte) sequences.
245 * UTF-8, UTF-16, ISO 2022, and EUC are examples of
246 * character-encoding schemes. Encoding schemes are often associated with
247 * a particular coded character set; UTF-8, for example, is used only to
248 * encode Unicode. Some schemes, however, are associated with multiple
249 * coded character sets; EUC, for example, can be used to encode
250 * characters in a variety of Asian coded character sets.
251 *
252 * <p> When a coded character set is used exclusively with a single
253 * character-encoding scheme then the corresponding charset is usually
254 * named for the coded character set; otherwise a charset is usually named
255 * for the encoding scheme and, possibly, the locale of the coded
256 * character sets that it supports. Hence {@code US-ASCII} is both the
257 * name of a coded character set and of the charset that encodes it, while
258 * {@code EUC-JP} is the name of the charset that encodes the
259 * JIS X 0201, JIS X 0208, and JIS X 0212
260 * coded character sets for the Japanese language.
261 *
262 * <p> The native character encoding of the Java programming language is
263 * UTF-16. A charset in the Java platform therefore defines a mapping
264 * between sequences of sixteen-bit UTF-16 code units (that is, sequences
265 * of chars) and sequences of bytes. </p>
266 *
267 *
268 * @author Mark Reinhold
269 * @author JSR-51 Expert Group
270 * @since 1.4
271 *
272 * @see CharsetDecoder
273 * @see CharsetEncoder
274 * @see java.nio.charset.spi.CharsetProvider
275 * @see java.lang.Character
276 */
277
278 public abstract class Charset
279 implements Comparable<Charset>
280 {
281
282 /* -- Static methods -- */
283
284 /**
285 * Checks that the given string is a legal charset name. </p>
286 *
287 * @param s
288 * A purported charset name
289 *
290 * @throws IllegalCharsetNameException
291 * If the given name is not a legal charset name
292 */
293 private static void checkName(String s) {
294 int n = s.length();
295 if (n == 0) {
296 throw new IllegalCharsetNameException(s);
297 }
298 for (int i = 0; i < n; i++) {
299 char c = s.charAt(i);
300 if (c >= 'A' && c <= 'Z') continue;
301 if (c >= 'a' && c <= 'z') continue;
302 if (c >= '0' && c <= '9') continue;
303 if (c == '-' && i != 0) continue;
304 if (c == '+' && i != 0) continue;
305 if (c == ':' && i != 0) continue;
306 if (c == '_' && i != 0) continue;
307 if (c == '.' && i != 0) continue;
308 throw new IllegalCharsetNameException(s);
309 }
310 }
311
312 /* The standard set of charsets */
313 private static final CharsetProvider standardProvider
314 = new sun.nio.cs.StandardCharsets();
315
316 private static final String[] zeroAliases = new String[0];
317
318 // Cache of the most-recently-returned charsets,
319 // along with the names that were used to find them
320 //
321 private static volatile Object[] cache1; // "Level 1" cache
322 private static volatile Object[] cache2; // "Level 2" cache
323
324 private static void cache(String charsetName, Charset cs) {
325 cache2 = cache1;
326 cache1 = new Object[] { charsetName, cs };
327 }
328
329 // Creates an iterator that walks over the available providers, ignoring
330 // those whose lookup or instantiation causes a security exception to be
331 // thrown. Should be invoked with full privileges.
332 //
333 private static Iterator<CharsetProvider> providers() {
334 return new Iterator<>() {
335 ClassLoader cl = ClassLoader.getSystemClassLoader();
336 ServiceLoader<CharsetProvider> sl =
337 ServiceLoader.load(CharsetProvider.class, cl);
338 Iterator<CharsetProvider> i = sl.iterator();
339 CharsetProvider next = null;
340
341 private boolean getNext() {
342 while (next == null) {
343 try {
344 if (!i.hasNext())
345 return false;
346 next = i.next();
347 } catch (ServiceConfigurationError sce) {
348 if (sce.getCause() instanceof SecurityException) {
349 // Ignore security exceptions
350 continue;
351 }
352 throw sce;
353 }
354 }
355 return true;
356 }
357
358 public boolean hasNext() {
359 return getNext();
360 }
361
362 public CharsetProvider next() {
363 if (!getNext())
364 throw new NoSuchElementException();
365 CharsetProvider n = next;
366 next = null;
367 return n;
368 }
369
370 public void remove() {
371 throw new UnsupportedOperationException();
372 }
373
374 };
375 }
376
377 // Thread-local gate to prevent recursive provider lookups
378 private static ThreadLocal<ThreadLocal<?>> gate =
379 new ThreadLocal<ThreadLocal<?>>();
380
381 private static Charset lookupViaProviders(final String charsetName) {
382
383 // The runtime startup sequence looks up standard charsets as a
384 // consequence of the VM's invocation of System.initializeSystemClass
385 // in order to, e.g., set system properties and encode filenames. At
386 // that point the application class loader has not been initialized,
387 // however, so we can't look for providers because doing so will cause
388 // that loader to be prematurely initialized with incomplete
389 // information.
390 //
391 if (!VM.isBooted())
392 return null;
393
394 if (gate.get() != null)
395 // Avoid recursive provider lookups
396 return null;
397 try {
398 gate.set(gate);
399
400 return AccessController.doPrivileged(
401 new PrivilegedAction<>() {
402 public Charset run() {
403 for (Iterator<CharsetProvider> i = providers();
404 i.hasNext();) {
405 CharsetProvider cp = i.next();
406 Charset cs = cp.charsetForName(charsetName);
407 if (cs != null)
408 return cs;
409 }
410 return null;
411 }
412 });
413
414 } finally {
415 gate.set(null);
416 }
417 }
418
419 /* The extended set of charsets */
420 private static class ExtendedProviderHolder {
421 static final CharsetProvider[] extendedProviders = extendedProviders();
422 // returns ExtendedProvider, if installed
423 private static CharsetProvider[] extendedProviders() {
424 return AccessController.doPrivileged(new PrivilegedAction<>() {
425 public CharsetProvider[] run() {
426 CharsetProvider[] cps = new CharsetProvider[1];
427 int n = 0;
428 ServiceLoader<CharsetProvider> sl =
429 ServiceLoader.loadInstalled(CharsetProvider.class);
430 for (CharsetProvider cp : sl) {
431 if (n + 1 > cps.length) {
432 cps = Arrays.copyOf(cps, cps.length << 1);
433 }
434 cps[n++] = cp;
435 }
436 return n == cps.length ? cps : Arrays.copyOf(cps, n);
437 }});
438 }
439 }
440
441 private static Charset lookupExtendedCharset(String charsetName) {
442 if (!VM.isBooted()) // see lookupViaProviders()
443 return null;
444 CharsetProvider[] ecps = ExtendedProviderHolder.extendedProviders;
445 for (CharsetProvider cp : ecps) {
446 Charset cs = cp.charsetForName(charsetName);
447 if (cs != null)
448 return cs;
449 }
450 return null;
451 }
452
453 private static Charset lookup(String charsetName) {
454 if (charsetName == null)
455 throw new IllegalArgumentException("Null charset name");
456 Object[] a;
457 if ((a = cache1) != null && charsetName.equals(a[0]))
458 return (Charset)a[1];
459 // We expect most programs to use one Charset repeatedly.
460 // We convey a hint to this effect to the VM by putting the
461 // level 1 cache miss code in a separate method.
462 return lookup2(charsetName);
463 }
464
465 private static Charset lookup2(String charsetName) {
466 Object[] a;
467 if ((a = cache2) != null && charsetName.equals(a[0])) {
468 cache2 = cache1;
469 cache1 = a;
470 return (Charset)a[1];
471 }
472 Charset cs;
473 if ((cs = standardProvider.charsetForName(charsetName)) != null ||
474 (cs = lookupExtendedCharset(charsetName)) != null ||
475 (cs = lookupViaProviders(charsetName)) != null)
476 {
477 cache(charsetName, cs);
478 return cs;
479 }
480
481 /* Only need to check the name if we didn't find a charset for it */
482 checkName(charsetName);
483 return null;
484 }
485
486 /**
487 * Tells whether the named charset is supported.
488 *
489 * @param charsetName
490 * The name of the requested charset; may be either
491 * a canonical name or an alias
492 *
493 * @return {@code true} if, and only if, support for the named charset
494 * is available in the current Java virtual machine
495 *
496 * @throws IllegalCharsetNameException
497 * If the given charset name is illegal
498 *
499 * @throws IllegalArgumentException
500 * If the given {@code charsetName} is null
501 */
502 public static boolean isSupported(String charsetName) {
503 return (lookup(charsetName) != null);
504 }
505
506 /**
507 * Returns a charset object for the named charset.
508 *
509 * @param charsetName
510 * The name of the requested charset; may be either
511 * a canonical name or an alias
512 *
513 * @return A charset object for the named charset
514 *
515 * @throws IllegalCharsetNameException
516 * If the given charset name is illegal
517 *
518 * @throws IllegalArgumentException
519 * If the given {@code charsetName} is null
520 *
521 * @throws UnsupportedCharsetException
522 * If no support for the named charset is available
523 * in this instance of the Java virtual machine
524 */
525 public static Charset forName(String charsetName) {
526 Charset cs = lookup(charsetName);
527 if (cs != null)
528 return cs;
529 throw new UnsupportedCharsetException(charsetName);
530 }
531
532 // Fold charsets from the given iterator into the given map, ignoring
533 // charsets whose names already have entries in the map.
534 //
535 private static void put(Iterator<Charset> i, Map<String,Charset> m) {
536 while (i.hasNext()) {
537 Charset cs = i.next();
538 if (!m.containsKey(cs.name()))
539 m.put(cs.name(), cs);
540 }
541 }
542
543 /**
544 * Constructs a sorted map from canonical charset names to charset objects.
545 *
546 * <p> The map returned by this method will have one entry for each charset
547 * for which support is available in the current Java virtual machine. If
548 * two or more supported charsets have the same canonical name then the
549 * resulting map will contain just one of them; which one it will contain
550 * is not specified. </p>
551 *
552 * <p> The invocation of this method, and the subsequent use of the
553 * resulting map, may cause time-consuming disk or network I/O operations
554 * to occur. This method is provided for applications that need to
555 * enumerate all of the available charsets, for example to allow user
556 * charset selection. This method is not used by the {@link #forName
557 * forName} method, which instead employs an efficient incremental lookup
558 * algorithm.
559 *
560 * <p> This method may return different results at different times if new
561 * charset providers are dynamically made available to the current Java
562 * virtual machine. In the absence of such changes, the charsets returned
563 * by this method are exactly those that can be retrieved via the {@link
564 * #forName forName} method. </p>
565 *
566 * @return An immutable, case-insensitive map from canonical charset names
567 * to charset objects
568 */
569 public static SortedMap<String,Charset> availableCharsets() {
570 return AccessController.doPrivileged(
571 new PrivilegedAction<>() {
572 public SortedMap<String,Charset> run() {
573 TreeMap<String,Charset> m =
574 new TreeMap<>(
575 String.CASE_INSENSITIVE_ORDER);
576 put(standardProvider.charsets(), m);
577 CharsetProvider[] ecps = ExtendedProviderHolder.extendedProviders;
578 for (CharsetProvider ecp :ecps) {
579 put(ecp.charsets(), m);
580 }
581 for (Iterator<CharsetProvider> i = providers(); i.hasNext();) {
582 CharsetProvider cp = i.next();
583 put(cp.charsets(), m);
584 }
585 return Collections.unmodifiableSortedMap(m);
586 }
587 });
588 }
589
590 private static volatile Charset defaultCharset;
591
592 /**
593 * Returns the default charset of this Java virtual machine.
594 *
595 * <p> The default charset is determined during virtual-machine startup and
596 * typically depends upon the locale and charset of the underlying
597 * operating system.
598 *
599 * @return A charset object for the default charset
600 *
601 * @since 1.5
602 */
603 public static Charset defaultCharset() {
604 if (defaultCharset == null) {
605 synchronized (Charset.class) {
606 String csn = GetPropertyAction
607 .privilegedGetProperty("file.encoding");
608 Charset cs = lookup(csn);
609 if (cs != null)
610 defaultCharset = cs;
611 else
612 defaultCharset = StandardCharsets.UTF_8;
613 }
614 }
615 return defaultCharset;
616 }
617
618
619 /* -- Instance fields and methods -- */
620
621 private final String name; // tickles a bug in oldjavac
622 private final String[] aliases; // tickles a bug in oldjavac
623 private Set<String> aliasSet = null;
624
625 /**
626 * Initializes a new charset with the given canonical name and alias
627 * set.
628 *
629 * @param canonicalName
630 * The canonical name of this charset
631 *
632 * @param aliases
633 * An array of this charset's aliases, or null if it has no aliases
634 *
635 * @throws IllegalCharsetNameException
636 * If the canonical name or any of the aliases are illegal
637 */
638 protected Charset(String canonicalName, String[] aliases) {
639 String[] as = Objects.requireNonNullElse(aliases, zeroAliases);
640
641 // Skip checks for the standard, built-in Charsets we always load
642 // during initialization.
643 if (canonicalName != "ISO-8859-1"
644 && canonicalName != "US-ASCII"
645 && canonicalName != "UTF-8") {
646 checkName(canonicalName);
647 for (int i = 0; i < as.length; i++) {
648 checkName(as[i]);
649 }
650 }
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 }