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