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