001 /* System.java -- useful methods to interface with the system
002 Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007
003 Free Software Foundation, Inc.
004
005 This file is part of GNU Classpath.
006
007 GNU Classpath is free software; you can redistribute it and/or modify
008 it under the terms of the GNU General Public License as published by
009 the Free Software Foundation; either version 2, or (at your option)
010 any later version.
011
012 GNU Classpath is distributed in the hope that it will be useful, but
013 WITHOUT ANY WARRANTY; without even the implied warranty of
014 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
015 General Public License for more details.
016
017 You should have received a copy of the GNU General Public License
018 along with GNU Classpath; see the file COPYING. If not, write to the
019 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
020 02110-1301 USA.
021
022 Linking this library statically or dynamically with other modules is
023 making a combined work based on this library. Thus, the terms and
024 conditions of the GNU General Public License cover the whole
025 combination.
026
027 As a special exception, the copyright holders of this library give you
028 permission to link this library with independent modules to produce an
029 executable, regardless of the license terms of these independent
030 modules, and to copy and distribute the resulting executable under
031 terms of your choice, provided that you also meet, for each linked
032 independent module, the terms and conditions of the license of that
033 module. An independent module is a module which is not derived from
034 or based on this library. If you modify this library, you may extend
035 this exception to your version of the library, but you are not
036 obligated to do so. If you do not wish to do so, delete this
037 exception statement from your version. */
038
039
040 package java.lang;
041
042 import gnu.classpath.SystemProperties;
043
044 import java.io.BufferedInputStream;
045 import java.io.BufferedOutputStream;
046 import java.io.FileDescriptor;
047 import java.io.FileInputStream;
048 import java.io.FileOutputStream;
049 import java.io.IOException;
050 import java.io.InputStream;
051 import java.io.PrintStream;
052 import java.nio.channels.Channel;
053 import java.nio.channels.spi.SelectorProvider;
054 import java.util.AbstractCollection;
055 import java.util.ArrayList;
056 import java.util.Collection;
057 import java.util.Collections;
058 import java.util.HashMap;
059 import java.util.Iterator;
060 import java.util.List;
061 import java.util.Map;
062 import java.util.Set;
063 import java.util.Properties;
064 import java.util.PropertyPermission;
065
066 /**
067 * System represents system-wide resources; things that represent the
068 * general environment. As such, all methods are static.
069 *
070 * @author John Keiser
071 * @author Eric Blake (ebb9@email.byu.edu)
072 * @since 1.0
073 * @status still missing 1.4 functionality
074 */
075 public final class System
076 {
077 // WARNING: System is a CORE class in the bootstrap cycle. See the comments
078 // in vm/reference/java/lang/Runtime for implications of this fact.
079
080 /**
081 * The standard InputStream. This is assigned at startup and starts its
082 * life perfectly valid. Although it is marked final, you can change it
083 * using {@link #setIn(InputStream)} through some hefty VM magic.
084 *
085 * <p>This corresponds to the C stdin and C++ cin variables, which
086 * typically input from the keyboard, but may be used to pipe input from
087 * other processes or files. That should all be transparent to you,
088 * however.
089 */
090 public static final InputStream in
091 = new BufferedInputStream(new FileInputStream(FileDescriptor.in));
092 /**
093 * The standard output PrintStream. This is assigned at startup and
094 * starts its life perfectly valid. Although it is marked final, you can
095 * change it using {@link #setOut(PrintStream)} through some hefty VM magic.
096 *
097 * <p>This corresponds to the C stdout and C++ cout variables, which
098 * typically output normal messages to the screen, but may be used to pipe
099 * output to other processes or files. That should all be transparent to
100 * you, however.
101 */
102 public static final PrintStream out
103 = new PrintStream(new BufferedOutputStream(new FileOutputStream(FileDescriptor.out)), true);
104 /**
105 * The standard output PrintStream. This is assigned at startup and
106 * starts its life perfectly valid. Although it is marked final, you can
107 * change it using {@link #setErr(PrintStream)} through some hefty VM magic.
108 *
109 * <p>This corresponds to the C stderr and C++ cerr variables, which
110 * typically output error messages to the screen, but may be used to pipe
111 * output to other processes or files. That should all be transparent to
112 * you, however.
113 */
114 public static final PrintStream err
115 = new PrintStream(new BufferedOutputStream(new FileOutputStream(FileDescriptor.err)), true);
116
117 /**
118 * A cached copy of the environment variable map.
119 */
120 private static Map<String,String> environmentMap;
121
122 /**
123 * This class is uninstantiable.
124 */
125 private System()
126 {
127 }
128
129 /**
130 * Set {@link #in} to a new InputStream. This uses some VM magic to change
131 * a "final" variable, so naturally there is a security check,
132 * <code>RuntimePermission("setIO")</code>.
133 *
134 * @param in the new InputStream
135 * @throws SecurityException if permission is denied
136 * @since 1.1
137 */
138 public static void setIn(InputStream in)
139 {
140 SecurityManager sm = SecurityManager.current; // Be thread-safe.
141 if (sm != null)
142 sm.checkPermission(new RuntimePermission("setIO"));
143 setIn0(in);
144 }
145
146 /**
147 * Set {@link #out} to a new PrintStream. This uses some VM magic to change
148 * a "final" variable, so naturally there is a security check,
149 * <code>RuntimePermission("setIO")</code>.
150 *
151 * @param out the new PrintStream
152 * @throws SecurityException if permission is denied
153 * @since 1.1
154 */
155 public static void setOut(PrintStream out)
156 {
157 SecurityManager sm = SecurityManager.current; // Be thread-safe.
158 if (sm != null)
159 sm.checkPermission(new RuntimePermission("setIO"));
160
161 setOut0(out);
162 }
163
164 /**
165 * Set {@link #err} to a new PrintStream. This uses some VM magic to change
166 * a "final" variable, so naturally there is a security check,
167 * <code>RuntimePermission("setIO")</code>.
168 *
169 * @param err the new PrintStream
170 * @throws SecurityException if permission is denied
171 * @since 1.1
172 */
173 public static void setErr(PrintStream err)
174 {
175 SecurityManager sm = SecurityManager.current; // Be thread-safe.
176 if (sm != null)
177 sm.checkPermission(new RuntimePermission("setIO"));
178 setErr0(err);
179 }
180
181 /**
182 * Set the current SecurityManager. If a security manager already exists,
183 * then <code>RuntimePermission("setSecurityManager")</code> is checked
184 * first. Since this permission is denied by the default security manager,
185 * setting the security manager is often an irreversible action.
186 *
187 * @param sm the new SecurityManager
188 * @throws SecurityException if permission is denied
189 */
190 public static synchronized void setSecurityManager(SecurityManager sm)
191 {
192 // Implementation note: the field lives in SecurityManager because of
193 // bootstrap initialization issues. This method is synchronized so that
194 // no other thread changes it to null before this thread makes the change.
195 if (SecurityManager.current != null)
196 SecurityManager.current.checkPermission
197 (new RuntimePermission("setSecurityManager"));
198 SecurityManager.current = sm;
199 }
200
201 /**
202 * Get the current SecurityManager. If the SecurityManager has not been
203 * set yet, then this method returns null.
204 *
205 * @return the current SecurityManager, or null
206 */
207 public static SecurityManager getSecurityManager()
208 {
209 return SecurityManager.current;
210 }
211
212 /**
213 * Get the current time, measured in the number of milliseconds from the
214 * beginning of Jan. 1, 1970. This is gathered from the system clock, with
215 * any attendant incorrectness (it may be timezone dependent).
216 *
217 * @return the current time
218 * @see java.util.Date
219 */
220 public static native long currentTimeMillis();
221
222 /**
223 * Get the current time, measured in nanoseconds. The result is as
224 * precise as possible, and is measured against a fixed epoch.
225 * However, unlike currentTimeMillis(), the epoch chosen is
226 * arbitrary and may vary by platform, etc.
227 * @since 1.5
228 */
229 public static native long nanoTime();
230
231 /**
232 * Copy one array onto another from <code>src[srcStart]</code> ...
233 * <code>src[srcStart+len-1]</code> to <code>dest[destStart]</code> ...
234 * <code>dest[destStart+len-1]</code>. First, the arguments are validated:
235 * neither array may be null, they must be of compatible types, and the
236 * start and length must fit within both arrays. Then the copying starts,
237 * and proceeds through increasing slots. If src and dest are the same
238 * array, this will appear to copy the data to a temporary location first.
239 * An ArrayStoreException in the middle of copying will leave earlier
240 * elements copied, but later elements unchanged.
241 *
242 * @param src the array to copy elements from
243 * @param srcStart the starting position in src
244 * @param dest the array to copy elements to
245 * @param destStart the starting position in dest
246 * @param len the number of elements to copy
247 * @throws NullPointerException if src or dest is null
248 * @throws ArrayStoreException if src or dest is not an array, if they are
249 * not compatible array types, or if an incompatible runtime type
250 * is stored in dest
251 * @throws IndexOutOfBoundsException if len is negative, or if the start or
252 * end copy position in either array is out of bounds
253 */
254 public static native void arraycopy(Object src, int srcStart,
255 Object dest, int destStart, int len);
256
257 /**
258 * Get a hash code computed by the VM for the Object. This hash code will
259 * be the same as Object's hashCode() method. It is usually some
260 * convolution of the pointer to the Object internal to the VM. It
261 * follows standard hash code rules, in that it will remain the same for a
262 * given Object for the lifetime of that Object.
263 *
264 * @param o the Object to get the hash code for
265 * @return the VM-dependent hash code for this Object
266 * @since 1.1
267 */
268 public static native int identityHashCode(Object o);
269
270 /**
271 * Get all the system properties at once. A security check may be performed,
272 * <code>checkPropertiesAccess</code>. Note that a security manager may
273 * allow getting a single property, but not the entire group.
274 *
275 * <p>The required properties include:
276 * <dl>
277 * <dt>java.version</dt> <dd>Java version number</dd>
278 * <dt>java.vendor</dt> <dd>Java vendor specific string</dd>
279 * <dt>java.vendor.url</dt> <dd>Java vendor URL</dd>
280 * <dt>java.home</dt> <dd>Java installation directory</dd>
281 * <dt>java.vm.specification.version</dt> <dd>VM Spec version</dd>
282 * <dt>java.vm.specification.vendor</dt> <dd>VM Spec vendor</dd>
283 * <dt>java.vm.specification.name</dt> <dd>VM Spec name</dd>
284 * <dt>java.vm.version</dt> <dd>VM implementation version</dd>
285 * <dt>java.vm.vendor</dt> <dd>VM implementation vendor</dd>
286 * <dt>java.vm.name</dt> <dd>VM implementation name</dd>
287 * <dt>java.specification.version</dt> <dd>Java Runtime Environment version</dd>
288 * <dt>java.specification.vendor</dt> <dd>Java Runtime Environment vendor</dd>
289 * <dt>java.specification.name</dt> <dd>Java Runtime Environment name</dd>
290 * <dt>java.class.version</dt> <dd>Java class version number</dd>
291 * <dt>java.class.path</dt> <dd>Java classpath</dd>
292 * <dt>java.library.path</dt> <dd>Path for finding Java libraries</dd>
293 * <dt>java.io.tmpdir</dt> <dd>Default temp file path</dd>
294 * <dt>java.compiler</dt> <dd>Name of JIT to use</dd>
295 * <dt>java.ext.dirs</dt> <dd>Java extension path</dd>
296 * <dt>os.name</dt> <dd>Operating System Name</dd>
297 * <dt>os.arch</dt> <dd>Operating System Architecture</dd>
298 * <dt>os.version</dt> <dd>Operating System Version</dd>
299 * <dt>file.separator</dt> <dd>File separator ("/" on Unix)</dd>
300 * <dt>path.separator</dt> <dd>Path separator (":" on Unix)</dd>
301 * <dt>line.separator</dt> <dd>Line separator ("\n" on Unix)</dd>
302 * <dt>user.name</dt> <dd>User account name</dd>
303 * <dt>user.home</dt> <dd>User home directory</dd>
304 * <dt>user.dir</dt> <dd>User's current working directory</dd>
305 * </dl>
306 *
307 * In addition, gnu defines several other properties, where ? stands for
308 * each character in '0' through '9':
309 * <dl>
310 * <dt>gnu.classpath.home</dt> <dd>Path to the classpath libraries.</dd>
311 * <dt>gnu.classpath.version</dt> <dd>Version of the classpath libraries.</dd>
312 * <dt>gnu.classpath.vm.shortname</dt> <dd>Succinct version of the VM name;
313 * used for finding property files in file system</dd>
314 * <dt>gnu.classpath.home.url</dt> <dd> Base URL; used for finding
315 * property files in file system</dd>
316 * <dt>gnu.cpu.endian</dt> <dd>big or little</dd>
317 * <dt>gnu.java.io.encoding_scheme_alias.ISO-8859-?</dt> <dd>8859_?</dd>
318 * <dt>gnu.java.io.encoding_scheme_alias.iso-8859-?</dt> <dd>8859_?</dd>
319 * <dt>gnu.java.io.encoding_scheme_alias.iso8859_?</dt> <dd>8859_?</dd>
320 * <dt>gnu.java.io.encoding_scheme_alias.iso-latin-_?</dt> <dd>8859_?</dd>
321 * <dt>gnu.java.io.encoding_scheme_alias.latin?</dt> <dd>8859_?</dd>
322 * <dt>gnu.java.io.encoding_scheme_alias.UTF-8</dt> <dd>UTF8</dd>
323 * <dt>gnu.java.io.encoding_scheme_alias.utf-8</dt> <dd>UTF8</dd>
324 * <dt>gnu.java.util.zoneinfo.dir</dt> <dd>Root of zoneinfo tree</dd>
325 * </dl>
326 *
327 * @return the system properties, will never be null
328 * @throws SecurityException if permission is denied
329 */
330 public static Properties getProperties()
331 {
332 SecurityManager sm = SecurityManager.current; // Be thread-safe.
333 if (sm != null)
334 sm.checkPropertiesAccess();
335 return SystemProperties.getProperties();
336 }
337
338 /**
339 * Set all the system properties at once. A security check may be performed,
340 * <code>checkPropertiesAccess</code>. Note that a security manager may
341 * allow setting a single property, but not the entire group. An argument
342 * of null resets the properties to the startup default.
343 *
344 * @param properties the new set of system properties
345 * @throws SecurityException if permission is denied
346 */
347 public static void setProperties(Properties properties)
348 {
349 SecurityManager sm = SecurityManager.current; // Be thread-safe.
350 if (sm != null)
351 sm.checkPropertiesAccess();
352 SystemProperties.setProperties(properties);
353 }
354
355 /**
356 * Get a single system property by name. A security check may be performed,
357 * <code>checkPropertyAccess(key)</code>.
358 *
359 * @param key the name of the system property to get
360 * @return the property, or null if not found
361 * @throws SecurityException if permission is denied
362 * @throws NullPointerException if key is null
363 * @throws IllegalArgumentException if key is ""
364 */
365 public static String getProperty(String key)
366 {
367 SecurityManager sm = SecurityManager.current; // Be thread-safe.
368 if (sm != null)
369 sm.checkPropertyAccess(key);
370 else if (key.length() == 0)
371 throw new IllegalArgumentException("key can't be empty");
372 return SystemProperties.getProperty(key);
373 }
374
375 /**
376 * Get a single system property by name. A security check may be performed,
377 * <code>checkPropertyAccess(key)</code>.
378 *
379 * @param key the name of the system property to get
380 * @param def the default
381 * @return the property, or def if not found
382 * @throws SecurityException if permission is denied
383 * @throws NullPointerException if key is null
384 * @throws IllegalArgumentException if key is ""
385 */
386 public static String getProperty(String key, String def)
387 {
388 SecurityManager sm = SecurityManager.current; // Be thread-safe.
389 if (sm != null)
390 sm.checkPropertyAccess(key);
391 return SystemProperties.getProperty(key, def);
392 }
393
394 /**
395 * Set a single system property by name. A security check may be performed,
396 * <code>checkPropertyAccess(key, "write")</code>.
397 *
398 * @param key the name of the system property to set
399 * @param value the new value
400 * @return the previous value, or null
401 * @throws SecurityException if permission is denied
402 * @throws NullPointerException if key is null
403 * @throws IllegalArgumentException if key is ""
404 * @since 1.2
405 */
406 public static String setProperty(String key, String value)
407 {
408 SecurityManager sm = SecurityManager.current; // Be thread-safe.
409 if (sm != null)
410 sm.checkPermission(new PropertyPermission(key, "write"));
411 return SystemProperties.setProperty(key, value);
412 }
413
414 /**
415 * Remove a single system property by name. A security check may be
416 * performed, <code>checkPropertyAccess(key, "write")</code>.
417 *
418 * @param key the name of the system property to remove
419 * @return the previous value, or null
420 * @throws SecurityException if permission is denied
421 * @throws NullPointerException if key is null
422 * @throws IllegalArgumentException if key is ""
423 * @since 1.5
424 */
425 public static String clearProperty(String key)
426 {
427 SecurityManager sm = SecurityManager.current; // Be thread-safe.
428 if (sm != null)
429 sm.checkPermission(new PropertyPermission(key, "write"));
430 // This handles both the null pointer exception and the illegal
431 // argument exception.
432 if (key.length() == 0)
433 throw new IllegalArgumentException("key can't be empty");
434 return SystemProperties.remove(key);
435 }
436
437 /**
438 * Gets the value of an environment variable.
439 *
440 * @param name the name of the environment variable
441 * @return the string value of the variable or null when the
442 * environment variable is not defined.
443 * @throws NullPointerException
444 * @throws SecurityException if permission is denied
445 * @since 1.5
446 * @specnote This method was deprecated in some JDK releases, but
447 * was restored in 1.5.
448 */
449 public static String getenv(String name)
450 {
451 if (name == null)
452 throw new NullPointerException();
453 SecurityManager sm = SecurityManager.current; // Be thread-safe.
454 if (sm != null)
455 sm.checkPermission(new RuntimePermission("getenv." + name));
456 return getenv0(name);
457 }
458
459 /**
460 * <p>
461 * Returns an unmodifiable view of the system environment variables.
462 * If the underlying system does not support environment variables,
463 * an empty map is returned.
464 * </p>
465 * <p>
466 * The returned map is read-only and does not accept queries using
467 * null keys or values, or those of a type other than <code>String</code>.
468 * Attempts to modify the map will throw an
469 * <code>UnsupportedOperationException</code>, while attempts
470 * to pass in a null value will throw a
471 * <code>NullPointerException</code>. Types other than <code>String</code>
472 * throw a <code>ClassCastException</code>.
473 * </p>
474 * <p>
475 * As the returned map is generated using data from the underlying
476 * platform, it may not comply with the <code>equals()</code>
477 * and <code>hashCode()</code> contracts. It is also likely that
478 * the keys of this map will be case-sensitive.
479 * </p>
480 * <p>
481 * Use of this method may require a security check for the
482 * RuntimePermission "getenv.*".
483 * </p>
484 *
485 * @return a map of the system environment variables.
486 * @throws SecurityException if the checkPermission method of
487 * an installed security manager prevents access to
488 * the system environment variables.
489 * @since 1.5
490 */
491 public static Map<String, String> getenv()
492 {
493 SecurityManager sm = SecurityManager.current; // Be thread-safe.
494 if (sm != null)
495 sm.checkPermission(new RuntimePermission("getenv.*"));
496 if (environmentMap == null)
497 {
498 // List<String> environ = (List<String>)VMSystem.environ();
499 // FIXME
500 List<String> environ = new ArrayList<String>();
501 Map<String,String> variables = new EnvironmentMap();
502 for (String pair : environ)
503 {
504 String[] parts = pair.split("=");
505 variables.put(parts[0], parts[1]);
506 }
507 environmentMap = Collections.unmodifiableMap(variables);
508 }
509 return environmentMap;
510 }
511
512 /**
513 * Terminate the Virtual Machine. This just calls
514 * <code>Runtime.getRuntime().exit(status)</code>, and never returns.
515 * Obviously, a security check is in order, <code>checkExit</code>.
516 *
517 * @param status the exit status; by convention non-zero is abnormal
518 * @throws SecurityException if permission is denied
519 * @see Runtime#exit(int)
520 */
521 public static void exit(int status)
522 {
523 Runtime.getRuntime().exit(status);
524 }
525
526 /**
527 * Calls the garbage collector. This is only a hint, and it is up to the
528 * implementation what this hint suggests, but it usually causes a
529 * best-effort attempt to reclaim unused memory from discarded objects.
530 * This calls <code>Runtime.getRuntime().gc()</code>.
531 *
532 * @see Runtime#gc()
533 */
534 public static void gc()
535 {
536 Runtime.getRuntime().gc();
537 }
538
539 /**
540 * Runs object finalization on pending objects. This is only a hint, and
541 * it is up to the implementation what this hint suggests, but it usually
542 * causes a best-effort attempt to run finalizers on all objects ready
543 * to be reclaimed. This calls
544 * <code>Runtime.getRuntime().runFinalization()</code>.
545 *
546 * @see Runtime#runFinalization()
547 */
548 public static void runFinalization()
549 {
550 Runtime.getRuntime().runFinalization();
551 }
552
553 /**
554 * Tell the Runtime whether to run finalization before exiting the
555 * JVM. This is inherently unsafe in multi-threaded applications,
556 * since it can force initialization on objects which are still in use
557 * by live threads, leading to deadlock; therefore this is disabled by
558 * default. There may be a security check, <code>checkExit(0)</code>. This
559 * calls <code>Runtime.getRuntime().runFinalizersOnExit()</code>.
560 *
561 * @param finalizeOnExit whether to run finalizers on exit
562 * @throws SecurityException if permission is denied
563 * @see Runtime#runFinalizersOnExit()
564 * @since 1.1
565 * @deprecated never rely on finalizers to do a clean, thread-safe,
566 * mop-up from your code
567 */
568 public static void runFinalizersOnExit(boolean finalizeOnExit)
569 {
570 Runtime.getRuntime().runFinalizersOnExit(finalizeOnExit);
571 }
572
573 /**
574 * Load a code file using its explicit system-dependent filename. A security
575 * check may be performed, <code>checkLink</code>. This just calls
576 * <code>Runtime.getRuntime().load(filename)</code>.
577 *
578 * <p>
579 * The library is loaded using the class loader associated with the
580 * class associated with the invoking method.
581 *
582 * @param filename the code file to load
583 * @throws SecurityException if permission is denied
584 * @throws UnsatisfiedLinkError if the file cannot be loaded
585 * @see Runtime#load(String)
586 */
587 public static void load(String filename)
588 {
589 Runtime.getRuntime().load(filename);
590 }
591
592 /**
593 * Load a library using its explicit system-dependent filename. A security
594 * check may be performed, <code>checkLink</code>. This just calls
595 * <code>Runtime.getRuntime().load(filename)</code>.
596 *
597 * <p>
598 * The library is loaded using the class loader associated with the
599 * class associated with the invoking method.
600 *
601 * @param libname the library file to load
602 * @throws SecurityException if permission is denied
603 * @throws UnsatisfiedLinkError if the file cannot be loaded
604 * @see Runtime#load(String)
605 */
606 public static void loadLibrary(String libname)
607 {
608 Runtime.getRuntime().loadLibrary(libname);
609 }
610
611 /**
612 * Convert a library name to its platform-specific variant.
613 *
614 * @param libname the library name, as used in <code>loadLibrary</code>
615 * @return the platform-specific mangling of the name
616 * @since 1.2
617 */
618 public static String mapLibraryName(String libname)
619 {
620 // XXX Fix this!!!!
621 return Runtime.nativeGetLibname("", libname);
622 }
623
624 /**
625 * Set {@link #in} to a new InputStream.
626 *
627 * @param in the new InputStream
628 * @see #setIn(InputStream)
629 */
630 private static native void setIn0(InputStream in);
631
632 /**
633 * Set {@link #out} to a new PrintStream.
634 *
635 * @param out the new PrintStream
636 * @see #setOut(PrintStream)
637 */
638 private static native void setOut0(PrintStream out);
639
640 /**
641 * Set {@link #err} to a new PrintStream.
642 *
643 * @param err the new PrintStream
644 * @see #setErr(PrintStream)
645 */
646 private static native void setErr0(PrintStream err);
647
648 /**
649 * Gets the value of an environment variable.
650 *
651 * @see #getenv(String)
652 */
653 static native String getenv0(String name);
654
655 /**
656 * Returns the inherited channel of the VM.
657 *
658 * This wraps the inheritedChannel() call of the system's default
659 * {@link SelectorProvider}.
660 *
661 * @return the inherited channel of the VM
662 *
663 * @throws IOException If an I/O error occurs
664 * @throws SecurityException If an installed security manager denies access
665 * to RuntimePermission("inheritedChannel")
666 *
667 * @since 1.5
668 */
669 public static Channel inheritedChannel()
670 throws IOException
671 {
672 return SelectorProvider.provider().inheritedChannel();
673 }
674
675 /**
676 * This is a specialised <code>Collection</code>, providing
677 * the necessary provisions for the collections used by the
678 * environment variable map. Namely, it prevents
679 * querying anything but <code>String</code>s.
680 *
681 * @author Andrew John Hughes (gnu_andrew@member.fsf.org)
682 */
683 private static class EnvironmentCollection
684 extends AbstractCollection<String>
685 {
686
687 /**
688 * The wrapped collection.
689 */
690 protected Collection<String> c;
691
692 /**
693 * Constructs a new environment collection, which
694 * wraps the elements of the supplied collection.
695 *
696 * @param coll the collection to use as a base for
697 * this collection.
698 */
699 public EnvironmentCollection(Collection<String> coll)
700 {
701 c = coll;
702 }
703
704 /**
705 * Blocks queries containing a null object or an object which
706 * isn't of type <code>String</code>. All other queries
707 * are forwarded to the underlying collection.
708 *
709 * @param obj the object to look for.
710 * @return true if the object exists in the collection.
711 * @throws NullPointerException if the specified object is null.
712 * @throws ClassCastException if the specified object is not a String.
713 */
714 public boolean contains(Object obj)
715 {
716 if (obj == null)
717 throw new
718 NullPointerException("This collection does not support " +
719 "null values.");
720 if (!(obj instanceof String))
721 throw new
722 ClassCastException("This collection only supports Strings.");
723 return c.contains(obj);
724 }
725
726 /**
727 * Blocks queries where the collection contains a null object or
728 * an object which isn't of type <code>String</code>. All other
729 * queries are forwarded to the underlying collection.
730 *
731 * @param coll the collection of objects to look for.
732 * @return true if the collection contains all elements in the collection.
733 * @throws NullPointerException if the collection is null.
734 * @throws NullPointerException if any collection entry is null.
735 * @throws ClassCastException if any collection entry is not a String.
736 */
737 public boolean containsAll(Collection<?> coll)
738 {
739 for (Object o: coll)
740 {
741 if (o == null)
742 throw new
743 NullPointerException("This collection does not support " +
744 "null values.");
745 if (!(o instanceof String))
746 throw new
747 ClassCastException("This collection only supports Strings.");
748 }
749 return c.containsAll(coll);
750 }
751
752 /**
753 * This returns an iterator over the map elements, with the
754 * same provisions as for the collection and underlying map.
755 *
756 * @return an iterator over the map elements.
757 */
758 public Iterator<String> iterator()
759 {
760 return c.iterator();
761 }
762
763 /**
764 * Blocks the removal of elements from the collection.
765 *
766 * @return true if the removal was sucessful.
767 * @throws NullPointerException if the collection is null.
768 * @throws NullPointerException if any collection entry is null.
769 * @throws ClassCastException if any collection entry is not a String.
770 */
771 public boolean remove(Object key)
772 {
773 if (key == null)
774 throw new
775 NullPointerException("This collection does not support " +
776 "null values.");
777 if (!(key instanceof String))
778 throw new
779 ClassCastException("This collection only supports Strings.");
780 return c.contains(key);
781 }
782
783 /**
784 * Blocks the removal of all elements in the specified
785 * collection from the collection.
786 *
787 * @param coll the collection of elements to remove.
788 * @return true if the elements were removed.
789 * @throws NullPointerException if the collection is null.
790 * @throws NullPointerException if any collection entry is null.
791 * @throws ClassCastException if any collection entry is not a String.
792 */
793 public boolean removeAll(Collection<?> coll)
794 {
795 for (Object o: coll)
796 {
797 if (o == null)
798 throw new
799 NullPointerException("This collection does not support " +
800 "null values.");
801 if (!(o instanceof String))
802 throw new
803 ClassCastException("This collection only supports Strings.");
804 }
805 return c.removeAll(coll);
806 }
807
808 /**
809 * Blocks the retention of all elements in the specified
810 * collection from the collection.
811 *
812 * @param c the collection of elements to retain.
813 * @return true if the other elements were removed.
814 * @throws NullPointerException if the collection is null.
815 * @throws NullPointerException if any collection entry is null.
816 * @throws ClassCastException if any collection entry is not a String.
817 */
818 public boolean retainAll(Collection<?> coll)
819 {
820 for (Object o: coll)
821 {
822 if (o == null)
823 throw new
824 NullPointerException("This collection does not support " +
825 "null values.");
826 if (!(o instanceof String))
827 throw new
828 ClassCastException("This collection only supports Strings.");
829 }
830 return c.containsAll(coll);
831 }
832
833 /**
834 * This simply calls the same method on the wrapped
835 * collection.
836 *
837 * @return the size of the underlying collection.
838 */
839 public int size()
840 {
841 return c.size();
842 }
843
844 } // class EnvironmentCollection<String>
845
846 /**
847 * This is a specialised <code>HashMap</code>, which
848 * prevents the addition or querying of anything other than
849 * <code>String</code> objects.
850 *
851 * @author Andrew John Hughes (gnu_andrew@member.fsf.org)
852 */
853 static class EnvironmentMap
854 extends HashMap<String,String>
855 {
856
857 /**
858 * Cache the entry set.
859 */
860 private transient Set<Map.Entry<String,String>> entries;
861
862 /**
863 * Cache the key set.
864 */
865 private transient Set<String> keys;
866
867 /**
868 * Cache the value collection.
869 */
870 private transient Collection<String> values;
871
872 /**
873 * Constructs a new empty <code>EnvironmentMap</code>.
874 */
875 EnvironmentMap()
876 {
877 super();
878 }
879
880 /**
881 * Constructs a new <code>EnvironmentMap</code> containing
882 * the contents of the specified map.
883 *
884 * @param m the map to be added to this.
885 * @throws NullPointerException if a key or value is null.
886 * @throws ClassCastException if a key or value is not a String.
887 */
888 EnvironmentMap(Map<String,String> m)
889 {
890 super(m);
891 }
892
893 /**
894 * Blocks queries containing a null key or one which is not
895 * of type <code>String</code>. All other queries
896 * are forwarded to the superclass.
897 *
898 * @param key the key to look for in the map.
899 * @return true if the key exists in the map.
900 * @throws NullPointerException if the specified key is null.
901 */
902 public boolean containsKey(Object key)
903 {
904 if (key == null)
905 throw new
906 NullPointerException("This map does not support null keys.");
907 if (!(key instanceof String))
908 throw new
909 ClassCastException("This map only allows queries using Strings.");
910 return super.containsKey(key);
911 }
912
913 /**
914 * Blocks queries using a null or non-<code>String</code> value.
915 * All other queries are forwarded to the superclass.
916 *
917 * @param value the value to look for in the map.
918 * @return true if the value exists in the map.
919 * @throws NullPointerException if the specified value is null.
920 */
921 public boolean containsValue(Object value)
922 {
923 if (value == null)
924 throw new
925 NullPointerException("This map does not support null values.");
926 if (!(value instanceof String))
927 throw new
928 ClassCastException("This map only allows queries using Strings.");
929 return super.containsValue(value);
930 }
931
932 /**
933 * Returns a set view of the map entries, with the same
934 * provisions as for the underlying map.
935 *
936 * @return a set containing the map entries.
937 */
938 public Set<Map.Entry<String,String>> entrySet()
939 {
940 if (entries == null)
941 entries = super.entrySet();
942 return entries;
943 }
944
945 /**
946 * Blocks queries containing a null or non-<code>String</code> key.
947 * All other queries are passed on to the superclass.
948 *
949 * @param key the key to retrieve the value for.
950 * @return the value associated with the given key.
951 * @throws NullPointerException if the specified key is null.
952 * @throws ClassCastException if the specified key is not a String.
953 */
954 public String get(Object key)
955 {
956 if (key == null)
957 throw new
958 NullPointerException("This map does not support null keys.");
959 if (!(key instanceof String))
960 throw new
961 ClassCastException("This map only allows queries using Strings.");
962 return super.get(key);
963 }
964
965 /**
966 * Returns a set view of the keys, with the same
967 * provisions as for the underlying map.
968 *
969 * @return a set containing the keys.
970 */
971 public Set<String> keySet()
972 {
973 if (keys == null)
974 keys = new EnvironmentSet(super.keySet());
975 return keys;
976 }
977
978 /**
979 * Associates the given key to the given value. If the
980 * map already contains the key, its value is replaced.
981 * The map does not accept null keys or values, or keys
982 * and values not of type {@link String}.
983 *
984 * @param key the key to map.
985 * @param value the value to be mapped.
986 * @return the previous value of the key, or null if there was no mapping
987 * @throws NullPointerException if a key or value is null.
988 * @throws ClassCastException if a key or value is not a String.
989 */
990 public String put(String key, String value)
991 {
992 if (key == null)
993 throw new NullPointerException("A new key is null.");
994 if (value == null)
995 throw new NullPointerException("A new value is null.");
996 if (!(key instanceof String))
997 throw new ClassCastException("A new key is not a String.");
998 if (!(value instanceof String))
999 throw new ClassCastException("A new value is not a String.");
1000 return super.put(key, value);
1001 }
1002
1003 /**
1004 * Removes a key-value pair from the map. The queried key may not
1005 * be null or of a type other than a <code>String</code>.
1006 *
1007 * @param key the key of the entry to remove.
1008 * @return the removed value.
1009 * @throws NullPointerException if the specified key is null.
1010 * @throws ClassCastException if the specified key is not a String.
1011 */
1012 public String remove(Object key)
1013 {
1014 if (key == null)
1015 throw new
1016 NullPointerException("This map does not support null keys.");
1017 if (!(key instanceof String))
1018 throw new
1019 ClassCastException("This map only allows queries using Strings.");
1020 return super.remove(key);
1021 }
1022
1023 /**
1024 * Returns a collection view of the values, with the same
1025 * provisions as for the underlying map.
1026 *
1027 * @return a collection containing the values.
1028 */
1029 public Collection<String> values()
1030 {
1031 if (values == null)
1032 values = new EnvironmentCollection(super.values());
1033 return values;
1034 }
1035
1036 }
1037
1038 /**
1039 * This is a specialised <code>Set</code>, providing
1040 * the necessary provisions for the collections used by the
1041 * environment variable map. Namely, it prevents
1042 * modifications and the use of queries with null
1043 * or non-<code>String</code> values.
1044 *
1045 * @author Andrew John Hughes (gnu_andrew@member.fsf.org)
1046 */
1047 private static class EnvironmentSet
1048 extends EnvironmentCollection
1049 implements Set<String>
1050 {
1051
1052 /**
1053 * Constructs a new environment set, which
1054 * wraps the elements of the supplied set.
1055 *
1056 * @param set the set to use as a base for
1057 * this set.
1058 */
1059 public EnvironmentSet(Set<String> set)
1060 {
1061 super(set);
1062 }
1063
1064 /**
1065 * This simply calls the same method on the wrapped
1066 * collection.
1067 *
1068 * @param obj the object to compare with.
1069 * @return true if the two objects are equal.
1070 */
1071 public boolean equals(Object obj)
1072 {
1073 return c.equals(obj);
1074 }
1075
1076 /**
1077 * This simply calls the same method on the wrapped
1078 * collection.
1079 *
1080 * @return the hashcode of the collection.
1081 */
1082 public int hashCode()
1083 {
1084 return c.hashCode();
1085 }
1086
1087 } // class EnvironmentSet<String>
1088
1089 } // class System