1 // ========================================================================
2 // Copyright (c) 2004-2009 Mort Bay Consulting Pty. Ltd.
3 // ------------------------------------------------------------------------
4 // All rights reserved. This program and the accompanying materials
5 // are made available under the terms of the Eclipse Public License v1.0
6 // and Apache License v2.0 which accompanies this distribution.
7 // The Eclipse Public License is available at
8 // http://www.eclipse.org/legal/epl-v10.html
9 // The Apache License v2.0 is available at
10 // http://www.opensource.org/licenses/apache2.0.php
11 // You may elect to redistribute this code under either of these licenses.
12 // ========================================================================
13
14 package org.eclipse.jetty.util;
15
16 import java.io.Serializable;
17 import java.lang.reflect.Array;
18 import java.util.ArrayList;
19 import java.util.Arrays;
20 import java.util.Collection;
21 import java.util.Collections;
22 import java.util.Iterator;
23 import java.util.List;
24 import java.util.ListIterator;
25
26 /* ------------------------------------------------------------ */
27 /** Lazy List creation.
28 * A List helper class that attempts to avoid unnecessary List
29 * creation. If a method needs to create a List to return, but it is
30 * expected that this will either be empty or frequently contain a
31 * single item, then using LazyList will avoid additional object
32 * creations by using {@link Collections#EMPTY_LIST} or
33 * {@link Collections#singletonList(Object)} where possible.
34 * <p>
35 * LazyList works by passing an opaque representation of the list in
36 * and out of all the LazyList methods. This opaque object is either
37 * null for an empty list, an Object for a list with a single entry
38 * or an {@link ArrayList} for a list of items.
39 *
40 * <p><h4>Usage</h4>
41 * <pre>
42 * Object lazylist =null;
43 * while(loopCondition)
44 * {
45 * Object item = getItem();
46 * if (item.isToBeAdded())
47 * lazylist = LazyList.add(lazylist,item);
48 * }
49 * return LazyList.getList(lazylist);
50 * </pre>
51 *
52 * An ArrayList of default size is used as the initial LazyList.
53 *
54 * @see java.util.List
55 */
56 public class LazyList
57 implements Cloneable, Serializable
58 {
59 private static final String[] __EMTPY_STRING_ARRAY = new String[0];
60
61 /* ------------------------------------------------------------ */
62 private LazyList()
63 {}
64
65 /* ------------------------------------------------------------ */
66 /** Add an item to a LazyList
67 * @param list The list to add to or null if none yet created.
68 * @param item The item to add.
69 * @return The lazylist created or added to.
70 */
71 @SuppressWarnings("unchecked")
72 public static Object add(Object list, Object item)
73 {
74 if (list==null)
75 {
76 if (item instanceof List || item==null)
77 {
78 List<Object> l = new ArrayList<Object>();
79 l.add(item);
80 return l;
81 }
82
83 return item;
84 }
85
86 if (list instanceof List)
87 {
88 ((List<Object>)list).add(item);
89 return list;
90 }
91
92 List<Object> l=new ArrayList<Object>();
93 l.add(list);
94 l.add(item);
95 return l;
96 }
97
98 /* ------------------------------------------------------------ */
99 /** Add an item to a LazyList
100 * @param list The list to add to or null if none yet created.
101 * @param index The index to add the item at.
102 * @param item The item to add.
103 * @return The lazylist created or added to.
104 */
105 @SuppressWarnings("unchecked")
106 public static Object add(Object list, int index, Object item)
107 {
108 if (list==null)
109 {
110 if (index>0 || item instanceof List || item==null)
111 {
112 List<Object> l = new ArrayList<Object>();
113 l.add(index,item);
114 return l;
115 }
116 return item;
117 }
118
119 if (list instanceof List)
120 {
121 ((List<Object>)list).add(index,item);
122 return list;
123 }
124
125 List<Object> l=new ArrayList<Object>();
126 l.add(list);
127 l.add(index,item);
128 return l;
129 }
130
131 /* ------------------------------------------------------------ */
132 /** Add the contents of a Collection to a LazyList
133 * @param list The list to add to or null if none yet created.
134 * @param collection The Collection whose contents should be added.
135 * @return The lazylist created or added to.
136 */
137 public static Object addCollection(Object list, Collection<?> collection)
138 {
139 Iterator<?> i=collection.iterator();
140 while(i.hasNext())
141 list=LazyList.add(list,i.next());
142 return list;
143 }
144
145 /* ------------------------------------------------------------ */
146 /** Add the contents of an array to a LazyList
147 * @param list The list to add to or null if none yet created.
148 * @param array The array whose contents should be added.
149 * @return The lazylist created or added to.
150 */
151 public static Object addArray(Object list, Object[] array)
152 {
153 for(int i=0;array!=null && i<array.length;i++)
154 list=LazyList.add(list,array[i]);
155 return list;
156 }
157
158 /* ------------------------------------------------------------ */
159 /** Ensure the capacity of the underlying list.
160 *
161 */
162 public static Object ensureSize(Object list, int initialSize)
163 {
164 if (list==null)
165 return new ArrayList<Object>(initialSize);
166 if (list instanceof ArrayList)
167 {
168 ArrayList<?> ol=(ArrayList<?>)list;
169 if (ol.size()>initialSize)
170 return ol;
171 ArrayList<Object> nl = new ArrayList<Object>(initialSize);
172 nl.addAll(ol);
173 return nl;
174 }
175 List<Object> l= new ArrayList<Object>(initialSize);
176 l.add(list);
177 return l;
178 }
179
180 /* ------------------------------------------------------------ */
181 public static Object remove(Object list, Object o)
182 {
183 if (list==null)
184 return null;
185
186 if (list instanceof List)
187 {
188 List<?> l = (List<?>)list;
189 l.remove(o);
190 if (l.size()==0)
191 return null;
192 return list;
193 }
194
195 if (list.equals(o))
196 return null;
197 return list;
198 }
199
200 /* ------------------------------------------------------------ */
201 public static Object remove(Object list, int i)
202 {
203 if (list==null)
204 return null;
205
206 if (list instanceof List)
207 {
208 List<?> l = (List<?>)list;
209 l.remove(i);
210 if (l.size()==0)
211 return null;
212 return list;
213 }
214
215 if (i==0)
216 return null;
217 return list;
218 }
219
220
221
222 /* ------------------------------------------------------------ */
223 /** Get the real List from a LazyList.
224 *
225 * @param list A LazyList returned from LazyList.add(Object)
226 * @return The List of added items, which may be an EMPTY_LIST
227 * or a SingletonList.
228 */
229 public static<E> List<E> getList(Object list)
230 {
231 return getList(list,false);
232 }
233
234
235 /* ------------------------------------------------------------ */
236 /** Get the real List from a LazyList.
237 *
238 * @param list A LazyList returned from LazyList.add(Object) or null
239 * @param nullForEmpty If true, null is returned instead of an
240 * empty list.
241 * @return The List of added items, which may be null, an EMPTY_LIST
242 * or a SingletonList.
243 */
244 @SuppressWarnings("unchecked")
245 public static<E> List<E> getList(Object list, boolean nullForEmpty)
246 {
247 if (list==null)
248 {
249 if (nullForEmpty)
250 return null;
251 return Collections.emptyList();
252 }
253 if (list instanceof List)
254 return (List<E>)list;
255
256 return (List<E>)Collections.singletonList(list);
257 }
258
259
260 /* ------------------------------------------------------------ */
261 public static String[] toStringArray(Object list)
262 {
263 if (list==null)
264 return __EMTPY_STRING_ARRAY;
265
266 if (list instanceof List)
267 {
268 List<?> l = (List<?>)list;
269 String[] a = new String[l.size()];
270 for (int i=l.size();i-->0;)
271 {
272 Object o=l.get(i);
273 if (o!=null)
274 a[i]=o.toString();
275 }
276 return a;
277 }
278
279 return new String[] {list.toString()};
280 }
281
282 /* ------------------------------------------------------------ */
283 /** Convert a lazylist to an array
284 * @param list The list to convert
285 * @param clazz The class of the array, which may be a primitive type
286 * @return array of the lazylist entries passed in
287 */
288 public static Object toArray(Object list,Class<?> clazz)
289 {
290 if (list==null)
291 return Array.newInstance(clazz,0);
292
293 if (list instanceof List)
294 {
295 List<?> l = (List<?>)list;
296 if (clazz.isPrimitive())
297 {
298 Object a = Array.newInstance(clazz,l.size());
299 for (int i=0;i<l.size();i++)
300 Array.set(a,i,l.get(i));
301 return a;
302 }
303 return l.toArray((Object[])Array.newInstance(clazz,l.size()));
304
305 }
306
307 Object a = Array.newInstance(clazz,1);
308 Array.set(a,0,list);
309 return a;
310 }
311
312 /* ------------------------------------------------------------ */
313 /** The size of a lazy List
314 * @param list A LazyList returned from LazyList.add(Object) or null
315 * @return the size of the list.
316 */
317 public static int size(Object list)
318 {
319 if (list==null)
320 return 0;
321 if (list instanceof List)
322 return ((List<?>)list).size();
323 return 1;
324 }
325
326 /* ------------------------------------------------------------ */
327 /** Get item from the list
328 * @param list A LazyList returned from LazyList.add(Object) or null
329 * @param i int index
330 * @return the item from the list.
331 */
332 @SuppressWarnings("unchecked")
333 public static <E> E get(Object list, int i)
334 {
335 if (list==null)
336 throw new IndexOutOfBoundsException();
337
338 if (list instanceof List)
339 return (E)((List<?>)list).get(i);
340
341 if (i==0)
342 return (E)list;
343
344 throw new IndexOutOfBoundsException();
345 }
346
347 /* ------------------------------------------------------------ */
348 public static boolean contains(Object list,Object item)
349 {
350 if (list==null)
351 return false;
352
353 if (list instanceof List)
354 return ((List<?>)list).contains(item);
355
356 return list.equals(item);
357 }
358
359
360 /* ------------------------------------------------------------ */
361 public static Object clone(Object list)
362 {
363 if (list==null)
364 return null;
365 if (list instanceof List)
366 return new ArrayList<Object>((List<?>)list);
367 return list;
368 }
369
370 /* ------------------------------------------------------------ */
371 public static String toString(Object list)
372 {
373 if (list==null)
374 return "[]";
375 if (list instanceof List)
376 return list.toString();
377 return "["+list+"]";
378 }
379
380 /* ------------------------------------------------------------ */
381 @SuppressWarnings("unchecked")
382 public static<E> Iterator<E> iterator(Object list)
383 {
384 if (list==null)
385 {
386 List<E> empty=Collections.emptyList();
387 return empty.iterator();
388 }
389 if (list instanceof List)
390 {
391 return ((List<E>)list).iterator();
392 }
393 List<E> l=getList(list);
394 return l.iterator();
395 }
396
397 /* ------------------------------------------------------------ */
398 @SuppressWarnings("unchecked")
399 public static<E> ListIterator<E> listIterator(Object list)
400 {
401 if (list==null)
402 {
403 List<E> empty=Collections.emptyList();
404 return empty.listIterator();
405 }
406 if (list instanceof List)
407 return ((List<E>)list).listIterator();
408
409 List<E> l=getList(list);
410 return l.listIterator();
411 }
412
413 /* ------------------------------------------------------------ */
414 /**
415 * @param array Any array of object
416 * @return A new <i>modifiable</i> list initialised with the elements from <code>array</code>.
417 */
418 public static<E> List<E> array2List(E[] array)
419 {
420 if (array==null || array.length==0)
421 return new ArrayList<E>();
422 return new ArrayList<E>(Arrays.asList(array));
423 }
424
425 /* ------------------------------------------------------------ */
426 /** Add element to an array
427 * @param array The array to add to (or null)
428 * @param item The item to add
429 * @param type The type of the array (in case of null array)
430 * @return new array with contents of array plus item
431 */
432 public static<T> T[] addToArray(T[] array, T item, Class<?> type)
433 {
434 if (array==null)
435 {
436 if (type==null && item!=null)
437 type= item.getClass();
438 @SuppressWarnings("unchecked")
439 T[] na = (T[])Array.newInstance(type, 1);
440 na[0]=item;
441 return na;
442 }
443 else
444 {
445 // TODO: Replace with Arrays.copyOf(T[] original, int newLength) from Java 1.6+
446 Class<?> c = array.getClass().getComponentType();
447 @SuppressWarnings("unchecked")
448 T[] na = (T[])Array.newInstance(c, Array.getLength(array)+1);
449 System.arraycopy(array, 0, na, 0, array.length);
450 na[array.length]=item;
451 return na;
452 }
453 }
454
455 /* ------------------------------------------------------------ */
456 public static<T> T[] removeFromArray(T[] array, Object item)
457 {
458 if (item==null || array==null)
459 return array;
460 for (int i=array.length;i-->0;)
461 {
462 if (item.equals(array[i]))
463 {
464 Class<?> c = array==null?item.getClass():array.getClass().getComponentType();
465 @SuppressWarnings("unchecked")
466 T[] na = (T[])Array.newInstance(c, Array.getLength(array)-1);
467 if (i>0)
468 System.arraycopy(array, 0, na, 0, i);
469 if (i+1<array.length)
470 System.arraycopy(array, i+1, na, i, array.length-(i+1));
471 return na;
472 }
473 }
474 return array;
475 }
476
477 }
478