1 //
2 // ========================================================================
3 // Copyright (c) 1995-2014 Mort Bay Consulting Pty. Ltd.
4 // ------------------------------------------------------------------------
5 // All rights reserved. This program and the accompanying materials
6 // are made available under the terms of the Eclipse Public License v1.0
7 // and Apache License v2.0 which accompanies this distribution.
8 //
9 // The Eclipse Public License is available at
10 // http://www.eclipse.org/legal/epl-v10.html
11 //
12 // The Apache License v2.0 is available at
13 // http://www.opensource.org/licenses/apache2.0.php
14 //
15 // You may elect to redistribute this code under either of these licenses.
16 // ========================================================================
17 //
18
19 package org.eclipse.jetty.util;
20
21 import java.io.Serializable;
22 import java.lang.reflect.Array;
23 import java.util.ArrayList;
24 import java.util.Collection;
25 import java.util.Collections;
26 import java.util.Iterator;
27 import java.util.List;
28 import java.util.ListIterator;
29
30 /* ------------------------------------------------------------ */
31 /** Lazy List creation.
32 * A List helper class that attempts to avoid unnecessary List
33 * creation. If a method needs to create a List to return, but it is
34 * expected that this will either be empty or frequently contain a
35 * single item, then using LazyList will avoid additional object
36 * creations by using {@link Collections#EMPTY_LIST} or
37 * {@link Collections#singletonList(Object)} where possible.
38 * <p>
39 * LazyList works by passing an opaque representation of the list in
40 * and out of all the LazyList methods. This opaque object is either
41 * null for an empty list, an Object for a list with a single entry
42 * or an {@link ArrayList} for a list of items.
43 *
44 * <p><h4>Usage</h4>
45 * <pre>
46 * Object lazylist =null;
47 * while(loopCondition)
48 * {
49 * Object item = getItem();
50 * if (item.isToBeAdded())
51 * lazylist = LazyList.add(lazylist,item);
52 * }
53 * return LazyList.getList(lazylist);
54 * </pre>
55 *
56 * An ArrayList of default size is used as the initial LazyList.
57 *
58 * @see java.util.List
59 */
60 @SuppressWarnings("serial")
61 public class LazyList
62 implements Cloneable, Serializable
63 {
64 private static final String[] __EMTPY_STRING_ARRAY = new String[0];
65
66 /* ------------------------------------------------------------ */
67 private LazyList()
68 {}
69
70 /* ------------------------------------------------------------ */
71 /** Add an item to a LazyList
72 * @param list The list to add to or null if none yet created.
73 * @param item The item to add.
74 * @return The lazylist created or added to.
75 */
76 @SuppressWarnings("unchecked")
77 public static Object add(Object list, Object item)
78 {
79 if (list==null)
80 {
81 if (item instanceof List || item==null)
82 {
83 List<Object> l = new ArrayList<Object>();
84 l.add(item);
85 return l;
86 }
87
88 return item;
89 }
90
91 if (list instanceof List)
92 {
93 ((List<Object>)list).add(item);
94 return list;
95 }
96
97 List<Object> l=new ArrayList<Object>();
98 l.add(list);
99 l.add(item);
100 return l;
101 }
102
103 /* ------------------------------------------------------------ */
104 /** Add an item to a LazyList
105 * @param list The list to add to or null if none yet created.
106 * @param index The index to add the item at.
107 * @param item The item to add.
108 * @return The lazylist created or added to.
109 */
110 @SuppressWarnings("unchecked")
111 public static Object add(Object list, int index, Object item)
112 {
113 if (list==null)
114 {
115 if (index>0 || item instanceof List || item==null)
116 {
117 List<Object> l = new ArrayList<Object>();
118 l.add(index,item);
119 return l;
120 }
121 return item;
122 }
123
124 if (list instanceof List)
125 {
126 ((List<Object>)list).add(index,item);
127 return list;
128 }
129
130 List<Object> l=new ArrayList<Object>();
131 l.add(list);
132 l.add(index,item);
133 return l;
134 }
135
136 /* ------------------------------------------------------------ */
137 /** Add the contents of a Collection to a LazyList
138 * @param list The list to add to or null if none yet created.
139 * @param collection The Collection whose contents should be added.
140 * @return The lazylist created or added to.
141 */
142 public static Object addCollection(Object list, Collection<?> collection)
143 {
144 Iterator<?> i=collection.iterator();
145 while(i.hasNext())
146 list=LazyList.add(list,i.next());
147 return list;
148 }
149
150 /* ------------------------------------------------------------ */
151 /** Add the contents of an array to a LazyList
152 * @param list The list to add to or null if none yet created.
153 * @param array The array whose contents should be added.
154 * @return The lazylist created or added to.
155 */
156 public static Object addArray(Object list, Object[] array)
157 {
158 for(int i=0;array!=null && i<array.length;i++)
159 list=LazyList.add(list,array[i]);
160 return list;
161 }
162
163 /* ------------------------------------------------------------ */
164 /** Ensure the capacity of the underlying list.
165 *
166 */
167 public static Object ensureSize(Object list, int initialSize)
168 {
169 if (list==null)
170 return new ArrayList<Object>(initialSize);
171 if (list instanceof ArrayList)
172 {
173 ArrayList<?> ol=(ArrayList<?>)list;
174 if (ol.size()>initialSize)
175 return ol;
176 ArrayList<Object> nl = new ArrayList<Object>(initialSize);
177 nl.addAll(ol);
178 return nl;
179 }
180 List<Object> l= new ArrayList<Object>(initialSize);
181 l.add(list);
182 return l;
183 }
184
185 /* ------------------------------------------------------------ */
186 public static Object remove(Object list, Object o)
187 {
188 if (list==null)
189 return null;
190
191 if (list instanceof List)
192 {
193 List<?> l = (List<?>)list;
194 l.remove(o);
195 if (l.size()==0)
196 return null;
197 return list;
198 }
199
200 if (list.equals(o))
201 return null;
202 return list;
203 }
204
205 /* ------------------------------------------------------------ */
206 public static Object remove(Object list, int i)
207 {
208 if (list==null)
209 return null;
210
211 if (list instanceof List)
212 {
213 List<?> l = (List<?>)list;
214 l.remove(i);
215 if (l.size()==0)
216 return null;
217 return list;
218 }
219
220 if (i==0)
221 return null;
222 return list;
223 }
224
225
226
227 /* ------------------------------------------------------------ */
228 /** Get the real List from a LazyList.
229 *
230 * @param list A LazyList returned from LazyList.add(Object)
231 * @return The List of added items, which may be an EMPTY_LIST
232 * or a SingletonList.
233 */
234 public static<E> List<E> getList(Object list)
235 {
236 return getList(list,false);
237 }
238
239
240 /* ------------------------------------------------------------ */
241 /** Get the real List from a LazyList.
242 *
243 * @param list A LazyList returned from LazyList.add(Object) or null
244 * @param nullForEmpty If true, null is returned instead of an
245 * empty list.
246 * @return The List of added items, which may be null, an EMPTY_LIST
247 * or a SingletonList.
248 */
249 @SuppressWarnings("unchecked")
250 public static<E> List<E> getList(Object list, boolean nullForEmpty)
251 {
252 if (list==null)
253 {
254 if (nullForEmpty)
255 return null;
256 return Collections.emptyList();
257 }
258 if (list instanceof List)
259 return (List<E>)list;
260
261 return (List<E>)Collections.singletonList(list);
262 }
263
264 /**
265 * Simple utility method to test if List has at least 1 entry.
266 *
267 * @param list
268 * a LazyList, {@link List} or {@link Object}
269 * @return true if not-null and is not empty
270 */
271 public static boolean hasEntry(Object list)
272 {
273 if (list == null)
274 return false;
275 if (list instanceof List)
276 return !((List<?>)list).isEmpty();
277 return true;
278 }
279
280 /**
281 * Simple utility method to test if List is empty
282 *
283 * @param list
284 * a LazyList, {@link List} or {@link Object}
285 * @return true if null or is empty
286 */
287 public static boolean isEmpty(Object list)
288 {
289 if (list == null)
290 return true;
291 if (list instanceof List)
292 return ((List<?>)list).isEmpty();
293 return false;
294 }
295
296
297 /* ------------------------------------------------------------ */
298 public static String[] toStringArray(Object list)
299 {
300 if (list==null)
301 return __EMTPY_STRING_ARRAY;
302
303 if (list instanceof List)
304 {
305 List<?> l = (List<?>)list;
306 String[] a = new String[l.size()];
307 for (int i=l.size();i-->0;)
308 {
309 Object o=l.get(i);
310 if (o!=null)
311 a[i]=o.toString();
312 }
313 return a;
314 }
315
316 return new String[] {list.toString()};
317 }
318
319 /* ------------------------------------------------------------ */
320 /** Convert a lazylist to an array
321 * @param list The list to convert
322 * @param clazz The class of the array, which may be a primitive type
323 * @return array of the lazylist entries passed in
324 */
325 public static Object toArray(Object list,Class<?> clazz)
326 {
327 if (list==null)
328 return Array.newInstance(clazz,0);
329
330 if (list instanceof List)
331 {
332 List<?> l = (List<?>)list;
333 if (clazz.isPrimitive())
334 {
335 Object a = Array.newInstance(clazz,l.size());
336 for (int i=0;i<l.size();i++)
337 Array.set(a,i,l.get(i));
338 return a;
339 }
340 return l.toArray((Object[])Array.newInstance(clazz,l.size()));
341
342 }
343
344 Object a = Array.newInstance(clazz,1);
345 Array.set(a,0,list);
346 return a;
347 }
348
349 /* ------------------------------------------------------------ */
350 /** The size of a lazy List
351 * @param list A LazyList returned from LazyList.add(Object) or null
352 * @return the size of the list.
353 */
354 public static int size(Object list)
355 {
356 if (list==null)
357 return 0;
358 if (list instanceof List)
359 return ((List<?>)list).size();
360 return 1;
361 }
362
363 /* ------------------------------------------------------------ */
364 /** Get item from the list
365 * @param list A LazyList returned from LazyList.add(Object) or null
366 * @param i int index
367 * @return the item from the list.
368 */
369 @SuppressWarnings("unchecked")
370 public static <E> E get(Object list, int i)
371 {
372 if (list==null)
373 throw new IndexOutOfBoundsException();
374
375 if (list instanceof List)
376 return (E)((List<?>)list).get(i);
377
378 if (i==0)
379 return (E)list;
380
381 throw new IndexOutOfBoundsException();
382 }
383
384 /* ------------------------------------------------------------ */
385 public static boolean contains(Object list,Object item)
386 {
387 if (list==null)
388 return false;
389
390 if (list instanceof List)
391 return ((List<?>)list).contains(item);
392
393 return list.equals(item);
394 }
395
396
397 /* ------------------------------------------------------------ */
398 public static Object clone(Object list)
399 {
400 if (list==null)
401 return null;
402 if (list instanceof List)
403 return new ArrayList<Object>((List<?>)list);
404 return list;
405 }
406
407 /* ------------------------------------------------------------ */
408 public static String toString(Object list)
409 {
410 if (list==null)
411 return "[]";
412 if (list instanceof List)
413 return list.toString();
414 return "["+list+"]";
415 }
416
417 /* ------------------------------------------------------------ */
418 @SuppressWarnings("unchecked")
419 public static<E> Iterator<E> iterator(Object list)
420 {
421 if (list==null)
422 {
423 List<E> empty=Collections.emptyList();
424 return empty.iterator();
425 }
426 if (list instanceof List)
427 {
428 return ((List<E>)list).iterator();
429 }
430 List<E> l=getList(list);
431 return l.iterator();
432 }
433
434 /* ------------------------------------------------------------ */
435 @SuppressWarnings("unchecked")
436 public static<E> ListIterator<E> listIterator(Object list)
437 {
438 if (list==null)
439 {
440 List<E> empty=Collections.emptyList();
441 return empty.listIterator();
442 }
443 if (list instanceof List)
444 return ((List<E>)list).listIterator();
445
446 List<E> l=getList(list);
447 return l.listIterator();
448 }
449
450 }
451