src/main/java/net/pterodactylus/sone/database/memory/MemoryDatabase.java

   1 /*
   2  * Sone - MemoryDatabase.java - Copyright © 2013 David Roden
   3  *
   4  * This program is free software: you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published by
   6  * the Free Software Foundation, either version 3 of the License, or
   7  * (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  16  */
  17
  18 package net.pterodactylus.sone.database.memory;
  19
  20 import static com.google.common.base.Optional.fromNullable;
  21 import static com.google.common.base.Preconditions.checkNotNull;
  22 import static com.google.common.base.Predicates.not;
  23 import static com.google.common.collect.FluentIterable.from;
  24 import static java.util.Collections.emptyList;
  25 import static net.pterodactylus.sone.data.Sone.LOCAL_SONE_FILTER;
  26
  27 import java.util.ArrayList;
  28 import java.util.Collection;
  29 import java.util.Collections;
  30 import java.util.Comparator;
  31 import java.util.HashMap;
  32 import java.util.HashSet;
  33 import java.util.List;
  34 import java.util.Map;
  35 import java.util.Set;
  36 import java.util.SortedSet;
  37 import java.util.TreeSet;
  38 import java.util.concurrent.locks.ReadWriteLock;
  39 import java.util.concurrent.locks.ReentrantReadWriteLock;
  40
  41 import net.pterodactylus.sone.data.Album;
  42 import net.pterodactylus.sone.data.Image;
  43 import net.pterodactylus.sone.data.Post;
  44 import net.pterodactylus.sone.data.PostReply;
  45 import net.pterodactylus.sone.data.Reply;
  46 import net.pterodactylus.sone.data.Sone;
  47 import net.pterodactylus.sone.database.Database;
  48 import net.pterodactylus.sone.database.DatabaseException;
  49 import net.pterodactylus.sone.database.PostBuilder;
  50 import net.pterodactylus.sone.database.PostDatabase;
  51 import net.pterodactylus.sone.database.PostReplyBuilder;
  52 import net.pterodactylus.sone.database.SoneBuilder;
  53 import net.pterodactylus.util.config.Configuration;
  54 import net.pterodactylus.util.config.ConfigurationException;
  55
  56 import com.google.common.base.Function;
  57 import com.google.common.base.Optional;
  58 import com.google.common.collect.ArrayListMultimap;
  59 import com.google.common.collect.ListMultimap;
  60 import com.google.common.collect.SortedSetMultimap;
  61 import com.google.common.collect.TreeMultimap;
  62 import com.google.common.util.concurrent.AbstractService;
  63 import com.google.inject.Inject;
  64
  65 /**
  66  * Memory-based {@link PostDatabase} implementation.
  67  *
  68  * @author <a href="mailto:bombe@pterodactylus.net">David ‘Bombe’ Roden</a>
  69  */
  70 public class MemoryDatabase extends AbstractService implements Database {
  71
  72         /** The lock. */
  73         private final ReadWriteLock lock = new ReentrantReadWriteLock();
  74
  75         /** The configuration. */
  76         private final Configuration configuration;
  77
  78         private final Map<String, Sone> sones = new HashMap<String, Sone>();
  79
  80         /** All posts by their ID. */
  81         private final Map<String, Post> allPosts = new HashMap<String, Post>();
  82
  83         /** All posts by their Sones. */
  84         private final Map<String, Collection<Post>> sonePosts = new HashMap<String, Collection<Post>>();
  85
  86         /** All posts by their recipient. */
  87         private final Map<String, Collection<Post>> recipientPosts = new HashMap<String, Collection<Post>>();
  88
  89         /** Whether posts are known. */
  90         private final Set<String> knownPosts = new HashSet<String>();
  91
  92         /** All post replies by their ID. */
  93         private final Map<String, PostReply> allPostReplies = new HashMap<String, PostReply>();
  94
  95         /** Replies sorted by Sone. */
  96         private final SortedSetMultimap<String, PostReply> sonePostReplies = TreeMultimap.create(new Comparator<String>() {
  97
  98                 @Override
  99                 public int compare(String leftString, String rightString) {
 100                         return leftString.compareTo(rightString);
 101                 }
 102         }, PostReply.TIME_COMPARATOR);
 103
 104         /** Replies by post. */
 105         private final Map<String, SortedSet<PostReply>> postReplies = new HashMap<String, SortedSet<PostReply>>();
 106
 107         /** Whether post replies are known. */
 108         private final Set<String> knownPostReplies = new HashSet<String>();
 109
 110         private final Map<String, Album> allAlbums = new HashMap<String, Album>();
 111         private final ListMultimap<String, String> albumChildren = ArrayListMultimap.create();
 112         private final ListMultimap<String, String> albumImages = ArrayListMultimap.create();
 113
 114         private final Map<String, Image> allImages = new HashMap<String, Image>();
 115
 116         /**
 117          * Creates a new memory database.
 118          *
 119          * @param configuration
 120          *              The configuration for loading and saving elements
 121          */
 122         @Inject
 123         public MemoryDatabase(Configuration configuration) {
 124                 this.configuration = configuration;
 125         }
 126
 127         //
 128         // DATABASE METHODS
 129         //
 130
 131         /**
 132          * Saves the database.
 133          *
 134          * @throws DatabaseException
 135          *              if an error occurs while saving
 136          */
 137         @Override
 138         public void save() throws DatabaseException {
 139                 saveKnownPosts();
 140                 saveKnownPostReplies();
 141         }
 142
 143         //
 144         // SERVICE METHODS
 145         //
 146
 147         /** {@inheritDocs} */
 148         @Override
 149         protected void doStart() {
 150                 loadKnownPosts();
 151                 loadKnownPostReplies();
 152                 notifyStarted();
 153         }
 154
 155         /** {@inheritDocs} */
 156         @Override
 157         protected void doStop() {
 158                 try {
 159                         save();
 160                         notifyStopped();
 161                 } catch (DatabaseException de1) {
 162                         notifyFailed(de1);
 163                 }
 164         }
 165
 166         @Override
 167         public Optional<Sone> getSone(String soneId) {
 168                 lock.readLock().lock();
 169                 try {
 170                         return fromNullable(sones.get(soneId));
 171                 } finally {
 172                         lock.readLock().unlock();
 173                 }
 174         }
 175
 176         @Override
 177         public Collection<Sone> getSones() {
 178                 lock.readLock().lock();
 179                 try {
 180                         return Collections.unmodifiableCollection(sones.values());
 181                 } finally {
 182                         lock.readLock().unlock();
 183                 }
 184         }
 185
 186         @Override
 187         public Collection<Sone> getLocalSones() {
 188                 lock.readLock().lock();
 189                 try {
 190                         return from(getSones()).filter(LOCAL_SONE_FILTER).toSet();
 191                 } finally {
 192                         lock.readLock().unlock();
 193                 }
 194         }
 195
 196         @Override
 197         public Collection<Sone> getRemoteSones() {
 198                 lock.readLock().lock();
 199                 try {
 200                         return from(getSones()).filter(not(LOCAL_SONE_FILTER)).toSet();
 201                 } finally {
 202                         lock.readLock().unlock();
 203                 }
 204         }
 205
 206         @Override
 207         public SoneBuilder newSoneBuilder() {
 208                 return null;
 209         }
 210
 211         //
 212         // POSTPROVIDER METHODS
 213         //
 214
 215         /** {@inheritDocs} */
 216         @Override
 217         public Optional<Post> getPost(String postId) {
 218                 lock.readLock().lock();
 219                 try {
 220                         return fromNullable(allPosts.get(postId));
 221                 } finally {
 222                         lock.readLock().unlock();
 223                 }
 224         }
 225
 226         /** {@inheritDocs} */
 227         @Override
 228         public Collection<Post> getPosts(String soneId) {
 229                 return new HashSet<Post>(getPostsFrom(soneId));
 230         }
 231
 232         /** {@inheritDocs} */
 233         @Override
 234         public Collection<Post> getDirectedPosts(String recipientId) {
 235                 lock.readLock().lock();
 236                 try {
 237                         Collection<Post> posts = recipientPosts.get(recipientId);
 238                         return (posts == null) ? Collections.<Post>emptySet() : new HashSet<Post>(posts);
 239                 } finally {
 240                         lock.readLock().unlock();
 241                 }
 242         }
 243
 244         //
 245         // POSTBUILDERFACTORY METHODS
 246         //
 247
 248         /** {@inheritDocs} */
 249         @Override
 250         public PostBuilder newPostBuilder() {
 251                 return new MemoryPostBuilder(this);
 252         }
 253
 254         //
 255         // POSTSTORE METHODS
 256         //
 257
 258         /** {@inheritDocs} */
 259         @Override
 260         public void storePost(Post post) {
 261                 checkNotNull(post, "post must not be null");
 262                 lock.writeLock().lock();
 263                 try {
 264                         allPosts.put(post.getId(), post);
 265                         getPostsFrom(post.getSone().getId()).add(post);
 266                         if (post.getRecipientId().isPresent()) {
 267                                 getPostsTo(post.getRecipientId().get()).add(post);
 268                         }
 269                 } finally {
 270                         lock.writeLock().unlock();
 271                 }
 272         }
 273
 274         /** {@inheritDocs} */
 275         @Override
 276         public void removePost(Post post) {
 277                 checkNotNull(post, "post must not be null");
 278                 lock.writeLock().lock();
 279                 try {
 280                         allPosts.remove(post.getId());
 281                         getPostsFrom(post.getSone().getId()).remove(post);
 282                         if (post.getRecipientId().isPresent()) {
 283                                 getPostsTo(post.getRecipientId().get()).remove(post);
 284                         }
 285                         post.getSone().removePost(post);
 286                 } finally {
 287                         lock.writeLock().unlock();
 288                 }
 289         }
 290
 291         /** {@inheritDocs} */
 292         @Override
 293         public void storePosts(Sone sone, Collection<Post> posts) throws IllegalArgumentException {
 294                 checkNotNull(sone, "sone must not be null");
 295                 /* verify that all posts are from the same Sone. */
 296                 for (Post post : posts) {
 297                         if (!sone.equals(post.getSone())) {
 298                                 throw new IllegalArgumentException(String.format("Post from different Sone found: %s", post));
 299                         }
 300                 }
 301
 302                 lock.writeLock().lock();
 303                 try {
 304                         /* remove all posts by the Sone. */
 305                         getPostsFrom(sone.getId()).clear();
 306                         for (Post post : posts) {
 307                                 allPosts.remove(post.getId());
 308                                 if (post.getRecipientId().isPresent()) {
 309                                         getPostsTo(post.getRecipientId().get()).remove(post);
 310                                 }
 311                         }
 312
 313                         /* add new posts. */
 314                         getPostsFrom(sone.getId()).addAll(posts);
 315                         for (Post post : posts) {
 316                                 allPosts.put(post.getId(), post);
 317                                 if (post.getRecipientId().isPresent()) {
 318                                         getPostsTo(post.getRecipientId().get()).add(post);
 319                                 }
 320                         }
 321                 } finally {
 322                         lock.writeLock().unlock();
 323                 }
 324         }
 325
 326         /** {@inheritDocs} */
 327         @Override
 328         public void removePosts(Sone sone) {
 329                 checkNotNull(sone, "sone must not be null");
 330                 lock.writeLock().lock();
 331                 try {
 332                         /* remove all posts by the Sone. */
 333                         getPostsFrom(sone.getId()).clear();
 334                         for (Post post : sone.getPosts()) {
 335                                 allPosts.remove(post.getId());
 336                                 if (post.getRecipientId().isPresent()) {
 337                                         getPostsTo(post.getRecipientId().get()).remove(post);
 338                                 }
 339                         }
 340                 } finally {
 341                         lock.writeLock().unlock();
 342                 }
 343         }
 344
 345         //
 346         // POSTREPLYPROVIDER METHODS
 347         //
 348
 349         /** {@inheritDocs} */
 350         @Override
 351         public Optional<PostReply> getPostReply(String id) {
 352                 lock.readLock().lock();
 353                 try {
 354                         return fromNullable(allPostReplies.get(id));
 355                 } finally {
 356                         lock.readLock().unlock();
 357                 }
 358         }
 359
 360         /** {@inheritDocs} */
 361         @Override
 362         public List<PostReply> getReplies(String postId) {
 363                 lock.readLock().lock();
 364                 try {
 365                         if (!postReplies.containsKey(postId)) {
 366                                 return emptyList();
 367                         }
 368                         return new ArrayList<PostReply>(postReplies.get(postId));
 369                 } finally {
 370                         lock.readLock().unlock();
 371                 }
 372         }
 373
 374         //
 375         // POSTREPLYBUILDERFACTORY METHODS
 376         //
 377
 378         /** {@inheritDocs} */
 379         @Override
 380         public PostReplyBuilder newPostReplyBuilder() {
 381                 return new MemoryPostReplyBuilder(this, this);
 382         }
 383
 384         //
 385         // POSTREPLYSTORE METHODS
 386         //
 387
 388         /** {@inheritDocs} */
 389         @Override
 390         public void storePostReply(PostReply postReply) {
 391                 lock.writeLock().lock();
 392                 try {
 393                         allPostReplies.put(postReply.getId(), postReply);
 394                         if (postReplies.containsKey(postReply.getPostId())) {
 395                                 postReplies.get(postReply.getPostId()).add(postReply);
 396                         } else {
 397                                 TreeSet<PostReply> replies = new TreeSet<PostReply>(Reply.TIME_COMPARATOR);
 398                                 replies.add(postReply);
 399                                 postReplies.put(postReply.getPostId(), replies);
 400                         }
 401                 } finally {
 402                         lock.writeLock().unlock();
 403                 }
 404         }
 405
 406         /** {@inheritDocs} */
 407         @Override
 408         public void storePostReplies(Sone sone, Collection<PostReply> postReplies) {
 409                 checkNotNull(sone, "sone must not be null");
 410                 /* verify that all posts are from the same Sone. */
 411                 for (PostReply postReply : postReplies) {
 412                         if (!sone.equals(postReply.getSone())) {
 413                                 throw new IllegalArgumentException(String.format("PostReply from different Sone found: %s", postReply));
 414                         }
 415                 }
 416
 417                 lock.writeLock().lock();
 418                 try {
 419                         /* remove all post replies of the Sone. */
 420                         for (PostReply postReply : getRepliesFrom(sone.getId())) {
 421                                 removePostReply(postReply);
 422                         }
 423                         for (PostReply postReply : postReplies) {
 424                                 allPostReplies.put(postReply.getId(), postReply);
 425                                 sonePostReplies.put(postReply.getSone().getId(), postReply);
 426                                 if (this.postReplies.containsKey(postReply.getPostId())) {
 427                                         this.postReplies.get(postReply.getPostId()).add(postReply);
 428                                 } else {
 429                                         TreeSet<PostReply> replies = new TreeSet<PostReply>(Reply.TIME_COMPARATOR);
 430                                         replies.add(postReply);
 431                                         this.postReplies.put(postReply.getPostId(), replies);
 432                                 }
 433                         }
 434                 } finally {
 435                         lock.writeLock().unlock();
 436                 }
 437         }
 438
 439         /** {@inheritDocs} */
 440         @Override
 441         public void removePostReply(PostReply postReply) {
 442                 lock.writeLock().lock();
 443                 try {
 444                         allPostReplies.remove(postReply.getId());
 445                         if (postReplies.containsKey(postReply.getPostId())) {
 446                                 postReplies.get(postReply.getPostId()).remove(postReply);
 447                                 if (postReplies.get(postReply.getPostId()).isEmpty()) {
 448                                         postReplies.remove(postReply.getPostId());
 449                                 }
 450                         }
 451                 } finally {
 452                         lock.writeLock().unlock();
 453                 }
 454         }
 455
 456         /** {@inheritDocs} */
 457         @Override
 458         public void removePostReplies(Sone sone) {
 459                 checkNotNull(sone, "sone must not be null");
 460
 461                 lock.writeLock().lock();
 462                 try {
 463                         for (PostReply postReply : sone.getReplies()) {
 464                                 removePostReply(postReply);
 465                         }
 466                 } finally {
 467                         lock.writeLock().unlock();
 468                 }
 469         }
 470
 471         //
 472         // ALBUMPROVDER METHODS
 473         //
 474
 475         @Override
 476         public Optional<Album> getAlbum(String albumId) {
 477                 lock.readLock().lock();
 478                 try {
 479                         return fromNullable(allAlbums.get(albumId));
 480                 } finally {
 481                         lock.readLock().unlock();
 482                 }
 483         }
 484
 485         @Override
 486         public List<Album> getAlbums(Album parent) {
 487                 lock.readLock().lock();
 488                 try {
 489                         return from(albumChildren.get(parent.getId())).transformAndConcat(getAlbum()).toList();
 490                 } finally {
 491                         lock.readLock().unlock();
 492                 }
 493         }
 494
 495         //
 496         // ALBUMSTORE METHODS
 497         //
 498
 499         @Override
 500         public void storeAlbum(Album album) {
 501                 lock.writeLock().lock();
 502                 try {
 503                         allAlbums.put(album.getId(), album);
 504                         albumChildren.put(album.getParent().getId(), album.getId());
 505                 } finally {
 506                         lock.writeLock().unlock();
 507                 }
 508         }
 509
 510         @Override
 511         public void removeAlbum(Album album) {
 512                 lock.writeLock().lock();
 513                 try {
 514                         allAlbums.remove(album.getId());
 515                         albumChildren.remove(album.getParent().getId(), album.getId());
 516                 } finally {
 517                         lock.writeLock().unlock();
 518                 }
 519         }
 520
 521         //
 522         // IMAGEPROVIDER METHODS
 523         //
 524
 525         @Override
 526         public Optional<Image> getImage(String imageId) {
 527                 lock.readLock().lock();
 528                 try {
 529                         return fromNullable(allImages.get(imageId));
 530                 } finally {
 531                         lock.readLock().unlock();
 532                 }
 533         }
 534
 535         @Override
 536         public List<Image> getImages(Album parent) {
 537                 lock.readLock().lock();
 538                 try {
 539                         return from(albumImages.get(parent.getId())).transformAndConcat(getImage()).toList();
 540                 } finally {
 541                         lock.readLock().unlock();
 542                 }
 543         }
 544
 545         //
 546         // IMAGESTORE METHODS
 547         //
 548
 549         @Override
 550         public void storeImage(Image image) {
 551                 lock.writeLock().lock();
 552                 try {
 553                         allImages.put(image.getId(), image);
 554                         albumImages.put(image.getAlbum().getId(), image.getId());
 555                 } finally {
 556                         lock.writeLock().unlock();
 557                 }
 558         }
 559
 560         @Override
 561         public void removeImage(Image image) {
 562                 lock.writeLock().lock();
 563                 try {
 564                         allImages.remove(image.getId());
 565                         albumImages.remove(image.getAlbum().getId(), image.getId());
 566                 } finally {
 567                         lock.writeLock().unlock();
 568                 }
 569         }
 570
 571         //
 572         // PACKAGE-PRIVATE METHODS
 573         //
 574
 575         /**
 576          * Returns whether the given post is known.
 577          *
 578          * @param post
 579          *              The post
 580          * @return {@code true} if the post is known, {@code false} otherwise
 581          */
 582         boolean isPostKnown(Post post) {
 583                 lock.readLock().lock();
 584                 try {
 585                         return knownPosts.contains(post.getId());
 586                 } finally {
 587                         lock.readLock().unlock();
 588                 }
 589         }
 590
 591         /**
 592          * Sets whether the given post is known.
 593          *
 594          * @param post
 595          *              The post
 596          * @param known
 597          *              {@code true} if the post is known, {@code false} otherwise
 598          */
 599         void setPostKnown(Post post, boolean known) {
 600                 lock.writeLock().lock();
 601                 try {
 602                         if (known) {
 603                                 knownPosts.add(post.getId());
 604                         } else {
 605                                 knownPosts.remove(post.getId());
 606                         }
 607                 } finally {
 608                         lock.writeLock().unlock();
 609                 }
 610         }
 611
 612         /**
 613          * Returns whether the given post reply is known.
 614          *
 615          * @param postReply
 616          *              The post reply
 617          * @return {@code true} if the given post reply is known, {@code false}
 618          *         otherwise
 619          */
 620         boolean isPostReplyKnown(PostReply postReply) {
 621                 lock.readLock().lock();
 622                 try {
 623                         return knownPostReplies.contains(postReply.getId());
 624                 } finally {
 625                         lock.readLock().unlock();
 626                 }
 627         }
 628
 629         /**
 630          * Sets whether the given post reply is known.
 631          *
 632          * @param postReply
 633          *              The post reply
 634          * @param known
 635          *              {@code true} if the post reply is known, {@code false} otherwise
 636          */
 637         void setPostReplyKnown(PostReply postReply, boolean known) {
 638                 lock.writeLock().lock();
 639                 try {
 640                         if (known) {
 641                                 knownPostReplies.add(postReply.getId());
 642                         } else {
 643                                 knownPostReplies.remove(postReply.getId());
 644                         }
 645                 } finally {
 646                         lock.writeLock().unlock();
 647                 }
 648         }
 649
 650         void moveUp(Album album) {
 651                 lock.writeLock().lock();
 652                 try {
 653                         List<String> albums = albumChildren.get(album.getParent().getId());
 654                         int currentIndex = albums.indexOf(album.getId());
 655                         if (currentIndex == 0) {
 656                                 return;
 657                         }
 658                         albums.remove(album.getId());
 659                         albums.add(currentIndex - 1, album.getId());
 660                 } finally {
 661                         lock.writeLock().unlock();
 662                 }
 663         }
 664
 665         void moveDown(Album album) {
 666                 lock.writeLock().lock();
 667                 try {
 668                         List<String> albums = albumChildren.get(album.getParent().getId());
 669                         int currentIndex = albums.indexOf(album.getId());
 670                         if (currentIndex == (albums.size() - 1)) {
 671                                 return;
 672                         }
 673                         albums.remove(album.getId());
 674                         albums.add(currentIndex + 1, album.getId());
 675                 } finally {
 676                         lock.writeLock().unlock();
 677                 }
 678         }
 679
 680         void moveUp(Image image) {
 681                 lock.writeLock().lock();
 682                 try {
 683                         List<String> images = albumImages.get(image.getAlbum().getId());
 684                         int currentIndex = images.indexOf(image.getId());
 685                         if (currentIndex == 0) {
 686                                 return;
 687                         }
 688                         images.remove(image.getId());
 689                         images.add(currentIndex - 1, image.getId());
 690                 } finally {
 691                         lock.writeLock().unlock();
 692                 }
 693         }
 694
 695         void moveDown(Image image) {
 696                 lock.writeLock().lock();
 697                 try {
 698                         List<String> images = albumChildren.get(image.getAlbum().getId());
 699                         int currentIndex = images.indexOf(image.getId());
 700                         if (currentIndex == (images.size() - 1)) {
 701                                 return;
 702                         }
 703                         images.remove(image.getId());
 704                         images.add(currentIndex + 1, image.getId());
 705                 } finally {
 706                         lock.writeLock().unlock();
 707                 }
 708         }
 709
 710         //
 711         // PRIVATE METHODS
 712         //
 713
 714         /**
 715          * Gets all posts for the given Sone, creating a new collection if there is
 716          * none yet.
 717          *
 718          * @param soneId
 719          *              The ID of the Sone to get the posts for
 720          * @return All posts
 721          */
 722         private Collection<Post> getPostsFrom(String soneId) {
 723                 Collection<Post> posts = null;
 724                 lock.readLock().lock();
 725                 try {
 726                         posts = sonePosts.get(soneId);
 727                 } finally {
 728                         lock.readLock().unlock();
 729                 }
 730                 if (posts != null) {
 731                         return posts;
 732                 }
 733
 734                 posts = new HashSet<Post>();
 735                 lock.writeLock().lock();
 736                 try {
 737                         sonePosts.put(soneId, posts);
 738                 } finally {
 739                         lock.writeLock().unlock();
 740                 }
 741
 742                 return posts;
 743         }
 744
 745         /**
 746          * Gets all posts that are directed the given Sone, creating a new collection
 747          * if there is none yet.
 748          *
 749          * @param recipientId
 750          *              The ID of the Sone to get the posts for
 751          * @return All posts
 752          */
 753         private Collection<Post> getPostsTo(String recipientId) {
 754                 Collection<Post> posts = null;
 755                 lock.readLock().lock();
 756                 try {
 757                         posts = recipientPosts.get(recipientId);
 758                 } finally {
 759                         lock.readLock().unlock();
 760                 }
 761                 if (posts != null) {
 762                         return posts;
 763                 }
 764
 765                 posts = new HashSet<Post>();
 766                 lock.writeLock().lock();
 767                 try {
 768                         recipientPosts.put(recipientId, posts);
 769                 } finally {
 770                         lock.writeLock().unlock();
 771                 }
 772
 773                 return posts;
 774         }
 775
 776         /** Loads the known posts. */
 777         private void loadKnownPosts() {
 778                 lock.writeLock().lock();
 779                 try {
 780                         int postCounter = 0;
 781                         while (true) {
 782                                 String knownPostId = configuration.getStringValue("KnownPosts/" + postCounter++ + "/ID").getValue(null);
 783                                 if (knownPostId == null) {
 784                                         break;
 785                                 }
 786                                 knownPosts.add(knownPostId);
 787                         }
 788                 } finally {
 789                         lock.writeLock().unlock();
 790                 }
 791         }
 792
 793         /**
 794          * Saves the known posts to the configuration.
 795          *
 796          * @throws DatabaseException
 797          *              if a configuration error occurs
 798          */
 799         private void saveKnownPosts() throws DatabaseException {
 800                 lock.readLock().lock();
 801                 try {
 802                         int postCounter = 0;
 803                         for (String knownPostId : knownPosts) {
 804                                 configuration.getStringValue("KnownPosts/" + postCounter++ + "/ID").setValue(knownPostId);
 805                         }
 806                         configuration.getStringValue("KnownPosts/" + postCounter + "/ID").setValue(null);
 807                 } catch (ConfigurationException ce1) {
 808                         throw new DatabaseException("Could not save database.", ce1);
 809                 } finally {
 810                         lock.readLock().unlock();
 811                 }
 812         }
 813
 814         /**
 815          * Returns all replies by the given Sone.
 816          *
 817          * @param id
 818          *              The ID of the Sone
 819          * @return The post replies of the Sone, sorted by time (newest first)
 820          */
 821         private Collection<PostReply> getRepliesFrom(String id) {
 822                 lock.readLock().lock();
 823                 try {
 824                         if (sonePostReplies.containsKey(id)) {
 825                                 return Collections.unmodifiableCollection(sonePostReplies.get(id));
 826                         }
 827                         return Collections.emptySet();
 828                 } finally {
 829                         lock.readLock().unlock();
 830                 }
 831         }
 832
 833         /** Loads the known post replies. */
 834         private void loadKnownPostReplies() {
 835                 lock.writeLock().lock();
 836                 try {
 837                         int replyCounter = 0;
 838                         while (true) {
 839                                 String knownReplyId = configuration.getStringValue("KnownReplies/" + replyCounter++ + "/ID").getValue(null);
 840                                 if (knownReplyId == null) {
 841                                         break;
 842                                 }
 843                                 knownPostReplies.add(knownReplyId);
 844                         }
 845                 } finally {
 846                         lock.writeLock().unlock();
 847                 }
 848         }
 849
 850         /**
 851          * Saves the known post replies to the configuration.
 852          *
 853          * @throws DatabaseException
 854          *              if a configuration error occurs
 855          */
 856         private void saveKnownPostReplies() throws DatabaseException {
 857                 lock.readLock().lock();
 858                 try {
 859                         int replyCounter = 0;
 860                         for (String knownReplyId : knownPostReplies) {
 861                                 configuration.getStringValue("KnownReplies/" + replyCounter++ + "/ID").setValue(knownReplyId);
 862                         }
 863                         configuration.getStringValue("KnownReplies/" + replyCounter + "/ID").setValue(null);
 864                 } catch (ConfigurationException ce1) {
 865                         throw new DatabaseException("Could not save database.", ce1);
 866                 } finally {
 867                         lock.readLock().unlock();
 868                 }
 869         }
 870
 871         private Function<String, Iterable<Album>> getAlbum() {
 872                 return new Function<String, Iterable<Album>>() {
 873                         @Override
 874                         public Iterable<Album> apply(String input) {
 875                                 return (input == null) ? Collections.<Album>emptyList() : getAlbum(input).asSet();
 876                         }
 877                 };
 878         }
 879
 880         private Function<String, Iterable<Image>> getImage() {
 881                 return new Function<String, Iterable<Image>>() {
 882                         @Override
 883                         public Iterable<Image> apply(String input) {
 884                                 return (input == null) ? Collections.<Image>emptyList() : getImage(input).asSet();
 885                         }
 886                 };
 887         }
 888
 889 }