java/src/main/com/google/appengine/api/blobstore/BlobInfoFactory.java

   1 // Copyright 2009 Google Inc. All Rights Reserved.
   2
   3 package com.google.appengine.api.blobstore;
   4
   5 import com.google.appengine.api.NamespaceManager;
   6 import com.google.appengine.api.blobstore.BlobKey;
   7 import com.google.appengine.api.datastore.DatastoreService;
   8 import com.google.appengine.api.datastore.DatastoreServiceFactory;
   9 import com.google.appengine.api.datastore.Entity;
  10 import com.google.appengine.api.datastore.EntityNotFoundException;
  11 import com.google.appengine.api.datastore.Key;
  12 import com.google.appengine.api.datastore.KeyFactory;
  13 import com.google.appengine.api.datastore.Query;
  14
  15 import java.util.Date;
  16 import java.util.Iterator;
  17
  18 /**
  19  * {@code BlobInfoFactory} provides a trivial interface for retrieving
  20  * {@link BlobInfo} metadata.
  21  *
  22  * <p>BlobInfo metadata is stored in read-only {@code __BlobInfo__}
  23  * entities in the datastore.  This class provides an easy way to
  24  * access these entities.  For more complex queries, you can use the
  25  * datastore directly.
  26  *
  27  */
  28 public class BlobInfoFactory {
  29   public static final String KIND = "__BlobInfo__";
  30   public static final String CONTENT_TYPE = "content_type";
  31   public static final String CREATION = "creation";
  32   public static final String FILENAME = "filename";
  33   public static final String SIZE = "size";
  34   public static final String MD5_HASH = "md5_hash";
  35
  36   private final DatastoreService datastoreService;
  37
  38   /**
  39    * Creates a {@code BlobInfoFactory} that uses the default
  40    * implementation of {@link DatastoreService}.
  41    */
  42   public BlobInfoFactory() {
  43     this(DatastoreServiceFactory.getDatastoreService());
  44   }
  45
  46   /**
  47    * Creates a {@code BlobInfoFactory} with the specified
  48    * implementation of {@link DatastoreService}.
  49    */
  50   public BlobInfoFactory(DatastoreService datastoreService) {
  51     this.datastoreService = datastoreService;
  52   }
  53
  54   /**
  55    * Loads the {@link BlobInfo} metadata for {@code blobKey}.  Returns
  56    * {@code null} if no matching blob is found.
  57    */
  58   public BlobInfo loadBlobInfo(BlobKey blobKey) {
  59     try {
  60       return createBlobInfo(datastoreService.get(getMetadataKeyForBlobKey(blobKey)));
  61     } catch (EntityNotFoundException ex) {
  62       return null;
  63     }
  64   }
  65
  66   /**
  67    * Queries for {@link BlobInfo} instances, beginning with the {@link
  68    * BlobKey} that appears first in lexicographic order.
  69    */
  70   public Iterator<BlobInfo> queryBlobInfos() {
  71     return queryBlobInfosAfter(null);
  72   }
  73
  74   /**
  75    * Queries for {@link BlobInfo} instances, beginning at the blob
  76    * following {@code previousBlob} in lexicographic order.  If {@code
  77    * previousBlob} is null, the first blob will be returned.
  78    *
  79    * <p>This is useful for displaying discrete pages of blobs.
  80    */
  81   public Iterator<BlobInfo> queryBlobInfosAfter(BlobKey previousBlob) {
  82     String origNamespace = NamespaceManager.get();
  83     Query query;
  84     try {
  85       NamespaceManager.set("");
  86       query = new Query(KIND, null);
  87     } finally {
  88       NamespaceManager.set(origNamespace);
  89     }
  90
  91     if (previousBlob != null) {
  92       query.addFilter(Entity.KEY_RESERVED_PROPERTY,
  93                       Query.FilterOperator.GREATER_THAN,
  94                       getMetadataKeyForBlobKey(previousBlob));
  95     }
  96
  97     final Iterator<Entity> parent = datastoreService.prepare(query).asIterator();
  98
  99     return new Iterator<BlobInfo>() {
 100       public boolean hasNext() {
 101         return parent.hasNext();
 102       }
 103
 104       public BlobInfo next() {
 105         return createBlobInfo(parent.next());
 106       }
 107
 108       public void remove() {
 109         throw new UnsupportedOperationException();
 110       }
 111     };
 112   }
 113
 114   /**
 115    * Creates a {@link BlobInfo} by extracting content from the
 116    * specified {@link Entity}.
 117    */
 118   public BlobInfo createBlobInfo(Entity entity) {
 119     if (entity.hasProperty(MD5_HASH)) {
 120       return new BlobInfo(
 121           new BlobKey(entity.getKey().getName()),
 122           (String) entity.getProperty(CONTENT_TYPE),
 123           (Date) entity.getProperty(CREATION),
 124           (String) entity.getProperty(FILENAME),
 125           (Long) entity.getProperty(SIZE),
 126           (String) entity.getProperty(MD5_HASH));
 127     } else {
 128       return new BlobInfo(
 129           new BlobKey(entity.getKey().getName()),
 130           (String) entity.getProperty(CONTENT_TYPE),
 131           (Date) entity.getProperty(CREATION),
 132           (String) entity.getProperty(FILENAME),
 133           (Long) entity.getProperty(SIZE));
 134     }
 135   }
 136
 137   private Key getMetadataKeyForBlobKey(BlobKey blobKey) {
 138     String origNamespace = NamespaceManager.get();
 139     try {
 140       NamespaceManager.set("");
 141       return KeyFactory.createKey(null, KIND, blobKey.getKeyString());
 142     } finally {
 143       NamespaceManager.set(origNamespace);
 144     }
 145   }
 146 }