DiskCacheStrategy.java

package com.bumptech.glide.load.engine;

import com.bumptech.glide.load.DataSource;
import com.bumptech.glide.load.EncodeStrategy;

/**
 * Set of available caching strategies for media.
 */
public abstract class DiskCacheStrategy {

  /**
   * Caches remote data with both {@link #DATA} and {@link #RESOURCE}, and local data with
   * {@link #RESOURCE} only.
   */
  public static final DiskCacheStrategy ALL = new DiskCacheStrategy() {
    @Override
    public boolean isDataCacheable(DataSource dataSource) {
      return dataSource == DataSource.REMOTE;
    }

    @Override
    public boolean isResourceCacheable(boolean isFromAlternateCacheKey, DataSource dataSource,
        EncodeStrategy encodeStrategy) {
      return dataSource != DataSource.RESOURCE_DISK_CACHE && dataSource != DataSource.MEMORY_CACHE;
    }

    @Override
    public boolean decodeCachedResource() {
      return true;
    }

    @Override
    public boolean decodeCachedData() {
      return true;
    }
  };

  /**
   * Saves no data to cache.
   */
  public static final DiskCacheStrategy NONE = new DiskCacheStrategy() {
    @Override
    public boolean isDataCacheable(DataSource dataSource) {
      return false;
    }

    @Override
    public boolean isResourceCacheable(boolean isFromAlternateCacheKey, DataSource dataSource,
        EncodeStrategy encodeStrategy) {
      return false;
    }

    @Override
    public boolean decodeCachedResource() {
      return false;
    }

    @Override
    public boolean decodeCachedData() {
      return false;
    }
  };

  /**
   * Writes retrieved data directly to the disk cache before it's decoded.
   */
  public static final DiskCacheStrategy DATA = new DiskCacheStrategy() {
    @Override
    public boolean isDataCacheable(DataSource dataSource) {
      return dataSource != DataSource.DATA_DISK_CACHE && dataSource != DataSource.MEMORY_CACHE;
    }

    @Override
    public boolean isResourceCacheable(boolean isFromAlternateCacheKey, DataSource dataSource,
        EncodeStrategy encodeStrategy) {
      return false;
    }

    @Override
    public boolean decodeCachedResource() {
      return false;
    }

    @Override
    public boolean decodeCachedData() {
      return true;
    }
  };

  /**
   * Writes resources to disk after they've been decoded.
   */
  public static final DiskCacheStrategy RESOURCE = new DiskCacheStrategy() {
    @Override
    public boolean isDataCacheable(DataSource dataSource) {
      return false;
    }

    @Override
    public boolean isResourceCacheable(boolean isFromAlternateCacheKey, DataSource dataSource,
        EncodeStrategy encodeStrategy) {
      return dataSource != DataSource.RESOURCE_DISK_CACHE && dataSource != DataSource.MEMORY_CACHE;
    }

    @Override
    public boolean decodeCachedResource() {
      return true;
    }

    @Override
    public boolean decodeCachedData() {
      return false;
    }
  };

  /**
   * Tries to intelligently choose a strategy based on the data source of the
   * {@link com.bumptech.glide.load.data.DataFetcher} and the
   * {@link com.bumptech.glide.load.EncodeStrategy} of the
   * {@link com.bumptech.glide.load.ResourceEncoder} (if an
   * {@link com.bumptech.glide.load.ResourceEncoder} is available).
   */
  public static final DiskCacheStrategy AUTOMATIC = new DiskCacheStrategy() {
    @Override
    public boolean isDataCacheable(DataSource dataSource) {
      return dataSource == DataSource.REMOTE;
    }

    @Override
    public boolean isResourceCacheable(boolean isFromAlternateCacheKey, DataSource dataSource,
        EncodeStrategy encodeStrategy) {
      return ((isFromAlternateCacheKey && dataSource == DataSource.DATA_DISK_CACHE)
          || dataSource == DataSource.LOCAL)
          && encodeStrategy == EncodeStrategy.TRANSFORMED;
    }

    @Override
    public boolean decodeCachedResource() {
      return true;
    }

    @Override
    public boolean decodeCachedData() {
      return true;
    }
  };

  /**
   * Returns true if this request should cache the original unmodified data.
   *
   * @param dataSource Indicates where the data was originally retrieved.
   */
  public abstract boolean isDataCacheable(DataSource dataSource);

  /**
   * Returns true if this request should cache the final transformed resource.
   *
   * @param isFromAlternateCacheKey {@code true} if the resource we've decoded was loaded using an
   *                                alternative, rather than the primary, cache key.
   * @param dataSource Indicates where the data used to decode the resource was originally
   *                   retrieved.
   * @param encodeStrategy The {@link EncodeStrategy} the {@link
   * com.bumptech.glide.load.ResourceEncoder} will use to encode the resource.
   */
  public abstract boolean isResourceCacheable(boolean isFromAlternateCacheKey,
      DataSource dataSource, EncodeStrategy encodeStrategy);

  /**
   * Returns true if this request should attempt to decode cached resource data.
   */
  public abstract boolean decodeCachedResource();

  /**
   * Returns true if this request should attempt to decode cached source data.
   */
  public abstract boolean decodeCachedData();
}