Package 

Class DiskLruCache

  • All Implemented Interfaces:
    java.io.Closeable , java.io.Flushable , java.lang.AutoCloseable 
    
public final class DiskLruCache
 implements Closeable, Flushable

    A cache that uses a bounded amount of space on a filesystem. Each cache entry has a string key and a fixed number of values. Each key must match the regex [a-z0-9_-]{1,64}. Values are byte sequences, accessible as streams or files. Each value must be between {@code 0} and {@code Integer.MAX_VALUE} bytes in length.

    The cache stores its data in a directory on the filesystem. This directory must be exclusive to the cache; the cache may delete or overwrite files from its directory. It is an error for multiple processes to use the same cache directory at the same time.

    This cache limits the number of bytes that it will store on the filesystem. When the number of stored bytes exceeds the limit, the cache will remove entries in the background until the limit is satisfied. The limit is not strict: the cache may temporarily exceed it while waiting for files to be deleted. The limit does not include filesystem overhead or the cache journal so space-sensitive applications should set a conservative limit.

    Clients call edit to create or update the values of an entry. An entry may have only one editor at one time; if a value is not available to be edited then edit will return null.

    • When an entry is being created it is necessary to supply a full set of values; the empty value should be used as a placeholder if necessary.
    • When an entry is being edited, it is not necessary to supply data for every value; values default to their previous value.

    Every edit call must be matched by a call to commit or . Committing is atomic: a read observes the full set of values as they were before or after the commit, but never a mix of values.

    Clients call get to read a snapshot of an entry. The read will observe the value at the time that get was called. Updates and removals after the call do not impact ongoing reads.

    This class is tolerant of some I/O errors. If files are missing from the filesystem, the corresponding entries will be dropped from the cache. If an error occurs while writing a cache value, the edit will fail silently. Callers should handle other problems by catching {@code * IOException} and responding appropriately.

    • Nested Class Summary

      Nested Classes 
      Modifier and Type Class Description
      public final class DiskLruCache.Snapshot

      A snapshot of the values for an entry.
      public final class DiskLruCache.Editor

      Edits the values for an entry.

    • Method Summary

      Modifier and Type Method Description
      File getDirectory() Returns the directory where this cache stores its data.
      synchronized long getMaxSize() Returns the maximum number of bytes that this cache should use to store its data.
      synchronized void setMaxSize(long maxSize) Changes the maximum number of bytes the cache can store and queues a job to trim the existingstore, if necessary.
      synchronized void initialize()
      static DiskLruCache create(FileSystem fileSystem, File directory, int appVersion, int valueCount, long maxSize) Create a cache which will reside in {@code directory}.
      synchronized DiskLruCache.Snapshot get(String key) Returns a snapshot of the entry named {@code key}, or null if it doesn't exist is not currentlyreadable.
      DiskLruCache.Editor edit(String key) Returns an editor for the entry named {@code key}, or null if another edit is in progress.
      synchronized long size() Returns the number of bytes currently being used to store the values in this cache.
      synchronized boolean remove(String key) Drops the entry for {@code key} if it exists and can be removed.
      synchronized boolean isClosed() Returns true if this cache has been closed.
      synchronized void flush() Force buffered operations to the filesystem.
      synchronized void close() Closes this cache.
      void delete() Closes the cache and deletes all of its stored values.
      synchronized void evictAll() Deletes all stored values from the cache.
      synchronized Iterator<DiskLruCache.Snapshot> snapshots() Returns an iterator over the cache's current entries.

      • Methods inherited from class java.io.Closeable

        close

      • Methods inherited from class java.io.Flushable

        flush

      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Method Detail

      • getDirectory

         File getDirectory()

        Returns the directory where this cache stores its data.

      • getMaxSize

         synchronized long getMaxSize()

        Returns the maximum number of bytes that this cache should use to store its data.

      • setMaxSize

         synchronized void setMaxSize(long maxSize)

        Changes the maximum number of bytes the cache can store and queues a job to trim the existingstore, if necessary.

      • create

         static DiskLruCache create(FileSystem fileSystem, File directory, int appVersion, int valueCount, long maxSize)

        Create a cache which will reside in {@code directory}. This cache is lazily initialized onfirst access and will be created if it does not exist.

        Parameters:
        directory - a writable directory
        valueCount - the number of values per cache entry.
        maxSize - the maximum number of bytes this cache should use to store

      • get

         synchronized DiskLruCache.Snapshot get(String key)

        Returns a snapshot of the entry named {@code key}, or null if it doesn't exist is not currentlyreadable. If a value is returned, it is moved to the head of the LRU queue.

      • size

         synchronized long size()

        Returns the number of bytes currently being used to store the values in this cache. This may begreater than the max size if a background deletion is pending.

      • remove

         synchronized boolean remove(String key)

        Drops the entry for {@code key} if it exists and can be removed. If the entry for {@code key} is currently being edited, that edit will complete normally but its value will not be stored.

      • isClosed

         synchronized boolean isClosed()

        Returns true if this cache has been closed.

      • flush

         synchronized void flush()

        Force buffered operations to the filesystem.

      • close

         synchronized void close()

        Closes this cache. Stored values will remain on the filesystem.

      • delete

         void delete()

        Closes the cache and deletes all of its stored values. This will delete all files in the cachedirectory including files that weren't created by the cache.

      • evictAll

         synchronized void evictAll()

        Deletes all stored values from the cache. In-flight edits will complete normally but theirvalues will not be stored.

      • snapshots

         synchronized Iterator<DiskLruCache.Snapshot> snapshots()

        Returns an iterator over the cache's current entries. This iterator doesn't throw {@code * ConcurrentModificationException}, but if new entries are added while iterating, those newentries will not be returned by the iterator. If existing entries are removed during iteration,they will be absent (unless they were already returned).

        If there are I/O problems during iteration, this iterator fails silently. For example, ifthe hosting filesystem becomes unreachable, the iterator will omit elements rather thanthrowing exceptions.

        The caller must close each snapshot returned by next. Failing to do so leaks open files!

        The returned iterator supports remove.