Package com.squareup.okhttp.internal

Class DiskLruCache

  • All Implemented Interfaces:
    Closeable, AutoCloseable
    public final class DiskLruCache
extends Object
implements Closeable
    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 0 and 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(java.lang.String) 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(java.lang.String) 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(java.lang.String) call must be matched by a call to DiskLruCache.Editor.commit() or DiskLruCache.Editor.abort(). 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(java.lang.String) to read a snapshot of an entry. The read will observe the value at the time that get(java.lang.String) 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 IOException and responding appropriately.

    • Method Detail

      • create

        public static DiskLruCache create​(FileSystem fileSystem,
                                  File directory,
                                  int appVersion,
                                  int valueCount,
                                  long maxSize)
        Create a cache which will reside in directory. This cache is lazily initialized on first access and will be created if it does not exist.
        Parameters:
        directory - a writable directory
        valueCount - the number of values per cache entry. Must be positive.
        maxSize - the maximum number of bytes this cache should use to store

      • get

        public DiskLruCache.Snapshot get​(String key)
                          throws IOException
        Returns a snapshot of the entry named key, or null if it doesn't exist is not currently readable. If a value is returned, it is moved to the head of the LRU queue.
        Throws:
        IOException

      • getDirectory

        public File getDirectory()
        Returns the directory where this cache stores its data.

      • getMaxSize

        public long getMaxSize()
        Returns the maximum number of bytes that this cache should use to store its data.

      • setMaxSize

        public void setMaxSize​(long maxSize)
        Changes the maximum number of bytes the cache can store and queues a job to trim the existing store, if necessary.

      • size

        public long size()
          throws IOException
        Returns the number of bytes currently being used to store the values in this cache. This may be greater than the max size if a background deletion is pending.
        Throws:
        IOException

      • remove

        public boolean remove​(String key)
               throws IOException
        Drops the entry for key if it exists and can be removed. If the entry for key is currently being edited, that edit will complete normally but its value will not be stored.
        Returns:
        true if an entry was removed.
        Throws:
        IOException

      • isClosed

        public boolean isClosed()
        Returns true if this cache has been closed.

      • flush

        public void flush()
           throws IOException
        Force buffered operations to the filesystem.
        Throws:
        IOException

      • delete

        public void delete()
            throws IOException
        Closes the cache and deletes all of its stored values. This will delete all files in the cache directory including files that weren't created by the cache.
        Throws:
        IOException

      • evictAll

        public void evictAll()
              throws IOException
        Deletes all stored values from the cache. In-flight edits will complete normally but their values will not be stored.
        Throws:
        IOException

      • snapshots

        public Iterator<DiskLruCache.Snapshot> snapshots()
                                          throws IOException
        Returns an iterator over the cache's current entries. This iterator doesn't throw ConcurrentModificationException, but if new entries are added while iterating, those new entries 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, if the hosting filesystem becomes unreachable, the iterator will omit elements rather than throwing exceptions.

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

        The returned iterator supports Iterator.remove().

        Throws:
        IOException