DiskLruCache (Disk LRU Cache 2.0.1 API)

java.lang.Object
- com.jakewharton.disklrucache.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.

Nested Class Summary

Nested Classes
Modifier and Type Class and Description

class DiskLruCache.Editor
Edits the values for an entry.

class DiskLruCache.Snapshot
A snapshot of the values for an entry.

Nested Classes
Modifier and Type	Class and Description
`class`	`DiskLruCache.Editor` Edits the values for an entry.
`class`	`DiskLruCache.Snapshot` A snapshot of the values for an entry.

Method Summary

Methods
Modifier and Type	Method and Description
`void`	`close()` Closes this cache.
`void`	`delete()` Closes the cache and deletes all of its stored values.
`DiskLruCache.Editor`	`edit(String key)` Returns an editor for the entry named `key`, or null if another edit is in progress.
`void`	`flush()` Force buffered operations to the filesystem.
`DiskLruCache.Snapshot`	`get(String key)` Returns a snapshot of the entry named `key`, or null if it doesn't exist is not currently readable.
`File`	`getDirectory()` Returns the directory where this cache stores its data.
`long`	`getMaxSize()` Returns the maximum number of bytes that this cache should use to store its data.
`boolean`	`isClosed()` Returns true if this cache has been closed.
`static DiskLruCache`	`open(File directory, int appVersion, int valueCount, long maxSize)` Opens the cache in `directory`, creating a cache if none exists there.
`boolean`	`remove(String key)` Drops the entry for `key` if it exists and can be removed.
`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.
`long`	`size()` Returns the number of bytes currently being used to store the values in this cache.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Method Detail
  - open
```
public static DiskLruCache open(File directory,
                int appVersion,
                int valueCount,
                long maxSize)
                         throws IOException
```
    Opens the cache in directory, creating a cache if none exists there.
    
    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
    
    Throws:
    
    IOException - if reading or writing the cache directory fails
  - 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
  - edit
```
public DiskLruCache.Editor edit(String key)
                         throws IOException
```
    Returns an editor for the entry named key, or null if another edit is in progress.
    
    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()
```
    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.
  - remove
```
public boolean remove(String key)
               throws IOException
```
    Drops the entry for key if it exists and can be removed. Entries actively being edited cannot be removed.
    
    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
  - close
```
public void close()
           throws IOException
```
    Closes this cache. Stored values will remain on the filesystem.
    
    Specified by:
    
    close in interface Closeable
    
    Specified by:
    
    close in interface AutoCloseable
    
    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

Class DiskLruCache

Nested Class Summary

Method Summary

Methods inherited from class java.lang.Object

Method Detail

open

get

edit

getDirectory

getMaxSize

setMaxSize

size

remove

isClosed

flush

close

delete