com.squareup.okhttp

Class Cache

java.lang.Object

com.squareup.okhttp.Cache

public final class Cache
extends Object

Caches HTTP and HTTPS responses to the filesystem so they may be reused, saving time and bandwidth.

Cache Optimization

To measure cache effectiveness, this class tracks three statistics:

• Request Count: the number of HTTP requests issued since this cache was created.
• Network Count: the number of those requests that required network use.
• Hit Count: the number of those requests whose responses were served by the cache.

Sometimes a request will result in a conditional cache hit. If the cache contains a stale copy of the response, the client will issue a conditional GET. The server will then send either the updated response if it has changed, or a short 'not modified' response if the client's copy is still valid. Such responses increment both the network count and hit count.

The best way to improve the cache hit rate is by configuring the web server to return cacheable responses. Although this client honors all HTTP/1.1 (RFC 2068) cache headers, it doesn't cache partial responses.

Force a Network Response

In some situations, such as after a user clicks a 'refresh' button, it may be necessary to skip the cache, and fetch data directly from the server. To force a full refresh, add the no-cache directive:

   connection.addRequestProperty("Cache-Control", "no-cache");
 

If it is only necessary to force a cached response to be validated by the server, use the more efficient max-age=0 instead:

   connection.addRequestProperty("Cache-Control", "max-age=0");
 

Force a Cache Response

Sometimes you'll want to show resources if they are available immediately, but not otherwise. This can be used so your application can show something while waiting for the latest data to be downloaded. To restrict a request to locally-cached resources, add the only-if-cached directive:

   try {
         connection.addRequestProperty("Cache-Control", "only-if-cached");
         InputStream cached = connection.getInputStream();
         // the resource was cached! show it
     } catch (FileNotFoundException e) {
         // the resource was not cached
     }
 

This technique works even better in situations where a stale response is better than no response. To permit stale cached responses, use the max-stale directive with the maximum staleness in seconds:

   int maxStale = 60 * 60 * 24 * 28; // tolerate 4-weeks stale
         connection.addRequestProperty("Cache-Control", "max-stale=" + maxStale);
 

Constructor Summary

Constructors

Constructor and Description
Cache(File directory, long maxSize)

Method Summary

Methods

Modifier and Type	Method and Description
void	close()
void	delete() Closes the cache and deletes all of its stored values.
void	flush()
File	getDirectory()
int	getHitCount()
long	getMaxSize()
int	getNetworkCount()
int	getRequestCount()
long	getSize()
int	getWriteAbortCount()
int	getWriteSuccessCount()
boolean	isClosed()

Methods inherited from class java.lang.Object

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

Constructor Detail

Cache

public Cache(File directory,
     long maxSize)
      throws IOException

Throws:

IOException

Method Detail

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

getWriteAbortCount

public int getWriteAbortCount()

getWriteSuccessCount

public int getWriteSuccessCount()

getSize

public long getSize()

getMaxSize

public long getMaxSize()

flush

public void flush()
           throws IOException

Throws:

IOException

close

public void close()
           throws IOException

Throws:

IOException

getDirectory

public File getDirectory()

isClosed

public boolean isClosed()

getNetworkCount

public int getNetworkCount()

getHitCount

public int getHitCount()

getRequestCount

public int getRequestCount()