public final class Cache extends Object
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 7234) cache headers, it doesn't cache partial responses.
no-cache
directive:
Request request = new Request.Builder()
.cacheControl(new CacheControl.Builder().noCache().build())
.url("http://publicobject.com/helloworld.txt")
.build();
If it is only necessary to force a cached response to be validated by the server, use the more
efficient max-age=0
directive instead:
Request request = new Request.Builder()
.cacheControl(new CacheControl.Builder()
.maxAge(0, TimeUnit.SECONDS)
.build())
.url("http://publicobject.com/helloworld.txt")
.build();
only-if-cached
directive:
Request request = new Request.Builder()
.cacheControl(new CacheControl.Builder()
.onlyIfCached()
.build())
.url("http://publicobject.com/helloworld.txt")
.build();
Response forceCacheResponse = client.newCall(request).execute();
if (forceCacheResponse.code() != 504) {
// The resource was cached! Show it.
} else {
// 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:
Request request = new Request.Builder()
.cacheControl(new CacheControl.Builder()
.maxStale(365, TimeUnit.DAYS)
.build())
.url("http://publicobject.com/helloworld.txt")
.build();
The CacheControl
class can configure request caching directives and parse response
caching directives. It even offers convenient constants CacheControl.FORCE_NETWORK
and
CacheControl.FORCE_CACHE
that address the use cases above.
Modifier and Type | Method and Description |
---|---|
void |
close() |
void |
delete()
Closes the cache and deletes all of its stored values.
|
void |
evictAll()
Deletes all values stored in the cache.
|
void |
flush() |
File |
getDirectory() |
int |
getHitCount() |
long |
getMaxSize() |
int |
getNetworkCount() |
int |
getRequestCount() |
long |
getSize() |
int |
getWriteAbortCount() |
int |
getWriteSuccessCount() |
void |
initialize()
Initialize the cache.
|
boolean |
isClosed() |
Iterator<String> |
urls()
Returns an iterator over the URLs in this cache.
|
public Cache(File directory, long maxSize)
public void initialize() throws IOException
The initialization time may vary depending on the journal file size and the current actual cache size. The application needs to be aware of calling this function during the initialization phase and preferably in a background worker thread.
Note that if the application chooses to not call this method to initialize the cache. By default, the okhttp will perform lazy initialization upon the first usage of the cache.
IOException
public void delete() throws IOException
IOException
public void evictAll() throws IOException
IOException
public Iterator<String> urls() throws IOException
ConcurrentModificationException
, but if new responses are added while iterating, their URLs
will not be returned. If existing responses are evicted during iteration, they will be absent
(unless they were already returned).
The iterator supports Iterator.remove(). Removing a URL from the iterator evicts the corresponding response from the cache. Use this to evict selected responses.
IOException
public int getWriteAbortCount()
public int getWriteSuccessCount()
public long getSize() throws IOException
IOException
public long getMaxSize()
public void flush() throws IOException
IOException
public void close() throws IOException
IOException
public File getDirectory()
public boolean isClosed()
public int getNetworkCount()
public int getHitCount()
public int getRequestCount()
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