public class

CachingHttpClient

extends Object
implements HttpClient
java.lang.Object
   ↳ org.apache.http.impl.client.cache.CachingHttpClient

Class Overview

The CachingHttpClient is meant to be a drop-in replacement for a DefaultHttpClient that transparently adds client-side caching. The current implementation is conditionally compliant with HTTP/1.1 (meaning all the MUST and MUST NOTs are obeyed), although quite a lot, though not all, of the SHOULDs and SHOULD NOTs are obeyed too. Generally speaking, you construct a CachingHttpClient by providing a "backend" HttpClient used for making actual network requests and provide an HttpCacheStorage instance to use for holding onto cached responses. Additional configuration options can be provided by passing in a CacheConfig. Note that all of the usual client related configuration you want to do vis-a-vis timeouts and connection pools should be done on this backend client before constructing a CachingHttpClient from it.

Generally speaking, the CachingHttpClient is implemented as a Decorator of the backend client; for any incoming request it attempts to satisfy it from the cache, but if it can't, or if it needs to revalidate a stale cache entry, it will use the backend client to make an actual request. However, a proper HTTP/1.1 cache won't change the semantics of a request and response; in particular, if you issue an unconditional request you will get a full response (although it may be served to you from the cache, or the cache may make a conditional request on your behalf to the origin). This notion of "semantic transparency" means you should be able to drop a CachingHttpClient into an existing application without breaking anything.

Folks that would like to experiment with alternative storage backends should look at the HttpCacheStorage interface and the related package documentation there. You may also be interested in the provided EhCache and memcached storage backends.

Summary

Constants
String CACHE_RESPONSE_STATUS This is the name under which the CacheResponseStatus of a request (for example, whether it resulted in a cache hit) will be recorded if an HttpContext is provided during execution.
Public Constructors
CachingHttpClient()
Constructs a CachingHttpClient with default caching settings that stores cache entries in memory and uses a vanilla DefaultHttpClient for backend requests.
CachingHttpClient(CacheConfig config)
Constructs a CachingHttpClient with the given caching options that stores cache entries in memory and uses a vanilla DefaultHttpClient for backend requests.
CachingHttpClient(HttpClient client)
Constructs a CachingHttpClient with default caching settings that stores cache entries in memory and uses the given HttpClient for backend requests.
CachingHttpClient(HttpClient client, CacheConfig config)
Constructs a CachingHttpClient with the given caching options that stores cache entries in memory and uses the given HttpClient for backend requests.
CachingHttpClient(HttpClient client, ResourceFactory resourceFactory, HttpCacheStorage storage, CacheConfig config)
Constructs a CachingHttpClient with the given caching options that stores cache entries in the provided storage backend and uses the given HttpClient for backend requests.
CachingHttpClient(HttpClient client, HttpCacheStorage storage, CacheConfig config)
Constructs a CachingHttpClient with the given caching options that stores cache entries in the provided storage backend and uses the given HttpClient for backend requests.
Public Methods
HttpResponse execute(HttpUriRequest request)
<T> T execute(HttpHost target, HttpRequest request, ResponseHandler<? extends T> responseHandler, HttpContext context)
HttpResponse execute(HttpUriRequest request, HttpContext context)
<T> T execute(HttpUriRequest request, ResponseHandler<? extends T> responseHandler)
<T> T execute(HttpHost target, HttpRequest request, ResponseHandler<? extends T> responseHandler)
<T> T execute(HttpUriRequest request, ResponseHandler<? extends T> responseHandler, HttpContext context)
HttpResponse execute(HttpHost target, HttpRequest request)
HttpResponse execute(HttpHost target, HttpRequest request, HttpContext context)
long getCacheHits()
Reports the number of times that the cache successfully responded to an HttpRequest without contacting the origin server.
long getCacheMisses()
Reports the number of times that the cache contacted the origin server because it had no appropriate response cached.
long getCacheUpdates()
Reports the number of times that the cache was able to satisfy a response by revalidating an existing but stale cache entry.
ClientConnectionManager getConnectionManager()
HttpParams getParams()
boolean isSharedCache()
Reports whether this CachingHttpClient is configured as a shared (public) or non-shared (private) cache.
boolean supportsRangeAndContentRangeHeaders()
Reports whether this CachingHttpClient implementation supports byte-range requests as specified by the Range and Content-Range headers.
[Expand]
Inherited Methods
From class java.lang.Object
From interface org.apache.http.client.HttpClient

Constants

public static final String CACHE_RESPONSE_STATUS

This is the name under which the CacheResponseStatus of a request (for example, whether it resulted in a cache hit) will be recorded if an HttpContext is provided during execution.

Constant Value: "http.cache.response.status"

Public Constructors

public CachingHttpClient ()

Constructs a CachingHttpClient with default caching settings that stores cache entries in memory and uses a vanilla DefaultHttpClient for backend requests.

public CachingHttpClient (CacheConfig config)

Constructs a CachingHttpClient with the given caching options that stores cache entries in memory and uses a vanilla DefaultHttpClient for backend requests.

Parameters
config cache module options

public CachingHttpClient (HttpClient client)

Constructs a CachingHttpClient with default caching settings that stores cache entries in memory and uses the given HttpClient for backend requests.

Parameters
client used to make origin requests

public CachingHttpClient (HttpClient client, CacheConfig config)

Constructs a CachingHttpClient with the given caching options that stores cache entries in memory and uses the given HttpClient for backend requests.

Parameters
client used to make origin requests
config cache module options

public CachingHttpClient (HttpClient client, ResourceFactory resourceFactory, HttpCacheStorage storage, CacheConfig config)

Constructs a CachingHttpClient with the given caching options that stores cache entries in the provided storage backend and uses the given HttpClient for backend requests. However, cached response bodies are managed using the given ResourceFactory.

Parameters
client used to make origin requests
resourceFactory how to manage cached response bodies
storage where to store cache entries
config cache module options

public CachingHttpClient (HttpClient client, HttpCacheStorage storage, CacheConfig config)

Constructs a CachingHttpClient with the given caching options that stores cache entries in the provided storage backend and uses the given HttpClient for backend requests.

Parameters
client used to make origin requests
storage where to store cache entries
config cache module options

Public Methods

public HttpResponse execute (HttpUriRequest request)

Throws
IOException

public T execute (HttpHost target, HttpRequest request, ResponseHandler<? extends T> responseHandler, HttpContext context)

Throws
IOException

public HttpResponse execute (HttpUriRequest request, HttpContext context)

Throws
IOException

public T execute (HttpUriRequest request, ResponseHandler<? extends T> responseHandler)

Throws
IOException

public T execute (HttpHost target, HttpRequest request, ResponseHandler<? extends T> responseHandler)

Throws
IOException

public T execute (HttpUriRequest request, ResponseHandler<? extends T> responseHandler, HttpContext context)

Throws
IOException

public HttpResponse execute (HttpHost target, HttpRequest request)

Throws
IOException

public HttpResponse execute (HttpHost target, HttpRequest request, HttpContext context)

Throws
IOException

public long getCacheHits ()

Reports the number of times that the cache successfully responded to an HttpRequest without contacting the origin server.

Returns
  • the number of cache hits

public long getCacheMisses ()

Reports the number of times that the cache contacted the origin server because it had no appropriate response cached.

Returns
  • the number of cache misses

public long getCacheUpdates ()

Reports the number of times that the cache was able to satisfy a response by revalidating an existing but stale cache entry.

Returns
  • the number of cache revalidations

public ClientConnectionManager getConnectionManager ()

public HttpParams getParams ()

public boolean isSharedCache ()

Reports whether this CachingHttpClient is configured as a shared (public) or non-shared (private) cache. See setSharedCache(boolean).

Returns
  • true if we are behaving as a shared (public) cache

public boolean supportsRangeAndContentRangeHeaders ()

Reports whether this CachingHttpClient implementation supports byte-range requests as specified by the Range and Content-Range headers.

Returns
  • true if byte-range requests are supported