An HTTP cookie is a token or short packet of state information that the HTTP agent and the target server can exchange to maintain a session. Netscape engineers used to refer to it as a "magic cookie" and the name stuck.

HttpClient uses the Cookie interface to represent an abstract cookie token. In its simplest form an HTTP cookie is merely a name / value pair. Usually an HTTP cookie also contains a number of attributes such a domain for which is valid, a path that specifies the subset of URLs on the origin server to which this cookie applies, and the maximum period of time for which the cookie is valid.

The SetCookie interface represents a Set-Cookie response header sent by the origin server to the HTTP agent in order to maintain a conversational state.

The ClientCookie interface extends Cookie interface with additional client specific functionality such as the ability to retrieve original cookie attributes exactly as they were specified by the origin server. This is important for generating the Cookie header because some cookie specifications require that the Cookie header should include certain attributes only if they were specified in the Set-Cookie header.

Here is an example of creating a client-side cookie object:

BasicClientCookie cookie = new BasicClientCookie("name", "value");
// Set effective domain and path attributes
cookie.setDomain(".mycompany.com");
cookie.setPath("/");
// Set attributes exactly as sent by the server
cookie.setAttribute(ClientCookie.PATH_ATTR, "/");
cookie.setAttribute(ClientCookie.DOMAIN_ATTR, ".mycompany.com");

The CookieSpec interface represents a cookie management specification. The cookie management specification is expected to enforce:

HttpClient ships with several CookieSpec implementations:

It is strongly recommended to use either Standard or Standard strict policy in new applications. Obsolete specifications should be used for compatibility with legacy systems only. Support for obsolete specifications will be removed in the next major release of HttpClient.

Cookie policy can be set at the HTTP client and overridden on the HTTP request level if required.

RequestConfig globalConfig = RequestConfig.custom()
        .setCookieSpec(CookieSpecs.DEFAULT)
        .build();
CloseableHttpClient httpclient = HttpClients.custom()
        .setDefaultRequestConfig(globalConfig)
        .build();
RequestConfig localConfig = RequestConfig.copy(globalConfig)
        .setCookieSpec(CookieSpecs.STANDARD_STRICT)
        .build();
HttpGet httpGet = new HttpGet("/");
httpGet.setConfig(localConfig);

In order to implement a custom cookie policy one should create a custom implementation of the CookieSpec interface, create a CookieSpecProvider implementation to create and initialize instances of the custom specification and register the factory with HttpClient. Once the custom specification has been registered, it can be activated the same way as a standard cookie specification.

PublicSuffixMatcher publicSuffixMatcher = PublicSuffixMatcherLoader.getDefault();

Registry<CookieSpecProvider> r = RegistryBuilder.<CookieSpecProvider>create()
        .register(CookieSpecs.DEFAULT,
                new DefaultCookieSpecProvider(publicSuffixMatcher))
        .register(CookieSpecs.STANDARD,
                new RFC6265CookieSpecProvider(publicSuffixMatcher))
        .register("easy", new EasySpecProvider())
        .build();

RequestConfig requestConfig = RequestConfig.custom()
        .setCookieSpec("easy")
        .build();

CloseableHttpClient httpclient = HttpClients.custom()
        .setDefaultCookieSpecRegistry(r)
        .setDefaultRequestConfig(requestConfig)
        .build();

HttpClient can work with any physical representation of a persistent cookie store that implements the CookieStore interface. The default CookieStore implementation called BasicCookieStore is a simple implementation backed by a java.util.ArrayList. Cookies stored in an BasicClientCookie object are lost when the container object get garbage collected. Users can provide more complex implementations if necessary.

// Create a local instance of cookie store
CookieStore cookieStore = new BasicCookieStore();
// Populate cookies if needed
BasicClientCookie cookie = new BasicClientCookie("name", "value");
cookie.setDomain(".mycompany.com");
cookie.setPath("/");
cookieStore.addCookie(cookie);
// Set the store
CloseableHttpClient httpclient = HttpClients.custom()
        .setDefaultCookieStore(cookieStore)
        .build();

In the course of HTTP request execution HttpClient adds the following state management related objects to the execution context:

The local HttpContext object can be used to customize the HTTP state management context prior to request execution, or to examine its state after the request has been executed. One can also use separate execution contexts in order to implement per user (or per thread) state management. A cookie specification registry and cookie store defined in the local context will take precedence over the default ones set at the HTTP client level

CloseableHttpClient httpclient = <...>

Lookup<CookieSpecProvider> cookieSpecReg = <...>
CookieStore cookieStore = <...>

HttpClientContext context = HttpClientContext.create();
context.setCookieSpecRegistry(cookieSpecReg);
context.setCookieStore(cookieStore);
HttpGet httpget = new HttpGet("http://somehost/");
CloseableHttpResponse response1 = httpclient.execute(httpget, context);
<...>
// Cookie origin details
CookieOrigin cookieOrigin = context.getCookieOrigin();
// Cookie spec used
CookieSpec cookieSpec = context.getCookieSpec();