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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html><head><title>HttpClient - Head Method</title><style type="text/css" media="all">
@import url("../style/maven-base.css");
@import url("../style/maven-theme.css");@import url("../style/project.css");</style><link rel="stylesheet" href="../style/print.css" type="text/css" media="print"></link><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"></meta><meta name="author" content="Adrian Sutton"></meta><meta name="email" content="adrian@ephox.com"></meta></head><body class="composite"><div id="banner"><a href="http://jakarta.apache.org/" id="organizationLogo"><img alt="Apache Software Foundation" src="http://jakarta.apache.org/images/jakarta-logo.gif"></img></a><a href="http://jakarta.apache.org/httpcomponents/httpclient-3.x/" id="projectLogo"><img alt="HttpClient" src="../images/httpclient_logo.png"></img></a><div class="clear"><hr></hr></div></div><div id="breadcrumbs"><div class="xleft">Last published: 18 August 2007
<span class="separator">|</span>Doc for 3.1
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<p>The HEAD method is identical to the <a href="get.html">GET</a> method
except that the server <i>must not</i> return a message-body in the
response. The metainformation contained in the HTTP headers in response
to a HEAD request <i>should</i> be identical to the information sent in
response to a GET request. This allows a client to obtain
meta-information about a resource without actually transferring the
resource itself.</p>
<p>The head method is often used for testing hyperlinks, accessibility
and for determining if a document has been recently modifed.</p>
<p>When your program is implementing caching, it is important to note
that if the HEAD response indicates that the cached entity differs from
the current entity, such as by a change in the Content-Length,
Content-MD5, ETag or Last-Modified, the cache <b>must</b> treat the
cached entry as stale.</p>
</div><div class="section"><a name="Typical_Usage"></a><h2>Typical Usage</h2>
<p>Typically the head method is used to retrieve the meta-information for
a resource, perhaps to check if the resource has been modifed. There are
no methods specific to HeadMethod as the headers can be retreived using
<code>getResponseHeaders()</code> as with any other method.</p>
<div class="source"><pre>
HeadMethod head = new HeadMethod("http://jakarta.apache.org");
// execute the method and handle any error responses.
...
// Retrieve all the headers.
Header[] headers = head.getResponseHeaders();
// Retrieve just the last modified header value.
String lastModified =
head.getResponseHeader("last-modified").getValue();
</pre></div>
</div><div class="section"><a name="Common_Problems"></a><h2>Common Problems</h2>
<p>None.</p>
</div><div class="section"><a name="RFC_Section"></a><h2>RFC Section</h2>
<p>The head method is defined in section 8.2 of <a href="http://www.ietf.org/rfc/rfc1945.txt" class="externalLink" title="External Link">RFC1945</a> and similarly
redefined for HTTP 1.1 in section 9.4 of <a href="http://www.ietf.org/rfc/rfc2616.txt" class="externalLink" title="External Link">RFC2616</a>.</p>
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