DefaultConnectionReuseStrategypublic class DefaultConnectionReuseStrategy extends Object implements ConnectionReuseStrategy| Default implementation of a strategy deciding about connection re-use.
The default implementation first checks some basics, for example
whether the connection is still open or whether the end of the
request entity can be determined without closing the connection.
If these checks pass, the tokens in the "Connection" header will
be examined. In the absence of a "Connection" header, the
non-standard but commonly used "Proxy-Connection" header takes
it's role. A token "close" indicates that the connection cannot
be reused. If there is no such token, a token "keep-alive" indicates
that the connection should be re-used. If neither token is found,
or if there are no "Connection" headers, the default policy for
the HTTP version is applied. Since HTTP/1.1, connections are re-used
by default. Up until HTTP/1.0, connections are not re-used by default. |
| Constructors Summary |
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public DefaultConnectionReuseStrategy()
super();
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| Methods Summary |
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| protected org.apache.http.TokenIterator | createTokenIterator(org.apache.http.HeaderIterator hit)Creates a token iterator from a header iterator.
This method can be overridden to replace the implementation of
the token iterator.
return new BasicTokenIterator(hit);
| | public boolean | keepAlive(org.apache.http.HttpResponse response, org.apache.http.protocol.HttpContext context)
if (response == null) {
throw new IllegalArgumentException
("HTTP response may not be null.");
}
if (context == null) {
throw new IllegalArgumentException
("HTTP context may not be null.");
}
HttpConnection conn = (HttpConnection)
context.getAttribute(ExecutionContext.HTTP_CONNECTION);
if (conn != null && !conn.isOpen())
return false;
// do NOT check for stale connection, that is an expensive operation
// Check for a self-terminating entity. If the end of the entity will
// be indicated by closing the connection, there is no keep-alive.
HttpEntity entity = response.getEntity();
ProtocolVersion ver = response.getStatusLine().getProtocolVersion();
if (entity != null) {
if (entity.getContentLength() < 0) {
if (!entity.isChunked() ||
ver.lessEquals(HttpVersion.HTTP_1_0)) {
// if the content length is not known and is not chunk
// encoded, the connection cannot be reused
return false;
}
}
}
// Check for the "Connection" header. If that is absent, check for
// the "Proxy-Connection" header. The latter is an unspecified and
// broken but unfortunately common extension of HTTP.
HeaderIterator hit = response.headerIterator(HTTP.CONN_DIRECTIVE);
if (!hit.hasNext())
hit = response.headerIterator("Proxy-Connection");
// Experimental usage of the "Connection" header in HTTP/1.0 is
// documented in RFC 2068, section 19.7.1. A token "keep-alive" is
// used to indicate that the connection should be persistent.
// Note that the final specification of HTTP/1.1 in RFC 2616 does not
// include this information. Neither is the "Connection" header
// mentioned in RFC 1945, which informally describes HTTP/1.0.
//
// RFC 2616 specifies "close" as the only connection token with a
// specific meaning: it disables persistent connections.
//
// The "Proxy-Connection" header is not formally specified anywhere,
// but is commonly used to carry one token, "close" or "keep-alive".
// The "Connection" header, on the other hand, is defined as a
// sequence of tokens, where each token is a header name, and the
// token "close" has the above-mentioned additional meaning.
//
// To get through this mess, we treat the "Proxy-Connection" header
// in exactly the same way as the "Connection" header, but only if
// the latter is missing. We scan the sequence of tokens for both
// "close" and "keep-alive". As "close" is specified by RFC 2068,
// it takes precedence and indicates a non-persistent connection.
// If there is no "close" but a "keep-alive", we take the hint.
if (hit.hasNext()) {
try {
TokenIterator ti = createTokenIterator(hit);
boolean keepalive = false;
while (ti.hasNext()) {
final String token = ti.nextToken();
if (HTTP.CONN_CLOSE.equalsIgnoreCase(token)) {
return false;
} else if (HTTP.CONN_KEEP_ALIVE.equalsIgnoreCase(token)) {
// continue the loop, there may be a "close" afterwards
keepalive = true;
}
}
if (keepalive)
return true;
// neither "close" nor "keep-alive", use default policy
} catch (ParseException px) {
// invalid connection header means no persistent connection
// we don't have logging in HttpCore, so the exception is lost
return false;
}
}
// default since HTTP/1.1 is persistent, before it was non-persistent
return !ver.lessEquals(HttpVersion.HTTP_1_0);
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