Apache
/
httpcomponents-client
mirror of https://github.com/apache/httpcomponents-client.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

Minor tweaks. 

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpclient/trunk@1041100 13f79535-47bb-0310-9956-ffa450edef68
This commit is contained in:
Sebastian Bazley 2010-12-01 17:39:22 +00:00
parent 66074eba84
commit 86c8730de2
1 changed files with 60 additions and 58 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

118
src/docbkx/connmgmt.xml
View File

@ -23,9 +23,9 @@
-->
<chapter id="connmgmt">
<title>Connection management</title>
<para>HttpClient has a complete control over the process of connection initialization and
<para>HttpClient assumes complete control over the process of connection initialization and
termination as well as I/O operations on active connections. However various aspects of
connection operations can be controlled using a number of parameters.</para>
connection operations can be influenced using a number of parameters.</para>
<section>
<title>Connection parameters</title>
<para>These are parameters that can influence connection operations:</para>
@ -38,19 +38,19 @@
a maximum period inactivity between two consecutive data packets). A timeout
value of zero is interpreted as an infinite timeout. This parameter expects
a value of type <classname>java.lang.Integer</classname>. If this parameter
is not set read operations will not time out (infinite timeout).</para>
is not set, read operations will not time out (infinite timeout).</para>
</formalpara>
</listitem>
<listitem>
<formalpara>
<title>'http.tcp.nodelay':</title>
<para>determines whether Nagle's algorithm is to be used. The Nagle's algorithm
<para>determines whether Nagle's algorithm is to be used. Nagle's algorithm
tries to conserve bandwidth by minimizing the number of segments that are
sent. When applications wish to decrease network latency and increase
performance, they can disable Nagle's algorithm (that is enable
<literal>TCP_NODELAY</literal>. Data will be sent earlier, at the cost
of an increase in bandwidth consumption. This parameter expects a value of
type <classname>java.lang.Boolean</classname>. If this parameter is not,
type <classname>java.lang.Boolean</classname>. If this parameter is not set,
<literal>TCP_NODELAY</literal> will be enabled (no delay).</para>
</formalpara>
</listitem>
@ -60,7 +60,7 @@
<para>determines the size of the internal socket buffer used to buffer data
while receiving / transmitting HTTP messages. This parameter expects a value
of type <classname>java.lang.Integer</classname>. If this parameter is not
set HttpClient will allocate 8192 byte socket buffers.</para>
set, HttpClient will allocate 8192 byte socket buffers.</para>
</formalpara>
</listitem>
<listitem>
@ -70,7 +70,7 @@
seconds. The maximum timeout value is platform specific. Value 0 implies
that the option is disabled. Value -1 implies that the JRE default is used.
The setting only affects the socket close operation. If this parameter is
not set value -1 (JRE default) will be assumed.</para>
not set, the value -1 (JRE default) will be assumed.</para>
</formalpara>
</listitem>
<listitem>
@ -79,7 +79,7 @@
<para>determines the timeout in milliseconds until a connection is established.
A timeout value of zero is interpreted as an infinite timeout. This
parameter expects a value of type <classname>java.lang.Integer</classname>.
If this parameter is not set connect operations will not time out (infinite
If this parameter is not set, connect operations will not time out (infinite
timeout).</para>
</formalpara>
</listitem>
@ -92,8 +92,8 @@
getting an I/O error when executing a request over a connection that has
been closed at the server side. This parameter expects a value of type
<classname>java.lang.Boolean</classname>. For performance critical
operations the check should be disabled. If this parameter is not set the
stale connection will be performed before each request execution.</para>
operations the check should be disabled. If this parameter is not set, the
stale connection check will be performed before each request execution.</para>
</formalpara>
</listitem>
<listitem>
@ -130,7 +130,7 @@
skip those surplus lines this way. This parameter expects a value of type
java.lang.Integer. 0 disallows all garbage/empty lines before the status
line. Use <constant>java.lang.Integer#MAX_VALUE</constant> for unlimited
number. If this parameter is not set unlimited number will be
number. If this parameter is not set, unlimited number will be
assumed.</para>
</formalpara>
</listitem>
@ -144,17 +144,17 @@
small HTTP messages. One can achieve a much higher data throughput if open connections
can be re-used to execute multiple requests.</para>
<para>HTTP/1.1 states that HTTP connections can be re-used for multiple requests per
default. HTTP/1.0 compliant endpoints can also use similar mechanism to explicitly
default. HTTP/1.0 compliant endpoints can also use a mechanism to explicitly
communicate their preference to keep connection alive and use it for multiple requests.
HTTP agents can also keep idle connections alive for a certain period time in case a
connection to the same target host may be needed for subsequent requests. The ability to
connection to the same target host is needed for subsequent requests. The ability to
keep connections alive is usually refered to as connection persistence. HttpClient fully
supports connection persistence.</para>
</section>
<section>
<title>HTTP connection routing</title>
<para>HttpClient is capable of establishing connections to the target host either directly
or via a route that may involve multiple intermediate connections also referred to as
or via a route that may involve multiple intermediate connections - also referred to as
hops. HttpClient differentiates connections of a route into plain, tunneled and layered.
The use of multiple intermediate proxies to tunnel connections to the target host is
referred to as proxy chaining.</para>
@ -166,10 +166,10 @@
proxies.</para>
<section>
<title>Route computation</title>
<para><interfacename>RouteInfo</interfacename> interface represents information about a
<para>The <interfacename>RouteInfo</interfacename> interface represents information about a
definitive route to a target host involving one or more intermediate steps or hops.
<classname>HttpRoute</classname> is a concrete implementation of
<interfacename>RouteInfo</interfacename>, which cannot be changed (is
the <interfacename>RouteInfo</interfacename>, which cannot be changed (is
immutable). <classname>HttpTracker</classname> is a mutable
<interfacename>RouteInfo</interfacename> implementation used internally by
HttpClient to track the remaining hops to the ultimate route target.
@ -180,13 +180,13 @@
<para><interfacename>HttpRoutePlanner</interfacename> is an interface representing a
strategy to compute a complete route to a given target based on the execution
context. HttpClient ships with two default
<interfacename>HttpRoutePlanner</interfacename> implementation.
<interfacename>HttpRoutePlanner</interfacename> implementations.
<classname>ProxySelectorRoutePlanner</classname> is based on
<classname>java.net.ProxySelector</classname>. By default, it will pick up the
proxy settings of the JVM, either from system properties or from the browser running
the application. <classname>DefaultHttpRoutePlanner</classname> implementation does
not make use of any Java system properties, nor of system or browser proxy settings.
It computes routes based exclusively on HTTP parameters described below.</para>
the application. The <classname>DefaultHttpRoutePlanner</classname> implementation does
not make use of any Java system properties, nor any system or browser proxy settings.
It computes routes based exclusively on the HTTP parameters described below.</para>
</section>
<section>
<title>Secure HTTP connections</title>
@ -199,14 +199,14 @@
</section>
<section>
<title>HTTP route parameters</title>
<para>These are parameters that can influence route computation:</para>
<para>These are the parameters that can influence route computation:</para>
<itemizedlist>
<listitem>
<formalpara>
<title>'http.route.default-proxy':</title>
<para>defines a proxy host to be used by default route planners that do not make
use of JRE settings. This parameter expects a value of type
<classname>HttpHost</classname>. If this parameter is not set direct
<classname>HttpHost</classname>. If this parameter is not set, direct
connections to the target will be attempted.</para>
</formalpara>
</listitem>
@ -218,7 +218,7 @@
select the network interface from which the connection originates. This
parameter expects a value of type
<classname>java.net.InetAddress</classname>. If this parameter is not
set a default local address will be used automatically.</para>
set, a default local address will be used automatically.</para>
</formalpara>
</listitem>
<listitem>
@ -235,8 +235,8 @@
<section>
<title>Socket factories</title>
<para>HTTP connections make use of a <classname>java.net.Socket</classname> object
internally to handle transmission of data across the wire. They, however, rely on
<interfacename>SchemeSocketFactory</interfacename> interface to create, initialize and
internally to handle transmission of data across the wire. However they rely on
the <interfacename>SchemeSocketFactory</interfacename> interface to create, initialize and
connect sockets. This enables the users of HttpClient to provide application specific
socket initialization code at runtime. <classname>PlainSocketFactory</classname> is the
default factory for creating and initializing plain (unencrypted) sockets.</para>
@ -254,7 +254,7 @@ sf.connectSocket(socket, address, null, params);
<section>
<title>Secure socket layering</title>
<para><interfacename>LayeredSchemeSocketFactory</interfacename> is an extension of
<interfacename>SchemeSocketFactory</interfacename> interface. Layered socket
the <interfacename>SchemeSocketFactory</interfacename> interface. Layered socket
factories are capable of creating sockets layered over an existing plain socket.
Socket layering is used primarily for creating secure sockets through proxies.
HttpClient ships with <classname>SSLSocketFactory</classname> that implements
@ -319,9 +319,11 @@ sf.connectSocket(socket, address, null, params);
the SSL/TLS protocol level, HttpClient can optionally verify whether the target
hostname matches the names stored inside the server's X.509 certificate, once the
connection has been established. This verification can provide additional guarantees
of authenticity of the server trust material. X509HostnameVerifier interface
of authenticity of the server trust material.
The <interfacename>X509HostnameVerifier</interfacename> interface
represents a strategy for hostname verification. HttpClient ships with three
X509HostnameVerifier. Important: hostname verification should not be confused with
<interfacename>X509HostnameVerifier</interfacename> implementations.
Important: hostname verification should not be confused with
SSL trust verification.</para>
<itemizedlist>
<listitem>
@ -337,7 +339,7 @@ sf.connectSocket(socket, address, null, params);
<listitem>
<formalpara>
<title><classname>BrowserCompatHostnameVerifier</classname>:</title>
<para>The hostname verifier that works the same way as Curl and Firefox. The
<para>This hostname verifier that works the same way as Curl and Firefox. The
hostname must match either the first CN, or any of the subject-alts. A
wildcard can occur in the CN, and in any of the subject-alts. The only
difference between <classname>BrowserCompatHostnameVerifier</classname>
@ -351,12 +353,12 @@ sf.connectSocket(socket, address, null, params);
<formalpara>
<title><classname>AllowAllHostnameVerifier</classname>:</title>
<para>This hostname verifier essentially turns hostname verification off.
This implementation is a no-op, and never throws the
This implementation is a no-op, and never throws
<exceptionname>javax.net.ssl.SSLException</exceptionname>.</para>
</formalpara>
</listitem>
</itemizedlist>
<para>Per default HttpClient uses <classname>BrowserCompatHostnameVerifier</classname>
<para>Per default HttpClient uses the <classname>BrowserCompatHostnameVerifier</classname>
implementation. One can specify a different hostname verifier implementation if
desired</para>
<programlisting><![CDATA[
@ -368,11 +370,11 @@ SSLSocketFactory sf = new SSLSocketFactory(
</section>
<section>
<title>Protocol schemes</title>
<para><classname>Scheme</classname> class represents a protocol scheme such as "http" or
<para>The <classname>Scheme</classname> class represents a protocol scheme such as "http" or
"https" and contains a number of protocol properties such as the default port and the
socket factory to be used to creating <classname>java.net.Socket</classname> instances
for the given protocol. <classname>SchemeRegistry</classname> class is used to maintain
a set of <classname>Scheme</classname>s HttpClient can choose from when trying to
socket factory to be used to create the <classname>java.net.Socket</classname> instances
for the given protocol. The <classname>SchemeRegistry</classname> class is used to maintain
a set of <classname>Scheme</classname>s that HttpClient can choose from when trying to
establish a connection by a request URI:</para>
<programlisting><![CDATA[
Scheme http = new Scheme("http", 80, PlainSocketFactory.getSocketFactory());
@ -399,7 +401,7 @@ DefaultHttpClient httpclient = new DefaultHttpClient();
HttpHost proxy = new HttpHost("someproxy", 8080);
httpclient.getParams().setParameter(ConnRoutePNames.DEFAULT_PROXY, proxy);
]]></programlisting>
<para>One can also instruct HttpClient to use standard JRE proxy selector to obtain proxy
<para>One can also instruct HttpClient to use the standard JRE proxy selector to obtain proxy
information:</para>
<programlisting><![CDATA[
DefaultHttpClient httpclient = new DefaultHttpClient();
@ -431,19 +433,19 @@ httpclient.setRoutePlanner(new HttpRoutePlanner() {
<title>HTTP connection managers</title>
<section>
<title>Connection operators</title>
<para>Operated connections are client side connections whose underlying socket or its
<para>Operated connections are client side connections whose underlying socket or
state can be manipulated by an external entity, usually referred to as a connection
operator. <interfacename>OperatedClientConnection</interfacename> interface extends
<interfacename>HttpClientConnection</interfacename> interface and define
additional methods to manage connection socket. The
operator. The <interfacename>OperatedClientConnection</interfacename> interface extends
the <interfacename>HttpClientConnection</interfacename> interface and defines
additional methods to manage connection sockets. The
<interfacename>ClientConnectionOperator</interfacename> interface represents a
strategy for creating <interfacename>OperatedClientConnection</interfacename>
instances and updating the underlying socket of those objects. Implementations will
most likely make use <interfacename>SchemeSocketFactory</interfacename>s to create
most likely make use a <interfacename>SchemeSocketFactory</interfacename> to create
<classname>java.net.Socket</classname> instances. The
<interfacename>ClientConnectionOperator</interfacename> interface enables the
<interfacename>ClientConnectionOperator</interfacename> interface enables
users of HttpClient to provide a custom strategy for connection operators as well as
an ability to provide alternative implementation of the
the ability to provide an alternative implementation of the
<interfacename>OperatedClientConnection</interfacename> interface.</para>
</section>
<section>
@ -457,7 +459,7 @@ httpclient.setRoutePlanner(new HttpRoutePlanner() {
persistent connections and synchronize access to persistent connections making sure
that only one thread can have access to a connection at a time.</para>
<para>Internally HTTP connection managers work with instances of
<interfacename>OperatedClientConnection</interfacename>, but they hands out
<interfacename>OperatedClientConnection</interfacename>, but they return
instances of <interfacename>ManagedClientConnection</interfacename> to the service
consumers. <interfacename>ManagedClientConnection</interfacename> acts as a wrapper
for a <interfacename>OperatedClientConnection</interfacename> instance that manages
@ -468,7 +470,7 @@ httpclient.setRoutePlanner(new HttpRoutePlanner() {
their link to the connection manager that spawned them and of the fact that they
must be returned back to the manager when no longer in use.
<interfacename>ManagedClientConnection</interfacename> classes also implement
<interfacename>ConnectionReleaseTrigger</interfacename> interface that can be
the <interfacename>ConnectionReleaseTrigger</interfacename> interface that can be
used to trigger the release of the connection back to the manager. Once the
connection release has been triggered the wrapped connection gets detached from the
<interfacename>ManagedClientConnection</interfacename> wrapper and the
@ -542,9 +544,9 @@ try {
ought to be used by one execution thread only.
<classname>SingleClientConnManager</classname> will make an effort to reuse the
connection for subsequent requests with the same route. It will, however, close the
existing connection and open it for the given route, if the route of the persistent
existing connection and re-open it for the given route, if the route of the persistent
connection does not match that of the connection request. If the connection has been
already been allocated
already been allocated, then
<exceptionname>java.lang.IllegalStateException</exceptionname> is thrown.</para>
<para><classname>SingleClientConnManager</classname> is used by HttpClient per
default.</para>
@ -554,15 +556,15 @@ try {
<para><classname>ThreadSafeClientConnManager</classname> is a more complex
implementation that manages a pool of client connections and is able to service
connection requests from multiple execution threads. Connections are pooled on a per
route basis. A request for a route which already the manager has persistent
connections for available in the pool will be services by leasing a connection from
route basis. A request for a route for which the manager already has a persistent
connection available in the pool will be serviced by leasing a connection from
the pool rather than creating a brand new connection.</para>
<para><classname>ThreadSafeClientConnManager</classname> maintains a maximum limit of
connection on a per route basis and in total. Per default this implementation will
connections on a per route basis and in total. Per default this implementation will
create no more than 2 concurrent connections per given route and no more 20
connections in total. For many real-world applications these limits may prove too
constraining, especially if they use HTTP as a transport protocol for their
services. Connection limits, however, can be adjusted using HTTP parameters.</para>
services. Connection limits can be adjusted using the appropriate HTTP parameters.</para>
<para>This example shows how the connection pool parameters can be adjusted:</para>
<programlisting><![CDATA[
SchemeRegistry schemeRegistry = new SchemeRegistry();
@ -602,12 +604,12 @@ httpclient.getConnectionManager().shutdown();
</section>
<section>
<title>Multithreaded request execution</title>
<para>When equipped with a pooling connection manager such as ThreadSafeClientConnManager
<para>When equipped with a pooling connection manager such as ThreadSafeClientConnManager,
HttpClient can be used to execute multiple requests simultaneously using multiple
threads of execution.</para>
<para><classname>ThreadSafeClientConnManager</classname> will allocate connections based on
<para>The <classname>ThreadSafeClientConnManager</classname> will allocate connections based on
its configuration. If all connections for a given route have already been leased, a
request for connection will block until a connection is released back to the pool. One
request for a connection will block until a connection is released back to the pool. One
can ensure the connection manager does not block indefinitely in the connection request
operation by setting <literal>'http.conn-manager.timeout'</literal> to a positive value.
If the connection request cannot be serviced within the given time period
@ -679,12 +681,12 @@ static class GetThread extends Thread {
</section>
<section>
<title>Connection eviction policy</title>
<para>One of the major shortcoming of the classic blocking I/O model is that the network
<para>One of the major shortcomings of the classic blocking I/O model is that the network
socket can react to I/O events only when blocked in an I/O operation. When a connection
is released back to the manager, it can be kept alive however it is unable to monitor
the status of the socket and react to any I/O events. If the connection gets closed on
the server side, the client side connection is unable to detect the change in the
connection state and react appropriately by closing the socket on its end.</para>
connection state (and react appropriately by closing the socket on its end).</para>
<para>HttpClient tries to mitigate the problem by testing whether the connection is 'stale',
that is no longer valid because it was closed on the server side, prior to using the
connection for executing an HTTP request. The stale connection check is not 100%
@ -738,12 +740,12 @@ public static class IdleConnectionMonitorThread extends Thread {
<section>
<title>Connection keep alive strategy</title>
<para>The HTTP specification does not specify how long a persistent connection may be and
should be kept alive. Some HTTP servers use non-standard <literal>Keep-Alive</literal>
should be kept alive. Some HTTP servers use a non-standard <literal>Keep-Alive</literal>
header to communicate to the client the period of time in seconds they intend to keep
the connection alive on the server side. HttpClient makes use of this information if
available. If the <literal>Keep-Alive</literal> header is not present in the response,
HttpClient assumes the connection can be kept alive indefinitely. However, many HTTP
servers out there are configured to drop persistent connections after a certain period
servers in general use are configured to drop persistent connections after a certain period
of inactivity in order to conserve system resources, quite often without informing the
client. In case the default strategy turns out to be too optimistic, one may want to
provide a custom keep-alive strategy.</para>