URLConnection for HTTP (RFC 2616
) used to send and
receive data over the web. Data may be of any type and length. This class may
be used to send and receive streaming data whose length is not known in
Uses of this class follow a pattern:
- Obtain a new
HttpURLConnection by calling
URL#openConnection() and casting the result to
- Prepare the request. The primary property of a request is its URI.
Request headers may also include metadata such as credentials, preferred
content types, and session cookies.
- Optionally upload a request body. Instances must be configured with
#setDoOutput(boolean) if they include a
request body. Transmit data by writing to the stream returned by
- Read the response. Response headers typically include metadata such as
the response body's content type and length, modified dates and session
cookies. The response body may be read from the stream returned by
#getInputStream(). If the response has no body, that method returns an
- Disconnect. Once the response body has been read, the
HttpURLConnection should be closed by calling
Disconnecting releases the resources held by a connection so they may
be closed or reused.
For example, to retrieve the webpage at
URL url = new URL("http://www.android.com/");finally
Secure Communication with HTTPS
URL#openConnection() on a URL with the "https"
scheme will return an
HttpsURLConnection, which allows for
overriding the default
javax.net.ssl.SSLSocketFactory. An application-supplied
SSLSocketFactorycreated from an
provide a custom
javax.net.ssl.X509TrustManager for verifying certificate chains and a custom
javax.net.ssl.X509KeyManager for supplying
client certificates. See
javax.net.ssl.HttpsURLConnection for more details.
HttpURLConnection will follow up to five HTTP redirects. It will
follow redirects from one origin server to another. This implementation
doesn't follow redirects from HTTPS to HTTP or vice versa.
If the HTTP response indicates that an error occurred,
#getInputStream() will throw an
#getErrorStream() to read the error response. The headers can be read in
the normal way using
To upload data to a web server, configure the connection for output using
For best performance, you should call either
#setFixedLengthStreamingMode(int) when the body length is known in advance,
#setChunkedStreamingMode(int) when it is not. Otherwise
HttpURLConnection will be forced to buffer the complete request body in
memory before it is transmitted, wasting (and possibly exhausting) heap and
For example, to perform an upload:
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();finally
The input and output streams returned by this class are not
. Most callers should wrap the returned streams with
java.io.BufferedOutputStream. Callers that do only bulk
reads or writes may omit buffering.
When transferring large amounts of data to or from a server, use streams
to limit how much data is in memory at once. Unless you need the entire
body to be in memory at once, process it as a stream (rather than storing
the complete body as a single byte array or string).
To reduce latency, this class may reuse the same underlying
Socketfor multiple request/response pairs. As a result, HTTP connections may be
held open longer than necessary. Calls to
#disconnect() may return
the socket to a pool of connected sockets. This behavior can be disabled by
http.keepAlive system property to
issuing any HTTP requests. The
http.maxConnections property may be
used to control how many idle connections to each server will be held.
By default, this implementation of
HttpURLConnection requests that
servers use gzip compression. Since
#getContentLength() returns the
number of bytes transmitted, you cannot use that method to predict how many
bytes can be read from
#getInputStream(). Instead, read that stream
until it is exhausted: when
InputStream#read returns -1. Gzip
compression can be disabled by setting the acceptable encodings in the
Handling Network Sign-On
Some Wi-Fi networks block Internet access until the user clicks through a
sign-on page. Such sign-on pages are typically presented by using HTTP
redirects. You can use
#getURL() to test if your connection has been
unexpectedly redirected. This check is not valid until after
the response headers have been received, which you can trigger by calling
#getInputStream(). For example, to
check that a response was not redirected to an unexpected host:
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();...
HttpURLConnection supports HTTP basic authentication
Authenticator to set the VM-wide authentication handler:
Authenticator.setDefault(new Authenticator() });
Unless paired with HTTPS, this is not
a secure mechanism for
user authentication. In particular, the username, password, request and
response are all transmitted over the network without encryption.
Sessions with Cookies
To establish and maintain a potentially long-lived session between client
HttpURLConnection includes an extensible cookie manager.
Enable VM-wide cookie management using
CookieManager cookieManager = new CookieManager();
CookieManager accepts cookies from the origin
only. Two other policies are included:
CookiePolicy to define a custom policy.
CookieManager keeps all accepted cookies in memory. It
will forget these cookies when the VM exits. Implement
define a custom cookie store.
In addition to the cookies set by HTTP responses, you may set cookies
programmatically. To be included in HTTP request headers, cookies must have
the domain and path properties set.
By default, new instances of
HttpCookie work only with servers
that support RFC 2965
cookies. Many web servers support only the older specification, RFC 2109. For compatibility
with the most web servers, set the cookie version to 0.
For example, to receive
www.twitter.com in French:
HttpCookie cookie = new HttpCookie("lang", "fr");
HttpURLConnection uses the
GET method by default. It will
#setDoOutput has been called.
Other HTTP methods (
TRACE) can be used with
By default, this class will connect directly to the origin
. It can also connect via an
Proxy.Type#SOCKS proxy. To use a proxy, use
URL#openConnection(Proxy) when creating the
This class includes transparent support for IPv6. For hosts with both IPv4
and IPv6 addresses, it will attempt to connect to each of a host's addresses
until a connection is established.
Android 4.0 (Ice Cream Sandwich, API level 15) includes a response cache. See
android.net.http.HttpResponseCache for instructions on enabling HTTP
caching in your application.
Avoiding Bugs In Earlier Releases
Prior to Android 2.2 (Froyo), this class had some frustrating bugs. In
close() on a readable
. Work around this by disabling connection pooling:
private void disableConnectionReuseIfNecessary() }}
Each instance of
HttpURLConnection may be used for one
request/response pair. Instances of this class are not thread safe.