public abstract class HttpURLConnection extends URLConnection
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
advance.
Uses of this class follow a pattern:
HttpURLConnection by calling URL.openConnection() and casting the result to
HttpURLConnection.
setDoOutput(true) if they include a
request body. Transmit data by writing to the stream returned by URLConnection.getOutputStream().
URLConnection.getInputStream(). If the response has no body, that method returns an
empty stream.
HttpURLConnection should be closed by calling disconnect().
Disconnecting releases the resources held by a connection so they may
be closed or reused.
For example, to retrieve the webpage at http://www.android.com/:
URL url = new URL("http://www.android.com/");
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
try {
InputStream in = new BufferedInputStream(urlConnection.getInputStream());
readStream(in);
} finally {
urlConnection.disconnect();
}
Calling URL.openConnection() on a URL with the "https"
scheme will return an HttpsURLConnection, which allows for
overriding the default HostnameVerifier and SSLSocketFactory. An application-supplied SSLSocketFactory
created from an SSLContext can
provide a custom X509TrustManager for verifying certificate chains and a custom
X509KeyManager for supplying
client certificates. See HttpsURLConnection for more details.
HttpURLConnection will follow up to twenty HTTP redirects from
KitKat onwards. Before KitKat it will only follow five. 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, URLConnection.getInputStream() will throw an IOException. Use getErrorStream() to read the error response. The headers can be read in
the normal way using URLConnection.getHeaderFields().
To upload data to a web server, configure the connection for output using
setDoOutput(true).
For best performance, you should call either setFixedLengthStreamingMode(int) when the body length is known in advance,
or 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
increasing latency.
For example, to perform an upload:
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
try {
urlConnection.setDoOutput(true);
urlConnection.setChunkedStreamingMode(0);
OutputStream out = new BufferedOutputStream(urlConnection.getOutputStream());
writeStream(out);
InputStream in = new BufferedInputStream(urlConnection.getInputStream());
readStream(in);
} finally {
urlConnection.disconnect();
}
The input and output streams returned by this class are not
buffered. Most callers should wrap the returned streams with BufferedInputStream or 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 Socket
for 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
setting the http.keepAlive system property to false before
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 and it automatically decompresses the data for
callers of URLConnection.getInputStream(). The Content-Encoding and Content-Length
response headers are cleared in this case. Gzip compression can be disabled by
setting the acceptable encodings in the request header:
urlConnection.setRequestProperty("Accept-Encoding", "identity");
Setting the Accept-Encoding request header explicitly disables automatic decompression and leaves the response headers intact; callers must handle decompression as needed, according to the Content-Encoding header of the response.
URLConnection.getContentLength() returns the number of bytes transmitted and
cannot be used to predict how many bytes can be read from
URLConnection.getInputStream() for compressed streams. Instead, read that stream
until it is exhausted, i.e. when InputStream.read() returns -1.
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 URLConnection.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
URLConnection.getHeaderFields() or URLConnection.getInputStream(). For example, to
check that a response was not redirected to an unexpected host:
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
try {
InputStream in = new BufferedInputStream(urlConnection.getInputStream());
if (!url.getHost().equals(urlConnection.getURL().getHost())) {
// we were redirected! Kick the user out to the browser to sign on?
}
...
} finally {
urlConnection.disconnect();
}
HttpURLConnection supports HTTP basic authentication. Use
Authenticator to set the VM-wide authentication handler:
Authenticator.setDefault(new Authenticator() {
protected PasswordAuthentication getPasswordAuthentication() {
return new PasswordAuthentication(username, password.toCharArray());
}
});
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.
To establish and maintain a potentially long-lived session between client
and server, HttpURLConnection includes an extensible cookie manager.
Enable VM-wide cookie management using CookieHandler and CookieManager:
CookieManager cookieManager = new CookieManager();
CookieHandler.setDefault(cookieManager);
By default, CookieManager accepts cookies from the origin
server only. Two other policies are included: CookiePolicy.ACCEPT_ALL and CookiePolicy.ACCEPT_NONE. Implement
CookiePolicy to define a custom policy.
The default CookieManager keeps all accepted cookies in memory. It
will forget these cookies when the VM exits. Implement CookieStore to
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");
cookie.setDomain("twitter.com");
cookie.setPath("/");
cookie.setVersion(0);
cookieManager.getCookieStore().add(new URI("http://twitter.com/"), cookie);
HttpURLConnection uses the GET method by default. It will
use POST if setDoOutput(true) has been called.
Other HTTP methods (OPTIONS, HEAD, PUT, DELETE and TRACE) can be used with setRequestMethod(java.lang.String).
By default, this class will connect directly to the origin
server. It can also connect via an HTTP or SOCKS proxy. To use a proxy, use URL.openConnection(Proxy) when creating the
connection.
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.
Prior to Android 2.2 (Froyo), this class had some frustrating bugs. In
particular, calling close() on a readable InputStream could
poison the
connection pool. Work around this by disabling connection pooling:
private void disableConnectionReuseIfNecessary() {
// Work around pre-Froyo bugs in HTTP connection reuse.
if (Integer.parseInt(Build.VERSION.SDK) < Build.VERSION_CODES.FROYO) {
System.setProperty("http.keepAlive", "false");
}
}
Each instance of HttpURLConnection may be used for one
request/response pair. Instances of this class are not thread safe.
| Modifier and Type | Field and Description |
|---|---|
protected int |
chunkLength
If the HTTP chunked encoding is enabled this parameter defines the
chunk-length.
|
protected int |
fixedContentLength
The byte count in the request body if it is both known and streamed; and
-1 otherwise.
|
protected long |
fixedContentLengthLong
The byte count in the request body if it is both known and streamed; and
-1 otherwise.
|
static int |
HTTP_ACCEPTED
Numeric status code, 202: Accepted
|
static int |
HTTP_BAD_GATEWAY
Numeric status code, 502: Bad Gateway
|
static int |
HTTP_BAD_METHOD
Numeric status code, 405: Bad Method
|
static int |
HTTP_BAD_REQUEST
Numeric status code, 400: Bad Request
|
static int |
HTTP_CLIENT_TIMEOUT
Numeric status code, 408: Client Timeout
|
static int |
HTTP_CONFLICT
Numeric status code, 409: Conflict
|
static int |
HTTP_CREATED
Numeric status code, 201: Created
|
static int |
HTTP_ENTITY_TOO_LARGE
Numeric status code, 413: Entity too large
|
static int |
HTTP_FORBIDDEN
Numeric status code, 403: Forbidden
|
static int |
HTTP_GATEWAY_TIMEOUT
Numeric status code, 504: Gateway timeout
|
static int |
HTTP_GONE
Numeric status code, 410: Gone
|
static int |
HTTP_INTERNAL_ERROR
Numeric status code, 500: Internal error
|
static int |
HTTP_LENGTH_REQUIRED
Numeric status code, 411: Length required
|
static int |
HTTP_MOVED_PERM
Numeric status code, 301 Moved permanently
|
static int |
HTTP_MOVED_TEMP
Numeric status code, 302: Moved temporarily
|
static int |
HTTP_MULT_CHOICE
Numeric status code, 300: Multiple choices
|
static int |
HTTP_NO_CONTENT
Numeric status code, 204: No content
|
static int |
HTTP_NOT_ACCEPTABLE
Numeric status code, 406: Not acceptable
|
static int |
HTTP_NOT_AUTHORITATIVE
Numeric status code, 203: Not authoritative
|
static int |
HTTP_NOT_FOUND
Numeric status code, 404: Not found
|
static int |
HTTP_NOT_IMPLEMENTED
Numeric status code, 501: Not implemented
|
static int |
HTTP_NOT_MODIFIED
Numeric status code, 304: Not modified
|
static int |
HTTP_OK
Numeric status code, 200: OK
|
static int |
HTTP_PARTIAL
Numeric status code, 206: Partial
|
static int |
HTTP_PAYMENT_REQUIRED
Numeric status code, 402: Payment required
|
static int |
HTTP_PRECON_FAILED
Numeric status code, 412: Precondition failed
|
static int |
HTTP_PROXY_AUTH
Numeric status code, 407: Proxy authentication required
|
static int |
HTTP_REQ_TOO_LONG
Numeric status code, 414: Request too long
|
static int |
HTTP_RESET
Numeric status code, 205: Reset
|
static int |
HTTP_SEE_OTHER
Numeric status code, 303: See other
|
static int |
HTTP_SERVER_ERROR
Deprecated.
Use
HTTP_INTERNAL_ERROR instead. |
static int |
HTTP_UNAUTHORIZED
Numeric status code, 401: Unauthorized
|
static int |
HTTP_UNAVAILABLE
Numeric status code, 503: Unavailable
|
static int |
HTTP_UNSUPPORTED_TYPE
Numeric status code, 415: Unsupported type
|
static int |
HTTP_USE_PROXY
Numeric status code, 305: Use proxy.
|
static int |
HTTP_VERSION
Numeric status code, 505: Version not supported
|
protected boolean |
instanceFollowRedirects
Flag to define whether the protocol will automatically follow redirects
or not.
|
protected String |
method
The HTTP request method of this
HttpURLConnection. |
protected int |
responseCode
The status code of the response obtained from the HTTP request.
|
protected String |
responseMessage
The HTTP response message which corresponds to the response code.
|
allowUserInteraction, connected, doInput, doOutput, ifModifiedSince, url, useCaches| Modifier | Constructor and Description |
|---|---|
protected |
HttpURLConnection(URL url)
Constructs a new
HttpURLConnection instance pointing to the
resource specified by the url. |
| Modifier and Type | Method and Description |
|---|---|
abstract void |
disconnect()
Releases this connection so that its resources may be either reused or
closed.
|
String |
getContentEncoding()
Returns the encoding used to transmit the response body over the network.
|
InputStream |
getErrorStream()
Returns an input stream from the server in the case of an error such as
the requested file has not been found on the remote server.
|
static boolean |
getFollowRedirects()
Returns the value of
followRedirects which indicates if this
connection follows a different URL redirected by the server. |
long |
getHeaderFieldDate(String field,
long defaultValue)
Returns the date value in milliseconds since
01.01.1970, 00:00h
corresponding to the header field field. |
boolean |
getInstanceFollowRedirects()
Returns whether this connection follows redirects.
|
Permission |
getPermission()
Returns the permission object (in this case
SocketPermission)
with the host and the port number as the target name and "resolve, connect" as the action list. |
String |
getRequestMethod()
Returns the request method which will be used to make the request to the
remote HTTP server.
|
int |
getResponseCode()
Returns the response code returned by the remote HTTP server.
|
String |
getResponseMessage()
Returns the response message returned by the remote HTTP server.
|
void |
setChunkedStreamingMode(int chunkLength)
Stream a request body whose length is not known in advance.
|
void |
setFixedLengthStreamingMode(int contentLength)
Equivalent to
setFixedLengthStreamingMode((long) contentLength),
but available on earlier versions of Android and limited to 2 GiB. |
void |
setFixedLengthStreamingMode(long contentLength)
Configures this connection to stream the request body with the known
fixed byte count of
contentLength. |
static void |
setFollowRedirects(boolean auto)
Sets the flag of whether this connection will follow redirects returned
by the remote server.
|
void |
setInstanceFollowRedirects(boolean followRedirects)
Sets whether this connection follows redirects.
|
void |
setRequestMethod(String method)
Sets the request command which will be sent to the remote HTTP server.
|
abstract boolean |
usingProxy()
Returns whether this connection uses a proxy server or not.
|
addRequestProperty, connect, getAllowUserInteraction, getConnectTimeout, getContent, getContent, getContentLength, getContentType, getDate, getDefaultAllowUserInteraction, getDefaultRequestProperty, getDefaultUseCaches, getDoInput, getDoOutput, getExpiration, getFileNameMap, getHeaderField, getHeaderField, getHeaderFieldInt, getHeaderFieldKey, getHeaderFields, getIfModifiedSince, getInputStream, getLastModified, getOutputStream, getReadTimeout, getRequestProperties, getRequestProperty, getURL, getUseCaches, guessContentTypeFromName, guessContentTypeFromStream, setAllowUserInteraction, setConnectTimeout, setContentHandlerFactory, setDefaultAllowUserInteraction, setDefaultRequestProperty, setDefaultUseCaches, setDoInput, setDoOutput, setFileNameMap, setIfModifiedSince, setReadTimeout, setRequestProperty, setUseCaches, toStringprotected String method
HttpURLConnection. The default
value is "GET".protected int responseCode
-1.
protected String responseMessage
protected boolean instanceFollowRedirects
true.protected int chunkLength
-1 that means the chunked encoding
mode is disabled.protected int fixedContentLength
Integer.MAX_VALUE (2 GiB)
then the value of this field will be Integer.MAX_VALUE. In that
case use fixedContentLengthLong to access the exact byte count.protected long fixedContentLengthLong
int-valued fixedContentLength on platforms that support both.public static final int HTTP_ACCEPTED
public static final int HTTP_BAD_GATEWAY
public static final int HTTP_BAD_METHOD
public static final int HTTP_BAD_REQUEST
public static final int HTTP_CLIENT_TIMEOUT
public static final int HTTP_CONFLICT
public static final int HTTP_CREATED
public static final int HTTP_ENTITY_TOO_LARGE
public static final int HTTP_FORBIDDEN
public static final int HTTP_GATEWAY_TIMEOUT
public static final int HTTP_GONE
public static final int HTTP_INTERNAL_ERROR
public static final int HTTP_LENGTH_REQUIRED
public static final int HTTP_MOVED_PERM
public static final int HTTP_MOVED_TEMP
public static final int HTTP_MULT_CHOICE
public static final int HTTP_NO_CONTENT
public static final int HTTP_NOT_ACCEPTABLE
public static final int HTTP_NOT_AUTHORITATIVE
public static final int HTTP_NOT_FOUND
public static final int HTTP_NOT_IMPLEMENTED
public static final int HTTP_NOT_MODIFIED
public static final int HTTP_OK
public static final int HTTP_PARTIAL
public static final int HTTP_PAYMENT_REQUIRED
public static final int HTTP_PRECON_FAILED
public static final int HTTP_PROXY_AUTH
public static final int HTTP_REQ_TOO_LONG
public static final int HTTP_RESET
public static final int HTTP_SEE_OTHER
@Deprecated public static final int HTTP_SERVER_ERROR
HTTP_INTERNAL_ERROR instead.public static final int HTTP_USE_PROXY
Like Firefox and Chrome, this class doesn't honor this response code. Other implementations respond to this status code by retrying the request using the HTTP proxy named by the response's Location header field.
public static final int HTTP_UNAUTHORIZED
public static final int HTTP_UNSUPPORTED_TYPE
public static final int HTTP_UNAVAILABLE
public static final int HTTP_VERSION
protected HttpURLConnection(URL url)
HttpURLConnection instance pointing to the
resource specified by the url.url - the URL of this connection.URL,
URLConnectionpublic abstract void disconnect()
Unlike other Java implementations, this will not necessarily close
socket connections that can be reused. You can disable all connection
reuse by setting the http.keepAlive system property to false before issuing any HTTP requests.
public InputStream getErrorStream()
public static boolean getFollowRedirects()
followRedirects which indicates if this
connection follows a different URL redirected by the server. It is
enabled by default.setFollowRedirects(boolean)public Permission getPermission() throws IOException
SocketPermission)
with the host and the port number as the target name and "resolve, connect" as the action list. If the port number of this URL
instance is lower than 0 the port will be set to 80.getPermission in class URLConnectionIOException - if an IO exception occurs during the creation of the
permission object.public String getRequestMethod()
method,
setRequestMethod(java.lang.String)public int getResponseCode()
throws IOException
IOException - if there is an IO error during the retrieval.getResponseMessage()public String getResponseMessage() throws IOException
null if no such response exists.IOException - if there is an error during the retrieval.getResponseCode()public static void setFollowRedirects(boolean auto)
auto - the value to enable or disable this option.public void setRequestMethod(String method) throws ProtocolException
method - the string representing the method to be used.ProtocolException - if this is called after connected, or the method is not
supported by this HTTP implementation.getRequestMethod(),
methodpublic abstract boolean usingProxy()
true if this connection passes a proxy server, false
otherwise.public String getContentEncoding()
content type, which may also include the
content's character encoding.getContentEncoding in class URLConnectioncontent-encoding.public boolean getInstanceFollowRedirects()
true if this connection follows redirects, false
otherwise.public void setInstanceFollowRedirects(boolean followRedirects)
followRedirects - true if this connection will follows redirects, false
otherwise.public long getHeaderFieldDate(String field, long defaultValue)
01.01.1970, 00:00h
corresponding to the header field field. The defaultValue
will be returned if no such field can be found in the response header.getHeaderFieldDate in class URLConnectionfield - the header field name.defaultValue - the default value to use if the specified header field wont be
found.public void setFixedLengthStreamingMode(long contentLength)
contentLength.contentLength - the fixed length of the HTTP request body.IllegalStateException - if already connected or another mode already set.IllegalArgumentException - if contentLength is less than zero.setChunkedStreamingMode(int)public void setFixedLengthStreamingMode(int contentLength)
setFixedLengthStreamingMode((long) contentLength),
but available on earlier versions of Android and limited to 2 GiB.public void setChunkedStreamingMode(int chunkLength)
When HTTP chunked encoding is used, the stream is divided into chunks, each prefixed with a header containing the chunk's size. A large chunk length requires a large internal buffer, potentially wasting memory. A small chunk length increases the number of bytes that must be transmitted because of the header on every chunk.
Implementation details: In some releases the chunkLength is
treated as a hint: chunks sent to the server may actually be larger or
smaller. To force a chunk to be sent to the server call
OutputStream.flush().
chunkLength - the length to use, or 0 for the default chunk
length.IllegalStateException - if already connected or another mode
already set.setFixedLengthStreamingMode(long)