- java.lang.Object
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- java.net.URLConnection
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- java.net.HttpURLConnection
 
 
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- Direct Known Subclasses:
- HttpsURLConnection
 
 public abstract class HttpURLConnection extends URLConnection A URLConnection with support for HTTP-specific features. See the spec for details.Each HttpURLConnection instance is used to make a single request but the underlying network connection to the HTTP server may be transparently shared by other instances. Calling the close() methods on the InputStream or OutputStream of an HttpURLConnection after a request may free network resources associated with this instance but has no effect on any shared persistent connection. Calling the disconnect() method may close the underlying socket if a persistent connection is otherwise idle at that time. The HTTP protocol handler has a few settings that can be accessed through System Properties. This covers Proxy settings as well as various other settings. Security permissions If a security manager is installed, and if a method is called which results in an attempt to open a connection, the caller must possess either: - a "connect" SocketPermissionto the host/port combination of the destination URL or
- a URLPermissionthat permits this request.
 If automatic redirection is enabled, and this request is redirected to another destination, then the caller must also have permission to connect to the redirected host/URL. - Since:
- 1.1
- See Also:
- disconnect()
 
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Field SummaryFields Modifier and Type Field Description protected intchunkLengthThe chunk-length when using chunked encoding streaming mode for output.protected intfixedContentLengthThe fixed content-length when using fixed-length streaming mode.protected longfixedContentLengthLongThe fixed content-length when using fixed-length streaming mode.static intHTTP_ACCEPTEDHTTP Status-Code 202: Accepted.static intHTTP_BAD_GATEWAYHTTP Status-Code 502: Bad Gateway.static intHTTP_BAD_METHODHTTP Status-Code 405: Method Not Allowed.static intHTTP_BAD_REQUESTHTTP Status-Code 400: Bad Request.static intHTTP_CLIENT_TIMEOUTHTTP Status-Code 408: Request Time-Out.static intHTTP_CONFLICTHTTP Status-Code 409: Conflict.static intHTTP_CREATEDHTTP Status-Code 201: Created.static intHTTP_ENTITY_TOO_LARGEHTTP Status-Code 413: Request Entity Too Large.static intHTTP_FORBIDDENHTTP Status-Code 403: Forbidden.static intHTTP_GATEWAY_TIMEOUTHTTP Status-Code 504: Gateway Timeout.static intHTTP_GONEHTTP Status-Code 410: Gone.static intHTTP_INTERNAL_ERRORHTTP Status-Code 500: Internal Server Error.static intHTTP_LENGTH_REQUIREDHTTP Status-Code 411: Length Required.static intHTTP_MOVED_PERMHTTP Status-Code 301: Moved Permanently.static intHTTP_MOVED_TEMPHTTP Status-Code 302: Temporary Redirect.static intHTTP_MULT_CHOICEHTTP Status-Code 300: Multiple Choices.static intHTTP_NO_CONTENTHTTP Status-Code 204: No Content.static intHTTP_NOT_ACCEPTABLEHTTP Status-Code 406: Not Acceptable.static intHTTP_NOT_AUTHORITATIVEHTTP Status-Code 203: Non-Authoritative Information.static intHTTP_NOT_FOUNDHTTP Status-Code 404: Not Found.static intHTTP_NOT_IMPLEMENTEDHTTP Status-Code 501: Not Implemented.static intHTTP_NOT_MODIFIEDHTTP Status-Code 304: Not Modified.static intHTTP_OKHTTP Status-Code 200: OK.static intHTTP_PARTIALHTTP Status-Code 206: Partial Content.static intHTTP_PAYMENT_REQUIREDHTTP Status-Code 402: Payment Required.static intHTTP_PRECON_FAILEDHTTP Status-Code 412: Precondition Failed.static intHTTP_PROXY_AUTHHTTP Status-Code 407: Proxy Authentication Required.static intHTTP_REQ_TOO_LONGHTTP Status-Code 414: Request-URI Too Large.static intHTTP_RESETHTTP Status-Code 205: Reset Content.static intHTTP_SEE_OTHERHTTP Status-Code 303: See Other.static intHTTP_SERVER_ERRORDeprecated.it is misplaced and shouldn't have existed.static intHTTP_UNAUTHORIZEDHTTP Status-Code 401: Unauthorized.static intHTTP_UNAVAILABLEHTTP Status-Code 503: Service Unavailable.static intHTTP_UNSUPPORTED_TYPEHTTP Status-Code 415: Unsupported Media Type.static intHTTP_USE_PROXYHTTP Status-Code 305: Use Proxy.static intHTTP_VERSIONHTTP Status-Code 505: HTTP Version Not Supported.protected booleaninstanceFollowRedirectsIftrue, the protocol will automatically follow redirects.protected StringmethodThe HTTP method (GET,POST,PUT,etc.).protected intresponseCodeAnintrepresenting the three digit HTTP Status-Code.protected StringresponseMessageThe HTTP response message.- 
Fields declared in class java.net.URLConnectionallowUserInteraction, connected, doInput, doOutput, ifModifiedSince, url, useCaches
 
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Constructor SummaryConstructors Modifier Constructor Description protectedHttpURLConnection(URL u)Constructor for the HttpURLConnection.
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Method SummaryAll Methods Static Methods Instance Methods Abstract Methods Concrete Methods Modifier and Type Method Description abstract voiddisconnect()Indicates that other requests to the server are unlikely in the near future.InputStreamgetErrorStream()Returns the error stream if the connection failed but the server sent useful data nonetheless.static booleangetFollowRedirects()Returns abooleanindicating whether or not HTTP redirects (3xx) should be automatically followed.StringgetHeaderField(int n)Returns the value for thenth header field.StringgetHeaderFieldKey(int n)Returns the key for thenth header field.booleangetInstanceFollowRedirects()Returns the value of thisHttpURLConnection'sinstanceFollowRedirectsfield.PermissiongetPermission()Returns aSocketPermissionobject representing the permission necessary to connect to the destination host and port.StringgetRequestMethod()Get the request method.intgetResponseCode()Gets the status code from an HTTP response message.StringgetResponseMessage()Gets the HTTP response message, if any, returned along with the response code from a server.voidsetAuthenticator(Authenticator auth)Supplies anAuthenticatorto be used when authentication is requested through the HTTP protocol for thisHttpURLConnection.voidsetChunkedStreamingMode(int chunklen)This method is used to enable streaming of a HTTP request body without internal buffering, when the content length is not known in advance.voidsetFixedLengthStreamingMode(int contentLength)This method is used to enable streaming of a HTTP request body without internal buffering, when the content length is known in advance.voidsetFixedLengthStreamingMode(long contentLength)This method is used to enable streaming of a HTTP request body without internal buffering, when the content length is known in advance.static voidsetFollowRedirects(boolean set)Sets whether HTTP redirects (requests with response code 3xx) should be automatically followed by this class.voidsetInstanceFollowRedirects(boolean followRedirects)Sets whether HTTP redirects (requests with response code 3xx) should be automatically followed by thisHttpURLConnectioninstance.voidsetRequestMethod(String method)Set the method for the URL request, one of: GET POST HEAD OPTIONS PUT DELETE TRACE are legal, subject to protocol restrictions.abstract booleanusingProxy()Indicates if the connection is going through a proxy.- 
Methods declared in class java.net.URLConnectionaddRequestProperty, connect, getAllowUserInteraction, getConnectTimeout, getContent, getContent, getContentEncoding, getContentLength, getContentLengthLong, getContentType, getDate, getDefaultAllowUserInteraction, getDefaultRequestProperty, getDefaultUseCaches, getDefaultUseCaches, getDoInput, getDoOutput, getExpiration, getFileNameMap, getHeaderField, getHeaderFieldDate, getHeaderFieldInt, getHeaderFieldLong, getHeaderFields, getIfModifiedSince, getInputStream, getLastModified, getOutputStream, getReadTimeout, getRequestProperties, getRequestProperty, getURL, getUseCaches, guessContentTypeFromName, guessContentTypeFromStream, setAllowUserInteraction, setConnectTimeout, setContentHandlerFactory, setDefaultAllowUserInteraction, setDefaultRequestProperty, setDefaultUseCaches, setDefaultUseCaches, setDoInput, setDoOutput, setFileNameMap, setIfModifiedSince, setReadTimeout, setRequestProperty, setUseCaches, toString
 
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Field Detail- 
methodprotected String method The HTTP method (GET,POST,PUT,etc.).
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chunkLengthprotected int chunkLength The chunk-length when using chunked encoding streaming mode for output. A value of-1means chunked encoding is disabled for output.- Since:
- 1.5
 
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fixedContentLengthprotected int fixedContentLength The fixed content-length when using fixed-length streaming mode. A value of-1means fixed-length streaming mode is disabled for output.NOTE: fixedContentLengthLongis recommended instead of this field, as it allows larger content lengths to be set.- Since:
- 1.5
 
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fixedContentLengthLongprotected long fixedContentLengthLong The fixed content-length when using fixed-length streaming mode. A value of-1means fixed-length streaming mode is disabled for output.- Since:
- 1.7
 
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responseCodeprotected int responseCode Anintrepresenting the three digit HTTP Status-Code.- 1xx: Informational
- 2xx: Success
- 3xx: Redirection
- 4xx: Client Error
- 5xx: Server Error
 
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responseMessageprotected String responseMessage The HTTP response message.
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instanceFollowRedirectsprotected boolean instanceFollowRedirects Iftrue, the protocol will automatically follow redirects. Iffalse, the protocol will not automatically follow redirects.This field is set by the setInstanceFollowRedirectsmethod. Its value is returned by thegetInstanceFollowRedirectsmethod.Its default value is based on the value of the static followRedirects at HttpURLConnection construction time. 
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HTTP_OKpublic static final int HTTP_OK HTTP Status-Code 200: OK.- See Also:
- Constant Field Values
 
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HTTP_CREATEDpublic static final int HTTP_CREATED HTTP Status-Code 201: Created.- See Also:
- Constant Field Values
 
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HTTP_ACCEPTEDpublic static final int HTTP_ACCEPTED HTTP Status-Code 202: Accepted.- See Also:
- Constant Field Values
 
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HTTP_NOT_AUTHORITATIVEpublic static final int HTTP_NOT_AUTHORITATIVE HTTP Status-Code 203: Non-Authoritative Information.- See Also:
- Constant Field Values
 
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HTTP_NO_CONTENTpublic static final int HTTP_NO_CONTENT HTTP Status-Code 204: No Content.- See Also:
- Constant Field Values
 
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HTTP_RESETpublic static final int HTTP_RESET HTTP Status-Code 205: Reset Content.- See Also:
- Constant Field Values
 
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HTTP_PARTIALpublic static final int HTTP_PARTIAL HTTP Status-Code 206: Partial Content.- See Also:
- Constant Field Values
 
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HTTP_MULT_CHOICEpublic static final int HTTP_MULT_CHOICE HTTP Status-Code 300: Multiple Choices.- See Also:
- Constant Field Values
 
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HTTP_MOVED_PERMpublic static final int HTTP_MOVED_PERM HTTP Status-Code 301: Moved Permanently.- See Also:
- Constant Field Values
 
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HTTP_MOVED_TEMPpublic static final int HTTP_MOVED_TEMP HTTP Status-Code 302: Temporary Redirect.- See Also:
- Constant Field Values
 
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HTTP_SEE_OTHERpublic static final int HTTP_SEE_OTHER HTTP Status-Code 303: See Other.- See Also:
- Constant Field Values
 
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HTTP_NOT_MODIFIEDpublic static final int HTTP_NOT_MODIFIED HTTP Status-Code 304: Not Modified.- See Also:
- Constant Field Values
 
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HTTP_USE_PROXYpublic static final int HTTP_USE_PROXY HTTP Status-Code 305: Use Proxy.- See Also:
- Constant Field Values
 
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HTTP_BAD_REQUESTpublic static final int HTTP_BAD_REQUEST HTTP Status-Code 400: Bad Request.- See Also:
- Constant Field Values
 
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HTTP_UNAUTHORIZEDpublic static final int HTTP_UNAUTHORIZED HTTP Status-Code 401: Unauthorized.- See Also:
- Constant Field Values
 
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HTTP_PAYMENT_REQUIREDpublic static final int HTTP_PAYMENT_REQUIRED HTTP Status-Code 402: Payment Required.- See Also:
- Constant Field Values
 
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HTTP_FORBIDDENpublic static final int HTTP_FORBIDDEN HTTP Status-Code 403: Forbidden.- See Also:
- Constant Field Values
 
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HTTP_NOT_FOUNDpublic static final int HTTP_NOT_FOUND HTTP Status-Code 404: Not Found.- See Also:
- Constant Field Values
 
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HTTP_BAD_METHODpublic static final int HTTP_BAD_METHOD HTTP Status-Code 405: Method Not Allowed.- See Also:
- Constant Field Values
 
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HTTP_NOT_ACCEPTABLEpublic static final int HTTP_NOT_ACCEPTABLE HTTP Status-Code 406: Not Acceptable.- See Also:
- Constant Field Values
 
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HTTP_PROXY_AUTHpublic static final int HTTP_PROXY_AUTH HTTP Status-Code 407: Proxy Authentication Required.- See Also:
- Constant Field Values
 
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HTTP_CLIENT_TIMEOUTpublic static final int HTTP_CLIENT_TIMEOUT HTTP Status-Code 408: Request Time-Out.- See Also:
- Constant Field Values
 
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HTTP_CONFLICTpublic static final int HTTP_CONFLICT HTTP Status-Code 409: Conflict.- See Also:
- Constant Field Values
 
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HTTP_GONEpublic static final int HTTP_GONE HTTP Status-Code 410: Gone.- See Also:
- Constant Field Values
 
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HTTP_LENGTH_REQUIREDpublic static final int HTTP_LENGTH_REQUIRED HTTP Status-Code 411: Length Required.- See Also:
- Constant Field Values
 
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HTTP_PRECON_FAILEDpublic static final int HTTP_PRECON_FAILED HTTP Status-Code 412: Precondition Failed.- See Also:
- Constant Field Values
 
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HTTP_ENTITY_TOO_LARGEpublic static final int HTTP_ENTITY_TOO_LARGE HTTP Status-Code 413: Request Entity Too Large.- See Also:
- Constant Field Values
 
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HTTP_REQ_TOO_LONGpublic static final int HTTP_REQ_TOO_LONG HTTP Status-Code 414: Request-URI Too Large.- See Also:
- Constant Field Values
 
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HTTP_UNSUPPORTED_TYPEpublic static final int HTTP_UNSUPPORTED_TYPE HTTP Status-Code 415: Unsupported Media Type.- See Also:
- Constant Field Values
 
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HTTP_SERVER_ERROR@Deprecated public static final int HTTP_SERVER_ERROR Deprecated.it is misplaced and shouldn't have existed.HTTP Status-Code 500: Internal Server Error.- See Also:
- Constant Field Values
 
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HTTP_INTERNAL_ERRORpublic static final int HTTP_INTERNAL_ERROR HTTP Status-Code 500: Internal Server Error.- See Also:
- Constant Field Values
 
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HTTP_NOT_IMPLEMENTEDpublic static final int HTTP_NOT_IMPLEMENTED HTTP Status-Code 501: Not Implemented.- See Also:
- Constant Field Values
 
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HTTP_BAD_GATEWAYpublic static final int HTTP_BAD_GATEWAY HTTP Status-Code 502: Bad Gateway.- See Also:
- Constant Field Values
 
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HTTP_UNAVAILABLEpublic static final int HTTP_UNAVAILABLE HTTP Status-Code 503: Service Unavailable.- See Also:
- Constant Field Values
 
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HTTP_GATEWAY_TIMEOUTpublic static final int HTTP_GATEWAY_TIMEOUT HTTP Status-Code 504: Gateway Timeout.- See Also:
- Constant Field Values
 
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HTTP_VERSIONpublic static final int HTTP_VERSION HTTP Status-Code 505: HTTP Version Not Supported.- See Also:
- Constant Field Values
 
 
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Constructor Detail- 
HttpURLConnectionprotected HttpURLConnection(URL u) Constructor for the HttpURLConnection.- Parameters:
- u- the URL
 
 
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Method Detail- 
setAuthenticatorpublic void setAuthenticator(Authenticator auth) Supplies anAuthenticatorto be used when authentication is requested through the HTTP protocol for thisHttpURLConnection. If no authenticator is supplied, the default authenticator will be used.- Implementation Requirements:
- The default behavior of this method is to unconditionally
           throw UnsupportedOperationException. Concrete implementations ofHttpURLConnectionwhich support supplying anAuthenticatorfor a specificHttpURLConnectioninstance should override this method to implement a different behavior.
- Implementation Note:
- Depending on authentication schemes, an implementation
           may or may not need to use the provided authenticator
           to obtain a password. For instance, an implementation that
           relies on third-party security libraries may still invoke the
           default authenticator if these libraries are configured
           to do so.
           Likewise, an implementation that supports transparent
           NTLM authentication may let the system attempt
           to connect using the system user credentials first,
           before invoking the provided authenticator.
           
 However, if an authenticator is specifically provided, then the underlying connection may only be reused forHttpURLConnectioninstances which share the sameAuthenticatorinstance, and authentication information, if cached, may only be reused for anHttpURLConnectionsharing that sameAuthenticator.
- Parameters:
- auth- The- Authenticatorthat should be used by this- HttpURLConnection.
- Throws:
- UnsupportedOperationException- if setting an Authenticator is not supported by the underlying implementation.
- IllegalStateException- if URLConnection is already connected.
- NullPointerException- if the supplied- authis- null.
- Since:
- 9
 
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getHeaderFieldKeypublic String getHeaderFieldKey(int n) Returns the key for thenth header field. Some implementations may treat the0th header field as special, i.e. as the status line returned by the HTTP server. In this case,getHeaderField(0)returns the status line, butgetHeaderFieldKey(0)returns null.- Overrides:
- getHeaderFieldKeyin class- URLConnection
- Parameters:
- n- an index, where- n >=0.
- Returns:
- the key for the nth header field, ornullif the key does not exist.
 
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setFixedLengthStreamingModepublic void setFixedLengthStreamingMode(int contentLength) This method is used to enable streaming of a HTTP request body without internal buffering, when the content length is known in advance.An exception will be thrown if the application attempts to write more data than the indicated content-length, or if the application closes the OutputStream before writing the indicated amount. When output streaming is enabled, authentication and redirection cannot be handled automatically. A HttpRetryException will be thrown when reading the response if authentication or redirection are required. This exception can be queried for the details of the error. This method must be called before the URLConnection is connected. NOTE: setFixedLengthStreamingMode(long)is recommended instead of this method as it allows larger content lengths to be set.- Parameters:
- contentLength- The number of bytes which will be written to the OutputStream.
- Throws:
- IllegalStateException- if URLConnection is already connected or if a different streaming mode is already enabled.
- IllegalArgumentException- if a content length less than zero is specified.
- Since:
- 1.5
- See Also:
- setChunkedStreamingMode(int)
 
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setFixedLengthStreamingModepublic void setFixedLengthStreamingMode(long contentLength) This method is used to enable streaming of a HTTP request body without internal buffering, when the content length is known in advance.An exception will be thrown if the application attempts to write more data than the indicated content-length, or if the application closes the OutputStream before writing the indicated amount. When output streaming is enabled, authentication and redirection cannot be handled automatically. A HttpRetryException will be thrown when reading the response if authentication or redirection are required. This exception can be queried for the details of the error. This method must be called before the URLConnection is connected. The content length set by invoking this method takes precedence over any value set by setFixedLengthStreamingMode(int).- Parameters:
- contentLength- The number of bytes which will be written to the OutputStream.
- Throws:
- IllegalStateException- if URLConnection is already connected or if a different streaming mode is already enabled.
- IllegalArgumentException- if a content length less than zero is specified.
- Since:
- 1.7
 
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setChunkedStreamingModepublic void setChunkedStreamingMode(int chunklen) This method is used to enable streaming of a HTTP request body without internal buffering, when the content length is not known in advance. In this mode, chunked transfer encoding is used to send the request body. Note, not all HTTP servers support this mode.When output streaming is enabled, authentication and redirection cannot be handled automatically. A HttpRetryException will be thrown when reading the response if authentication or redirection are required. This exception can be queried for the details of the error. This method must be called before the URLConnection is connected. - Parameters:
- chunklen- The number of bytes to write in each chunk. If chunklen is less than or equal to zero, a default value will be used.
- Throws:
- IllegalStateException- if URLConnection is already connected or if a different streaming mode is already enabled.
- Since:
- 1.5
- See Also:
- setFixedLengthStreamingMode(int)
 
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getHeaderFieldpublic String getHeaderField(int n) Returns the value for thenth header field. Some implementations may treat the0th header field as special, i.e. as the status line returned by the HTTP server.This method can be used in conjunction with the getHeaderFieldKeymethod to iterate through all the headers in the message.- Overrides:
- getHeaderFieldin class- URLConnection
- Parameters:
- n- an index, where- n>=0.
- Returns:
- the value of the nth header field, ornullif the value does not exist.
- See Also:
- getHeaderFieldKey(int)
 
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setFollowRedirectspublic static void setFollowRedirects(boolean set) Sets whether HTTP redirects (requests with response code 3xx) should be automatically followed by this class. True by default. Applets cannot change this variable.If there is a security manager, this method first calls the security manager's checkSetFactorymethod to ensure the operation is allowed. This could result in a SecurityException.- Parameters:
- set- a- booleanindicating whether or not to follow HTTP redirects.
- Throws:
- SecurityException- if a security manager exists and its- checkSetFactorymethod doesn't allow the operation.
- See Also:
- SecurityManager.checkSetFactory(),- getFollowRedirects()
 
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getFollowRedirectspublic static boolean getFollowRedirects() Returns abooleanindicating whether or not HTTP redirects (3xx) should be automatically followed.- Returns:
- trueif HTTP redirects should be automatically followed,- falseif not.
- See Also:
- setFollowRedirects(boolean)
 
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setInstanceFollowRedirectspublic void setInstanceFollowRedirects(boolean followRedirects) Sets whether HTTP redirects (requests with response code 3xx) should be automatically followed by thisHttpURLConnectioninstance.The default value comes from followRedirects, which defaults to true. - Parameters:
- followRedirects- a- booleanindicating whether or not to follow HTTP redirects.
- Since:
- 1.3
- See Also:
- instanceFollowRedirects,- getInstanceFollowRedirects()
 
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getInstanceFollowRedirectspublic boolean getInstanceFollowRedirects() Returns the value of thisHttpURLConnection'sinstanceFollowRedirectsfield.- Returns:
- the value of this HttpURLConnection'sinstanceFollowRedirectsfield.
- Since:
- 1.3
- See Also:
- instanceFollowRedirects,- setInstanceFollowRedirects(boolean)
 
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setRequestMethodpublic void setRequestMethod(String method) throws ProtocolException Set the method for the URL request, one of:- GET
- POST
- HEAD
- OPTIONS
- PUT
- DELETE
- TRACE
 - Parameters:
- method- the HTTP method
- Throws:
- ProtocolException- if the method cannot be reset or if the requested method isn't valid for HTTP.
- SecurityException- if a security manager is set and the method is "TRACE", but the "allowHttpTrace" NetPermission is not granted.
- See Also:
- getRequestMethod()
 
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getRequestMethodpublic String getRequestMethod() Get the request method.- Returns:
- the HTTP request method
- See Also:
- setRequestMethod(java.lang.String)
 
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getResponseCodepublic int getResponseCode() throws IOExceptionGets the status code from an HTTP response message. For example, in the case of the following status lines:HTTP/1.0 200 OK HTTP/1.0 401 Unauthorized It will return 200 and 401 respectively. Returns -1 if no code can be discerned from the response (i.e., the response is not valid HTTP).- Returns:
- the HTTP Status-Code, or -1
- Throws:
- IOException- if an error occurred connecting to the server.
 
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getResponseMessagepublic String getResponseMessage() throws IOException Gets the HTTP response message, if any, returned along with the response code from a server. From responses like:HTTP/1.0 200 OK HTTP/1.0 404 Not Found Extracts the Strings "OK" and "Not Found" respectively. Returns null if none could be discerned from the responses (the result was not valid HTTP).- Returns:
- the HTTP response message, or null
- Throws:
- IOException- if an error occurred connecting to the server.
 
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disconnectpublic abstract void disconnect() Indicates that other requests to the server are unlikely in the near future. Calling disconnect() should not imply that this HttpURLConnection instance can be reused for other requests.
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usingProxypublic abstract boolean usingProxy() Indicates if the connection is going through a proxy.- Returns:
- a boolean indicating if the connection is using a proxy.
 
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getPermissionpublic Permission getPermission() throws IOException Returns aSocketPermissionobject representing the permission necessary to connect to the destination host and port.- Overrides:
- getPermissionin class- URLConnection
- Returns:
- a SocketPermissionobject representing the permission necessary to connect to the destination host and port.
- Throws:
- IOException- if an error occurs while computing the permission.
 
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getErrorStreampublic InputStream getErrorStream() Returns the error stream if the connection failed but the server sent useful data nonetheless. The typical example is when an HTTP server responds with a 404, which will cause a FileNotFoundException to be thrown in connect, but the server sent an HTML help page with suggestions as to what to do.This method will not cause a connection to be initiated. If the connection was not connected, or if the server did not have an error while connecting or if the server had an error but no error data was sent, this method will return null. This is the default. - Returns:
- an error stream if any, null if there have been no errors, the connection is not connected or the server sent no useful data.
 
 
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