Class URLConnection
- Direct Known Subclasses:
HttpURLConnection,JarURLConnection
URLConnection is the superclass
of all classes that represent a communications link between the
application and a URL. Instances of this class can be used both to
read from and to write to the resource referenced by the URL.
In general, creating a connection to a URL is a multistep process:
- The connection object is created by invoking the
openConnectionmethod on a URL. - The setup parameters and general request properties are manipulated.
- The actual connection to the remote object is made, using the
connectmethod. - The remote object becomes available. The header fields and the contents of the remote object can be accessed.
The setup parameters are modified using the following methods:
setAllowUserInteractionsetDoInputsetDoOutputsetIfModifiedSincesetUseCaches
and the general request properties are modified using the method:
setRequestProperty
Default values for the AllowUserInteraction and
UseCaches parameters can be set using the methods
setDefaultAllowUserInteraction and
setDefaultUseCaches.
Each of the above set methods has a corresponding
get method to retrieve the value of the parameter or
general request property. The specific parameters and general
request properties that are applicable are protocol specific.
The following methods are used to access the header fields and the contents after the connection is made to the remote object:
getContentgetHeaderFieldgetInputStreamgetOutputStream
Certain header fields are accessed frequently. The methods:
getContentEncodinggetContentLengthgetContentTypegetDategetExpirationgetLastModified
provide convenient access to these fields. The
getContentType method is used by the
getContent method to determine the type of the remote
object; subclasses may find it convenient to override the
getContentType method.
In the common case, all of the pre-connection parameters and
general request properties can be ignored: the pre-connection
parameters and request properties default to sensible values. For
most clients of this interface, there are only two interesting
methods: getInputStream and getContent,
which are mirrored in the URL class by convenience methods.
More information on the request properties and header fields of
an http connection can be found at:
Invoking thehttp://www.ietf.org/rfc/rfc2616.txt
close() methods on the InputStream or OutputStream of an
URLConnection after a request may free network resources associated with this
instance, unless particular protocol specifications specify different behaviours
for it.- Since:
- 1.0
- External Specifications
- See Also:
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Field Summary
FieldsModifier and TypeFieldDescriptionprotected booleanIftrue, thisURLis being examined in a context in which it makes sense to allow user interactions such as popping up an authentication dialog.protected booleanIffalse, this connection object has not created a communications link to the specified URL.protected booleanThis variable is set by thesetDoInputmethod.protected booleanThis variable is set by thesetDoOutputmethod.protected longSome protocols support skipping the fetching of the object unless the object has been modified more recently than a certain time.protected URLThe URL represents the remote object on the World Wide Web to which this connection is opened.protected booleanIftrue, the protocol is allowed to use caching whenever it can. -
Constructor Summary
ConstructorsModifierConstructorDescriptionprotectedURLConnection(URL url) Constructs a URL connection to the specified URL. -
Method Summary
Modifier and TypeMethodDescriptionvoidaddRequestProperty(String key, String value) Adds a general request property specified by a key-value pair.abstract voidconnect()Opens a communications link to the resource referenced by this URL, if such a connection has not already been established.booleanReturns the value of theallowUserInteractionfield for this object.intReturns setting for connect timeout.Retrieves the contents of this URL connection.getContent(Class<?>[] classes) Retrieves the contents of this URL connection.Returns the value of thecontent-encodingheader field.intReturns the value of thecontent-lengthheader field.longReturns the value of thecontent-lengthheader field as a long.Returns the value of thecontent-typeheader field.longgetDate()Returns the value of thedateheader field.static booleanReturns the default value of theallowUserInteractionfield.static StringDeprecated.The instance specific getRequestProperty method should be used after an appropriate instance of URLConnection is obtained.booleanReturns the default value of aURLConnection'suseCachesflag.static booleangetDefaultUseCaches(String protocol) Returns the default value of theuseCachesflag for the given protocol.booleanReturns the value of thisURLConnection'sdoInputflag.booleanReturns the value of thisURLConnection'sdoOutputflag.longReturns the value of theexpiresheader field.static FileNameMapLoads filename map (a mimetable) from a data file.getHeaderField(int n) Returns the value for thenth header field.getHeaderField(String name) Returns the value of the named header field.longgetHeaderFieldDate(String name, long defaultValue) Returns the value of the named field parsed as date.intgetHeaderFieldInt(String name, int defaultValue) Returns the value of the named field parsed as a number.getHeaderFieldKey(int n) Returns the key for thenth header field.longgetHeaderFieldLong(String name, long defaultValue) Returns the value of the named field parsed as a number.Returns an unmodifiable Map of the header fields.longReturns the value of this object'sifModifiedSincefield.Returns an input stream that reads from this open connection.longReturns the value of thelast-modifiedheader field.Returns an output stream that writes to this connection.Returns a permission object representing the permission necessary to make the connection represented by this object.intReturns setting for read timeout. 0 return implies that the option is disabled (i.e., timeout of infinity).Returns an unmodifiable Map of general request properties for this connection.getRequestProperty(String key) Returns the value of the named general request property for this connection.getURL()Returns the value of thisURLConnection'sURLfield.booleanReturns the value of thisURLConnection'suseCachesfield.static StringguessContentTypeFromName(String fname) Tries to determine the content type of an object, based on the specified "file" component of a URL.static StringTries to determine the type of an input stream based on the characters at the beginning of the input stream.voidsetAllowUserInteraction(boolean allowuserinteraction) Set the value of theallowUserInteractionfield of thisURLConnection.voidsetConnectTimeout(int timeout) Sets a specified timeout value, in milliseconds, to be used when opening a communications link to the resource referenced by this URLConnection.static voidSets theContentHandlerFactoryof an application.static voidsetDefaultAllowUserInteraction(boolean defaultallowuserinteraction) Sets the default value of theallowUserInteractionfield for all futureURLConnectionobjects to the specified value.static voidsetDefaultRequestProperty(String key, String value) Deprecated.The instance specific setRequestProperty method should be used after an appropriate instance of URLConnection is obtained.voidsetDefaultUseCaches(boolean defaultusecaches) Sets the default value of theuseCachesfield to the specified value.static voidsetDefaultUseCaches(String protocol, boolean defaultVal) Sets the default value of theuseCachesfield for the named protocol to the given value.voidsetDoInput(boolean doinput) Sets the value of thedoInputfield for thisURLConnectionto the specified value.voidsetDoOutput(boolean dooutput) Sets the value of thedoOutputfield for thisURLConnectionto the specified value.static voidSets the FileNameMap.voidsetIfModifiedSince(long ifmodifiedsince) Sets the value of theifModifiedSincefield of thisURLConnectionto the specified value.voidsetReadTimeout(int timeout) Sets the read timeout to a specified timeout, in milliseconds.voidsetRequestProperty(String key, String value) Sets the general request property.voidsetUseCaches(boolean usecaches) Sets the value of theuseCachesfield of thisURLConnectionto the specified value.toString()Returns aStringrepresentation of this URL connection.
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Field Details
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url
The URL represents the remote object on the World Wide Web to which this connection is opened.The value of this field can be accessed by the
getURLmethod.The default value of this variable is the value of the URL argument in the
URLConnectionconstructor.- See Also:
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doInput
protected boolean doInputThis variable is set by thesetDoInputmethod. Its value is returned by thegetDoInputmethod.A URL connection can be used for input and/or output. Setting the
doInputflag totrueindicates that the application intends to read data from the URL connection.The default value of this field is
true.- See Also:
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doOutput
protected boolean doOutputThis variable is set by thesetDoOutputmethod. Its value is returned by thegetDoOutputmethod.A URL connection can be used for input and/or output. Setting the
doOutputflag totrueindicates that the application intends to write data to the URL connection.The default value of this field is
false.- See Also:
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allowUserInteraction
protected boolean allowUserInteractionIftrue, thisURLis being examined in a context in which it makes sense to allow user interactions such as popping up an authentication dialog. Iffalse, then no user interaction is allowed.The value of this field can be set by the
setAllowUserInteractionmethod. Its value is returned by thegetAllowUserInteractionmethod. Its default value is the value of the argument in the last invocation of thesetDefaultAllowUserInteractionmethod.- See Also:
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useCaches
protected boolean useCachesIftrue, the protocol is allowed to use caching whenever it can. Iffalse, the protocol must always try to get a fresh copy of the object.This field is set by the
setUseCachesmethod. Its value is returned by thegetUseCachesmethod.Its default value is the value given in the last invocation of the
setDefaultUseCachesmethod.The default setting may be overridden per protocol with
setDefaultUseCaches(String,boolean).- See Also:
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ifModifiedSince
protected long ifModifiedSinceSome protocols support skipping the fetching of the object unless the object has been modified more recently than a certain time.A nonzero value gives a time as the number of milliseconds since January 1, 1970, GMT. The object is fetched only if it has been modified more recently than that time.
This variable is set by the
setIfModifiedSincemethod. Its value is returned by thegetIfModifiedSincemethod.The default value of this field is
0, indicating that the fetching must always occur.- See Also:
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connected
protected boolean connectedIffalse, this connection object has not created a communications link to the specified URL. Iftrue, the communications link has been established.
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Constructor Details
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URLConnection
Constructs a URL connection to the specified URL. A connection to the object referenced by the URL is not created.- Parameters:
url- the specified URL.
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Method Details
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getFileNameMap
Loads filename map (a mimetable) from a data file. It will first try to load the user-specific table, defined by "content.types.user.table" property. If that fails, it tries to load the default built-in table.- Returns:
- the FileNameMap
- Since:
- 1.2
- See Also:
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setFileNameMap
Sets the FileNameMap.- Parameters:
map- the FileNameMap to be set- Since:
- 1.2
- See Also:
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connect
Opens a communications link to the resource referenced by this URL, if such a connection has not already been established.If the
connectmethod is called when the connection has already been opened (indicated by theconnectedfield having the valuetrue), the call is ignored.URLConnection objects go through two phases: first they are created, then they are connected. After being created, and before being connected, various options can be specified (e.g., doInput and UseCaches). After connecting, it is an error to try to set them. Operations that depend on being connected, like getContentLength, will implicitly perform the connection, if necessary.
- Throws:
SocketTimeoutException- if the timeout expires before the connection can be establishedIOException- if an I/O error occurs while opening the connection.- See Also:
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setConnectTimeout
public void setConnectTimeout(int timeout) Sets a specified timeout value, in milliseconds, to be used when opening a communications link to the resource referenced by this URLConnection. If the timeout expires before the connection can be established, a java.net.SocketTimeoutException is raised. A timeout of zero is interpreted as an infinite timeout.Some non-standard implementation of this method may ignore the specified timeout. To see the connect timeout set, please call getConnectTimeout().
- Parameters:
timeout- anintthat specifies the connect timeout value in milliseconds- Throws:
IllegalArgumentException- if the timeout parameter is negative- Since:
- 1.5
- See Also:
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getConnectTimeout
public int getConnectTimeout()Returns setting for connect timeout.0 return implies that the option is disabled (i.e., timeout of infinity).
- Returns:
- an
intthat indicates the connect timeout value in milliseconds - Since:
- 1.5
- See Also:
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setReadTimeout
public void setReadTimeout(int timeout) Sets the read timeout to a specified timeout, in milliseconds. A non-zero value specifies the timeout when reading from Input stream when a connection is established to a resource. If the timeout expires before there is data available for read, a java.net.SocketTimeoutException is raised. A timeout of zero is interpreted as an infinite timeout.Some non-standard implementation of this method ignores the specified timeout. To see the read timeout set, please call getReadTimeout().
- Parameters:
timeout- anintthat specifies the timeout value to be used in milliseconds- Throws:
IllegalArgumentException- if the timeout parameter is negative- Since:
- 1.5
- See Also:
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getReadTimeout
public int getReadTimeout()Returns setting for read timeout. 0 return implies that the option is disabled (i.e., timeout of infinity).- Returns:
- an
intthat indicates the read timeout value in milliseconds - Since:
- 1.5
- See Also:
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getURL
Returns the value of thisURLConnection'sURLfield.- Returns:
- the value of this
URLConnection'sURLfield. - See Also:
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getContentLength
public int getContentLength()Returns the value of thecontent-lengthheader field.Note:
getContentLengthLong()should be preferred over this method, since it returns alonginstead and is therefore more portable.- Returns:
- the content length of the resource that this connection's URL
references,
-1if the content length is not known, or if the content length is greater than Integer.MAX_VALUE.
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getContentLengthLong
public long getContentLengthLong()Returns the value of thecontent-lengthheader field as a long.- Returns:
- the content length of the resource that this connection's URL
references, or
-1if the content length is not known. - Since:
- 1.7
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getContentType
Returns the value of thecontent-typeheader field.- Returns:
- the content type of the resource that the URL references,
or
nullif not known. - See Also:
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getContentEncoding
Returns the value of thecontent-encodingheader field.- Returns:
- the content encoding of the resource that the URL references,
or
nullif not known. - See Also:
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getExpiration
public long getExpiration()Returns the value of theexpiresheader field.- Returns:
- the expiration date of the resource that this URL references, or 0 if not known. The value is the number of milliseconds since January 1, 1970 GMT.
- See Also:
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getDate
public long getDate()Returns the value of thedateheader field.- Returns:
- the sending date of the resource that the URL references,
or
0if not known. The value returned is the number of milliseconds since January 1, 1970 GMT. - See Also:
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getLastModified
public long getLastModified()Returns the value of thelast-modifiedheader field. The result is the number of milliseconds since January 1, 1970 GMT.- Returns:
- the date the resource referenced by this
URLConnectionwas last modified, or 0 if not known. - See Also:
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getHeaderField
Returns the value of the named header field.If called on a connection that sets the same header multiple times with possibly different values, only the last value is returned.
- Parameters:
name- the name of a header field.- Returns:
- the value of the named header field, or
nullif there is no such field in the header.
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getHeaderFields
Returns an unmodifiable Map of the header fields. The Map keys are Strings that represent the response-header field names. Each Map value is an unmodifiable List of Strings that represents the corresponding field values. This method is overridden by the subclasses ofURLConnection. In the implementation of these methods, if a given key has multiple corresponding values, they must be returned in the order they were added, preserving the insertion-order.- Implementation Requirements:
- The default implementation of this method returns an empty map always.
- Returns:
- a Map of header fields
- Since:
- 1.4
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getHeaderFieldInt
Returns the value of the named field parsed as a number.This form of
getHeaderFieldexists because some connection types (e.g.,http-ng) have pre-parsed headers. Classes for that connection type can override this method and short-circuit the parsing.- Parameters:
name- the name of the header field.defaultValue- the default value.- Returns:
- the value of the named field, parsed as an integer. The
defaultValuevalue is returned if the field is missing or malformed.
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getHeaderFieldLong
Returns the value of the named field parsed as a number.This form of
getHeaderFieldexists because some connection types (e.g.,http-ng) have pre-parsed headers. Classes for that connection type can override this method and short-circuit the parsing.- Parameters:
name- the name of the header field.defaultValue- the default value.- Returns:
- the value of the named field, parsed as a long. The
defaultValuevalue is returned if the field is missing or malformed. - Since:
- 1.7
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getHeaderFieldDate
Returns the value of the named field parsed as date. The result is the number of milliseconds since January 1, 1970 GMT represented by the named field.This form of
getHeaderFieldexists because some connection types (e.g.,http-ng) have pre-parsed headers. Classes for that connection type can override this method and short-circuit the parsing.- Parameters:
name- the name of the header field.defaultValue- a default value.- Returns:
- the value of the field, parsed as a date. The value of the
defaultValueargument is returned if the field is missing or malformed.
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getHeaderFieldKey
Returns the key for thenth header field. Some implementations may treat the0th header field as special, in which case,getHeaderField(0)may return some value, butgetHeaderFieldKey(0)returnsnull. Forn > 0it returnsnullif there are fewer thann+1fields.- Parameters:
n- an index, wheren>=0- Returns:
- the key for the
nth header field, ornullif there are fewer thann+1fields whenn > 0.
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getHeaderField
Returns the value for thenth header field. It returnsnullif there are fewer thann+1fields.This method can be used in conjunction with the
getHeaderFieldKeymethod to iterate through all the headers in the message.- Parameters:
n- an index, wheren>=0- Returns:
- the value of the
nth header field ornullif there are fewer thann+1fields - See Also:
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getContent
Retrieves the contents of this URL connection.This method first determines the content type of the object by calling the
getContentTypemethod. If this is the first time that the application has seen that specific content type, a content handler for that content type is created.This is done as follows:
- If the application has set up a content handler factory instance
using the
setContentHandlerFactorymethod, thecreateContentHandlermethod of that instance is called with the content type as an argument; the result is a content handler for that content type. - If no
ContentHandlerFactoryhas yet been set up, or if the factory'screateContentHandlermethod returnsnull, then the ServiceLoader mechanism is used to locate ContentHandlerFactory implementations using the system class loader. The order that factories are located is implementation specific, and an implementation is free to cache the located factories. A ServiceConfigurationError,ErrororRuntimeExceptionthrown from thecreateContentHandler, if encountered, will be propagated to the calling thread. ThecreateContentHandlermethod of each factory, if instantiated, is invoked, with the content type, until a factory returns non-null, or all factories have been exhausted. - Failing that, this method tries to load a content handler
class as defined by
ContentHandler. If the class does not exist, or is not a subclass ofContentHandler, then anUnknownServiceExceptionis thrown.
- Returns:
- the object fetched. The
instanceofoperator should be used to determine the specific kind of object returned. - Throws:
IOException- if an I/O error occurs while getting the content.UnknownServiceException- if the protocol does not support the content type.- See Also:
- If the application has set up a content handler factory instance
using the
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getContent
Retrieves the contents of this URL connection.- Parameters:
classes- theClassarray indicating the requested types- Returns:
- the object fetched that is the first match of the type
specified in the classes array. null if none of
the requested types are supported.
The
instanceofoperator should be used to determine the specific kind of object returned. - Throws:
IOException- if an I/O error occurs while getting the content.UnknownServiceException- if the protocol does not support the content type.- Since:
- 1.3
- See Also:
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getPermission
Returns a permission object representing the permission necessary to make the connection represented by this object. This method returns null if no permission is required to make the connection. By default, this method returnsjava.security.AllPermission. Subclasses should override this method and return the permission that best represents the permission required to make a connection to the URL. For example, aURLConnectionrepresenting afile:URL would return ajava.io.FilePermissionobject.The permission returned may dependent upon the state of the connection. For example, the permission before connecting may be different from that after connecting. For example, an HTTP sever, say foo.com, may redirect the connection to a different host, say bar.com. Before connecting the permission returned by the connection will represent the permission needed to connect to foo.com, while the permission returned after connecting will be to bar.com.
Permissions are generally used for two purposes: to protect caches of objects obtained through URLConnections, and to check the right of a recipient to learn about a particular URL. In the first case, the permission should be obtained after the object has been obtained. For example, in an HTTP connection, this will represent the permission to connect to the host from which the data was ultimately fetched. In the second case, the permission should be obtained and tested before connecting.
- Returns:
- the permission object representing the permission necessary to make the connection represented by this URLConnection.
- Throws:
IOException- if the computation of the permission requires network or file I/O and an exception occurs while computing it.
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getInputStream
Returns an input stream that reads from this open connection. A SocketTimeoutException can be thrown when reading from the returned input stream if the read timeout expires before data is available for read.- API Note:
- The
InputStreamreturned by this method can wrap anInflaterInputStream, whoseread(byte[], int, int)method can modify any element of the output buffer. - Returns:
- an input stream that reads from this open connection.
- Throws:
IOException- if an I/O error occurs while creating the input stream.UnknownServiceException- if the protocol does not support input.- See Also:
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getOutputStream
Returns an output stream that writes to this connection.- Returns:
- an output stream that writes to this connection.
- Throws:
IOException- if an I/O error occurs while creating the output stream.UnknownServiceException- if the protocol does not support output.
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toString
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setDoInput
public void setDoInput(boolean doinput) Sets the value of thedoInputfield for thisURLConnectionto the specified value.A URL connection can be used for input and/or output. Set the doInput flag to true if you intend to use the URL connection for input, false if not. The default is true.
- Parameters:
doinput- the new value.- Throws:
IllegalStateException- if already connected- See Also:
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getDoInput
public boolean getDoInput()Returns the value of thisURLConnection'sdoInputflag.- Returns:
- the value of this
URLConnection'sdoInputflag. - See Also:
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setDoOutput
public void setDoOutput(boolean dooutput) Sets the value of thedoOutputfield for thisURLConnectionto the specified value.A URL connection can be used for input and/or output. Set the doOutput flag to true if you intend to use the URL connection for output, false if not. The default is false.
- Parameters:
dooutput- the new value.- Throws:
IllegalStateException- if already connected- See Also:
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getDoOutput
public boolean getDoOutput()Returns the value of thisURLConnection'sdoOutputflag.- Returns:
- the value of this
URLConnection'sdoOutputflag. - See Also:
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setAllowUserInteraction
public void setAllowUserInteraction(boolean allowuserinteraction) Set the value of theallowUserInteractionfield of thisURLConnection.- Parameters:
allowuserinteraction- the new value.- Throws:
IllegalStateException- if already connected- See Also:
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getAllowUserInteraction
public boolean getAllowUserInteraction()Returns the value of theallowUserInteractionfield for this object.- Returns:
- the value of the
allowUserInteractionfield for this object. - See Also:
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setDefaultAllowUserInteraction
public static void setDefaultAllowUserInteraction(boolean defaultallowuserinteraction) Sets the default value of theallowUserInteractionfield for all futureURLConnectionobjects to the specified value.- Parameters:
defaultallowuserinteraction- the new value.- See Also:
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getDefaultAllowUserInteraction
public static boolean getDefaultAllowUserInteraction()Returns the default value of theallowUserInteractionfield.This default is "sticky", being a part of the static state of all URLConnections. This flag applies to the next, and all following URLConnections that are created.
- Returns:
- the default value of the
allowUserInteractionfield. - See Also:
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setUseCaches
public void setUseCaches(boolean usecaches) Sets the value of theuseCachesfield of thisURLConnectionto the specified value.Some protocols do caching of documents. Occasionally, it is important to be able to "tunnel through" and ignore the caches (e.g., the "reload" button in a browser). If the UseCaches flag on a connection is true, the connection is allowed to use whatever caches it can. If false, caches are to be ignored. The default value comes from defaultUseCaches, which defaults to true. A default value can also be set per-protocol using
setDefaultUseCaches(String,boolean).- Parameters:
usecaches- abooleanindicating whether or not to allow caching- Throws:
IllegalStateException- if already connected- See Also:
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getUseCaches
public boolean getUseCaches()Returns the value of thisURLConnection'suseCachesfield.- Returns:
- the value of this
URLConnection'suseCachesfield. - See Also:
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setIfModifiedSince
public void setIfModifiedSince(long ifmodifiedsince) Sets the value of theifModifiedSincefield of thisURLConnectionto the specified value.- Parameters:
ifmodifiedsince- the new value.- Throws:
IllegalStateException- if already connected- See Also:
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getIfModifiedSince
public long getIfModifiedSince()Returns the value of this object'sifModifiedSincefield.- Returns:
- the value of this object's
ifModifiedSincefield. - See Also:
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getDefaultUseCaches
public boolean getDefaultUseCaches()Returns the default value of aURLConnection'suseCachesflag.This default is "sticky", being a part of the static state of all URLConnections. This flag applies to the next, and all following URLConnections that are created. This default value can be over-ridden per protocol using
setDefaultUseCaches(String,boolean)- Returns:
- the default value of a
URLConnection'suseCachesflag. - See Also:
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setDefaultUseCaches
public void setDefaultUseCaches(boolean defaultusecaches) Sets the default value of theuseCachesfield to the specified value. This default value can be over-ridden per protocol usingsetDefaultUseCaches(String,boolean)- Parameters:
defaultusecaches- the new value.- See Also:
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setDefaultUseCaches
Sets the default value of theuseCachesfield for the named protocol to the given value. This value overrides any default setting set bysetDefaultUseCaches(boolean)for the given protocol. Successive calls to this method change the setting and affect the default value for all future connections of that protocol. The protocol name is case insensitive.- Parameters:
protocol- the protocol to set the default fordefaultVal- whether caching is enabled by default for the given protocol- Since:
- 9
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getDefaultUseCaches
Returns the default value of theuseCachesflag for the given protocol. IfsetDefaultUseCaches(String,boolean)was called for the given protocol, then that value is returned. Otherwise, ifsetDefaultUseCaches(boolean)was called, then that value is returned. If neither method was called, the return value istrue. The protocol name is case insensitive.- Parameters:
protocol- the protocol whose defaultUseCaches setting is required- Returns:
- the default value of the
useCachesflag for the given protocol. - Since:
- 9
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setRequestProperty
Sets the general request property. If a property with the key already exists, overwrite its value with the new value.NOTE: HTTP requires all request properties which can legally have multiple instances with the same key to use a comma-separated list syntax which enables multiple properties to be appended into a single property.
- Parameters:
key- the keyword by which the request is known (e.g., "Accept").value- the value associated with it.- Throws:
IllegalStateException- if already connectedNullPointerException- if key isnull- See Also:
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addRequestProperty
Adds a general request property specified by a key-value pair. This method will not overwrite existing values associated with the same key. This method could be a no-op if appending a value to the map is not supported by the protocol being used in a given subclass.- Parameters:
key- the keyword by which the request is known (e.g., "Accept").value- the value associated with it.- Throws:
IllegalStateException- if already connectedNullPointerException- if key is null- Since:
- 1.4
- See Also:
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getRequestProperty
Returns the value of the named general request property for this connection.- Parameters:
key- the keyword by which the request is known (e.g., "Accept").- Returns:
- the value of the named general request property for this connection. If key is null, then null is returned.
- Throws:
IllegalStateException- if already connected- See Also:
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getRequestProperties
Returns an unmodifiable Map of general request properties for this connection. The Map keys are Strings that represent the request-header field names. Each Map value is a unmodifiable List of Strings that represents the corresponding field values. If multiple values for a given key are added via theaddRequestProperty(String, String)method, these values will be returned in the order they were added. This method must preserve the insertion order of such values. The default implementation of this method preserves the insertion order when multiple values are added for a given key. The values are returned in the order they were added.- Returns:
- a Map of the general request properties for this connection.
- Throws:
IllegalStateException- if already connected- Since:
- 1.4
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setDefaultRequestProperty
Deprecated.The instance specific setRequestProperty method should be used after an appropriate instance of URLConnection is obtained. Invoking this method will have no effect.Sets the default value of a general request property. When aURLConnectionis created, it is initialized with these properties.- Parameters:
key- the keyword by which the request is known (e.g., "Accept").value- the value associated with the key.- See Also:
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getDefaultRequestProperty
Deprecated.The instance specific getRequestProperty method should be used after an appropriate instance of URLConnection is obtained.Returns the value of the default request property. Default request properties are set for every connection.- Parameters:
key- the keyword by which the request is known (e.g., "Accept").- Returns:
- the value of the default request property for the specified key.
- See Also:
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setContentHandlerFactory
Sets theContentHandlerFactoryof an application. It can be called at most once by an application.The
ContentHandlerFactoryinstance is used to construct a content handler from a content type.- Parameters:
fac- the desired factory.- Throws:
Error- if the factory has already been defined.- See Also:
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guessContentTypeFromName
Tries to determine the content type of an object, based on the specified "file" component of a URL. This is a convenience method that can be used by subclasses that override thegetContentTypemethod.- Parameters:
fname- a filename.- Returns:
- a guess as to what the content type of the object is, based upon its file name.
- See Also:
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guessContentTypeFromStream
Tries to determine the type of an input stream based on the characters at the beginning of the input stream. This method can be used by subclasses that override thegetContentTypemethod.Ideally, this routine would not be needed. But many
httpservers return the incorrect content type; in addition, there are many nonstandard extensions. Direct inspection of the bytes to determine the content type is often more accurate than believing the content type claimed by thehttpserver.- Parameters:
is- an input stream that supports marks.- Returns:
- a guess at the content type, or
nullif none can be determined. - Throws:
IOException- if an I/O error occurs while reading the input stream.- See Also:
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