- Direct Known Subclasses:
HttpURLConnection
,JarURLConnection
public abstract class URLConnection extends Object
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
openConnection
method on a URL. - The setup parameters and general request properties are manipulated.
- The actual connection to the remote object is made, using the
connect
method. - 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:
setAllowUserInteraction
setDoInput
setDoOutput
setIfModifiedSince
setUseCaches
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:
getContent
getHeaderField
getInputStream
getOutputStream
Certain header fields are accessed frequently. The methods:
getContentEncoding
getContentLength
getContentType
getDate
getExpiration
getLastModified
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
- See Also:
URL.openConnection()
,connect()
,getContent()
,getContentEncoding()
,getContentLength()
,getContentType()
,getDate()
,getExpiration()
,getHeaderField(int)
,getHeaderField(java.lang.String)
,getInputStream()
,getLastModified()
,getOutputStream()
,setAllowUserInteraction(boolean)
,setDefaultUseCaches(boolean)
,setDoInput(boolean)
,setDoOutput(boolean)
,setIfModifiedSince(long)
,setRequestProperty(java.lang.String, java.lang.String)
,setUseCaches(boolean)
-
Field Summary
Fields Modifier and Type Field Description protected boolean
allowUserInteraction
Iftrue
, thisURL
is being examined in a context in which it makes sense to allow user interactions such as popping up an authentication dialog.protected boolean
connected
Iffalse
, this connection object has not created a communications link to the specified URL.protected boolean
doInput
This variable is set by thesetDoInput
method.protected boolean
doOutput
This variable is set by thesetDoOutput
method.protected long
ifModifiedSince
Some protocols support skipping the fetching of the object unless the object has been modified more recently than a certain time.protected URL
url
The URL represents the remote object on the World Wide Web to which this connection is opened.protected boolean
useCaches
Iftrue
, the protocol is allowed to use caching whenever it can. -
Constructor Summary
Constructors Modifier Constructor Description protected
URLConnection(URL url)
Constructs a URL connection to the specified URL. -
Method Summary
Modifier and Type Method Description void
addRequestProperty(String key, String value)
Adds a general request property specified by a key-value pair.abstract void
connect()
Opens a communications link to the resource referenced by this URL, if such a connection has not already been established.boolean
getAllowUserInteraction()
Returns the value of theallowUserInteraction
field for this object.int
getConnectTimeout()
Returns setting for connect timeout.Object
getContent()
Retrieves the contents of this URL connection.Object
getContent(Class<?>[] classes)
Retrieves the contents of this URL connection.String
getContentEncoding()
Returns the value of thecontent-encoding
header field.int
getContentLength()
Returns the value of thecontent-length
header field.long
getContentLengthLong()
Returns the value of thecontent-length
header field as a long.String
getContentType()
Returns the value of thecontent-type
header field.long
getDate()
Returns the value of thedate
header field.static boolean
getDefaultAllowUserInteraction()
Returns the default value of theallowUserInteraction
field.static String
getDefaultRequestProperty(String key)
Deprecated.The instance specific getRequestProperty method should be used after an appropriate instance of URLConnection is obtained.boolean
getDefaultUseCaches()
Returns the default value of aURLConnection
'suseCaches
flag.static boolean
getDefaultUseCaches(String protocol)
Returns the default value of theuseCaches
flag for the given protocol.boolean
getDoInput()
Returns the value of thisURLConnection
'sdoInput
flag.boolean
getDoOutput()
Returns the value of thisURLConnection
'sdoOutput
flag.long
getExpiration()
Returns the value of theexpires
header field.static FileNameMap
getFileNameMap()
Loads filename map (a mimetable) from a data file.String
getHeaderField(int n)
Returns the value for then
th header field.String
getHeaderField(String name)
Returns the value of the named header field.long
getHeaderFieldDate(String name, long Default)
Returns the value of the named field parsed as date.int
getHeaderFieldInt(String name, int Default)
Returns the value of the named field parsed as a number.String
getHeaderFieldKey(int n)
Returns the key for then
th header field.long
getHeaderFieldLong(String name, long Default)
Returns the value of the named field parsed as a number.Map<String,List<String>>
getHeaderFields()
Returns an unmodifiable Map of the header fields.long
getIfModifiedSince()
Returns the value of this object'sifModifiedSince
field.InputStream
getInputStream()
Returns an input stream that reads from this open connection.long
getLastModified()
Returns the value of thelast-modified
header field.OutputStream
getOutputStream()
Returns an output stream that writes to this connection.Permission
getPermission()
Returns a permission object representing the permission necessary to make the connection represented by this object.int
getReadTimeout()
Returns setting for read timeout. 0 return implies that the option is disabled (i.e., timeout of infinity).Map<String,List<String>>
getRequestProperties()
Returns an unmodifiable Map of general request properties for this connection.String
getRequestProperty(String key)
Returns the value of the named general request property for this connection.URL
getURL()
Returns the value of thisURLConnection
'sURL
field.boolean
getUseCaches()
Returns the value of thisURLConnection
'suseCaches
field.static String
guessContentTypeFromName(String fname)
Tries to determine the content type of an object, based on the specified "file" component of a URL.static String
guessContentTypeFromStream(InputStream is)
Tries to determine the type of an input stream based on the characters at the beginning of the input stream.void
setAllowUserInteraction(boolean allowuserinteraction)
Set the value of theallowUserInteraction
field of thisURLConnection
.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.static void
setContentHandlerFactory(ContentHandlerFactory fac)
Sets theContentHandlerFactory
of an application.static void
setDefaultAllowUserInteraction(boolean defaultallowuserinteraction)
Sets the default value of theallowUserInteraction
field for all futureURLConnection
objects to the specified value.static void
setDefaultRequestProperty(String key, String value)
Deprecated.The instance specific setRequestProperty method should be used after an appropriate instance of URLConnection is obtained.void
setDefaultUseCaches(boolean defaultusecaches)
Sets the default value of theuseCaches
field to the specified value.static void
setDefaultUseCaches(String protocol, boolean defaultVal)
Sets the default value of theuseCaches
field for the named protocol to the given value.void
setDoInput(boolean doinput)
Sets the value of thedoInput
field for thisURLConnection
to the specified value.void
setDoOutput(boolean dooutput)
Sets the value of thedoOutput
field for thisURLConnection
to the specified value.static void
setFileNameMap(FileNameMap map)
Sets the FileNameMap.void
setIfModifiedSince(long ifmodifiedsince)
Sets the value of theifModifiedSince
field of thisURLConnection
to the specified value.void
setReadTimeout(int timeout)
Sets the read timeout to a specified timeout, in milliseconds.void
setRequestProperty(String key, String value)
Sets the general request property.void
setUseCaches(boolean usecaches)
Sets the value of theuseCaches
field of thisURLConnection
to the specified value.String
toString()
Returns aString
representation of this URL connection.
-
Field Details
-
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
getURL
method.The default value of this variable is the value of the URL argument in the
URLConnection
constructor. -
doInput
protected boolean doInputThis variable is set by thesetDoInput
method. Its value is returned by thegetDoInput
method.A URL connection can be used for input and/or output. Setting the
doInput
flag totrue
indicates that the application intends to read data from the URL connection.The default value of this field is
true
.- See Also:
getDoInput()
,setDoInput(boolean)
-
doOutput
protected boolean doOutputThis variable is set by thesetDoOutput
method. Its value is returned by thegetDoOutput
method.A URL connection can be used for input and/or output. Setting the
doOutput
flag totrue
indicates that the application intends to write data to the URL connection.The default value of this field is
false
.- See Also:
getDoOutput()
,setDoOutput(boolean)
-
allowUserInteraction
protected boolean allowUserInteractionIftrue
, thisURL
is 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
setAllowUserInteraction
method. Its value is returned by thegetAllowUserInteraction
method. Its default value is the value of the argument in the last invocation of thesetDefaultAllowUserInteraction
method. -
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
setUseCaches
method. Its value is returned by thegetUseCaches
method.Its default value is the value given in the last invocation of the
setDefaultUseCaches
method.The default setting may be overridden per protocol with
setDefaultUseCaches(String,boolean)
. -
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
setIfModifiedSince
method. Its value is returned by thegetIfModifiedSince
method.The default value of this field is
0
, indicating that the fetching must always occur.- See Also:
getIfModifiedSince()
,setIfModifiedSince(long)
-
connected
protected boolean connectedIffalse
, this connection object has not created a communications link to the specified URL. Iftrue
, the communications link has been established.
-
-
Constructor Details
-
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.
-
-
Method Details
-
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:
setFileNameMap(java.net.FileNameMap)
-
setFileNameMap
Sets the FileNameMap.If there is a security manager, this method first calls the security manager's
checkSetFactory
method to ensure the operation is allowed. This could result in a SecurityException.- Parameters:
map
- the FileNameMap to be set- Throws:
SecurityException
- if a security manager exists and itscheckSetFactory
method doesn't allow the operation.- Since:
- 1.2
- See Also:
SecurityManager.checkSetFactory()
,getFileNameMap()
-
connect
Opens a communications link to the resource referenced by this URL, if such a connection has not already been established.If the
connect
method is called when the connection has already been opened (indicated by theconnected
field 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:
connected
,getConnectTimeout()
,setConnectTimeout(int)
-
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
- anint
that specifies the connect timeout value in milliseconds- Throws:
IllegalArgumentException
- if the timeout parameter is negative- Since:
- 1.5
- See Also:
getConnectTimeout()
,connect()
-
getConnectTimeout
public int getConnectTimeout()Returns setting for connect timeout.0 return implies that the option is disabled (i.e., timeout of infinity).
- Returns:
- an
int
that indicates the connect timeout value in milliseconds - Since:
- 1.5
- See Also:
setConnectTimeout(int)
,connect()
-
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
- anint
that specifies the timeout value to be used in milliseconds- Throws:
IllegalArgumentException
- if the timeout parameter is negative- Since:
- 1.5
- See Also:
getReadTimeout()
,InputStream.read()
-
getReadTimeout
public int getReadTimeout()Returns setting for read timeout. 0 return implies that the option is disabled (i.e., timeout of infinity).- Returns:
- an
int
that indicates the read timeout value in milliseconds - Since:
- 1.5
- See Also:
setReadTimeout(int)
,InputStream.read()
-
getURL
Returns the value of thisURLConnection
'sURL
field.- Returns:
- the value of this
URLConnection
'sURL
field. - See Also:
url
-
getContentLength
public int getContentLength()Returns the value of thecontent-length
header field.Note:
getContentLengthLong()
should be preferred over this method, since it returns along
instead and is therefore more portable.- Returns:
- the content length of the resource that this connection's URL
references,
-1
if the content length is not known, or if the content length is greater than Integer.MAX_VALUE.
-
getContentLengthLong
public long getContentLengthLong()Returns the value of thecontent-length
header field as a long.- Returns:
- the content length of the resource that this connection's URL
references, or
-1
if the content length is not known. - Since:
- 1.7
-
getContentType
Returns the value of thecontent-type
header field.- Returns:
- the content type of the resource that the URL references,
or
null
if not known. - See Also:
getHeaderField(java.lang.String)
-
getContentEncoding
Returns the value of thecontent-encoding
header field.- Returns:
- the content encoding of the resource that the URL references,
or
null
if not known. - See Also:
getHeaderField(java.lang.String)
-
getExpiration
public long getExpiration()Returns the value of theexpires
header 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:
getHeaderField(java.lang.String)
-
getDate
public long getDate()Returns the value of thedate
header field.- Returns:
- the sending date of the resource that the URL references,
or
0
if not known. The value returned is the number of milliseconds since January 1, 1970 GMT. - See Also:
getHeaderField(java.lang.String)
-
getLastModified
public long getLastModified()Returns the value of thelast-modified
header field. The result is the number of milliseconds since January 1, 1970 GMT.- Returns:
- the date the resource referenced by this
URLConnection
was last modified, or 0 if not known. - See Also:
getHeaderField(java.lang.String)
-
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
null
if there is no such field in the header.
-
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.- Returns:
- a Map of header fields
- Since:
- 1.4
-
getHeaderFieldInt
Returns the value of the named field parsed as a number.This form of
getHeaderField
exists 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.Default
- the default value.- Returns:
- the value of the named field, parsed as an integer. The
Default
value is returned if the field is missing or malformed.
-
getHeaderFieldLong
Returns the value of the named field parsed as a number.This form of
getHeaderField
exists 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.Default
- the default value.- Returns:
- the value of the named field, parsed as a long. The
Default
value is returned if the field is missing or malformed. - Since:
- 1.7
-
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
getHeaderField
exists 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.Default
- a default value.- Returns:
- the value of the field, parsed as a date. The value of the
Default
argument is returned if the field is missing or malformed.
-
getHeaderFieldKey
Returns the key for then
th header field. Some implementations may treat the0
th header field as special, in which case,getHeaderField(0)
may return some value, butgetHeaderFieldKey(0)
returnsnull
. Forn > 0
it returnsnull
if there are fewer thann+1
fields.- Parameters:
n
- an index, wheren>=0
- Returns:
- the key for the
n
th header field, ornull
if there are fewer thann+1
fields whenn > 0
.
-
getHeaderField
Returns the value for then
th header field. It returnsnull
if there are fewer thann+1
fields.This method can be used in conjunction with the
getHeaderFieldKey
method to iterate through all the headers in the message.- Parameters:
n
- an index, wheren>=0
- Returns:
- the value of the
n
th header field ornull
if there are fewer thann+1
fields - See Also:
getHeaderFieldKey(int)
-
getContent
Retrieves the contents of this URL connection.This method first determines the content type of the object by calling the
getContentType
method. 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
setContentHandlerFactory
method, thecreateContentHandler
method of that instance is called with the content type as an argument; the result is a content handler for that content type. - If no
ContentHandlerFactory
has yet been set up, or if the factory'screateContentHandler
method 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,Error
orRuntimeException
thrown from thecreateContentHandler
, if encountered, will be propagated to the calling thread. ThecreateContentHandler
method 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 anUnknownServiceException
is thrown.
- Returns:
- the object fetched. The
instanceof
operator 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:
ContentHandlerFactory.createContentHandler(java.lang.String)
,getContentType()
,setContentHandlerFactory(java.net.ContentHandlerFactory)
- If the application has set up a content handler factory instance
using the
-
getContent
Retrieves the contents of this URL connection.- Parameters:
classes
- theClass
array 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
instanceof
operator 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:
getContent()
,ContentHandlerFactory.createContentHandler(java.lang.String)
,getContent(java.lang.Class[])
,setContentHandlerFactory(java.net.ContentHandlerFactory)
-
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, aURLConnection
representing afile:
URL would return ajava.io.FilePermission
object.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.
-
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.- 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:
setReadTimeout(int)
,getReadTimeout()
-
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.
-
toString
Returns aString
representation of this URL connection. -
setDoInput
public void setDoInput(boolean doinput)Sets the value of thedoInput
field for thisURLConnection
to 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:
doInput
,getDoInput()
-
getDoInput
public boolean getDoInput()Returns the value of thisURLConnection
'sdoInput
flag.- Returns:
- the value of this
URLConnection
'sdoInput
flag. - See Also:
setDoInput(boolean)
-
setDoOutput
public void setDoOutput(boolean dooutput)Sets the value of thedoOutput
field for thisURLConnection
to 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:
getDoOutput()
-
getDoOutput
public boolean getDoOutput()Returns the value of thisURLConnection
'sdoOutput
flag.- Returns:
- the value of this
URLConnection
'sdoOutput
flag. - See Also:
setDoOutput(boolean)
-
setAllowUserInteraction
public void setAllowUserInteraction(boolean allowuserinteraction)Set the value of theallowUserInteraction
field of thisURLConnection
.- Parameters:
allowuserinteraction
- the new value.- Throws:
IllegalStateException
- if already connected- See Also:
getAllowUserInteraction()
-
getAllowUserInteraction
public boolean getAllowUserInteraction()Returns the value of theallowUserInteraction
field for this object.- Returns:
- the value of the
allowUserInteraction
field for this object. - See Also:
setAllowUserInteraction(boolean)
-
setDefaultAllowUserInteraction
public static void setDefaultAllowUserInteraction(boolean defaultallowuserinteraction)Sets the default value of theallowUserInteraction
field for all futureURLConnection
objects to the specified value.- Parameters:
defaultallowuserinteraction
- the new value.- See Also:
getDefaultAllowUserInteraction()
-
getDefaultAllowUserInteraction
public static boolean getDefaultAllowUserInteraction()Returns the default value of theallowUserInteraction
field.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
allowUserInteraction
field. - See Also:
setDefaultAllowUserInteraction(boolean)
-
setUseCaches
public void setUseCaches(boolean usecaches)Sets the value of theuseCaches
field of thisURLConnection
to 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
- aboolean
indicating whether or not to allow caching- Throws:
IllegalStateException
- if already connected- See Also:
getUseCaches()
-
getUseCaches
public boolean getUseCaches()Returns the value of thisURLConnection
'suseCaches
field.- Returns:
- the value of this
URLConnection
'suseCaches
field. - See Also:
setUseCaches(boolean)
-
setIfModifiedSince
public void setIfModifiedSince(long ifmodifiedsince)Sets the value of theifModifiedSince
field of thisURLConnection
to the specified value.- Parameters:
ifmodifiedsince
- the new value.- Throws:
IllegalStateException
- if already connected- See Also:
getIfModifiedSince()
-
getIfModifiedSince
public long getIfModifiedSince()Returns the value of this object'sifModifiedSince
field.- Returns:
- the value of this object's
ifModifiedSince
field. - See Also:
setIfModifiedSince(long)
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getDefaultUseCaches
public boolean getDefaultUseCaches()Returns the default value of aURLConnection
'suseCaches
flag.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
'suseCaches
flag. - See Also:
setDefaultUseCaches(boolean)
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setDefaultUseCaches
public void setDefaultUseCaches(boolean defaultusecaches)Sets the default value of theuseCaches
field to the specified value. This default value can be over-ridden per protocol usingsetDefaultUseCaches(String,boolean)
- Parameters:
defaultusecaches
- the new value.- See Also:
getDefaultUseCaches()
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setDefaultUseCaches
Sets the default value of theuseCaches
field 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
-
getDefaultUseCaches
Returns the default value of theuseCaches
flag 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
useCaches
flag for the given protocol. - Since:
- 9
-
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:
getRequestProperty(java.lang.String)
-
addRequestProperty
Adds a general request property specified by a key-value pair. This method will not overwrite existing values associated with the same key.- 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:
getRequestProperties()
-
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:
setRequestProperty(java.lang.String, java.lang.String)
-
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.- Returns:
- a Map of the general request properties for this connection.
- Throws:
IllegalStateException
- if already connected- Since:
- 1.4
-
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 aURLConnection
is 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:
setRequestProperty(java.lang.String,java.lang.String)
,getDefaultRequestProperty(java.lang.String)
-
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:
getRequestProperty(java.lang.String)
,setDefaultRequestProperty(java.lang.String, java.lang.String)
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setContentHandlerFactory
Sets theContentHandlerFactory
of an application. It can be called at most once by an application.The
ContentHandlerFactory
instance is used to construct a content handler from a content type.If there is a security manager, this method first calls the security manager's
checkSetFactory
method to ensure the operation is allowed. This could result in a SecurityException.- Parameters:
fac
- the desired factory.- Throws:
Error
- if the factory has already been defined.SecurityException
- if a security manager exists and itscheckSetFactory
method doesn't allow the operation.- See Also:
ContentHandlerFactory
,getContent()
,SecurityManager.checkSetFactory()
-
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 thegetContentType
method.- Parameters:
fname
- a filename.- Returns:
- a guess as to what the content type of the object is, based upon its file name.
- See Also:
getContentType()
-
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 thegetContentType
method.Ideally, this routine would not be needed. But many
http
servers 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 thehttp
server.- Parameters:
is
- an input stream that supports marks.- Returns:
- a guess at the content type, or
null
if none can be determined. - Throws:
IOException
- if an I/O error occurs while reading the input stream.- See Also:
InputStream.mark(int)
,InputStream.markSupported()
,getContentType()
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