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# Class java.net.URLConnection

    java.lang.Object
       |
       +----java.net.URLConnection

public class URLConnection
extends Object

A class to represent an active connection to an object represented by a URL. It is an abstract class that must be subclassed to implement a connection.

##

allowUserInteraction
connected
doInput
doOutput
fileNameMap
ifModifiedSince
url
useCaches

##

URLConnection(URL)
  Constructs a URL connection to the specified URL.

##

connect()
  URLConnection objects go through two phases: first they are created, then they are connected.
getAllowUserInteraction()
getContent()
  Gets the object referred to by this URL.
getContentEncoding()
  Gets the content encoding.
getContentLength()
  Gets the content length.
getContentType()
  Gets the content type.
getDate()
  Gets the sending date of the object.
getDefaultAllowUserInteraction()
getDefaultRequestProperty(String)
getDefaultUseCaches()
  Sets/gets the default value of the UseCaches flag.
getDoInput()
getDoOutput()
getExpiration()
  Gets the expriation date of the object.
getHeaderField(int)
  Returns the value for the nth header field.
getHeaderField(String)
  Gets a header field by name.
getHeaderFieldDate(String, long)
  Gets a header field by name.
getHeaderFieldInt(String, int)
  Gets a header field by name.
getHeaderFieldKey(int)
  Returns the key for the nth header field.
getIfModifiedSince()
getInputStream()
  Calls this routine to get an InputStream that reads from the object.
getLastModified()
  Gets the last modified date of the object.
getOutputStream()
  Calls this routine to get an OutputStream that writes to the object.
getRequestProperty(String)
getURL()
  Gets the URL for this connection.
getUseCaches()
guessContentTypeFromName(String)
  A useful utility routine that tries to guess the content-type of an object based upon its extension.
guessContentTypeFromStream(InputStream)
  This method is used to check for files that have some type that can be determined by inspection.
setAllowUserInteraction(boolean)
  Some URL connections occasionally need to to interactions with the user.
setContentHandlerFactory(ContentHandlerFactory)
  Sets the ContentHandler factory.
setDefaultAllowUserInteraction(boolean)
  Sets/gets the default value of the allowUserInteraction flag.
setDefaultRequestProperty(String, String)
  Sets/gets the default value of a general request property.
setDefaultUseCaches(boolean)
setDoInput(boolean)
  A URL connection can be used for input and/or output.
setDoOutput(boolean)
  A URL connection can be used for input and/or output.
setIfModifiedSince(long)
  Some protocols support skipping fetching unless the object is newer than some amount of time.
setRequestProperty(String, String)
  Sets/gets a general request property.
setUseCaches(boolean)
  Some protocols do caching of documents.
toString()
  Returns the String representation of the URL connection.

##

url

      protected URL url

doInput

      protected boolean doInput

doOutput

      protected boolean doOutput

allowUserInteraction

      protected boolean allowUserInteraction

useCaches

      protected boolean useCaches

ifModifiedSince

      protected long ifModifiedSince

fileNameMap

      public static FileNameMap fileNameMap

connected

      protected boolean connected

##

URLConnection

      protected URLConnection(URL url)

  Constructs a URL connection to the specified URL.

  Parameters:
    url - the specified URL

##

connect

      public abstract void connect() throws IOException

  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 (eg. doInput, 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. Connecting when already connected does nothing.

getURL

      public URL getURL()

  Gets the URL for this connection.

getContentLength

      public int getContentLength()

  Gets the content length. Returns -1 if not known.

getContentType

      public String getContentType()

  Gets the content type. Returns null if not known.

getContentEncoding

      public String getContentEncoding()

  Gets the content encoding. Returns null if not known.

getExpiration

      public long getExpiration()

  Gets the expriation date of the object. Returns 0 if not known.

getDate

      public long getDate()

  Gets the sending date of the object. Returns 0 if not known.

getLastModified

      public long getLastModified()

  Gets the last modified date of the object. Returns 0 if not known.

getHeaderField

      public String getHeaderField(String name)

  Gets a header field by name. Returns null if not known.

  Parameters:
    name - the name of the header field

getHeaderFieldInt

      public int getHeaderFieldInt(String name,
                                   int Default)

  Gets a header field by name. Returns null if not known. The field is parsed as an integer. This form of getHeaderField exists because some connection types (e.g. http-ng) have pre-parsed headers and this allows them to override this method and short-circuit the parsing.

  Parameters:
    name - the name of the header field
    Default - the value to return if the field is missing or malformed.

getHeaderFieldDate

      public long getHeaderFieldDate(String name,
                                     long Default)

  Gets a header field by name. Returns null if not known. The field will be parsed as a date. This form of getHeaderField exists because some connection types (eg. http-ng) have pre-parsed headers. This allows them to override this method and short-circuit the parsing.

  Parameters:
    name - the name of the header field
    Default - the value to return if the field is missing or malformed.

getHeaderFieldKey

      public String getHeaderFieldKey(int n)

  Returns the key for the nth header field. Returns null if there are fewer than n fields. This can be used to iterate through all the headers in the message.

getHeaderField

      public String getHeaderField(int n)

  Returns the value for the nth header field. Returns null if there are fewer than n fields. This can be used in conjunction with getHeaderFieldKey to iterate through all the headers in the message.

getContent

      public Object getContent() throws IOException

  Gets the object referred to by this URL. For example, if it refers to an image the object will be some subclass of Image. The instanceof operator should be used to determine what kind of object was returned.

  Returns:
    the object that was fetched.
  Throws: UnknownServiceException
    If the protocol does not support content.

getInputStream

      public InputStream getInputStream() throws IOException

  Calls this routine to get an InputStream that reads from the object. Protocol implementors should use this if appropriate.

  Throws: UnknownServiceException
    If the protocol does not support input.

getOutputStream

      public OutputStream getOutputStream() throws IOException

  Calls this routine to get an OutputStream that writes to the object. Protocol implementors should use this if appropriate.

  Throws: UnknownServiceException
    If the protocol does not support output.

toString

      public String toString()

  Returns the String representation of the URL connection.

  Overrides:
    toString in class Object

setDoInput

      public void setDoInput(boolean doinput)

  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 unless DoOutput is explicitly set to true, in which case DoInput defaults to false.

getDoInput

      public boolean getDoInput()

setDoOutput

      public void setDoOutput(boolean dooutput)

  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.

getDoOutput

      public boolean getDoOutput()

setAllowUserInteraction

      public void setAllowUserInteraction(boolean allowuserinteraction)

  Some URL connections occasionally need to to interactions with the user. For example, the http protocol may need to pop up an authentication dialog. But this is only appropriate if the application is running in a context where there is a user. The allowUserInteraction flag allows these interactions when true. When it is false, they are not allowed and an exception is tossed. The default value can be set/gotten using setDefaultAllowUserInteraction, which defaults to false.

getAllowUserInteraction

      public boolean getAllowUserInteraction()

setDefaultAllowUserInteraction

      public static void setDefaultAllowUserInteraction(boolean defaultallowuserinteraction)

  Sets/gets the default value of the allowUserInteraction 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.

getDefaultAllowUserInteraction

      public static boolean getDefaultAllowUserInteraction()

setUseCaches

      public void setUseCaches(boolean usecaches)

  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.

getUseCaches

      public boolean getUseCaches()

setIfModifiedSince

      public void setIfModifiedSince(long ifmodifiedsince)

  Some protocols support skipping fetching unless the object is newer than some amount of time. The ifModifiedSince field may be set/gotten to define this time.

getIfModifiedSince

      public long getIfModifiedSince()

getDefaultUseCaches

      public boolean getDefaultUseCaches()

  Sets/gets the default value of the UseCaches 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.

setDefaultUseCaches

      public void setDefaultUseCaches(boolean defaultusecaches)

setRequestProperty

      public void setRequestProperty(String key,
                                     String value)

  Sets/gets a general request property.

  Parameters:
    key - The keyword by which the request is known (eg "accept")
    value - The value associated with it.

getRequestProperty

      public String getRequestProperty(String key)

setDefaultRequestProperty

      public static void setDefaultRequestProperty(String key,
                                                   String value)

  Sets/gets the default value of a general request property. When a URLConnection is created, it is initialized with these properties.

  Parameters:
    key - The keyword by which the request is known (eg "accept")
    value - The value associated with it.

getDefaultRequestProperty

      public static String getDefaultRequestProperty(String key)

setContentHandlerFactory

      public static synchronized void setContentHandlerFactory(ContentHandlerFactory fac)

  Sets the ContentHandler factory.

  Parameters:
    fac - the desired factory
  Throws: Error
    If the factory has already been defined.

guessContentTypeFromName

      protected static String guessContentTypeFromName(String fname)

  A useful utility routine that tries to guess the content-type of an object based upon its extension.

guessContentTypeFromStream

      public static String guessContentTypeFromStream(InputStream is) throws IOException

  This method is used to check for files that have some type that can be determined by inspection. The bytes at the beginning of the file are examined loosely. In an ideal world, this routine would not be needed, but in a world where http servers lie about content-types and extensions are often non-standard, direct inspection of the bytes can make the system more robust. The stream must support marks (e.g. have a BufferedInputStream somewhere).

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