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