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public abstract class

URLConnection

extends Object
java.lang.Object
   ↳ java.net.URLConnection
Known Direct Subclasses
Known Indirect Subclasses

Class Overview

The URLConnection class is responsible for establishing a connection to an URL for a given protocol. The correct URLConnection subclass to call is determined by URLStreamHandler.openConnection().

Summary

Fields
protected boolean allowUserInteraction
protected boolean connected
protected boolean doInput
protected boolean doOutput
protected long ifModifiedSince
protected URL url
protected boolean useCaches
Protected Constructors
URLConnection(URL url)
Creates a URLConnection pointing to the resource specified by the url
Public Methods
void addRequestProperty(String field, String newValue)
Adds the given request property.
abstract void connect()
Establishes the connection to the resource specified by this URL with this method, along with other options that can only be set before this connection is made.
boolean getAllowUserInteraction()
Returns the value of allowUserInteraction which indicates if this connection allows user interaction
int getConnectTimeout()
Returns a timeout of connection by milliseconds
Object getContent(Class[] types)
Returns the object pointed to by this URL.
Object getContent()
Returns the object pointed to by this URL.
String getContentEncoding()
Returns the Content encoding type of the response body, null if no such field is found in the header response.
int getContentLength()
Returns the length of the content or body in the response header in bytes.
String getContentType()
Returns the type of the content.
long getDate()
Returns the date in milliseconds since epoch when this response header was created, or 0 if the field Date is not found in the header.
static boolean getDefaultAllowUserInteraction()
Returns whether this connection allow user interaction by default.
static String getDefaultRequestProperty(String field)
This method is deprecated. Use getRequestProperty(String)
boolean getDefaultUseCaches()
Returns whether this connection use caches by default.
boolean getDoInput()
Returns whether this connection supports input.
boolean getDoOutput()
Returns whether this connection supports output.
long getExpiration()
Returns the date in milliseconds since epoch when this response header expires or 0 if the field Expires is not found in the header.
static FileNameMap getFileNameMap()
Returns the MIME table of this URL connection.
String getHeaderField(int pos)
Returns the value of the field at position pos.
String getHeaderField(String key)
Returns the value of the field corresponding to the key Returns null if there is no such field.
long getHeaderFieldDate(String field, long defaultValue)
Returns the date value in the form of milliseconds since epoch corresponding to the field field.
int getHeaderFieldInt(String field, int defaultValue)
Returns the integer value of the specified field.
String getHeaderFieldKey(int posn)
Returns the name of the field at position specified by posn, null if there are fewer than posn fields.
Map<String, List<String>> getHeaderFields()
Provides an unmodifiable map of the connection header values.
long getIfModifiedSince()
Returns the value of ifModifiedSince of this connection in milliseconds since epoch
InputStream getInputStream()
Creates an InputStream for reading from this URL Connection.
long getLastModified()
Returns the value of the field Last-Modified in the response header, 0 if no such field exists
OutputStream getOutputStream()
Creates an OutputStream for writing to this URL Connection.
Permission getPermission()
Returns the permissions necessary to make the connection.
int getReadTimeout()
Returns a timeout of reading by milliseconds
Map<String, List<String>> getRequestProperties()
Provides an unmodifiable map of the request properties.
String getRequestProperty(String field)
Returns the value corresponding to the field in the request Header, null if no such field exists.
URL getURL()
Returns the URL of this connection
boolean getUseCaches()
Returns whether this connection uses caches
static String guessContentTypeFromName(String url)
Determines the MIME type of the file specified by the string URL, using the filename extension.
static String guessContentTypeFromStream(InputStream is)
Examines the bytes of the input stream and returns the MIME type, null if no content type can be deduced.
void setAllowUserInteraction(boolean newValue)
Sets the flag indicating whether this connection allows user interaction This can only be called prior to connection establishment.
void setConnectTimeout(int timeout)
Sets a timeout for connection to perform non-block.
synchronized static void setContentHandlerFactory(ContentHandlerFactory contentFactory)
Sets the current content handler factory to be contentFactory.
static void setDefaultAllowUserInteraction(boolean allows)
Set whether user interaction is allowed by default.
static void setDefaultRequestProperty(String field, String value)
This method is deprecated. Use getRequestProperty(String)
void setDefaultUseCaches(boolean newValue)
Set whether caches are used by default.
void setDoInput(boolean newValue)
Sets whether this URLConnection allows input.
void setDoOutput(boolean newValue)
Sets whether this URLConnection allows output.
static void setFileNameMap(FileNameMap map)
With permission from the security manager, this method sets the map to be the MIME Table of this URL connection.
void setIfModifiedSince(long newValue)
Sets the header field ifModifiedSince.
void setReadTimeout(int timeout)
Sets a timeout for reading to perform non-block.
void setRequestProperty(String field, String newValue)
Sets the value of the request header field field to newValue Only the current URL Connection is affected.
void setUseCaches(boolean newValue)
Sets the flag indicating if this connection uses caches.
String toString()
Returns the name of the class of the URLConnection
[Expand]
Inherited Methods
From class java.lang.Object

Fields

protected boolean allowUserInteraction

protected boolean connected

protected boolean doInput

protected boolean doOutput

protected long ifModifiedSince

protected URL url

protected boolean useCaches

Protected Constructors

protected URLConnection (URL url)

Creates a URLConnection pointing to the resource specified by the url

Public Methods

public void addRequestProperty (String field, String newValue)

Adds the given request property. Will not overwrite any existing properties associated with the given field name.

Parameters
field the request property field name
newValue the property value
Throws
IllegalStateException - if connection already established
NullPointerException - if field is null

public abstract void connect ()

Establishes the connection to the resource specified by this URL with this method, along with other options that can only be set before this connection is made.

Throws
IOException If an error occurs while connecting
See Also

public boolean getAllowUserInteraction ()

Returns the value of allowUserInteraction which indicates if this connection allows user interaction

Returns
  • the value of the flag
See Also

public int getConnectTimeout ()

Returns a timeout of connection by milliseconds

Returns
  • timeout of connection by milliseconds

public Object getContent (Class[] types)

Returns the object pointed to by this URL. It first attempts to get the content type from getContentType(), which looks for the response header field "Content-Type". If none is found, it will guess the content type from the filename extension. If that fails, it will guess by inspecting the stream.

Parameters
types The list of acceptable content types
Returns
  • Object The object of the resource pointed by this URL, or null if the content does not match a specified content type.
Throws
IOException If an error occurred obtaining the content.

public Object getContent ()

Returns the object pointed to by this URL. It first attempts to get the content type from getContentType(), which looks for the response header field "Content-Type". If none is found, it will guess the content type from the filename extension. If that fails, it will guess by inspecting the stream.

Returns
  • a non-null object
Throws
IOException if an IO error occurred
See Also

public String getContentEncoding ()

Returns the Content encoding type of the response body, null if no such field is found in the header response.

Returns
  • The content encoding type
See Also

public int getContentLength ()

Returns the length of the content or body in the response header in bytes. Answer -1 if Content-Length cannot be found in the response header.

Returns
  • The length of the content
See Also

public String getContentType ()

Returns the type of the content. Returns null if there's no such field.

Returns
  • The type of the content
See Also

public long getDate ()

Returns the date in milliseconds since epoch when this response header was created, or 0 if the field Date is not found in the header.

Returns
  • Date in millisecond since epoch
See Also

public static boolean getDefaultAllowUserInteraction ()

Returns whether this connection allow user interaction by default.

Returns
  • the value of defaultAllowUserInteraction
See Also

public static String getDefaultRequestProperty (String field)

This method is deprecated.Use getRequestProperty(String)

Returns the default value for the field specified by field, null if there's no such field.

Parameters
field the field to get the request property for
Returns
  • the field to be looked up

public boolean getDefaultUseCaches ()

Returns whether this connection use caches by default.

Returns
  • true if this connection use caches by default, false otherwise
See Also

public boolean getDoInput ()

Returns whether this connection supports input.

Returns
  • true if this connection supports input, false otherwise
See Also

public boolean getDoOutput ()

Returns whether this connection supports output.

Returns
  • true if this connection supports output, false otherwise
See Also

public long getExpiration ()

Returns the date in milliseconds since epoch when this response header expires or 0 if the field Expires is not found in the header.

Returns
  • Date in milliseconds since epoch
See Also

public static FileNameMap getFileNameMap ()

Returns the MIME table of this URL connection.

Returns
  • FileNameMap

public String getHeaderField (int pos)

Returns the value of the field at position pos. Returns null if there are fewer than pos fields in the response header.

Parameters
pos the position of the field
Returns
  • The value of the field
See Also

public String getHeaderField (String key)

Returns the value of the field corresponding to the key Returns null if there is no such field.

Parameters
key the name of the header field
Returns
  • The value of the header field
See Also

public long getHeaderFieldDate (String field, long defaultValue)

Returns the date value in the form of milliseconds since epoch corresponding to the field field. Returns defaultValue if no such field can be found in the response header.

Parameters
field the field in question
defaultValue the default value if no field is found
Returns
  • milliseconds since epoch
See Also

public int getHeaderFieldInt (String field, int defaultValue)

Returns the integer value of the specified field. Returns default value defaultValue if no such field exists.

Parameters
field the field to return
defaultValue to be returned if field> does not exist
Returns
  • value of the field

public String getHeaderFieldKey (int posn)

Returns the name of the field at position specified by posn, null if there are fewer than posn fields.

Parameters
posn the position to look for; the first field being 0
Returns
  • the name of the field
See Also

public Map<String, List<String>> getHeaderFields ()

Provides an unmodifiable map of the connection header values. The map keys are the String header field names. Each map value is a List of the header field values associated with that key name.

Returns
  • the mapping of header field names to values

public long getIfModifiedSince ()

Returns the value of ifModifiedSince of this connection in milliseconds since epoch

Returns
  • the time since epoch
See Also

public InputStream getInputStream ()

Creates an InputStream for reading from this URL Connection. It throws UnknownServiceException by default. This method should be overridden by its subclasses

Returns
  • The InputStream to read from
Throws
IOException If an InputStream could not be created
See Also

public long getLastModified ()

Returns the value of the field Last-Modified in the response header, 0 if no such field exists

Returns
  • the value of the field last modified
See Also

public OutputStream getOutputStream ()

Creates an OutputStream for writing to this URL Connection. It throws UnknownServiceException by default. This method should be overridden by subclasses.

Returns
  • The OutputStream to write to
Throws
IOException If an OutputStream could not be created
See Also

public Permission getPermission ()

Returns the permissions necessary to make the connection. Depending on the protocol, this can be any of the permission subclasses. The permission returned may also depend on the state of the connection, E.G In the case of HTTP, redirection can change the applicable permission if the host changed.

By default, this methods returns AllPermission. Subclasses should override this and return the appropriate permission object.

Returns
  • the permission object governing the connection
Throws
IOException if an IO exception occurs during the creation of the permission object.

public int getReadTimeout ()

Returns a timeout of reading by milliseconds

Returns
  • timeout of reading by milliseconds

public Map<String, List<String>> getRequestProperties ()

Provides an unmodifiable map of the request properties. The map keys are Strings, the map values are each a List of Strings, with each request property name mapped to its corresponding property values.

Returns
  • the mapping of request property names to values

public String getRequestProperty (String field)

Returns the value corresponding to the field in the request Header, null if no such field exists.

Parameters
field the field to get the property for
Returns
  • the field to look up
Throws
IllegalStateException - if connection already established
See Also

public URL getURL ()

Returns the URL of this connection

Returns
  • the URL of this connection
See Also

public boolean getUseCaches ()

Returns whether this connection uses caches

Returns
  • the value of the flag

public static String guessContentTypeFromName (String url)

Determines the MIME type of the file specified by the string URL, using the filename extension. Any fragment identifier is removed before processing.

Parameters
url the MIME type of the file.
Returns
  • the string representation of an URL
See Also

public static String guessContentTypeFromStream (InputStream is)

Examines the bytes of the input stream and returns the MIME type, null if no content type can be deduced.

Parameters
is the input stream for the URL
Returns
  • the type of the input stream
Throws
IOException If an IO error occurs

public void setAllowUserInteraction (boolean newValue)

Sets the flag indicating whether this connection allows user interaction This can only be called prior to connection establishment.

Parameters
newValue the value of the flag to be set
Throws
IllegalStateException if this method attempts to change the flag after a connection has been established

public void setConnectTimeout (int timeout)

Sets a timeout for connection to perform non-block. Default is zero. Timeout of zero means infinite.

Parameters
timeout timeout for connection in milliseconds.
Throws
IllegalArgumentException if timeout is less than zero.

public static synchronized void setContentHandlerFactory (ContentHandlerFactory contentFactory)

Sets the current content handler factory to be contentFactory. It can only do so with the permission of the security manager. The ContentFactory can only be specified once during the lifetime of an application.

Parameters
contentFactory the factory
Throws
Error if a ContentFactory has been created before SecurityException if the security manager does not allow this action
See Also

public static void setDefaultAllowUserInteraction (boolean allows)

Set whether user interaction is allowed by default. Existing URLConnections are unaffected.

Parameters
allows allow user interaction

public static void setDefaultRequestProperty (String field, String value)

This method is deprecated.Use getRequestProperty(String)

Sets the field in the default request header with the value value

Parameters
field the request header field to be set
value the new value

public void setDefaultUseCaches (boolean newValue)

Set whether caches are used by default. Existing URLConnections are unaffected.

Parameters
newValue the value of the flag to be set
See Also

public void setDoInput (boolean newValue)

Sets whether this URLConnection allows input. It cannot be set after the connection is made.

Parameters
newValue boolean
Throws
IllegalAccessError Exception thrown when this method attempts to change the value after connected
See Also

public void setDoOutput (boolean newValue)

Sets whether this URLConnection allows output. It cannot be set after the connection is made.

Parameters
newValue boolean
Throws
IllegalAccessError Exception thrown when this method attempts to change the value after connected
See Also

public static void setFileNameMap (FileNameMap map)

With permission from the security manager, this method sets the map to be the MIME Table of this URL connection.

Parameters
map the MIME table to be set.

public void setIfModifiedSince (long newValue)

Sets the header field ifModifiedSince.

Parameters
newValue number of milliseconds since epoch
Throws
IllegalStateException if already connected.

public void setReadTimeout (int timeout)

Sets a timeout for reading to perform non-block. Default is zero. Timeout of zero means infinite.

Parameters
timeout timeout for reading in milliseconds.
Throws
IllegalArgumentException if timeout is less than zero.

public void setRequestProperty (String field, String newValue)

Sets the value of the request header field field to newValue Only the current URL Connection is affected. It can only be called before the connection is made

Parameters
field the field
newValue the field's new value
Throws
IllegalStateException - if connection already established
NullPointerException - if field is null
See Also

public void setUseCaches (boolean newValue)

Sets the flag indicating if this connection uses caches. This value cannot be set after the connection is made.

Parameters
newValue the value of the flag to be set
Throws
IllegalStateException Exception thrown when this method attempts to change the value after connected
See Also

public String toString ()

Returns the name of the class of the URLConnection

Returns
  • The string representation of this URLConnection
See Also