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public  abstract  class  java.net.URLConnection
    extends  java.lang.Object  (I-§1.12)
{
        // Fields
    protected boolean allowUserInteraction;	§4.9.1
    protected boolean connected;	§4.9.2
    protected boolean doInput;	§4.9.3
    protected boolean doOutput;	§4.9.4
    protected long ifModifiedSince;	§4.9.5
    protected URL url;	§4.9.6
    protected boolean useCaches;	§4.9.7

        // Constructors
    protected URLConnection(URL  url);	§4.9.8

        // Methods
    public abstract void connect();	§4.9.9
    public boolean getAllowUserInteraction();	§4.9.10
    public Object getContent();	§4.9.11
    public String getContentEncoding();	§4.9.12
    public int getContentLength();	§4.9.13
    public String getContentType();	§4.9.14
    public long getDate();	§4.9.15
    public static boolean getDefaultAllowUserInteraction();	§4.9.16
    public static String 	§4.9.17
        getDefaultRequestProperty(String  key);
    public boolean getDefaultUseCaches();	§4.9.18
    public boolean getDoInput();	§4.9.19
    public boolean getDoOutput();	§4.9.20
    public long getExpiration();	§4.9.21
    public String getHeaderField(int  n);	§4.9.22
    public String getHeaderField(String  name);	§4.9.23
    public long getHeaderFieldDate(String  name, long  Default); §4.9.24
    public int getHeaderFieldInt(String  name, int  Default);	§4.9.25
    public String getHeaderFieldKey(int  n);	§4.9.26
    public long getIfModifiedSince();	§4.9.27
    public InputStream getInputStream();	§4.9.28
    public long getLastModified();	§4.9.29
    public OutputStream getOutputStream();	§4.9.30
    public String getRequestProperty(String  key);	§4.9.31
    public URL getURL();	§4.9.32
    public boolean getUseCaches();	§4.9.33
    protected static String	§4.9.34
        guessContentTypeFromName(String  fname);
    protected static String	§4.9.35
        guessContentTypeFromStream(InputStream  is);
    public void	§4.9.36
        setAllowUserInteraction(boolean  allowuserinteraction);
    public static void	§4.9.37
        setContentHandlerFactory(ContentHandlerFactory  fac);
    public static void	§4.9.38
     setDefaultAllowUserInteraction(boolean  defaultallowuserinteraction);
    public static void	§4.9.39
        setDefaultRequestProperty(String  key, String  value);
    public void	§4.9.40
        setDefaultUseCaches(boolean  defaultusecaches);
    public void setDoInput(boolean  doinput);	§4.9.41
    public void setDoOutput(boolean  dooutput);	§4.9.42
    public void setIfModifiedSince(long  ifmodifiedsince);	§4.9.43
    public void setRequestProperty(String  key, ;String  value);  §4.9.44
    public void setUseCaches(boolean  usecaches);	§4.9.45
    public String toString();	§4.9.46
}

The abstract class 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 multi-step process:

First, the connection object is created by invoking openConnection on a URL, then setup parameters are manipulated, then the actual connection to the remote object is made, and finally the remote object is available. There are a set of properties that apply before the connection is made, and a set that apply after:

before connect	after connect
AllowUserInteraction	ContentEncoding
RequestProperty	ContentLength
UseCaches	ContentType
DoOutput	HeaderField
DoInput	InputStream
IfModifiedSince	OutputStream
	LastModified
	Date
	LastModified
	Expiration

Most of these properties have a set and a get method. The first three in the "before" column also have corresponding "Default" properties that specify the default values used in subsequent requests where the property is not specified.

In the common case, all of these properties can be ignored: the pre-connection properties default to sensible values, and the post-connection properties are often uninteresting. For most clients of this interface, there are only two interesting methods: getInputStream and getObject, which are mirrored in the URL class by convenience methods.

If true, this URL is being examined in a context which it makes sense to allow user interactions such as popping up an authentication dialog. If false, then no user interaction is allowed.

This value of this field can be set by the set-Allow-User-Interaction method (I-§4.9.36). Its value can be accessed by the get-Allow-UserInteraction method (I-§4.9.10). Its default value is the value of the argument method to the last call to the set--Default-Allow-User-Interaction method (I-§4.9.38)

If false, this connection object has not created a communications link to the specified URL. If true, the communications link has been established.

This variable is set by the setDoInput method (I-§4.9.41). Its value can be accessed by the getDoInput method (I-§4.9.19).

A URL connection can be used for input and/or output. Setting the do-Input flag to true indicates that the application intends to read data from the URL connection.

The default value of this field is true.

This variable is set by the setDoOutput method (I-§4.9.42). Its value can be accessed by the getDoInput method (I-§4.9.20).

A URL connection can be used for input and/or output. Setting the do-Output flag to true indicates that the application intends to write data to the URL connection.

The default value of this field is false.

Some protocols support skipping the fetching of the object unless the object has been modified more recently than a certain time.

A non-zero value is interpreted as the time corresponding to if-Modified-Since seconds 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 (I-§4.9.43). Its value can be accessed by the getIfModifiedSince method (I-§4.9.27).

The default value of this field is 0, indicating that the fetching must always occur.

The URL representing 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 (I-§4.9.32).

The default value of this variable is the value of the URL argument in the URLConnection constructor (I-§4.9.6).

If true, the protocol is allowed to use caching whenever it can. If false, the protocol must always try to get a fresh copy of the object.

This field is set by the setUseCaches method (I-§4.9.45). Its value can be accessed by the getUseCaches method (I-§4.9.33). Its default value is the value of the last argument to the method set-Default-Use-Caches (I-§4.9.40).

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

Opens a communications link to the resource referenced by this URL, if such a connection hasn't already been established.

It the connect method is called when the connection has already been opened (indicated by the connected field (I-§4.9.2) having the value true), the call is ignored.

Throws

IOException (I-§2.29)

If an IO error occurs while opening the connection.

Returns:

the value of the allowUserInteraction (I-§4.9.1) field for this object..

Retrieves the contents of this URL connection.

This method first determines the content type of the object by calling the method getContentType (I-§4.9.1). If this is the first time that the application has seen that specific content type, a content handler for that content type is created:

1. If the application has set up a content handler factory instace using the setContentHandlerFactory (I-§4.9.37) method, the create--Content-Handler (I-§4.12.1) method of that instance is called with the content type as an argument; the result is a content handler for that content type.

1. If no content handler factory has yet been set up, or if the factory's createContentHandler method returns null, then the application loads the class named
   sun.net.www.content.<contentType>
   where <contentType> is formed by taking the content type string, replacing all slash characters with a period '.', and all other non-alphanumeric characters with the underscore character '_'. If the specified class does not exist, or is not a subclass of ContentHandler, then an UnknownServiceException is thrown.
   Returns:
   the object fetched. The instanceof operation should be used to determine the specific kind of object returned.
   Throws
   IOException (I-§2.29)
   If an IO error occurs while getting the content.
   Throws
   UnknownServiceException (I-§4.19)
   If the protocol does not support the content type.

Determines the value of the content-encoding attribute.

Returns:

the content encoding of the resource that the URL references, or null if not known.

Determines the value of the content-length attribute.

Returns:

the content length of the resource that this connection's URL referncees, or -1 if the content length is not known.

Determines the value of the content-type attribute.

Returns:

the content type of the resource that the URL references, or null if not known.

Determines the value of the date attribute.

Returns:

the sending date of the resource that the URL refernces, or 0 if not known. The value returned is the number of seconds since January 1, 1970 GMT.

Returns:

The default value of the allowUserInteraction (I-§4.9.1) field.

Gets the value of the default request property. Default request properties are set for every connection.

Returns:

the value of the default rnequest property for the specified key.

See Also:

setDefaultRequestProperty (I-§4.9.39).

Returns:

the default value of this URLConnection's useCaches (I-§4.9.7) flag.

Returns:

the value of this URLConnection's doInput (I-§4.9.3) flag.

Returns:

the value of this URLConnection's doOutput (I-§4.9.4) flag.

Determines the value of the expires attribute.

Returns:

the expiration date of the resource that this URL references, or 0 if not known. The value is number of seconds since January 1, 1970 GMT.

Gets the value for the nth header field. It returns null if there are fewer than n fields.

This method can be used in conjunction with the getHeaderFieldKey method (I-§4.9.26)to iterate through all the headers in the message.

Parameters:

n - an index

Returns:

the value of the nth header field.

Parameters:

name - the name of a header field

Returns:

the value of the named header field, or null if not known.

The named header field is parsed as a date. The result is the number of seconds 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.

The named header field is parsed as a number. The value is returned.

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.

Parameters:

n - an index

Returns:

the key for the nth header field, or null if there are fewer than n fields.

Returns:

the value of this object's ifModifiedSince (I-§4.9.5) field.

Returns:

an input stream that reads from this open connection.

Throws

IOException (I-§2.29)

If an IO error occurs while creating the input stream.

Throws

UnknownServiceException (I-§4.19)

If the protocol does not support input.

Determines the value of the last-modified attribute.

Returns:

the date the resource referenced by this URLConnection was last modified, or 0 if not known. The result is the number of seconds since January 1, 1970 GMT.

Returns:

an output stream that writes to this connection.

Throws

IOException (I-§2.29)

If an IO error occurs while creating the output stream.

Throws

UnknownServiceException (I-§4.19)

If the protocol does not support output.

Returns:

The value of the named general request property for this connection.

Returns:

the value of this URLConnection's URL (I-§4.9.6) field.

Returns:

the value of this URLConnection's useCaches (I-§4.9.7) field

Makes a guess as to what the content type of an object is, based upon the argument, which should be the "information" component of a URL. This is a convenience method which can be used by subclasses which override the getContentType method (I-§4.9.14).

Parameters:

fname - a file name

Returns:

a guess as to what the content type of the object is, based upon its name.

Tries to determine the type of an input stream based on the characters at the beginning of the input stream. This is a convenience method which can be used by subclasses which override the getContentType method (I-§4.9.14)

Ideally, this routine would not be needed. But many http servers return the incorrect content type; in addition, there are many non-standard extensions. Direct inspection of the bytes to determine the content-type is often more accurate than believing the content-type claimed by the http server.

Parameters:

is - an input stream that supports marks.(that is, it must be built on top of a BufferedInputStream)

Returns:

a guess at the content type, or null if none can be determined.

Throws

IOException (I-§2.29)

If an IO error occurs while reading the input stream.

Set the value of the allowUserInteraction (I-§4.9.1) field of this URLConnection.

Parameters:

allowuserinteraction -

the new value

Sets the ContentHandlerFactory (I-§4.12) of an application. It can be called at most once by an application.

The ContentHandlerFactory instance is used to construct a content handler (I-§4.9.11) from a content type

Parameters:

fac - the desired factory

Throws

Error (I-§1.48)

If the factory has already been defined.

Sets the default value of the allow-User-Interaction (I-§4.9.1) flag for this URLConnection to the specified value.

Parameters:

defaultallowuserinteraction -

the new value

Sets the default value of a general request property. When a URL-Connection 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 the key.

Sets the default value of the useCaches (I-§4.9.7) flag for this URLConnection to the specified value.

Parameters:

defaultusecaches -

the new value

Sets the value of the doInput (I-§4.9.3) flag for this URLConnection to the specified value.

Parameters:

value - the new value

Sets the value of the doOutput (I-§4.9.4) flag for this URL-Connection to the specified value.

Parameters:

value - the new value

Sets the value of the ifModifiedSince (I-§4.9.5) field of this URLConnection to the specified value

Parameters:

value - the new value

Sets the general request property.

Parameters:

key - the keyword by which the request is known (eg "accept")

value - the value associated with it

Sets the value of the useCaches (I-§4.9.7) field of this URL-Connection to the specified value.

Returns:

a string representation of this URLConnection.

Overrides:

toString in class Object (I-§1.12.9).

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