If the connect method is called when the connection has already been opened (indicated by the connected field having the value true), 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 established
- IOException - if an I/O error occurs while opening the connection.
See Also: URLConnection.connected, URLConnection.getConnectTimeout(), URLConnection.setConnectTimeout(int),

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: URLConnection.setConnectTimeout(int), URLConnection.connect(),

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:

1. If the application has set up a content handler factory instance using the setContentHandlerFactory method, the createContentHandler method of that instance is called with the content type as an argument; the result is a content handler for that content type.
2. 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 '_'. The alphanumeric characters are specifically the 26 uppercase ASCII letters 'A' through 'Z', the 26 lowercase ASCII letters 'a' through 'z', and the 10 ASCII digits '0' through '9'. If the specified class does not exist, or is not a subclass of ContentHandler, then an UnknownServiceException is thrown.

Ths 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: URLConnection.setDefaultAllowUserInteraction(boolean),

Ths 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 a URLConnection's useCaches flag.
See Also: URLConnection.setDefaultUseCaches(boolean),

This method can be used in conjunction with the getHeaderFieldKey method to iterate through all the headers in the message.
Returns: the value of the n^th header field or null if there are fewer than n+1 fields
Parameters:
- n - an index, where n>=0
See Also: URLConnection.getHeaderFieldKey(int),

If called on a connection that sets the same header multiple times with possibly different values, only the last value is returned.
Returns: the value of the named header field, or null if there is no such field in the header.
Parameters:
- name - the name of a header 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.
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.
Parameters:
- name - the name of the header field.
- Default - a default value.

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.
Returns: the value of the named field, parsed as an integer. The Default value is returned if the field is missing or malformed.
Parameters:
- name - the name of the header field.
- Default - the default value.

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.

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 the http server.
Returns: a guess at the content type, or null if none can be determined.
Parameters:
- is - an input stream that supports marks.
Throws:
- IOException - if an I/O error occurs while reading the input stream.
See Also: InputStream.mark(int), InputStream.markSupported(), URLConnection.getContentType(),

Some non-standard implmentation of this method may ignore the specified timeout. To see the connect timeout set, please call getConnectTimeout().
Parameters:
- timeout - an int that specifies the connect timeout value in milliseconds
Throws:
- IllegalArgumentException - if the timeout parameter is negative
Since: 1.5
See Also: URLConnection.getConnectTimeout(), URLConnection.connect(),

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 its checkSetFactory method doesn't allow the operation.
See Also: ContentHandlerFactory, URLConnection.getContent(), SecurityManager.checkSetFactory(),

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: URLConnection.doInput, URLConnection.getDoInput(),

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: URLConnection.getDoOutput(),

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 its checkSetFactory method doesn't allow the operation.
Since: 1.2
See Also: SecurityManager.checkSetFactory(), URLConnection.getFileNameMap(),

Some non-standard implementation of this method ignores the specified timeout. To see the read timeout set, please call getReadTimeout().
Parameters:
- timeout - an int that specifies the timeout value to be used in milliseconds
Throws:
- IllegalArgumentException - if the timeout parameter is negative
Since: 1.5
See Also: URLConnection.getReadTimeout(), InputStream.read(),

NOTE: HTTP requires all request properties which can legally have multiple instances with the same key to use a comma-seperated 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 connected
- NullPointerException - if key is null
See Also: URLConnection.getRequestProperty(java.lang.String),

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.
Parameters:
- usecaches - a boolean indicating whether or not to allow caching
Throws:
- IllegalStateException - if already connected
See Also: URLConnection.getUseCaches(),