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Summary: Nested Field Constr Method Detail: Field Constr Method

java.net

Class URL

public final class URL extends Object implements Serializable

This final class represents an Internet Uniform Resource Locator (URL). For details on the syntax of URL's and what they can be used for, refer to RFC 1738, available from http://ds.internic.net/rfcs/rfc1738.txt

There are a great many protocols supported by URL's such as "http", "ftp", and "file". This object can handle any arbitrary URL for which a URLStreamHandler object can be written. Default protocol handlers are provided for the "http" and "ftp" protocols. Additional protocols handler implementations may be provided in the future. In any case, an application or applet can install its own protocol handlers that can be "chained" with other protocol hanlders in the system to extend the base functionality provided with this class. (Note, however, that unsigned applets cannot access properties by default or install their own protocol handlers).

This chaining is done via the system property java.protocol.handler.pkgs If this property is set, it is assumed to be a "|" separated list of package names in which to attempt locating protocol handlers. The protocol handler is searched for by appending the string ".<protocol>.Handler" to each packed in the list until a hander is found. If a protocol handler is not found in this list of packages, or if the property does not exist, then the default protocol handler of "gnu.java.net.<protocol>.Handler" is tried. If this is unsuccessful, a MalformedURLException is thrown.

All of the constructor methods of URL attempt to load a protocol handler and so any needed protocol handlers must be installed when the URL is constructed.

Here is an example of how URL searches for protocol handlers. Assume the value of java.protocol.handler.pkgs is "com.foo|com.bar" and the URL is "news://comp.lang.java.programmer". URL would looking the following places for protocol handlers: 

 com.foo.news.Handler
 com.bar.news.Handler
 gnu.java.net.news.Handler

If the protocol handler is not found in any of those locations, a MalformedURLException would be thrown.

Please note that a protocol handler must be a subclass of URLStreamHandler.

Normally, this class caches protocol handlers. Once it finds a handler for a particular protocol, it never tries to look up a new handler again. However, if the system property gnu.java.net.nocache_protocol_handlers is set, then this caching behavior is disabled. This property is specific to this implementation. Sun's JDK may or may not do protocol caching, but it almost certainly does not examine this property.

Please also note that an application can install its own factory for loading protocol handlers (see setURLStreamHandlerFactory). If this is done, then the above information is superseded and the behavior of this class in loading protocol handlers is dependent on that factory.

See Also: URLStreamHandler

Constructor Summary
URL(String protocol, String host, int port, String file)
Constructs a URL and loads a protocol handler for the values passed as arguments.
URL(String protocol, String host, String file)
Constructs a URL and loads a protocol handler for the values passed in as arugments.
URL(String protocol, String host, int port, String file, URLStreamHandler ph)
This method initializes a new instance of URL with the specified protocol, host, port, and file.
URL(String spec)
Initializes a URL from a complete string specification such as "http://www.urbanophile.com/arenn/".
URL(URL context, String spec)
This method parses a String representation of a URL within the context of an existing URL.
URL(URL context, String spec, URLStreamHandler ph)
Creates an URL from given arguments This method parses a String representation of a URL within the context of an existing URL.
Method Summary
booleanequals(Object obj)
Test another URL for equality with this one.
StringgetAuthority()
Returns the authority of the URL
ObjectgetContent()
Returns the contents of this URL as an object by first opening a connection, then calling the getContent() method against the connection
ObjectgetContent(Class[] classes)
Gets the contents of this URL
intgetDefaultPort()
Returns the default port of the URL.
StringgetFile()
Returns the file portion of the URL.
StringgetHost()
Returns the host of the URL
StringgetPath()
Returns the path of the URL.
intgetPort()
Returns the port number of this URL or -1 if the default port number is being used.
StringgetProtocol()
Returns the protocol of the URL
StringgetQuery()
Returns the query of the URL.
StringgetRef()
Returns the ref (sometimes called the "# reference" or "anchor") portion of the URL.
StringgetUserInfo()
Returns the user information of the URL.
inthashCode()
Returns a hashcode computed by the URLStreamHandler of this URL
URLConnectionopenConnection()
Returns a URLConnection object that represents a connection to the remote object referred to by the URL.
InputStreamopenStream()
Opens a connection to this URL and returns an InputStream for reading from that connection
booleansameFile(URL url)
Tests whether or not another URL refers to the same "file" as this one.
protected voidset(String protocol, String host, int port, String file, String ref)
Sets the specified fields of the URL.
protected voidset(String protocol, String host, int port, String authority, String userInfo, String path, String query, String ref)
Sets the specified fields of the URL.
static voidsetURLStreamHandlerFactory(URLStreamHandlerFactory fac)
Sets the URLStreamHandlerFactory for this class.
StringtoExternalForm()
Returns a String representing this URL.
StringtoString()
Returns a String representing this URL.
URItoURI()
Returns the equivalent URI object for this URL.

Constructor Detail

URL

public URL(String protocol, String host, int port, String file)
Constructs a URL and loads a protocol handler for the values passed as arguments.

Parameters: protocol The protocol for this URL ("http", "ftp", etc) host The hostname or IP address to connect to port The port number to use, or -1 to use the protocol's default port file The "file" portion of the URL.

Throws: MalformedURLException If a protocol handler cannot be loaded or a parse error occurs.

URL

public URL(String protocol, String host, String file)
Constructs a URL and loads a protocol handler for the values passed in as arugments. Uses the default port for the protocol.

Parameters: protocol The protocol for this URL ("http", "ftp", etc) host The hostname or IP address for this URL file The "file" portion of this URL.

Throws: MalformedURLException If a protocol handler cannot be loaded or a parse error occurs.

URL

public URL(String protocol, String host, int port, String file, URLStreamHandler ph)
This method initializes a new instance of URL with the specified protocol, host, port, and file. Additionally, this method allows the caller to specify a protocol handler to use instead of the default. If this handler is specified, the caller must have the "specifyStreamHandler" permission (see NetPermission) or a SecurityException will be thrown.

Parameters: protocol The protocol for this URL ("http", "ftp", etc) host The hostname or IP address to connect to port The port number to use, or -1 to use the protocol's default port file The "file" portion of the URL. ph The protocol handler to use with this URL.

Throws: MalformedURLException If no protocol handler can be loaded for the specified protocol. SecurityException If the SecurityManager exists and does not allow the caller to specify its own protocol handler.

Since: 1.2

URL

public URL(String spec)
Initializes a URL from a complete string specification such as "http://www.urbanophile.com/arenn/". First the protocol name is parsed out of the string. Then a handler is located for that protocol and the parseURL() method of that protocol handler is used to parse the remaining fields.

Parameters: spec The complete String representation of a URL

Throws: MalformedURLException If a protocol handler cannot be found or the URL cannot be parsed

URL

public URL(URL context, String spec)
This method parses a String representation of a URL within the context of an existing URL. Principally this means that any fields not present the URL are inheritied from the context URL. This allows relative URL's to be easily constructed. If the context argument is null, then a complete URL must be specified in the URL string. If the protocol parsed out of the URL is different from the context URL's protocol, then then URL String is also expected to be a complete URL.

Parameters: context The context on which to parse the specification spec The string to parse an URL

Throws: MalformedURLException If a protocol handler cannot be found for the URL cannot be parsed

URL

public URL(URL context, String spec, URLStreamHandler ph)
Creates an URL from given arguments This method parses a String representation of a URL within the context of an existing URL. Principally this means that any fields not present the URL are inheritied from the context URL. This allows relative URL's to be easily constructed. If the context argument is null, then a complete URL must be specified in the URL string. If the protocol parsed out of the URL is different from the context URL's protocol, then then URL String is also expected to be a complete URL.

Additionally, this method allows the caller to specify a protocol handler to use instead of the default. If this handler is specified, the caller must have the "specifyStreamHandler" permission (see NetPermission) or a SecurityException will be thrown.

Parameters: context The context in which to parse the specification spec The string to parse as an URL ph The stream handler for the URL

Throws: MalformedURLException If a protocol handler cannot be found or the URL cannot be parsed SecurityException If the SecurityManager exists and does not allow the caller to specify its own protocol handler.

Since: 1.2

Method Detail

equals

public boolean equals(Object obj)
Test another URL for equality with this one. This will be true only if the argument is non-null and all of the fields in the URL's match exactly (ie, protocol, host, port, file, and ref). Overrides Object.equals(), implemented by calling the equals method of the handler.

Parameters: obj The URL to compare with

Returns: true if the URL is equal, false otherwise

getAuthority

public String getAuthority()
Returns the authority of the URL

Returns: The authority specified in this URL.

Since: 1.3

getContent

public Object getContent()
Returns the contents of this URL as an object by first opening a connection, then calling the getContent() method against the connection

Returns: A content object for this URL

Throws: IOException If opening the connection or getting the content fails.

Since: 1.3

getContent

public Object getContent(Class[] classes)
Gets the contents of this URL

Parameters: classes The allow classes for the content object.

Returns: a context object for this URL.

Throws: IOException If an error occurs

getDefaultPort

public int getDefaultPort()
Returns the default port of the URL. If the StreamHandler for the URL protocol does not define a default port it returns -1.

Returns: The default port of the current protocol.

getFile

public String getFile()
Returns the file portion of the URL. Defined as path[?query]. Returns the empty string if there is no file portion.

Returns: The filename specified in this URL, or an empty string if empty.

getHost

public String getHost()
Returns the host of the URL

Returns: The host specified in this URL.

getPath

public String getPath()
Returns the path of the URL. This is the part of the file before any '?' character.

Returns: The path specified in this URL, or null if empty.

Since: 1.3

getPort

public int getPort()
Returns the port number of this URL or -1 if the default port number is being used.

Returns: The port number

See Also: getDefaultPort

getProtocol

public String getProtocol()
Returns the protocol of the URL

Returns: The specified protocol.

getQuery

public String getQuery()
Returns the query of the URL. This is the part of the file before the '?'.

Returns: the query part of the file, or null when there is no query part.

getRef

public String getRef()
Returns the ref (sometimes called the "# reference" or "anchor") portion of the URL.

Returns: The ref

getUserInfo

public String getUserInfo()
Returns the user information of the URL. This is the part of the host name before the '@'.

Returns: the user at a particular host or null when no user defined.

hashCode

public int hashCode()
Returns a hashcode computed by the URLStreamHandler of this URL

Returns: The hashcode for this URL.

openConnection

public URLConnection openConnection()
Returns a URLConnection object that represents a connection to the remote object referred to by the URL. The URLConnection is created by calling the openConnection() method of the protocol handler

Returns: A URLConnection for this URL

Throws: IOException If an error occurs

openStream

public InputStream openStream()
Opens a connection to this URL and returns an InputStream for reading from that connection

Returns: An InputStream for this URL.

Throws: IOException If an error occurs

sameFile

public boolean sameFile(URL url)
Tests whether or not another URL refers to the same "file" as this one. This will be true if and only if the passed object is not null, is a URL, and matches all fields but the ref (ie, protocol, host, port, and file);

Parameters: url The URL object to test with

Returns: true if URL matches this URL's file, false otherwise

set

protected void set(String protocol, String host, int port, String file, String ref)
Sets the specified fields of the URL. This is not a public method so that only URLStreamHandlers can modify URL fields. This might be called by the parseURL() method in that class. URLs are otherwise constant. If the given protocol does not exist, it will keep the previously set protocol.

Parameters: protocol The protocol name for this URL host The hostname or IP address for this URL port The port number of this URL file The "file" portion of this URL. ref The anchor portion of this URL.

set

protected void set(String protocol, String host, int port, String authority, String userInfo, String path, String query, String ref)
Sets the specified fields of the URL. This is not a public method so that only URLStreamHandlers can modify URL fields. URLs are otherwise constant. If the given protocol does not exist, it will keep the previously set protocol.

Parameters: protocol The protocol name for this URL. host The hostname or IP address for this URL. port The port number of this URL. authority The authority of this URL. userInfo The user and password (if needed) of this URL. path The "path" portion of this URL. query The query of this URL. ref The anchor portion of this URL.

Since: 1.3

setURLStreamHandlerFactory

public static void setURLStreamHandlerFactory(URLStreamHandlerFactory fac)
Sets the URLStreamHandlerFactory for this class. This factory is responsible for returning the appropriate protocol handler for a given URL.

Parameters: fac The URLStreamHandlerFactory class to use

Throws: Error If the factory is alread set. SecurityException If a security manager exists and its checkSetFactory method doesn't allow the operation

toExternalForm

public String toExternalForm()
Returns a String representing this URL. The String returned is created by calling the protocol handler's toExternalForm() method.

Returns: A string for this URL

toString

public String toString()
Returns a String representing this URL. Identical to toExternalForm(). The value returned is created by the protocol handler's toExternalForm method. Overrides Object.toString()

Returns: A string for this URL

toURI

public URI toURI()
Returns the equivalent URI object for this URL. This is the same as calling new URI(this.toString()). RFC2396-compliant URLs are guaranteed a successful conversion to a URI instance. However, there are some values which form valid URLs, but which do not also form RFC2396-compliant URIs.

Throws: URISyntaxException if this URL is not RFC2396-compliant, and thus can not be successfully converted to a URI.

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Summary: Nested Field Constr Method Detail: Field Constr Method