ewe.net
Class URL

java.lang.Object
  ewe.net.URL

public final class URL

extends Object

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 "..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..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

Field Summary

String

url

Constructor Summary

URL(String spec)
Initializes a URL from a complete string specification such as "http://www.urbanophile.com/arenn/".

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, int port, String file, URLStreamHandler ph)
This method initializes a new instance of URL with the specified protocol, host, port, and file.

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

URL(URL context, String spec)

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

static String	decodeURL(String url) Decode a URL encoded with '%##' notation.
static String	encodeURL(String url, boolean spaceToPlus) Encode the URL using %## notation.
boolean	equals(Object obj) Test another URL for equality with this one.
String	getAuthority() Returns the authority of the URL
String	getFile() Returns the file portion of the URL.
String	getHost() Returns the host of the URL
String	getPath() Returns the path of the URL.
int	getPort() Returns the port number of this URL or -1 if the default port number is being used.
String	getProtocol() Returns the protocol of the URL
String	getQuery() Returns the query of the URL.
String	getRef() Returns the ref (sometimes called the "# reference" or "anchor") portion of the URL.
String	getUserInfo() Returns the user information of the URL.
int	hashCode() Returns a hashcode computed by the URLStreamHandler of this URL
URLConnection	openConnection()
protected void	set(String protocol, String host, int port, String file, String ref) Sets the specified fields of the URL.
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.
String	toExternalForm() Returns a String representing this URL.
String	toString() Returns a String representing this URL.

Methods inherited from class java.lang.Object

clone, finalize, getClass

Field Detail

url

public String url

Constructor Detail

URL

public URL(String protocol,
           String host,
           int port,
           String file)
    throws MalformedURLException

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)
    throws MalformedURLException

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)
    throws MalformedURLException

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)
    throws MalformedURLException

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)
    throws MalformedURLException

URL

public URL(URL context,
           String spec,
           URLStreamHandler ph)
    throws MalformedURLException

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.

Overrides:

equals in class Object

Parameters:

obj - Another object to compare to.

Returns:

true if the URL is equal, false otherwise

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.

getPath

public String getPath()

Returns the path of the URL. This is the part of the file before any '?' character.

Since:

1.3

getAuthority

public String getAuthority()

Returns the authority of the URL

Since:

1.3

getHost

public String getHost()

Returns the host of the URL

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

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.

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.

hashCode

public int hashCode()

Returns a hashcode computed by the URLStreamHandler of this URL

Overrides:

hashCode in class Object

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.

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.

Since:

1.3

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()

Overrides:

toString in class Object

Returns:

A string for this URL

encodeURL

public static String encodeURL(String url,
                               boolean spaceToPlus)

Encode the URL using %## notation.

Parameters:

url - The unencoded URL.

spaceToPlus - true if you wish a space to be encoded as a '+', false to encode it as %20

Returns:

The encoded URL.

decodeURL

public static String decodeURL(String url)

Decode a URL encoded with '%##' notation.

Parameters:

url - The possibly encoded URL.

Returns:

The decoded URL.

openConnection

public URLConnection openConnection()
                             throws IOException

Throws:

IOException