java.net.URL
is new.
java.lang.Object
Class URL represents a Uniform Resource Locator, a pointer to a "resource" on the World Wide Web. A resource can be something as simple as a file or a directory, or it can be a reference to a more complicated object, such as a query to a database or to a search engine. More information on the types of URLs and their formats can be found at:
http://archive.ncsa.uiuc.edu/SDG/Software/Mosaic/Demo/url-primer.html
In general, a URL can be broken into several parts. The previous example of a URL indicates that the protocol to use is http (HyperText Transfer Protocol) and that the information resides on a host machine named www.ncsa.uiuc.edu. The information on that host machine is named /SDG/Software/Mosaic/Demo/url-primer.html. The exact meaning of this name on the host machine is both protocol dependent and host dependent. The information normally resides in a file, but it could be generated on the fly. This component of the URL is called the path component.
A URL can optionally specify a "port", which is the port number to which the TCP connection is made on the remote host machine. If the port is not specified, the default port for the protocol is used instead. For example, the default port for http is 80. An alternative port could be specified as:
http://archive.ncsa.uiuc.edu:80/SDG/Software/Mosaic/Demo/url-primer.html
The syntax of URL is defined by
RFC 2396: Uniform Resource Identifiers (URI): Generic Syntax
, amended by
RFC 2732: Format for Literal IPv6 Addresses in URLs
.
The Literal IPv6 address format also supports scope_ids. The syntax and usage of scope_ids is described
here
.
A URL may have appended to it a "fragment", also known as a "ref" or a "reference". The fragment is indicated by the sharp sign character "#" followed by more characters. For example,
http://java.sun.com/index.html#chapter1
This fragment is not technically part of the URL. Rather, it indicates that after the specified resource is retrieved, the application is specifically interested in that part of the document that has the tag chapter1 attached to it. The meaning of a tag is resource specific.
An application can also specify a "relative URL", which contains only enough information to reach the resource relative to another URL. Relative URLs are frequently used within HTML pages. For example, if the contents of the URL:
http://java.sun.com/index.html
contained within it the relative URL:
FAQ.html
it would be a shorthand for:
http://java.sun.com/FAQ.html
The relative URL need not specify all the components of a URL. If the protocol, host name, or port number is missing, the value is inherited from the fully specified URL. The file component must be specified. The optional fragment is not inherited.
The URL class does not itself encode or decode any URL components according to the escaping mechanism defined in RFC2396. It is the responsibility of the caller to encode any fields, which need to be escaped prior to calling URL, and also to decode any escaped fields, that are returned from URL. Furthermore, because URL has no knowledge of URL escaping, it does not recognise equivalence between the encoded or decoded form of the same URL. For example, the two URLs:
http://foo.com/hello world/ and http://foo.com/hello%20world
would be considered not equal to each other.
Note, the
URI
class does perform escaping of its component fields in certain circumstances. The recommended way to manage the encoding and decoding of URLs is to use
URI
, and to convert between these two classes using
toURI()
and
URI.toURL()
.
The
URLEncoder
and
URLDecoder
classes can also be used, but only for HTML form encoding, which is not the same as the encoding scheme defined in RFC2396.
| Constructor Summary | |
|---|---|
|
URL
(
String
spec) Creates a URL object from the String representation. |
|
|
URL
(
String
protocol,
String
host, int port,
String
file) Creates a URL object from the specified protocol, host, port number, and file. |
|
|
URL
(
String
protocol,
String
host, int port,
String
file,
URLStreamHandler
handler) Creates a URL object from the specified protocol, host, port number, file, and handler. |
|
|
URL
(
String
protocol,
String
host,
String
file) Creates a URL from the specified protocol name, host name, and file name. |
|
|
URL
(
URL
context,
String
spec) Creates a URL by parsing the given spec within a specified context. |
|
|
URL
(
URL
context,
String
spec,
URLStreamHandler
handler) Creates a URL by parsing the given spec with the specified handler within a specified context. |
|
| Method Summary | |
|---|---|
| boolean |
equals
(
Object
obj) Compares this URL for equality with another object. |
| String |
getAuthority
() Gets the authority part of this URL. |
| Object |
getContent
() Gets the contents of this URL. |
| Object |
getContent
(
Class
[] classes) Gets the contents of this URL. |
| int |
getDefaultPort
() Gets the default port number of the protocol associated with this URL. |
| String |
getFile
() Gets the file name of this URL. |
| String |
getHost
() Gets the host name of this URL, if applicable. |
| String |
getPath
() Gets the path part of this URL. |
| int |
getPort
() Gets the port number of this URL. |
| String |
getProtocol
() Gets the protocol name of this URL. |
| String |
getQuery
() Gets the query part of this URL. |
| String |
getRef
() Gets the anchor (also known as the "reference") of this URL. |
| String |
getUserInfo
() Gets the userInfo part of this URL. |
| int |
hashCode
() Creates an integer suitable for hash table indexing. |
| URLConnection |
openConnection
() Returns a URLConnection object that represents a connection to the remote object referred to by the URL. |
|
URLConnection
|
openConnection
(
Proxy
Same as openConnection(), except that the connection will be made through the specified proxy; Protocol handlers that do not support proxing will ignore the proxy parameter and make a normal connection.
|
| InputStream |
openStream
() Opens a connection to this URL and returns an InputStream for reading from that connection. |
| boolean |
sameFile
(
URL
other) Compares two URLs, excluding the fragment component. |
| protected void |
set
(
String
protocol,
String
host, int port,
String
file,
String
ref) Sets the 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 8 fields of the URL. |
| static void |
setURLStreamHandlerFactory
(
URLStreamHandlerFactory
fac) Sets an application's URLStreamHandlerFactory. |
| String |
toExternalForm
() Constructs a string representation of this URL. |
| String |
toString
() Constructs a string representation of this URL. |
|
URI
|
toURI
()
Returns a
URI
|
| Methods inherited from class java.lang. Object |
|---|
| clone , finalize , getClass , notify , notifyAll , wait , wait , wait |
| Constructor Detail |
|---|
public URL(String protocol,
String host,
int port,
String file)
throws MalformedURLException
host can be expressed as a host name or a literal IP address. If IPv6 literal address is used, it should be enclosed in square brackets ( '[' and ']' ), as specified by RFC 2732 ; However, the literal IPv6 address format defined in RFC 2373: IP Version 6 Addressing Architecture is also accepted.
Specifying a port number of -1 indicates that the URL should use the default port for the protocol.
If this is the first URL object being created with the specified protocol, a stream protocol handler object, an instance of class URLStreamHandler, is created for that protocol:
java.protocol.handler.pkgs
If the value of that system property is not null, it is interpreted as a list of packages separated by a vertical slash character '|'. The constructor tries to load the class named:
<package>.<protocol>.Handler
where <
package
> is replaced by the name of the package and <
protocol
> is replaced by the name of the protocol. If this class does not exist, or if the class exists but it is not a subclass of URLStreamHandler, then the next package in the list is tried.
<system default package>.<protocol>.Handler
If this class does not exist, or if the class exists but it is not a subclass of URLStreamHandler, then a MalformedURLException is thrown.
Protocol handlers for the following protocols are guaranteed to exist on the search path :-
http, https, ftp, file, and jar
Protocol handlers for additional protocols may also be available.
No validation of the inputs is performed by this constructor.
public URL(String protocol,
String host,
String file)
throws MalformedURLException
This method is equivalent to calling the four-argument constructor with the arguments being protocol, host, -1, and file. No validation of the inputs is performed by this constructor.
public URL(String protocol,
String host,
int port,
String file,
URLStreamHandler handler)
throws MalformedURLException
If the handler is not null and there is a security manager, the security manager's checkPermission method is called with a NetPermission("specifyStreamHandler") permission. This may result in a SecurityException. No validation of the inputs is performed by this constructor.
public URL(String spec)
throws MalformedURLException
This constructor is equivalent to a call to the two-argument constructor with a null first argument.
public URL(URL context,
String spec)
throws MalformedURLException
<scheme>://<authority><path>?<query>#<fragment>
The reference is parsed into the scheme, authority, path, query and fragment parts. If the path component is empty and the scheme, authority, and query components are undefined, then the new URL is a reference to the current document. Otherwise, the fragment and query parts present in the spec are used in the new URL. If the scheme component is defined in the given spec and does not match the scheme of the context, then the new URL is created as an absolute URL based on the spec alone. Otherwise the scheme component is inherited from the context URL.
If the authority component is present in the spec then the spec is treated as absolute and the spec authority and path will replace the context authority and path. If the authority component is absent in the spec then the authority of the new URL will be inherited from the context.
If the spec's path component begins with a slash character "/" then the path is treated as absolute and the spec path replaces the context path.
Otherwise, the path is treated as a relative path and is appended to the context path, as described in RFC2396. Also, in this case, the path is canonicalized through the removal of directory changes made by occurences of ".." and ".".
For a more detailed description of URL parsing, refer to RFC2396.
public URL(URL context,
String spec,
URLStreamHandler handler)
throws MalformedURLException
| Method Detail |
|---|
protected void set(String protocol,
String host,
int port,
String file,
String ref)
protected void set(String protocol,
String host,
int port,
String authority,
String userInfo,
String path,
String query,
String ref)
public String getQuery()
public String getPath()
public String getUserInfo()
public String getAuthority()
public int getPort()
public int getDefaultPort()
public String getProtocol()
public String getHost()
public String getFile()
public String getRef()
public boolean equals(Object obj)
If the given object is not a URL then this method immediately returns false.
Two URL objects are equal if they have the same protocol, reference equivalent hosts, have the same port number on the host, and the same file and fragment of the file.
Two hosts are considered equivalent if both host names can be resolved into the same IP addresses; else if either host name can't be resolved, the host names must be equal without regard to case; or both host names equal to null.
Since hosts comparison requires name resolution, this operation is a blocking operation.
Note: The defined behavior for equals is known to be inconsistent with virtual hosting in HTTP.
public int hashCode()
The hash code is based upon all the URL components relevant for URL comparison. As such, this operation is a blocking operation.
public boolean sameFile(URL other)
Returns true if this URL and the other argument are equal without taking the fragment component into consideration.
public String toString()
public String toExternalForm()
toURI
Returns a
URI
equivalent to this URL. This method functions in the same way as new URI (this.toString()).
Note, any URL instance that complies with RFC 2396 can be converted to a URI. However, some URLs that are not strictly in compliance can not be converted to a URI.
Returns:
a URI instance equivalent to this URL.
Throws:
URISyntaxException
- if this URL is not formatted strictly according to to RFC2396 and cannot be converted to a URI.
Since:
1.5
public URLConnection openConnection()
throws IOException
A new connection is opened every time by calling the openConnection method of the protocol handler for this URL.
If for the URL's protocol (such as HTTP or JAR), there exists a public, specialized URLConnection subclass belonging to one of the following packages or one of their subpackages: java.lang, java.io, java.util, java.net, the connection returned will be of that subclass. For example, for HTTP an HttpURLConnection will be returned, and for JAR a JarURLConnection will be returned.
openConnection
Same as openConnection(), except that the connection will be made through the specified proxy; Protocol handlers that do not support proxing will ignore the proxy parameter and make a normal connection. Calling this method preempts the system's default ProxySelector settings.
Parameters:
proxy - the Proxy through which this connection will be made. If direct connection is desired, Proxy.NO_PROXY should be specified.
Returns:
a URLConnection to the URL.
Throws:
IOException
- if an I/O exception occurs.
SecurityException
- if a security manager is present and the caller doesn't have permission to connect to the proxy.
IllegalArgumentException
- will be thrown if proxy is null, or proxy has the wrong type
UnsupportedOperationException
- if the subclass that implements the protocol handler doesn't support this method.
See Also:
URL(java.lang.String, java.lang.String, int, java.lang.String)
,
URLConnection
,
URLStreamHandler.openConnection(java.net.URL, java.net.Proxy)
public final InputStream openStream()
throws IOException
openConnection().getInputStream()
public final Object getContent()
throws IOException
openConnection().getContent()
public final Object getContent(Class[] classes)
throws IOException
openConnection().getContent(Class[])
public static void setURLStreamHandlerFactory(URLStreamHandlerFactory fac)
The URLStreamHandlerFactory instance is used toconstruct a stream protocol handler from a protocol name.
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.