Class URL
- java.lang.Object
-
- java.net.URL
- All Implemented Interfaces:
Serializable
public final class URL extends Object implements Serializable
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: Types of URL
In general, a URL can be broken into several parts. Consider the following example:
http://www.example.com/docs/resource1.html
The URL above indicates that the protocol to use is http
(HyperText Transfer Protocol) and that the information resides on a host machine named www.example.com
. The information on that host machine is named /docs/resource1.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://www.example.com:1080/docs/resource1.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.htmlcontained within it the relative URL:
FAQ.htmlit 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%20worldwould 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.
- Since:
- 1.0
- See Also:
- Serialized Form
Constructor Summary
Constructor | Description |
---|---|
URL(String spec) | Creates a |
URL(String protocol,
String host,
int port,
String file) | Creates a |
URL(String protocol,
String host,
int port,
String file,
URLStreamHandler handler) | Creates a |
URL(String protocol,
String host,
String file) | Creates a URL from the specified |
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
Modifier and Type | Method | Description |
---|---|---|
boolean | equals(Object obj) | Compares this URL for equality with another object. |
String | getAuthority() | Gets the authority part of this |
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 |
String | getFile() | Gets the file name of this |
String | getHost() | Gets the host name of this |
String | getPath() | Gets the path part of this |
int | getPort() | Gets the port number of this |
String | getProtocol() | Gets the protocol name of this |
String | getQuery() | Gets the query part of this |
String | getRef() | Gets the anchor (also known as the "reference") of this |
String | getUserInfo() | Gets the userInfo part of this |
int | hashCode() | Creates an integer suitable for hash table indexing. |
URLConnection | openConnection() | Returns a |
URLConnection | openConnection(Proxy proxy) | Same as |
InputStream | openStream() | Opens a connection to this |
boolean | sameFile(URL other) | Compares two URLs, excluding the fragment component. |
static void | setURLStreamHandlerFactory(URLStreamHandlerFactory fac) | Sets an application's |
String | toExternalForm() | Constructs a string representation of this |
String | toString() | Constructs a string representation of this |
URI | toURI() | Returns a |
Methods declared in class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
Constructor Detail
URL
public URL(String protocol, String host, int port, String file) throws MalformedURLException
Creates a URL
object from the specified protocol
, host
, port
number, and file
.
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:
- If the application has previously set up an instance of
URLStreamHandlerFactory
as the stream handler factory, then thecreateURLStreamHandler
method of that instance is called with the protocol string as an argument to create the stream protocol handler. - If no
URLStreamHandlerFactory
has yet been set up, or if the factory'screateURLStreamHandler
method returnsnull
, then the ServiceLoader mechanism is used to locate URLStreamHandlerProvider implementations using the system class loader. The order that providers are located is implementation specific, and an implementation is free to cache the located providers. A ServiceConfigurationError,Error
orRuntimeException
thrown from thecreateURLStreamHandler
, if encountered, will be propagated to the calling thread. ThecreateURLStreamHandler
method of each provider, if instantiated, is invoked, with the protocol string, until a provider returns non-null, or all providers have been exhausted. - If the previous step fails to find a protocol handler, the constructor reads the value of the system property:
java.protocol.handler.pkgs
If the value of that system property is notnull
, 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 ofURLStreamHandler
, then the next package in the list is tried. - If the previous step fails to find a protocol handler, then the constructor tries to load a built-in protocol handler. If this class does not exist, or if the class exists but it is not a subclass of
URLStreamHandler
, then aMalformedURLException
is thrown.
Protocol handlers for the following protocols are guaranteed to exist on the search path :-
http, https, file, and jarProtocol handlers for additional protocols may also be available. Some protocol handlers, for example those used for loading platform classes or classes on the class path, may not be overridden. The details of such restrictions, and when those restrictions apply (during initialization of the runtime for example), are implementation specific and therefore not specified
No validation of the inputs is performed by this constructor.
- Parameters:
-
protocol
- the name of the protocol to use. -
host
- the name of the host. -
port
- the port number on the host. -
file
- the file on the host - Throws:
-
MalformedURLException
- if an unknown protocol or the port is a negative number other than -1 - See Also:
-
System.getProperty(java.lang.String)
,setURLStreamHandlerFactory( java.net.URLStreamHandlerFactory)
,URLStreamHandler
,URLStreamHandlerFactory.createURLStreamHandler( java.lang.String)
URL
public URL(String protocol, String host, String file) throws MalformedURLException
Creates a URL from the specified protocol
name, host
name, and file
name. The default port for the specified protocol is used.
This constructor is equivalent to the four-argument constructor with the only difference of using the default port for the specified protocol. No validation of the inputs is performed by this constructor.
- Parameters:
-
protocol
- the name of the protocol to use. -
host
- the name of the host. -
file
- the file on the host. - Throws:
-
MalformedURLException
- if an unknown protocol is specified. - See Also:
URL(java.lang.String, java.lang.String, int, java.lang.String)
URL
public URL(String protocol, String host, int port, String file, URLStreamHandler handler) throws MalformedURLException
Creates a URL
object from the specified protocol
, host
, port
number, file
, and handler
. Specifying a port
number of -1
indicates that the URL should use the default port for the protocol. Specifying a handler
of null
indicates that the URL should use a default stream handler for the protocol, as outlined for: java.net.URL#URL(java.lang.String, java.lang.String, int, java.lang.String)
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.
- Parameters:
-
protocol
- the name of the protocol to use. -
host
- the name of the host. -
port
- the port number on the host. -
file
- the file on the host -
handler
- the stream handler for the URL. - Throws:
-
MalformedURLException
- if an unknown protocol or the port is a negative number other than -1 -
SecurityException
- if a security manager exists and itscheckPermission
method doesn't allow specifying a stream handler explicitly. - See Also:
-
System.getProperty(java.lang.String)
,setURLStreamHandlerFactory( java.net.URLStreamHandlerFactory)
,URLStreamHandler
,URLStreamHandlerFactory.createURLStreamHandler( java.lang.String)
,SecurityManager.checkPermission(java.security.Permission)
,NetPermission
URL
public URL(String spec) throws MalformedURLException
Creates a URL
object from the String
representation.
This constructor is equivalent to a call to the two-argument constructor with a null
first argument.
- Parameters:
-
spec
- theString
to parse as a URL. - Throws:
-
MalformedURLException
- if no protocol is specified, or an unknown protocol is found, orspec
isnull
, or the parsed URL fails to comply with the specific syntax of the associated protocol. - See Also:
URL(java.net.URL, java.lang.String)
URL
public URL(URL context, String spec) throws MalformedURLException
Creates a URL by parsing the given spec within a specified context. The new URL is created from the given context URL and the spec argument as described in RFC2396 "Uniform Resource Identifiers : Generic * Syntax" :
<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 occurrences of ".." and ".".
For a more detailed description of URL parsing, refer to RFC2396.
- Parameters:
-
context
- the context in which to parse the specification. -
spec
- theString
to parse as a URL. - Throws:
-
MalformedURLException
- if no protocol is specified, or an unknown protocol is found, orspec
isnull
, or the parsed URL fails to comply with the specific syntax of the associated protocol. - See Also:
-
URL(java.lang.String, java.lang.String, int, java.lang.String)
,URLStreamHandler
,URLStreamHandler.parseURL(java.net.URL, java.lang.String, int, int)
URL
public URL(URL context, String spec, URLStreamHandler handler) throws MalformedURLException
Creates a URL by parsing the given spec with the specified handler within a specified context. If the handler is null, the parsing occurs as with the two argument constructor.
- Parameters:
-
context
- the context in which to parse the specification. -
spec
- theString
to parse as a URL. -
handler
- the stream handler for the URL. - Throws:
-
MalformedURLException
- if no protocol is specified, or an unknown protocol is found, orspec
isnull
, or the parsed URL fails to comply with the specific syntax of the associated protocol. -
SecurityException
- if a security manager exists and itscheckPermission
method doesn't allow specifying a stream handler. - See Also:
-
URL(java.lang.String, java.lang.String, int, java.lang.String)
,URLStreamHandler
,URLStreamHandler.parseURL(java.net.URL, java.lang.String, int, int)
Method Detail
getQuery
public String getQuery()
Gets the query part of this URL
.
- Returns:
- the query part of this
URL
, ornull
if one does not exist - Since:
- 1.3
getPath
public String getPath()
Gets the path part of this URL
.
- Returns:
- the path part of this
URL
, or an empty string if one does not exist - Since:
- 1.3
getUserInfo
public String getUserInfo()
Gets the userInfo part of this URL
.
- Returns:
- the userInfo part of this
URL
, ornull
if one does not exist - Since:
- 1.3
getAuthority
public String getAuthority()
Gets the authority part of this URL
.
- Returns:
- the authority part of this
URL
- Since:
- 1.3
getPort
public int getPort()
Gets the port number of this URL
.
- Returns:
- the port number, or -1 if the port is not set
getDefaultPort
public int getDefaultPort()
Gets the default port number of the protocol associated with this URL
. If the URL scheme or the URLStreamHandler for the URL do not define a default port number, then -1 is returned.
- Returns:
- the port number
- Since:
- 1.4
getProtocol
public String getProtocol()
Gets the protocol name of this URL
.
- Returns:
- the protocol of this
URL
.
getHost
public String getHost()
Gets the host name of this URL
, if applicable. The format of the host conforms to RFC 2732, i.e. for a literal IPv6 address, this method will return the IPv6 address enclosed in square brackets ('['
and ']'
).
- Returns:
- the host name of this
URL
.
getFile
public String getFile()
Gets the file name of this URL
. The returned file portion will be the same as getPath()
, plus the concatenation of the value of getQuery()
, if any. If there is no query portion, this method and getPath()
will return identical results.
- Returns:
- the file name of this
URL
, or an empty string if one does not exist
getRef
public String getRef()
Gets the anchor (also known as the "reference") of this URL
.
- Returns:
- the anchor (also known as the "reference") of this
URL
, ornull
if one does not exist
equals
public boolean equals(Object obj)
Compares this URL for equality with another object.
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.
- Overrides:
-
equals
in classObject
- Parameters:
-
obj
- the URL to compare against. - Returns:
-
true
if the objects are the same;false
otherwise. - See Also:
-
Object.hashCode()
,HashMap
hashCode
public int hashCode()
Creates an integer suitable for hash table indexing.
The hash code is based upon all the URL components relevant for URL comparison. As such, this operation is a blocking operation.
- Overrides:
-
hashCode
in classObject
- Returns:
- a hash code for this
URL
. - See Also:
-
Object.equals(java.lang.Object)
,System.identityHashCode(java.lang.Object)
sameFile
public boolean sameFile(URL other)
Compares two URLs, excluding the fragment component.
Returns true
if this URL
and the other
argument are equal without taking the fragment component into consideration.
- Parameters:
-
other
- theURL
to compare against. - Returns:
-
true
if they reference the same remote object;false
otherwise.
toString
public String toString()
Constructs a string representation of this URL
. The string is created by calling the toExternalForm
method of the stream protocol handler for this object.
- Overrides:
-
toString
in classObject
- Returns:
- a string representation of this object.
- See Also:
-
URL(java.lang.String, java.lang.String, int, java.lang.String)
,URLStreamHandler.toExternalForm(java.net.URL)
toExternalForm
public String toExternalForm()
Constructs a string representation of this URL
. The string is created by calling the toExternalForm
method of the stream protocol handler for this object.
- Returns:
- a string representation of this object.
- See Also:
-
URL(java.lang.String, java.lang.String, int, java.lang.String)
,URLStreamHandler.toExternalForm(java.net.URL)
toURI
public URI toURI() throws URISyntaxException
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
openConnection
public URLConnection openConnection() throws IOException
Returns a URLConnection
instance that represents a connection to the remote object referred to by the URL
.
A new instance of URLConnection is created every time when invoking the URLStreamHandler.openConnection(URL) method of the protocol handler for this URL.
It should be noted that a URLConnection instance does not establish the actual network connection on creation. This will happen only when calling URLConnection.connect().
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.
- Returns:
- a
URLConnection
linking to the URL. - Throws:
-
IOException
- if an I/O exception occurs. - See Also:
URL(java.lang.String, java.lang.String, int, java.lang.String)
openConnection
public URLConnection openConnection(Proxy proxy) throws IOException
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. Invoking 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. - Since:
- 1.5
- See Also:
-
URL(java.lang.String, java.lang.String, int, java.lang.String)
,URLConnection
,URLStreamHandler.openConnection(java.net.URL, java.net.Proxy)
openStream
public final InputStream openStream() throws IOException
Opens a connection to this URL
and returns an InputStream
for reading from that connection. This method is a shorthand for:
openConnection().getInputStream()
- Returns:
- an input stream for reading from the URL connection.
- Throws:
-
IOException
- if an I/O exception occurs. - See Also:
-
openConnection()
,URLConnection.getInputStream()
getContent
public final Object getContent() throws IOException
Gets the contents of this URL. This method is a shorthand for:
openConnection().getContent()
- Returns:
- the contents of this URL.
- Throws:
-
IOException
- if an I/O exception occurs. - See Also:
URLConnection.getContent()
getContent
public final Object getContent(Class<?>[] classes) throws IOException
Gets the contents of this URL. This method is a shorthand for:
openConnection().getContent(classes)
- Parameters:
-
classes
- an array of Java types - Returns:
- the content object of this URL that is the first match of the types specified in the classes array. null if none of the requested types are supported.
- Throws:
-
IOException
- if an I/O exception occurs. - Since:
- 1.3
- See Also:
URLConnection.getContent(Class[])
setURLStreamHandlerFactory
public static void setURLStreamHandlerFactory(URLStreamHandlerFactory fac)
Sets an application's URLStreamHandlerFactory
. This method can be called at most once in a given Java Virtual Machine.
The URLStreamHandlerFactory
instance is used to construct 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.
- Parameters:
-
fac
- the desired factory. - Throws:
-
Error
- if the application has already set a factory. -
SecurityException
- if a security manager exists and itscheckSetFactory
method doesn't allow the operation. - See Also:
-
URL(java.lang.String, java.lang.String, int, java.lang.String)
,URLStreamHandlerFactory
,SecurityManager.checkSetFactory()