public final class URI extends Object
An instance of this class represents a URI reference as defined by RFC 2396: Uniform Resource Identifiers (URI): Generic Syntax, amended by RFC 2732: Format for Literal IPv6 Addresses in URLs and with the minor deviations noted below. This class provides constructors for creating URI instances from their components or by parsing their string forms, methods for accessing the various components of an instance, and methods for normalizing, resolving, and relativizing URI instances. Instances of this class are immutable.
[scheme:]scheme-specific-part[#fragment]where square brackets [...] delineate optional components and the characters : and # stand for themselves.
An absolute URI specifies a scheme; a URI that is not absolute is said to be relative. URIs are also classified according to whether they are opaque or hierarchical.
An opaque URI is an absolute URI whose scheme-specific part does not begin with a slash character ('/'). Opaque URIs are not subject to further parsing. Some examples of opaque URIs are:
mailto:java-net@java.sun.com news:comp.lang.java urn:isbn:096139210x
A hierarchical URI is either an absolute URI whose scheme-specific part begins with a slash character, or a relative URI, that is, a URI that does not specify a scheme. Some examples of hierarchical URIs are:
http://java.sun.com/j2se/1.3/
docs/guide/collections/designfaq.html#28 ../../../demo/jfc/SwingSet2/src/SwingSet2.java file:///~/calendar
A hierarchical URI is subject to further parsing according to the syntax
[scheme:][//authority][path][?query][#fragment]where the characters :, /, ?, and # stand for themselves. The scheme-specific part of a hierarchical URI consists of the characters between the scheme and fragment components.
The authority component of a hierarchical URI is, if specified, either server-based or registry-based. A server-based authority parses according to the familiar syntax
[user-info@]host[:port]where the characters @ and : stand for themselves. Nearly all URI schemes currently in use are server-based. An authority component that does not parse in this way is considered to be registry-based.
The path component of a hierarchical URI is itself said to be absolute if it begins with a slash character ('/'); otherwise it is relative. The path of a hierarchical URI that is either absolute or specifies an authority is always absolute.
All told, then, a URI instance has the following nine components:
In a given instance any particular component is either undefined or defined with a distinct value. Undefined string components are represented by null, while undefined integer components are represented by -1. A string component may be defined to have the empty string as its value; this is not equivalent to that component being undefined.
Component Type scheme String scheme-specific-part String authority String user-info String host String port int path String query String fragment String
Whether a particular component is or is not defined in an instance depends upon the type of the URI being represented. An absolute URI has a scheme component. An opaque URI has a scheme, a scheme-specific part, and possibly a fragment, but has no other components. A hierarchical URI always has a path (though it may be empty) and a scheme-specific-part (which at least contains the path), and may have any of the other components. If the authority component is present and is server-based then the host component will be defined and the user-information and port components may be defined.
Normalization is the process of removing unnecessary "." and ".." segments from the path component of a hierarchical URI. Each "." segment is simply removed. A ".." segment is removed only if it is preceded by a non-".." segment. Normalization has no effect upon opaque URIs.
Resolution is the process of resolving one URI against another, base URI. The resulting URI is constructed from components of both URIs in the manner specified by RFC 2396, taking components from the base URI for those not specified in the original. For hierarchical URIs, the path of the original is resolved against the path of the base and then normalized. The result, for example, of resolving
docs/guide/collections/designfaq.html#28 (1)against the base URI http://java.sun.com/j2se/1.3/ is the result URI
http://java.sun.com/j2se/1.3/docs/guide/collections/designfaq.html#28Resolving the relative URI
../../../demo/jfc/SwingSet2/src/SwingSet2.java (2)against this result yields, in turn,
http://java.sun.com/j2se/1.3/demo/jfc/SwingSet2/src/SwingSet2.javaResolution of both absolute and relative URIs, and of both absolute and relative paths in the case of hierarchical URIs, is supported. Resolving the URI file:///~calendar against any other URI simply yields the original URI, since it is absolute. Resolving the relative URI (2) above against the relative base URI (1) yields the normalized, but still relative, URI
demo/jfc/SwingSet2/src/SwingSet2.java
Relativization, finally, is the inverse of resolution: For any two normalized URIs u and v,
u.relativize(u.resolve(v)).equals(v) andThis operation is often useful when constructing a document containing URIs that must be made relative to the base URI of the document wherever possible. For example, relativizing the URI
u.resolve(u.relativize(v)).equals(v) .
http://java.sun.com/j2se/1.3/docs/guide/index.htmlagainst the base URI
http://java.sun.com/j2se/1.3yields the relative URI docs/guide/index.html.
alpha The US-ASCII alphabetic characters, 'A' through 'Z' and 'a' through 'z' digit The US-ASCII decimal digit characters, '0' through '9' alphanum All alpha and digit characters unreserved All alphanum characters together with those in the string "_-!.~'()*" punct The characters in the string ",;:$&+=" reserved All punct characters together with those in the string "?/[]@" escaped Escaped octets, that is, triplets consisting of the percent character ('%') followed by two hexadecimal digits ('0'-'9', 'A'-'F', and 'a'-'f') other The Unicode characters that are not in the US-ASCII character set, are not control characters (according to the Character.isISOControl
method), and are not space characters (according to theCharacter.isSpaceChar
method) (Deviation from RFC 2396, which is limited to US-ASCII)
An illegal character is quoted simply by
encoding it. The space character, for example, is quoted by replacing it
with "%20". UTF-8 contains US-ASCII, hence for US-ASCII
characters this transformation has exactly the effect required by
RFC 2396.
A sequence of escaped octets is decoded by
replacing it with the sequence of characters that it represents in the
UTF-8 character set. UTF-8 contains US-ASCII, hence decoding has the
effect of de-quoting any quoted US-ASCII characters as well as that of
decoding any encoded non-US-ASCII characters. If a decoding error occurs
when decoding the escaped octets then the erroneous octets are replaced by
'\uFFFD', the Unicode replacement character. The The The The The The The conceptual distinction between URIs and URLs is reflected in the
differences between this class and the An instance of this class represents a URI reference in the syntactic
sense defined by RFC 2396. A URI may be either absolute or relative.
A URI string is parsed according to the generic syntax without regard to the
scheme, if any, that it specifies. No lookup of the host, if any, is
performed, and no scheme-dependent stream handler is constructed. Equality,
hashing, and comparison are defined strictly in terms of the character
content of the instance. In other words, a URI instance is little more than
a structured string that supports the syntactic, scheme-independent
operations of comparison, normalization, resolution, and relativization.
An instance of the
single-argument
constructor
requires any illegal characters in its argument to be
quoted and preserves any escaped octets and other characters that
are present.
multi-argument constructors
quote illegal characters as
required by the components in which they appear. The percent character
('%') is always quoted by these constructors. Any other
characters are preserved.
getRawUserInfo
, getRawPath
, getRawQuery
, getRawFragment
, getRawAuthority
, and getRawSchemeSpecificPart
methods return the
values of their corresponding components in raw form, without interpreting
any escaped octets. The strings returned by these methods may contain
both escaped octets and other characters, and will not contain any
illegal characters. getUserInfo
, getPath
, getQuery
, getFragment
, getAuthority
, and getSchemeSpecificPart
methods decode any escaped
octets in their corresponding components. The strings returned by these
methods may contain both other characters and illegal characters,
and will not contain any escaped octets. toString
method returns a URI string with
all necessary quotation but which may contain other characters.
toASCIIString
method returns a fully
quoted and encoded URI string that does not contain any other
characters. Identities
For any URI u, it is always the case that
new URI(u.toString()).equals(u) .
For any URI u that does not contain redundant syntax such as two
slashes before an empty authority (as in file:///tmp/ ) or a
colon following a host name but no port (as in
http://java.sun.com: ), and that does not encode characters
except those that must be quoted, the following identities also hold:
new URI(u.getScheme(),
in all cases,
u.getSchemeSpecificPart(),
u.getFragment())
.equals(u)
new URI(u.getScheme(),
if u is hierarchical, and
u.getUserInfo(), u.getAuthority(),
u.getPath(), u.getQuery(),
u.getFragment())
.equals(u)
new URI(u.getScheme(),
if u is hierarchical and has either no authority or a server-based
authority.
u.getUserInfo(), u.getHost(), u.getPort(),
u.getPath(), u.getQuery(),
u.getFragment())
.equals(u)
URIs, URLs, and URNs
A URI is a uniform resource identifier while a URL is a uniform
resource locator. Hence every URL is a URI, abstractly speaking, but
not every URI is a URL. This is because there is another subcategory of
URIs, uniform resource names (URNs), which name resources but do not
specify how to locate them. The mailto, news, and
isbn URIs shown above are examples of URNs.
URL
class.
URL
class, by contrast, represents the
syntactic components of a URL together with some of the information required
to access the resource that it describes. A URL must be absolute, that is,
it must always specify a scheme. A URL string is parsed according to its
scheme. A stream handler is always established for a URL, and in fact it is
impossible to create a URL instance for a scheme for which no handler is
available. Equality and hashing depend upon both the scheme and the
Internet address of the host, if any; comparison is not defined. In other
words, a URL is a structured string that supports the syntactic operation of
resolution as well as the network I/O operations of looking up the host and
opening a connection to the specified resource.
Constructor and Description |
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URI(String url)
Constructs a URI by parsing the given string.
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URI(String scheme,
String ssp,
String fragment)
Constructs a URI from the given components.
|
URI(String scheme,
String userInfo,
String host,
int port,
String path,
String query,
String fragment)
Constructs a hierarchical URI from the given components.
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Modifier and Type | Method and Description |
---|---|
static URI |
create(String str)
Creates a URI by parsing the given string.
|
String |
getHost()
Returns the host component of this URI.
|
String |
getPath()
Returns the decoded path component of this URI.
|
String |
getScheme()
Returns the scheme component of this URI.
|
boolean |
isAbsolute()
Tells whether or not this URI is absolute.
|
boolean |
isOpaque()
Tells whether or not this URI is opaque.
|
Object |
normalize()
Normalizes this URI's path.
|
String |
toString()
Returns the content of this URI as a string.
|
URL |
toURL()
Constructs a URL from this URI.
|
public URI(String scheme, String ssp, String fragment) throws MalformedURLException
A component may be left undefined by passing null.
This constructor first builds a URI in string form using the given components as follows:
Initially, the result string is empty.
If a scheme is given then it is appended to the result, followed by a colon character (':').
If a scheme-specific part is given then it is appended. Any character that is not a legal URI character is quoted.
Finally, if a fragment is given then a hash character ('#') is appended to the string, followed by the fragment. Any character that is not a legal URI character is quoted.
The resulting URI string is then parsed in order to create the new
URI instance as if by invoking the URI.URI(String)
constructor;
this may cause a URISyntaxException
to be thrown.
scheme
- Scheme namessp
- Scheme-specific partfragment
- FragmentMalformedURLException
- If the URI string constructed from the given components
violates RFC 2396public URI(String url) throws MalformedURLException
This constructor parses the given string exactly as specified by the grammar in RFC 2396, Appendix A, except for the following deviations:
An empty authority component is permitted as long as it is followed by a non-empty path, a query component, or a fragment component. This allows the parsing of URIs such as "file:///foo/bar", which seems to be the intent of RFC 2396 although the grammar does not permit it. If the authority component is empty then the user-information, host, and port components are undefined.
Empty relative paths are permitted; this seems to be the intent of RFC 2396 although the grammar does not permit it. The primary consequence of this deviation is that a standalone fragment such as "#foo" parses as a relative URI with an empty path and the given fragment, and can be usefully resolved against a base URI.
IPv4 addresses in host components are parsed rigorously, as specified by RFC 2732: Each element of a dotted-quad address must contain no more than three decimal digits. Each element is further constrained to have a value no greater than 255.
Hostnames in host components that comprise only a single domain label are permitted to start with an alphanum character. This seems to be the intent of RFC 2396 section 3.2.2 although the grammar does not permit it. The consequence of this deviation is that the authority component of a hierarchical URI such as s://123, will parse as a server-based authority.
IPv6 addresses are permitted for the host component. An IPv6 address must be enclosed in square brackets ('[' and ']') as specified by RFC 2732. The IPv6 address itself must parse according to RFC 2373. IPv6 addresses are further constrained to describe no more than sixteen bytes of address information, a constraint implicit in RFC 2373 but not expressible in the grammar.
Characters in the other category are permitted wherever RFC 2396 permits escaped octets, that is, in the user-information, path, query, and fragment components, as well as in the authority component if the authority is registry-based. This allows URIs to contain Unicode characters beyond those in the US-ASCII character set.
url
- The string to be parsed into a URINullPointerException
- If str is nullMalformedURLException
- If the given string violates RFC 2396, as augmented
by the above deviationspublic URI(String scheme, String userInfo, String host, int port, String path, String query, String fragment) throws MalformedURLException
If a scheme is given then the path, if also given, must either be empty or begin with a slash character ('/'). Otherwise a component of the new URI may be left undefined by passing null for the corresponding parameter or, in the case of the port parameter, by passing -1.
This constructor first builds a URI string from the given components according to the rules specified in RFC 2396, section 5.2, step 7:
Initially, the result string is empty.
If a scheme is given then it is appended to the result, followed by a colon character (':').
If user information, a host, or a port are given then the string "//" is appended.
If user information is given then it is appended, followed by a commercial-at character ('@'). Any character not in the unreserved, punct, escaped, or other categories is quoted.
If a host is given then it is appended. If the host is a literal IPv6 address but is not enclosed in square brackets ('[' and ']') then the square brackets are added.
If a port number is given then a colon character (':') is appended, followed by the port number in decimal.
If a path is given then it is appended. Any character not in the unreserved, punct, escaped, or other categories, and not equal to the slash character ('/') or the commercial-at character ('@'), is quoted.
If a query is given then a question-mark character ('?') is appended, followed by the query. Any character that is not a legal URI character is quoted.
Finally, if a fragment is given then a hash character ('#') is appended, followed by the fragment. Any character that is not a legal URI character is quoted.
The resulting URI string is then parsed as if by invoking the URI.URI(String)
constructor and then invoking the URI.parseServerAuthority()
method upon the result; this may cause a URISyntaxException
to be thrown.
scheme
- Scheme nameuserInfo
- User name and authorization informationhost
- Host nameport
- Port numberpath
- Pathquery
- Queryfragment
- FragmentMalformedURLException
- If both a scheme and a path are given but the path is relative,
if the URI string constructed from the given components violates
RFC 2396, or if the authority component of the string is
present but cannot be parsed as a server-based authoritypublic Object normalize() throws MalformedURLException
If this URI is opaque, or if its path is already in normal form, then this URI is returned. Otherwise a new URI is constructed that is identical to this URI except that its path is computed by normalizing this URI's path in a manner consistent with RFC 2396, section 5.2, step 6, sub-steps c through f; that is:
All "." segments are removed.
If a ".." segment is preceded by a non-".." segment then both of these segments are removed. This step is repeated until it is no longer applicable.
If the path is relative, and if its first segment contains a colon character (':'), then a "." segment is prepended. This prevents a relative URI with a path such as "a:b/c/d" from later being re-parsed as an opaque URI with a scheme of "a" and a scheme-specific part of "b/c/d". (Deviation from RFC 2396)
A normalized path will begin with one or more ".." segments if there were insufficient non-".." segments preceding them to allow their removal. A normalized path will begin with a "." segment if one was inserted by step 3 above. Otherwise, a normalized path will not contain any "." or ".." segments.
MalformedURLException
public String getScheme()
The scheme component of a URI, if defined, only contains characters in the alphanum category and in the string "-.+". A scheme always starts with an alpha character.
The scheme component of a URI cannot contain escaped octets, hence this method does not perform any decoding.public static URI create(String str) throws MalformedURLException
This convenience factory method works as if by invoking the URI.URI(String)
constructor; any URISyntaxException
thrown by the
constructor is caught and wrapped in a new IllegalArgumentException
object, which is then thrown.
This method is provided for use in situations where it is known that
the given string is a legal URI, for example for URI constants declared
within in a program, and so it would be considered a programming error
for the string not to parse as such. The constructors, which throw
URISyntaxException
directly, should be used situations where a
URI is being constructed from user input or from some other source that
may be prone to errors.
str
- The string to be parsed into a URIMalformedURLException
NullPointerException
- If str is nullIllegalArgumentException
- If the given string violates RFC 2396public URL toURL() throws MalformedURLException
This convenience method works as if invoking it were equivalent to evaluating the expression new URL(this.toString()) after first checking that this URI is absolute.
IllegalArgumentException
- If this URL is not absoluteMalformedURLException
- If a protocol handler for the URL could not be found,
or if some other error occurred while constructing the URLpublic boolean isOpaque()
A URI is opaque if, and only if, it is absolute and its scheme-specific part does not begin with a slash character ('/'). An opaque URI has a scheme, a scheme-specific part, and possibly a fragment; all other components are undefined.
public boolean isAbsolute()
A URI is absolute if, and only if, it has a scheme component.
public String toString()
If this URI was created by invoking one of the constructors in this class then a string equivalent to the original input string, or to the string computed from the originally-given components, as appropriate, is returned. Otherwise this URI was created by normalization, resolution, or relativization, and so a string is constructed from this URI's components according to the rules specified in RFC 2396, section 5.2, step 7.
public String getHost()
The host component of a URI, if defined, will have one of the following forms:
A domain name consisting of one or more labels separated by period characters ('.'), optionally followed by a period character. Each label consists of alphanum characters as well as hyphen characters ('-'), though hyphens never occur as the first or last characters in a label. The last, or only, label in a domain name begins with an alpha character.
A dotted-quad IPv4 address of the form digit+.digit+.digit+.digit+, where no digit sequence is longer than three characters and no sequence has a value larger than 255.
An IPv6 address enclosed in square brackets ('[' and ']') and consisting of hexadecimal digits, colon characters (':'), and possibly an embedded IPv4 address. The full syntax of IPv6 addresses is specified in RFC 2373: IPv6 Addressing Architecture.
public String getPath() throws MalformedURLException
The string returned by this method is equal to that returned by the getRawPath() method except that all sequences of escaped octets are decoded.
MalformedURLException
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