net.sf.saxon.om
Class NamePool

java.lang.Object
  net.sf.saxon.om.NamePool

All Implemented Interfaces:

Serializable

Direct Known Subclasses:

DiagnosticNamePool

public class NamePool
extends Object
implements Serializable

A NamePool holds a collection of expanded names, each containing a namespace URI, a namespace prefix, and a local name; plus a collection of namespaces, each consisting of a prefix/URI pair.

Each expanded name is allocated a unique integer namecode. The namecode enables all three parts of the expanded name to be determined, that is, the prefix, the URI, and the local name.

The equivalence betweem names depends only on the URI and the local name. The namecode is designed so that if two namecodes represent names with the same URI and local name, the two namecodes are the same in the bottom 20 bits. It is therefore possible to compare two names for equivalence by performing an integer comparison of these 20 bits. The bottom 20 bits of a namecode are referred to as a fingerprint.

The NamePool eliminates duplicate names if they have the same prefix, uri, and local part. It retains duplicates if they have different prefixes

Internally the NamePool is organized as a fixed number of hash chains. The selection of a hash chain is based on hashing the local name, because it is unusual to have many names that share the same local name but use different URIs. There are 1024 hash chains and the identifier of the hash chain forms the bottom ten bits of the namecode. The next ten bits represent the sequential position of an entry within the hash chain. The upper bits represent the selection of prefix, from among the list of prefixes that have been used with a given URI. A prefix part of zero means no prefix; if the two prefixes used with a particular namespace are "xs" and "xsd", say, then these will be prefix codes 1 and 2.

Fingerprints in the range 0 to 1023 are reserved for system use, and are allocated as constants mainly to names in the XSLT and XML Schema namespaces: constants representing these names are found in StandardNames.

Operations that update the NamePool, or that have the potential to update it, are synchronized. Read-only operations are done without synchronization. Although technically unsafe, this has not led to any problems in practice. Performance problems due to excessive contention on the NamePool have occasionally been observed: if this happens, the best strategy is to consider splitting the workload to use multiple Configurations each with a separate NamePool.

Internal organization of the NamePool

The NamePool holds two kinds of entry: name entries, representing expanded names (local name + prefix + URI), identified by a name code, and namespace entries (prefix + URI) identified by a namespace code.

The data structure of the name table is as follows.

There is a fixed size hash table; names are allocated to slots in this table by hashing on the local name. Each entry in the table is the head of a chain of NameEntry objects representing names that have the same hash code.

Each NameEntry represents a distinct name (same URI and local name). It contains the local name as a string, plus a short integer representing the URI (as an offset into the array uris[] - this is known as the URIcode).

The fingerprint of a name consists of the hash slot number (in the bottom 10 bits) concatenated with the depth of the entry down the chain of hash synonyms (in the next 10 bits). Fingerprints with depth 0 (i.e., in the range 0-1023) are reserved for predefined names (names of XSLT elements and attributes, and of built-in types). These names are not stored in the name pool, but are accessible as if they were.

A nameCode contains the fingerprint in the bottom 20 bits. It also contains a 10-bit prefix index. This distinguishes the prefix used, among all the prefixes that have been used with this namespace URI. If the prefix index is zero, the prefix is null. Otherwise, it indexes an array of prefix Strings associated with the namespace URI. Note that the data structures and algorithms are optimized for the case where URIs usually use the same prefix.

The nameCode -1 is reserved to mean "not known" or inapplicable. The fingerprint -1 has the same meaning. Note that masking the nameCode -1 to extract its bottom 20 bits is incorrect, and will lead to errors.

Author:

Michael H. Kay

See Also:

Serialized Form

Nested Class Summary

static class

NamePool.NamePoolLimitException Uncaught Exception raised when some limit in the design of the name pool is exceeded

Field Summary

static int	FP_MASK FP_MASK is a mask used to obtain a fingerprint from a nameCode.
static int	MAX_PREFIXES_PER_URI
static int	USER_DEFINED_MASK

Constructor Summary

NamePool()
Create a NamePool

Method Summary

int	allocate(String prefix, String uri, String localName) Allocate a name from the pool, or a new Name if there is not a matching one there
int	allocateClarkName(String expandedName) Allocate a fingerprint given a Clark Name
short	allocateCodeForURI(String uri) Allocate the uri code for a given URI; create one if not found
int	allocateLexicalQName(CharSequence qname, boolean useDefault, NamespaceResolver resolver, NameChecker checker) Get the nameCode for a lexical QName, given a namespace resolver.
int	allocateNamespaceCode(String prefix, String uri) Allocate the namespace code for a namespace prefix/URI pair.
void	diagnosticDump() Diagnostic print of the namepool contents.
String	getClarkName(int nameCode) Get the Clark form of a name, given its name code or fingerprint
Object	getClientData(Class key) Retrieve client data on behalf of a user of the namepool
short	getCodeForPrefix(String prefix) Get the prefix code for a given Prefix
short	getCodeForURI(String uri) Get the uri code for a given URI
String	getDisplayName(int nameCode) Get the display form of a name (the QName), given its name code or fingerprint
int	getFingerprint(String uri, String localName) Get a fingerprint for the name with a given uri and local name.
String	getLocalName(int nameCode) Get the local part of a name, given its name code or fingerprint
int	getNamespaceCode(int namecode) Get the namespace code allocated to a given namecode.
int	getNamespaceCode(String prefix, String uri) Get the existing namespace code for a namespace prefix/URI pair.
String	getPrefix(int nameCode) Get the prefix part of a name, given its name code
String	getPrefixFromNamespaceCode(int code) Get the namespace prefix from a namespace code.
static int	getPrefixIndex(int nameCode) Get the prefix index from a namecode
String	getURI(int nameCode) Get the namespace-URI of a name, given its name code or fingerprint
short	getURICode(int nameCode) Get the URI code of a name, given its name code or fingerprint
String	getURIFromNamespaceCode(int code) Get the namespace URI from a namespace code.
String	getURIFromURICode(short code) Get the namespace URI from a URI code.
static boolean	isPrefixed(int nameCode) Determine whether a given namecode has a non-empty prefix (and therefore, in the case of attributes, whether the name is in a non-null namespace
static String[]	parseClarkName(String expandedName) Parse a Clark-format expanded name, returning the URI and local name
void	setClientData(Class key, Object value) Save client data on behalf of a user of the namepool
void	statistics() Statistics summarizing the namepool contents.
String	suggestPrefixForURI(String URI) Suggest a prefix for a given URI.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

FP_MASK

public static final int FP_MASK

FP_MASK is a mask used to obtain a fingerprint from a nameCode. Given a nameCode nc, the fingerprint is nc & NamePool.FP_MASK. (In practice, Saxon code often uses the literal constant 0xfffff, to extract the bottom 20 bits).

The difference between a fingerprint and a nameCode is that a nameCode contains information about the prefix of a name, the fingerprint depends only on the namespace URI and local name. Note that the "null" nameCode (-1) does not produce the "null" fingerprint (also -1) when this mask is applied.

See Also:

Constant Field Values

USER_DEFINED_MASK

public static final int USER_DEFINED_MASK

See Also:

Constant Field Values

MAX_PREFIXES_PER_URI

public static final int MAX_PREFIXES_PER_URI

See Also:

Constant Field Values

Constructor Detail

NamePool

public NamePool()

Create a NamePool

Method Detail

allocateNamespaceCode

public int allocateNamespaceCode(String prefix,
                                 String uri)

Allocate the namespace code for a namespace prefix/URI pair. Create it if not already present

Parameters:

prefix - the namespace prefix

uri - the namespace URI

Returns:

an integer code identifying the namespace. The namespace code identifies both the prefix and the URI.

getNamespaceCode

public int getNamespaceCode(String prefix,
                            String uri)

Get the existing namespace code for a namespace prefix/URI pair.

Parameters:

prefix - the namespace prefix. May be "" for the default namespace

uri - the namespace URI. May be "" for the "null namespace"

Returns:

the integer namespace code that identifies this namespace binding; or -1 if this binding is not present in the name pool

getNamespaceCode

public int getNamespaceCode(int namecode)

Get the namespace code allocated to a given namecode.

Parameters:

namecode - a code identifying an expanded QName, e.g. of an element or attribute

Returns:

a code identifying the namespace used in the given name. The namespace code identifies both the prefix and the URI.

Return -1 if no namespace code has been allocated. This should not happen for a legitimate namecode, since a namespace code is always allocated at the time the namecode is created.

getPrefixIndex

public static int getPrefixIndex(int nameCode)

Get the prefix index from a namecode

Parameters:

nameCode - the name code

Returns:

the prefix index. A value of zero means the name is unprefixed (which in the case of an attribute, means that it is in the null namespace)

isPrefixed

public static boolean isPrefixed(int nameCode)

Determine whether a given namecode has a non-empty prefix (and therefore, in the case of attributes, whether the name is in a non-null namespace

Parameters:

nameCode - the name code to be tested

Returns:

true if the name has a non-empty prefix

allocateCodeForURI

public short allocateCodeForURI(String uri)

Allocate the uri code for a given URI; create one if not found

Parameters:

uri - The namespace URI. Supply "" or null for the "null namespace"

Returns:

an integer code that uniquely identifies this URI within the namepool.

getCodeForURI

public short getCodeForURI(String uri)

Get the uri code for a given URI

Parameters:

uri - the URI whose code is required

Returns:

the associated integer URI code, or -1 if not present in the name pool

getCodeForPrefix

public short getCodeForPrefix(String prefix)

Get the prefix code for a given Prefix

Parameters:

prefix - the prefix. Supply "" for the null prefix representing the default namespace.

Returns:

a code uniquely identifying this prefix within the name pool, or -1 if not found

suggestPrefixForURI

public String suggestPrefixForURI(String URI)

Suggest a prefix for a given URI. If there are several, it's undefined which one is returned. If there are no prefixes registered for this URI, return null.

Parameters:

URI - the namespace URI

Returns:

a prefix that has previously been associated with this URI, if available; otherwise null

allocate

public int allocate(String prefix,
                    String uri,
                    String localName)

Allocate a name from the pool, or a new Name if there is not a matching one there

Parameters:

prefix - the namespace prefix. Use "" for the null prefix, representing the absent namespace

uri - the namespace URI. Use "" or null for the non-namespace.

localName - the local part of the name

Returns:

an integer (the "namecode") identifying the name within the namepool. The Name itself may be retrieved using the getName(int) method

getURI

public String getURI(int nameCode)

Get the namespace-URI of a name, given its name code or fingerprint

Parameters:

nameCode - the name code or fingerprint of a name

Returns:

the namespace URI corresponding to this name code. Returns "" for the null namespace.

Throws:

IllegalArgumentException - if the nameCode is not known to the NamePool.

getURICode

public short getURICode(int nameCode)

Get the URI code of a name, given its name code or fingerprint

Parameters:

nameCode - the name code or fingerprint of a name in the name pool

Returns:

the integer code identifying the namespace URI part of the name

getLocalName

public String getLocalName(int nameCode)

Get the local part of a name, given its name code or fingerprint

Parameters:

nameCode - the integer name code or fingerprint of the name

Returns:

the local part of the name represented by this name code or fingerprint

getPrefix

public String getPrefix(int nameCode)

Get the prefix part of a name, given its name code

Parameters:

nameCode - the integer name code of a name in the name pool

Returns:

the prefix of this name. Note that if a fingerprint rather than a full name code is supplied the returned prefix will be ""

getDisplayName

public String getDisplayName(int nameCode)

Get the display form of a name (the QName), given its name code or fingerprint

Parameters:

nameCode - the integer name code or fingerprint of a name in the name pool

Returns:

the corresponding lexical QName (if a fingerprint was supplied, this will simply be the local name)

getClarkName

public String getClarkName(int nameCode)

Get the Clark form of a name, given its name code or fingerprint

Parameters:

nameCode - the integer name code or fingerprint of a name in the name pool

Returns:

the local name if the name is in the null namespace, or "{uri}local" otherwise. The name is always interned.

allocateClarkName

public int allocateClarkName(String expandedName)

Allocate a fingerprint given a Clark Name

Parameters:

expandedName - the name in Clark notation, that is "localname" or "{uri}localName"

Returns:

the fingerprint of the name, which need not previously exist in the name pool

parseClarkName

public static String[] parseClarkName(String expandedName)

Parse a Clark-format expanded name, returning the URI and local name

Parameters:

expandedName - the name in Clark notation, that is "localname" or "{uri}localName"

Returns:

an array of two strings, the URI and the local name respectively

getFingerprint

public int getFingerprint(String uri,
                          String localName)

Get a fingerprint for the name with a given uri and local name. These must be present in the NamePool. The fingerprint has the property that if two fingerprint are the same, the names are the same (ie. same local name and same URI).

Parameters:

uri - the namespace URI of the required QName

localName - the local part of the required QName

Returns:

the integer fingerprint, or -1 if this is not found in the name pool

getURIFromNamespaceCode

public String getURIFromNamespaceCode(int code)

Get the namespace URI from a namespace code.

Parameters:

code - a namespace code, representing the binding of a prefix to a namespace URI

Returns:

the namespace URI represented by this namespace binding

getURIFromURICode

public String getURIFromURICode(short code)

Get the namespace URI from a URI code.

Parameters:

code - a code that identifies the URI within the name pool

Returns:

the URI represented by this code

getPrefixFromNamespaceCode

public String getPrefixFromNamespaceCode(int code)

Get the namespace prefix from a namespace code.

Parameters:

code - a namespace code representing the binding of a prefix to a URI)

Returns:

the prefix represented by this namespace binding

allocateLexicalQName

public int allocateLexicalQName(CharSequence qname,
                                boolean useDefault,
                                NamespaceResolver resolver,
                                NameChecker checker)
                         throws XPathException

Get the nameCode for a lexical QName, given a namespace resolver.

Parameters:

qname - the lexical QName (with leading and trailing whitespace allowed).

useDefault - if true, an absent prefix is resolved by the NamespaceResolver to the namespace URI assigned to the prefix "". If false, an absent prefix is interpreted as meaning the name is in no namespace.

resolver - NamespaceResolver used to resolve the namespace prefix to a namespace URI

checker - NameChecker used to check names against the XML 1.0 or 1.1 specification

Returns:

the corresponding nameCode

Throws:

XPathException - if the string is not a valid lexical QName or if the namespace prefix has not been declared

setClientData

public void setClientData(Class key,
                          Object value)

Save client data on behalf of a user of the namepool

Parameters:

key - the class that is maintaining private data in the name pool

value - the private data maintained in the name pool on behalf of this class

getClientData

public Object getClientData(Class key)

Retrieve client data on behalf of a user of the namepool

Parameters:

key - the class that is maintaining private data in the name pool

Returns:

the private data maintained in the name pool on behalf of this class

diagnosticDump

public void diagnosticDump()

Diagnostic print of the namepool contents.

statistics

public void statistics()

Statistics summarizing the namepool contents. This method outputs summary statistical information to System.err