XMLStreamReader (Java EE 5 SDK)

javax.xml.stream Interface XMLStreamReader

所有父接口:

XMLStreamConstants

所有已知实现子孙类:

StreamReaderDelegate

public interface XMLStreamReader

extends XMLStreamConstants

The XMLStreamReader interface allows forward, read-only access to XML. It is designed to be the lowest level and most efficient way to read XML data.

The XMLStreamReader is designed to iterate over XML using next() and hasNext(). The data can be accessed using methods such as getEventType(), getNamespaceURI(), getLocalName() and getText();

The next() method causes the reader to read the next parse event. The next() method returns an integer which identifies the type of event just read.

The event type can be determined using getEventType().

Parsing events are defined as the XML Declaration, a DTD, start tag, character data, white space, end tag, comment, or processing instruction. An attribute or namespace event may be encountered at the root level of a document as the result of a query operation.

For XML 1.0 compliance an XML processor must pass the identifiers of declared unparsed entities, notation declarations and their associated identifiers to the application. This information is provided through the property API on this interface. The following two properties allow access to this information: javax.xml.stream.notations and javax.xml.stream.entities. When the current event is a DTD the following call will return a list of Notations List l = (List) getProperty("javax.xml.stream.notations"); The following call will return a list of entity declarations: List l = (List) getProperty("javax.xml.stream.entities"); These properties can only be accessed during a DTD event and are defined to return null if the information is not available.

The following table describes which methods are valid in what state. If a method is called in an invalid state the method will throw a java.lang.IllegalStateException.

版本:

1.0

作者:

Copyright (c) 2003 by BEA Systems. All Rights Reserved.

另请参见:

XMLEvent, XMLInputFactory, XMLStreamWriter

getProperty

Object getProperty(String name)
                   throws IllegalArgumentException

Get the value of a feature/property from the underlying implementation

参数:

name - The name of the property, may not be null

返回:

The value of the property

抛出异常:

IllegalArgumentException - if name is null

next

int next()
         throws XMLStreamException

Get next parsing event - a processor may return all contiguous character data in a single chunk, or it may split it into several chunks. If the property javax.xml.stream.isCoalescing is set to true element content must be coalesced and only one CHARACTERS event must be returned for contiguous element content or CDATA Sections. By default entity references must be expanded and reported transparently to the application. An exception will be thrown if an entity reference cannot be expanded. If element content is empty (i.e. content is "") then no CHARACTERS event will be reported.

Given the following XML:
<foo><!--description-->content text<![CDATA[<greeting>Hello</greeting>]]>other content</foo>
The behavior of calling next() when being on foo will be:
1- the comment (COMMENT)
2- then the characters section (CHARACTERS)
3- then the CDATA section (another CHARACTERS)
4- then the next characters section (another CHARACTERS)
5- then the END_ELEMENT

注意: empty element (such as <tag/>) will be reported with two separate events: START_ELEMENT, END_ELEMENT - This preserves parsing equivalency of empty element to <tag></tag>. This method will throw an IllegalStateException if it is called after hasNext() returns false.

返回:

the integer code corresponding to the current parse event

抛出异常:

NoSuchElementException - if this is called when hasNext() returns false

XMLStreamException - if there is an error processing the underlying XML source

另请参见:

XMLEvent

require

void require(int type,
             String namespaceURI,
             String localName)
             throws XMLStreamException

Test if the current event is of the given type and if the namespace and name match the current namespace and name of the current event. If the namespaceURI is null it is not checked for equality, if the localName is null it is not checked for equality.

参数:

type - the event type

namespaceURI - the uri of the event, may be null

localName - the localName of the event, may be null

抛出异常:

XMLStreamException - if the required values are not matched.

getElementText

String getElementText()
                      throws XMLStreamException

Reads the content of a text-only element, an exception is thrown if this is not a text-only element. Regardless of value of javax.xml.stream.isCoalescing this method always returns coalesced content.
Precondition: the current event is START_ELEMENT.
Postcondition: the current event is the corresponding END_ELEMENT.
The method does the following (implementations are free to optimized but must do equivalent processing):

 if(getEventType() != XMLStreamConstants.START_ELEMENT) {
 throw new XMLStreamException(
 "parser must be on START_ELEMENT to read next text", getLocation());
 }
 int eventType = next();
 StringBuffer content = new StringBuffer();
 while(eventType != XMLStreamConstants.END_ELEMENT ) {
 if(eventType == XMLStreamConstants.CHARACTERS
 || eventType == XMLStreamConstants.CDATA
 || eventType == XMLStreamConstants.SPACE
 || eventType == XMLStreamConstants.ENTITY_REFERENCE) {
 buf.append(getText());
 } else if(eventType == XMLStreamConstants.PROCESSING_INSTRUCTION
 || eventType == XMLStreamConstants.COMMENT) {
 // skipping
 } else if(eventType == XMLStreamConstants.END_DOCUMENT) {
 throw new XMLStreamException(
 "unexpected end of document when reading element text content", this);
 } else if(eventType == XMLStreamConstants.START_ELEMENT) {
 throw new XMLStreamException(
 "element text content may not contain START_ELEMENT", getLocation());
 } else {
 throw new XMLStreamException(
 "Unexpected event type "+eventType, getLocation());
 }
 eventType = next();
 }
 return buf.toString();
 

抛出异常:

XMLStreamException - if the current event is not a START_ELEMENT or if a non text element is encountered

nextTag

int nextTag()
            throws XMLStreamException

Skips any white space (isWhiteSpace() returns true), COMMENT, or PROCESSING_INSTRUCTION, until a START_ELEMENT or END_ELEMENT is reached. If other than white space characters, COMMENT, PROCESSING_INSTRUCTION, START_ELEMENT, END_ELEMENT are encountered, an exception is thrown. This method should be used when processing element-only content seperated by white space.
Precondition: none
Postcondition: the current event is START_ELEMENT or END_ELEMENT and cursor may have moved over any whitespace event.
Essentially it does the following (implementations are free to optimized but must do equivalent processing):

 int eventType = next();
 while((eventType == XMLStreamConstants.CHARACTERS && isWhiteSpace()) // skip whitespace
 || (eventType == XMLStreamConstants.CDATA && isWhiteSpace()) 
 // skip whitespace
 || eventType == XMLStreamConstants.SPACE
 || eventType == XMLStreamConstants.PROCESSING_INSTRUCTION
 || eventType == XMLStreamConstants.COMMENT
 ) {
 eventType = next();
 }
 if (eventType != XMLStreamConstants.START_ELEMENT && eventType != XMLStreamConstants.END_ELEMENT) {
 throw new String XMLStreamException("expected start or end tag", getLocation());
 }
 return eventType;
 

返回:

the event type of the element read (START_ELEMENT or END_ELEMENT)

抛出异常:

XMLStreamException - if the current event is not white space, PROCESSING_INSTRUCTION, START_ELEMENT or END_ELEMENT

NoSuchElementException - if this is called when hasNext() returns false

hasNext

boolean hasNext()
                throws XMLStreamException

Returns true if there are more parsing events and false if there are no more events. This method will return false if the current state of the XMLStreamReader is END_DOCUMENT

返回:

true if there are more events, false otherwise

抛出异常:

XMLStreamException - if there is a fatal error detecting the next state

close

void close()
           throws XMLStreamException

Frees any resources associated with this Reader. This method does not close the underlying input source.

抛出异常:

XMLStreamException - if there are errors freeing associated resources

getNamespaceURI

String getNamespaceURI(String prefix)

Return the uri for the given prefix. The uri returned depends on the current state of the processor.

NOTE:The 'xml' prefix is bound as defined in Namespaces in XML specification to "http://www.w3.org/XML/1998/namespace".

NOTE: The 'xmlns' prefix must be resolved to following namespace http://www.w3.org/2000/xmlns/

参数:

prefix - The prefix to lookup, may not be null

返回:

the uri bound to the given prefix or null if it is not bound

抛出异常:

IllegalArgumentException - if the prefix is null

isStartElement

boolean isStartElement()

Returns true if the cursor points to a start tag (otherwise false)

返回:

true if the cursor points to a start tag, false otherwise

isEndElement

boolean isEndElement()

Returns true if the cursor points to an end tag (otherwise false)

返回:

true if the cursor points to an end tag, false otherwise

isCharacters

boolean isCharacters()

Returns true if the cursor points to a character data event

返回:

true if the cursor points to character data, false otherwise

isWhiteSpace

boolean isWhiteSpace()

Returns true if the cursor points to a character data event that consists of all whitespace

返回:

true if the cursor points to all whitespace, false otherwise

getAttributeValue

String getAttributeValue(String namespaceURI,
                         String localName)

Returns the normalized attribute value of the attribute with the namespace and localName If the namespaceURI is null the namespace is not checked for equality

参数:

namespaceURI - the namespace of the attribute

localName - the local name of the attribute, cannot be null

返回:

returns the value of the attribute , returns null if not found

抛出异常:

IllegalStateException - if this is not a START_ELEMENT or ATTRIBUTE

getAttributeCount

int getAttributeCount()

Returns the count of attributes on this START_ELEMENT, this method is only valid on a START_ELEMENT or ATTRIBUTE. This count excludes namespace definitions. Attribute indices are zero-based.

返回:

returns the number of attributes

抛出异常:

IllegalStateException - if this is not a START_ELEMENT or ATTRIBUTE

getAttributeName

QName getAttributeName(int index)

Returns the qname of the attribute at the provided index

参数:

index - the position of the attribute

返回:

the QName of the attribute

抛出异常:

IllegalStateException - if this is not a START_ELEMENT or ATTRIBUTE

getAttributeNamespace

String getAttributeNamespace(int index)

Returns the namespace of the attribute at the provided index

参数:

index - the position of the attribute

返回:

the namespace URI (can be null)

抛出异常:

IllegalStateException - if this is not a START_ELEMENT or ATTRIBUTE

getAttributeLocalName

String getAttributeLocalName(int index)

Returns the localName of the attribute at the provided index

参数:

index - the position of the attribute

返回:

the localName of the attribute

抛出异常:

IllegalStateException - if this is not a START_ELEMENT or ATTRIBUTE

getAttributePrefix

String getAttributePrefix(int index)

Returns the prefix of this attribute at the provided index

参数:

index - the position of the attribute

返回:

the prefix of the attribute

抛出异常:

IllegalStateException - if this is not a START_ELEMENT or ATTRIBUTE

getAttributeType

String getAttributeType(int index)

Returns the XML type of the attribute at the provided index

参数:

index - the position of the attribute

返回:

the XML type of the attribute

抛出异常:

IllegalStateException - if this is not a START_ELEMENT or ATTRIBUTE

getAttributeValue

String getAttributeValue(int index)

Returns the value of the attribute at the index

参数:

index - the position of the attribute

返回:

the attribute value

抛出异常:

IllegalStateException - if this is not a START_ELEMENT or ATTRIBUTE

isAttributeSpecified

boolean isAttributeSpecified(int index)

Returns a boolean which indicates if this attribute was created by default

参数:

index - the position of the attribute

返回:

true if this is a default attribute

抛出异常:

IllegalStateException - if this is not a START_ELEMENT or ATTRIBUTE

getNamespaceCount

int getNamespaceCount()

Returns the count of namespaces declared on this START_ELEMENT or END_ELEMENT, this method is only valid on a START_ELEMENT, END_ELEMENT or NAMESPACE. On an END_ELEMENT the count is of the namespaces that are about to go out of scope. This is the equivalent of the information reported by SAX callback for an end element event.

返回:

returns the number of namespace declarations on this specific element

抛出异常:

IllegalStateException - if this is not a START_ELEMENT, END_ELEMENT or NAMESPACE

getNamespacePrefix

String getNamespacePrefix(int index)

Returns the prefix for the namespace declared at the index. Returns null if this is the default namespace declaration

参数:

index - the position of the namespace declaration

返回:

returns the namespace prefix

抛出异常:

IllegalStateException - if this is not a START_ELEMENT, END_ELEMENT or NAMESPACE

getNamespaceURI

String getNamespaceURI(int index)

Returns the uri for the namespace declared at the index.

参数:

index - the position of the namespace declaration

返回:

returns the namespace uri

抛出异常:

IllegalStateException - if this is not a START_ELEMENT, END_ELEMENT or NAMESPACE

getNamespaceContext

NamespaceContext getNamespaceContext()

Returns a read only namespace context for the current position. The context is transient and only valid until a call to next() changes the state of the reader.

返回:

return a namespace context

getEventType

int getEventType()

Returns an integer code that indicates the type of the event the cursor is pointing to.

getText

String getText()

Returns the current value of the parse event as a string, this returns the string value of a CHARACTERS event, returns the value of a COMMENT, the replacement value for an ENTITY_REFERENCE, the string value of a CDATA section, the string value for a SPACE event, or the String value of the internal subset of the DTD. If an ENTITY_REFERENCE has been resolved, any character data will be reported as CHARACTERS events.

返回:

the current text or null

抛出异常:

IllegalStateException - if this state is not a valid text state.

getTextCharacters

char[] getTextCharacters()

Returns an array which contains the characters from this event. This array should be treated as read-only and transient. I.e. the array will contain the text characters until the XMLStreamReader moves on to the next event. Attempts to hold onto the character array beyond that time or modify the contents of the array are breaches of the contract for this interface.

返回:

the current text or an empty array

抛出异常:

IllegalStateException - if this state is not a valid text state.

getTextCharacters

int getTextCharacters(int sourceStart,
                      char[] target,
                      int targetStart,
                      int length)
                      throws XMLStreamException

Gets the the text associated with a CHARACTERS, SPACE or CDATA event. Text starting a "sourceStart" is copied into "target" starting at "targetStart". Up to "length" characters are copied. The number of characters actually copied is returned. The "sourceStart" argument must be greater or equal to 0 and less than or equal to the number of characters associated with the event. Usually, one requests text starting at a "sourceStart" of 0. If the number of characters actually copied is less than the "length", then there is no more text. Otherwise, subsequent calls need to be made until all text has been retrieved. For example: int length = 1024; char[] myBuffer = new char[ length ]; for ( int sourceStart = 0 ; ; sourceStart += length ) { int nCopied = stream.getTextCharacters( sourceStart, myBuffer, 0, length ); if (nCopied < length) break; } XMLStreamException may be thrown if there are any XML errors in the underlying source. The "targetStart" argument must be greater than or equal to 0 and less than the length of "target", Length must be greater than 0 and "targetStart + length" must be less than or equal to length of "target".

参数:

sourceStart - the index of the first character in the source array to copy

target - the destination array

targetStart - the start offset in the target array

length - the number of characters to copy

返回:

the number of characters actually copied

抛出异常:

XMLStreamException - if the underlying XML source is not well-formed

IndexOutOfBoundsException - if targetStart < 0 or > than the length of target

IndexOutOfBoundsException - if length < 0 or targetStart + length > length of target

UnsupportedOperationException - if this method is not supported

NullPointerException - is if target is null

getTextStart

int getTextStart()

Returns the offset into the text character array where the first character (of this text event) is stored.

抛出异常:

IllegalStateException - if this state is not a valid text state.

getTextLength

int getTextLength()

Returns the length of the sequence of characters for this Text event within the text character array.

抛出异常:

IllegalStateException - if this state is not a valid text state.

getEncoding

String getEncoding()

Return input encoding if known or null if unknown.

返回:

the encoding of this instance or null

hasText

boolean hasText()

Return true if the current event has text, false otherwise The following events have text: CHARACTERS,DTD ,ENTITY_REFERENCE, COMMENT, SPACE

getLocation

Location getLocation()

Return the current location of the processor. If the Location is unknown the processor should return an implementation of Location that returns -1 for the location and null for the publicId and systemId. The location information is only valid until next() is called.

getName

QName getName()

Returns a QName for the current START_ELEMENT or END_ELEMENT event

返回:

the QName for the current START_ELEMENT or END_ELEMENT event

抛出异常:

IllegalStateException - if this is not a START_ELEMENT or END_ELEMENT

getLocalName

String getLocalName()

Returns the (local) name of the current event. For START_ELEMENT or END_ELEMENT returns the (local) name of the current element. For ENTITY_REFERENCE it returns entity name. The current event must be START_ELEMENT or END_ELEMENT, or ENTITY_REFERENCE

返回:

the localName

抛出异常:

IllegalStateException - if this not a START_ELEMENT, END_ELEMENT or ENTITY_REFERENCE

hasName

boolean hasName()

returns true if the current event has a name (is a START_ELEMENT or END_ELEMENT) returns false otherwise

getNamespaceURI

String getNamespaceURI()

If the current event is a START_ELEMENT or END_ELEMENT this method returns the URI of the prefix or the default namespace. Returns null if the event does not have a prefix.

返回:

the URI bound to this elements prefix, the default namespace, or null

getPrefix

String getPrefix()

Returns the prefix of the current event or null if the event does not have a prefix

返回:

the prefix or null

getVersion

String getVersion()

Get the xml version declared on the xml declaration Returns null if none was declared

返回:

the XML version or null

isStandalone

boolean isStandalone()

Get the standalone declaration from the xml declaration

返回:

true if this is standalone, or false otherwise

standaloneSet

boolean standaloneSet()

Checks if standalone was set in the document

返回:

true if standalone was set in the document, or false otherwise

getCharacterEncodingScheme

String getCharacterEncodingScheme()

Returns the character encoding declared on the xml declaration Returns null if none was declared

返回:

the encoding declared in the document or null

getPITarget

String getPITarget()

Get the target of a processing instruction

返回:

the target or null

getPIData

String getPIData()

Get the data section of a processing instruction

返回:

the data or null

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