com.sun.msv.verifier
Interface Acceptor

All Known Implementing Classes:

ExpressionAcceptor

public interface Acceptor

exposes the low-level validation engine interface.

represents a pseudo-automaton acceptor. this interface is used to validate content models.

Perform Validation

To perform validation, call the createAcceptor method of the DocumentDeclaration interface to obtain an Acceptor for validating the document element.

 Acceptor a = vgm.createAcceptor();
 

One acceptor is responsible for validating one element. So you also need some form of stack. If you are using a "push" interface like SAX, you need an explicit stack. If you are validating in "pull" fashion (like DOM), then you can use a recursion instead of an explicit stack. The following explanation assumes SAX-like interface.

Now, get back to the story. Whenever you encounter a start tag, create a new acceptor, which validates the children of newly encountered element.

 stack.push(a);
 a = a.createChildAcceptor( sti, null );
 

If this tag name was unexpected, then this method returns null. See javadoc for more details.

Then, for every attributes, call the onAttribute(java.lang.String, java.lang.String, java.lang.String, java.lang.String, com.sun.msv.grammar.IDContextProvider, com.sun.msv.util.StringRef, com.sun.msv.util.DatatypeRef) method. After that you call the onEndAttributes(com.sun.msv.util.StartTagInfo, com.sun.msv.util.StringRef) method.

 for( int i=0; i<atts.getLength(); i++ )
   a.onAttribute( atts.getURI(i), .... );
 a.onEndAttributes();
 

An error can occur at any method. See the method documentations for details.

If you find an end tag, make sure that the acceptor is satisfied. An acceptor is said to be unsatisfied when it needs more elements/text to complete the content model. For example, if the content model is (A,B,C) and it only sees (A,B), then the acceptor is not satisfied because it needs to see C.

 if(!a.isAcceptState(null))
   ; // error because the acceptor is unsatisfied.
 Acceptor child = a;
 a = stack.pop();
 a.stepForward(child,null);
 

Then, call the stepForward method of the parent acceptor and pass the child acceptor to it.

Finally, whenever you see a text, call the onText method. If the text was unexpected or not allowed, then this method returns null. See the documentation for details.

 a.onText("text",context,null,null);
 

In this way, you can better control the validation process.

If you need even finer control of the validation process (e.g., you need to know the list of allowed elements/attributes), you may want to rely on the regexp implementation of VGM. see REDocumentDeclaration for detail.

Downcasting

It is often useful to downcast the Acceptor interface to appropriate derived class. For example, if you are using REDocumentDeclaration, then you can always downcast an Acceptor to ExpressionAcceptor, which provides more predictable behaviors and some useful methods.

Author:

Kohsuke KAWAGUCHI

See Also:

DocumentDeclaration

Field Summary

static int	STRING_IGNORE character literals are allowed, but Acceptor doesn't care its contents and where it is appeared.
static int	STRING_PROHIBITED only whitespaces are allowed.
static int	STRING_STRICT attentive handling of characters is required.

Method Summary

Acceptor	createChildAcceptor(StartTagInfo sti, StringRef refErr) creates an Acceptor that will accept the content model of the children of this moment.
Acceptor	createClone() clones this acceptor.
Object	getOwnerType() gets the "type" object for which this acceptor is working.
int	getStringCareLevel() gets how this acceptor handles characters.
boolean	isAcceptState(StringRef errRef) checks if this Acceptor is satisifed.
boolean	onAttribute(String namespaceURI, String localName, String qName, String value, IDContextProvider context, StringRef refErr, DatatypeRef refType) processes an attribute.
boolean	onEndAttributes(StartTagInfo sti, StringRef refErr) notifies the end of attributes.
boolean	onText(String literal, IDContextProvider context, StringRef refErr, DatatypeRef refType) processes a string literal.
boolean	stepForward(Acceptor child, StringRef errRef) eats a child element

Field Detail

STRING_PROHIBITED

public static final int STRING_PROHIBITED

only whitespaces are allowed. Acceptor will reject any string if it's not whitespaces. for example, <elementRule> of RELAX doesn't allow characters (except whitespaces) at all.

STRING_IGNORE

public static final int STRING_IGNORE

character literals are allowed, but Acceptor doesn't care its contents and where it is appeared. The caller doesn't need to call onText for literal. This mode is used for mixed contents.

STRING_STRICT

public static final int STRING_STRICT

attentive handling of characters is required. Verifier has to keep track of exact contents of string and it must call onText for string accordingly.

Method Detail

createChildAcceptor

public Acceptor createChildAcceptor(StartTagInfo sti,
                                    StringRef refErr)

creates an Acceptor that will accept the content model of the children of this moment.

Once you create an acceptor, you need to call the onAttribute(java.lang.String, java.lang.String, java.lang.String, java.lang.String, com.sun.msv.grammar.IDContextProvider, com.sun.msv.util.StringRef, com.sun.msv.util.DatatypeRef) method for each present attribute, and then you need to call the onEndAttributes(com.sun.msv.util.StartTagInfo, com.sun.msv.util.StringRef) method.

If an error occurs at this method, the bottom line is that the user cannot write this element here.

Parameters:

refErr - if this parameter is non-null, the implementation should try to detect the reason of error and recover from it. and this object should have the error message as its str field.

sti - this parameter provides the information about the start tag to the acceptor object. Usually attribute information is ignored, but sometimes they are used as hints.

Returns:

null If refErr is null, return null if the given start tag is not accepted. If refErr is non-null, return null only when the recovery is impossible.

onAttribute

public boolean onAttribute(String namespaceURI,
                           String localName,
                           String qName,
                           String value,
                           IDContextProvider context,
                           StringRef refErr,
                           DatatypeRef refType)

processes an attribute.

For every attribute present in the document, you need to call this method.

An error at this method typically indicates that

1. this attribute is not allowed to appear here
2. the attribute name was OK, but the value was incorrect.

Parameters:

refErr - In case of an error, this object will receive the localized error message. Null is a valid value for this parameter. The implementation must provide some kind of message.

refType - If this parameter is non-null, this object will receive the datatype assigned to the attribute value.

This feature is optional and therefore the implementation is not necessarily provide this information.

Returns:

false if an error happens and refErr parameter was not provided. Otherwise true.

onEndAttributes

public boolean onEndAttributes(StartTagInfo sti,
                               StringRef refErr)

notifies the end of attributes.

This method needs to be called after the onAttribute(java.lang.String, java.lang.String, java.lang.String, java.lang.String, com.sun.msv.grammar.IDContextProvider, com.sun.msv.util.StringRef, com.sun.msv.util.DatatypeRef) method is called for each present attribute.

An error at this method typically indicates that some required attributes are missing.

Parameters:

sti - This information is used to produce the error message if that is necessary.

refErr - In case of an error, this object will receive the localized error message. Null is a valid value for this parameter. The implementation must provide some kind of message.

Returns:

false if an error happens and refErr parameter was not provided. Otherwise true.

onText

public boolean onText(String literal,
                      IDContextProvider context,
                      StringRef refErr,
                      DatatypeRef refType)

processes a string literal.

Parameters:

context - an object that provides context information necessary to validate some datatypes.

refErr - if this parameter is non-null, the implementation should try to detect the reason of error and recover from it. and this object should have the error message as its str field.

refType - if this parameter is non-null and the callee supports type-assignment, the callee will assign the DataType object to this variable. Caller must initialize refType.type to null before calling this method. If the callee doesn't support type-assignment or type-assignment is impossible for this literal (possibly by ambiguous grammar), this variable must kept null.

Returns:

false if the literal at this position is not allowed.

stepForward

public boolean stepForward(Acceptor child,
                           StringRef errRef)

eats a child element

A child acceptor created by the createChildAcceptor method will be ultimately consumed by the parent through this method.

It is the caller's responsibility to make sure that child acceptor is in the accept state. If it's not, that indicates that some required elements are missing (in other words, contents are not allowed to end here).

It is the callee's responsibility to recover from error of unsatisified child acceptor. That is, even if the caller finds that there are missing elements, it is possible to call this method as if there was no such error.

Returns:

false if an error happens. For example, if the implementation passes an acceptor which is NOT a child of this acceptor, then the callee can return false.

isAcceptState

public boolean isAcceptState(StringRef errRef)

checks if this Acceptor is satisifed.

Acceptor is said to be satisfied when given sequence of elements/strings is accepted by the content model. This method should be called before calling the stepForward method to make sure that the children is written properly.

Parameters:

errRef - If this value is non-null, implementation can diagnose the error and sets the message to the object.

getOwnerType

public Object getOwnerType()

gets the "type" object for which this acceptor is working. This method is used for type assignment. Actual Java type of return value depends on the implementation.

Returns:

null the callee should return null when it doesn't support type-assignment feature, or type-assignment is impossible for this acceptor (for example by ambiguous grammar).

createClone

public Acceptor createClone()

clones this acceptor.

You can keep a "bookmark" of the acceptor by cloning it. This is useful when you are trying to perform "partial validation".

Cloned acceptor will behave in exactly the same way as the original one.

getStringCareLevel

public int getStringCareLevel()

gets how this acceptor handles characters.

This method makes it possible to optimize character handling. For many elements of data-oriented schemas, characters are completely prohibited. For example, In SVG, only handful elements are allowed to have #PCDATA and all other elements have element-only content model. Also, for many elements of document-oriented schemas, #PCDATA is allowed just about anywhere.

In the former case, this method returns STRING_PROHIBITED. In other words, this declares that any onText(String) method with non-whitespace characters will always result in a failure. The caller can then exploit this property of the content model and can immediately signal an error when it finds characters, or discard any whitespace characters without keeping them in memory.

In the latter case, this method returns STRING_IGNORE. This declares that any onText(String) call does not change anything at all. The caller can then exploit this property and discard any characeters it found.

If non of the above applies, or the implementation is simply not capable of providing this information, then this method returns STRING_STRICT. In this case, the caller has to faithfully call the onText(String) method for all characeters it found.

Although this method can be called anytime, it is intended to be called only once when the acceptor is first created.

Returns:

one of the three constant values shown below.