Source Code Cross Referenced for CardinalityChecker.java in  » XML » saxonb » net » sf » saxon » expr » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » XML » saxonb » net.sf.saxon.expr 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        package net.sf.saxon.expr;
002:
003:        import net.sf.saxon.event.SequenceReceiver;
004:        import net.sf.saxon.event.TypeCheckingFilter;
005:        import net.sf.saxon.om.*;
006:        import net.sf.saxon.pattern.DocumentNodeTest;
007:        import net.sf.saxon.trans.XPathException;
008:        import net.sf.saxon.type.ItemType;
009:        import net.sf.saxon.type.Type;
010:        import net.sf.saxon.type.TypeHierarchy;
011:        import net.sf.saxon.value.Cardinality;
012:
013:        /**
014:         * A CardinalityChecker implements the cardinality checking of "treat as": that is,
015:         * it returns the supplied sequence, checking that its cardinality is correct
016:         */
017:
018:        public final class CardinalityChecker extends UnaryExpression {
019:
020:            private int requiredCardinality = -1;
021:            private RoleLocator role;
022:
023:            /**
024:             * Private Constructor: use factory method
025:             */
026:
027:            private CardinalityChecker(Expression sequence, int cardinality,
028:                    RoleLocator role) {
029:                super (sequence);
030:                this .requiredCardinality = cardinality;
031:                this .role = role;
032:                computeStaticProperties();
033:                adoptChildExpression(sequence);
034:            }
035:
036:            /**
037:             * Factory method to construct a CardinalityChecker. The method may create an expression that combines
038:             * the cardinality checking with the functionality of the underlying expression class
039:             * @param sequence
040:             * @param cardinality
041:             * @param role
042:             * @return
043:             */
044:
045:            public static ComputedExpression makeCardinalityChecker(
046:                    Expression sequence, int cardinality, RoleLocator role) {
047:                if (sequence instanceof  Atomizer
048:                        && !Cardinality.allowsMany(cardinality)) {
049:                    Expression base = ((Atomizer) sequence).getBaseExpression();
050:                    if (base instanceof  ComputedExpression) {
051:                        ((ComputedExpression) base)
052:                                .setParentExpression(sequence
053:                                        .getParentExpression());
054:                    }
055:                    return new SingletonAtomizer(base, role, Cardinality
056:                            .allowsZero(cardinality));
057:                } else {
058:                    return new CardinalityChecker(sequence, cardinality, role);
059:                }
060:            }
061:
062:            /**
063:             * Get the required cardinality
064:             */
065:
066:            public int getRequiredCardinality() {
067:                return requiredCardinality;
068:            }
069:
070:            /**
071:             * Type-check the expression
072:             */
073:
074:            public Expression typeCheck(StaticContext env,
075:                    ItemType contextItemType) throws XPathException {
076:                operand = operand.typeCheck(env, contextItemType);
077:                if (requiredCardinality == StaticProperty.ALLOWS_ZERO_OR_MORE) {
078:                    return operand;
079:                }
080:                if (Cardinality.subsumes(requiredCardinality, operand
081:                        .getCardinality())) {
082:                    return operand;
083:                }
084:                return this ;
085:            }
086:
087:            /**
088:             * Perform optimisation of an expression and its subexpressions.
089:             * <p/>
090:             * <p>This method is called after all references to functions and variables have been resolved
091:             * to the declaration of the function or variable, and after all type checking has been done.</p>
092:             *
093:             * @param opt             the optimizer in use. This provides access to supporting functions; it also allows
094:             *                        different optimization strategies to be used in different circumstances.
095:             * @param env             the static context of the expression
096:             * @param contextItemType the static type of "." at the point where this expression is invoked.
097:             *                        The parameter is set to null if it is known statically that the context item will be undefined.
098:             *                        If the type of the context item is not known statically, the argument is set to
099:             *                        {@link net.sf.saxon.type.Type#ITEM_TYPE}
100:             * @return the original expression, rewritten if appropriate to optimize execution
101:             * @throws net.sf.saxon.trans.StaticError if an error is discovered during this phase
102:             *                                        (typically a type error)
103:             */
104:
105:            public Expression optimize(Optimizer opt, StaticContext env,
106:                    ItemType contextItemType) throws XPathException {
107:                operand = operand.optimize(opt, env, contextItemType);
108:                if (requiredCardinality == StaticProperty.ALLOWS_ZERO_OR_MORE) {
109:                    return operand;
110:                }
111:                if (Cardinality.subsumes(requiredCardinality, operand
112:                        .getCardinality())) {
113:                    return operand;
114:                }
115:                return this ;
116:            }
117:
118:            /**
119:             * Set the error code to be returned (this is used when evaluating the functions such
120:             * as exactly-one() which have their own error codes)
121:             */
122:
123:            public void setErrorCode(String code) {
124:                role.setErrorCode(code);
125:            }
126:
127:            /**
128:             * An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
129:             * This method indicates which of these methods is provided. This implementation provides both iterate() and
130:             * process() methods natively.
131:             */
132:
133:            public int getImplementationMethod() {
134:                int m = ITERATE_METHOD | PROCESS_METHOD;
135:                if (!Cardinality.allowsMany(requiredCardinality)) {
136:                    m |= EVALUATE_METHOD;
137:                }
138:                return m;
139:            }
140:
141:            /**
142:             * Iterate over the sequence of values
143:             */
144:
145:            public SequenceIterator iterate(XPathContext context)
146:                    throws XPathException {
147:                SequenceIterator base = operand.iterate(context);
148:
149:                // If the base iterator knows how many items there are, then check it now rather than wasting time
150:
151:                if ((base.getProperties() & SequenceIterator.LAST_POSITION_FINDER) != 0) {
152:                    int count = ((LastPositionFinder) base).getLastPosition();
153:                    if (count == 0
154:                            && !Cardinality.allowsZero(requiredCardinality)) {
155:                        typeError("An empty sequence is not allowed as the "
156:                                + role.getMessage(), role.getErrorCode(),
157:                                context);
158:                    }
159:                    if (count > 1
160:                            && !Cardinality.allowsMany(requiredCardinality)) {
161:                        typeError(
162:                                "A sequence of more than one item is not allowed as the "
163:                                        + role.getMessage(), role
164:                                        .getErrorCode(), context);
165:                    }
166:                    return base;
167:                }
168:
169:                // Otherwise return an iterator that does the checking on the fly
170:
171:                if (!Cardinality.allowsZero(requiredCardinality)) {
172:                    // To check for an empty sequence, we using a ClosingIterator which causes a close()
173:                    // method to be called after the last item has been read
174:                    final XPathContext callingContext = context;
175:                    ClosingAction onClose = new ClosingAction() {
176:                        public void close(SequenceIterator base, int count)
177:                                throws XPathException {
178:                            if (count == 0) {
179:                                typeError(
180:                                        "An empty sequence is not allowed as the "
181:                                                + role.getMessage(), role
182:                                                .getErrorCode(), callingContext);
183:                            }
184:                        }
185:                    };
186:                    base = new ClosingIterator(base, onClose);
187:                }
188:                if (!Cardinality.allowsMany(requiredCardinality)) {
189:                    CardinalityCheckingFunction map = new CardinalityCheckingFunction();
190:                    map.iterator = base;
191:                    base = new MappingIterator(base, map, null);
192:                }
193:                return base;
194:            }
195:
196:            /**
197:             * Mapping function used to check for sequences of length > 1 when this is not permitted
198:             */
199:
200:            private class CardinalityCheckingFunction implements 
201:                    MappingFunction {
202:
203:                public SequenceIterator iterator;
204:
205:                public Object map(Item item, XPathContext context)
206:                        throws XPathException {
207:                    if (iterator.position() == 2) {
208:                        typeError(
209:                                "A sequence of more than one item is not allowed as the "
210:                                        + role.getMessage(), role
211:                                        .getErrorCode(), context);
212:                        return null;
213:                    }
214:                    return item;
215:                }
216:            }
217:
218:            /**
219:             * Evaluate as an Item.
220:             */
221:
222:            public Item evaluateItem(XPathContext context)
223:                    throws XPathException {
224:                SequenceIterator iter = operand.iterate(context);
225:                Item item = null;
226:                while (true) {
227:                    Item nextItem = iter.next();
228:                    if (nextItem == null)
229:                        break;
230:                    if (item != null) {
231:                        typeError(
232:                                "A sequence of more than one item is not allowed as the "
233:                                        + role.getMessage(), role
234:                                        .getErrorCode(), context);
235:                        return null;
236:                    }
237:                    item = nextItem;
238:                }
239:                if (item == null
240:                        && !Cardinality.allowsZero(requiredCardinality)) {
241:                    typeError("An empty sequence is not allowed as the "
242:                            + role.getMessage(), role.getErrorCode(), context);
243:                    return null;
244:                }
245:                return item;
246:            }
247:
248:            /**
249:             * Process the instruction, without returning any tail calls
250:             *
251:             * @param context The dynamic context, giving access to the current node,
252:             *                the current variables, etc.
253:             */
254:
255:            public void process(XPathContext context) throws XPathException {
256:                Expression next = operand;
257:                ItemType type = Type.ITEM_TYPE;
258:                if (next instanceof  ItemChecker) {
259:                    type = ((ItemChecker) next).getRequiredType();
260:                    next = ((ItemChecker) next).getBaseExpression();
261:                }
262:                if ((next.getImplementationMethod() & PROCESS_METHOD) != 0
263:                        && !(type instanceof  DocumentNodeTest)) {
264:                    SequenceReceiver out = context.getReceiver();
265:                    TypeCheckingFilter filter = new TypeCheckingFilter();
266:                    filter.setUnderlyingReceiver(out);
267:                    filter.setPipelineConfiguration(out
268:                            .getPipelineConfiguration());
269:                    filter.setRequiredType(type, requiredCardinality, role);
270:                    context.setReceiver(filter);
271:                    next.process(context);
272:                    filter.close();
273:                    context.setReceiver(out);
274:                } else {
275:                    super .process(context);
276:                }
277:            }
278:
279:            /**
280:             * Determine the data type of the items returned by the expression, if possible
281:             * @return a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER, Type.NODE,
282:             * or Type.ITEM (meaning not known in advance)
283:             * @param th
284:             */
285:
286:            public ItemType getItemType(TypeHierarchy th) {
287:                return operand.getItemType(th);
288:            }
289:
290:            /**
291:             * Determine the static cardinality of the expression
292:             */
293:
294:            public int computeCardinality() {
295:                return requiredCardinality;
296:            }
297:
298:            /**
299:             * Get the static properties of this expression (other than its type). The result is
300:             * bit-signficant. These properties are used for optimizations. In general, if
301:             * property bit is set, it is true, but if it is unset, the value is unknown.
302:             */
303:
304:            public int computeSpecialProperties() {
305:                return operand.getSpecialProperties();
306:            }
307:
308:            /**
309:             * Is this expression the same as another expression?
310:             */
311:
312:            public boolean equals(Object other) {
313:                return super .equals(other)
314:                        && this .requiredCardinality == ((CardinalityChecker) other).requiredCardinality;
315:            }
316:
317:            /**
318:             * Diagnostic print of expression structure
319:             */
320:
321:            public String displayOperator(NamePool pool) {
322:                return "checkCardinality ("
323:                        + Cardinality.toString(requiredCardinality) + ')';
324:            }
325:
326:        }
327:
328:        //
329:        // The contents of this file are subject to the Mozilla Public License Version 1.0 (the "License");
330:        // you may not use this file except in compliance with the License. You may obtain a copy of the
331:        // License at http://www.mozilla.org/MPL/
332:        //
333:        // Software distributed under the License is distributed on an "AS IS" basis,
334:        // WITHOUT WARRANTY OF ANY KIND, either express or implied.
335:        // See the License for the specific language governing rights and limitations under the License.
336:        //
337:        // The Original Code is: all this file.
338:        //
339:        // The Initial Developer of the Original Code is Michael H. Kay
340:        //
341:        // Portions created by (your name) are Copyright (C) (your legal entity). All Rights Reserved.
342:        //
343:        // Contributor(s): none.
344:        //
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