source: Dev/trunk/rdfapi/syntax/JsonSerializer.php @ 260

<?php
/**
 * This class provides capabilities to serialize MemModels to json strings.
 *
 * @package syntax
 * @author Philipp Frischmuth <philipp@frischmuth24.de>
 * @version $Id: JsonSerializer.php 555 2007-12-11 20:27:34Z p_frischmuth $
 */
class JsonSerializer extends Object {
        
        /**
         * This method takes a MemModel object ad parameter and serializes all contained triples to rdf/json format.
         * 
         * @see http://n2.talis.com/wiki/RDF_JSON_Specification#rdf.2Fjson
         * @param MemModel $model
         * @return string Returns a string containing the serialized model.
         */
        public function serialize(MemModel $model) {
                
                // create the root json object (root object)
                $jsonString = '{';
                $subjects = array();
                
                // sort triples by subject
                foreach ($model->triples as $triple) {
                        $subjects[$triple->toStringSubject()][] = $triple;
                }
                
                // sort alphabetically
                ksort($subjects);
                        
                // triples are sorted by subject now, each key is a subject uri, containing all triples with this subject uri
                $i = 0;
                foreach ($subjects as $predicatesArray) {
                        $predicates = array();
                        
                        if ($i > 0) {
                                $jsonString .= ',';
                        }
                        $i++;
                        
                        $subj = $predicatesArray[0]->getSubject();
                        
                        // add special _: sequence for blank node only
                        if ($subj instanceof BlankNode) {
                                $jsonString .= '"_:' . $this->_escapeValue($subj->getLabel()) . '":';
                        } else {
                                $jsonString .= '"' . $this->_escapeValue($subj->getLabel()) . '":';
                        }
                        
                        
                        
                        // create a json object for each subject (subject object)
                        $jsonString .= '{';
                        
                        // sort triples with current subject by predicate
                        foreach ($predicatesArray as $triple) { 
                                $predicates[$triple->toStringPredicate()][] = $triple;
                        }
                        
                        // sort alphabetically
                        ksort($predicates);
                        
                        $j = 0;
                        foreach ($predicates as $valueArray) {
                                
                                if ($j > 0) {
                                        $jsonString .= ',';
                                }
                                $j++;
                                
                                $jsonString .= '"' . $this->_escapeValue($valueArray[0]->getLabelPredicate()) . '":';
                                
                                // create a json array (value array) 
                                $jsonString .= '[';
                                
                                $k = 0;
                                foreach ($valueArray as $triple) {
                                        if ($k > 0) {
                                                $jsonString .= ',';
                                        }
                                        $k++;
                                        
                                        // create json value object (value object)
                                        $jsonString .= '{';
                                        
                                        $obj = $triple->getObject();
                                        
                                        // add special _: sequence for blank nodes only
                                        if ($obj instanceof BlankNode) {
                                                $jsonString .= '"value":"_:' . $this->_escapeValue($obj->getLabel()) . '",';
                                        } else if ($obj instanceof Literal) {
                                                $jsonString .= '"value":"' . $this->_escapeValue($obj->getLabel()) . '",';
                                        } else {
                                                $jsonString .= '"value":"' . $this->_escapeValue($obj->getLabel()) . '",';
                                        }
                                        
                                        // add type of object
                                        if ($obj instanceof Literal) {
                                                $jsonString .= '"type":"literal"';
                                        } else if ($obj instanceof BlankNode) {
                                                $jsonString .= '"type":"bnode"';
                                        } else {
                                                $jsonString .= '"type":"uri"';
                                        }
                                        
                                        if ($obj instanceof Literal) {
                                                if ($obj->getLanguage() != '') {
                                                        $jsonString .= ',"lang":"' . $this->_escapeValue($obj->getLanguage()) . '"';
                                                }
                                                if ($obj->getDatatype() != '') {
                                                        $jsonString .= ',"datatype":"' . $this->_escapeValue($obj->getDatatype()) . '"';
                                                }
                                                
                                        }
                                        
                                        // close value object
                                        $jsonString .= '}';
                                }
                                
                                // close the value array
                                $jsonString .= ']';
                        }
                        
                        // close the json object (for the subject) (subject object)
                        $jsonString .= '}';
                }
                
                // close root json object (root object)
                $jsonString .= '}';
                
                return $jsonString;
        }
        
        /*
         * Escapes the following chars as specified at json.org:
         * 
         * " -> \"
         * \ -> \\
         * / -> \/
         * \b -> \\b
         * \f -> \\f
         * \n -> \\n
         * \r -> \\r
         * \t -> \\t
         * \uXXXX -> \\uXXXX
         */
        protected function _escapeValue($value) {
                
                
                $value = str_replace("\\", '\\\\', $value);
                #$value = str_replace("/", '\/', $value);
                $value = str_replace("\n", '\\n', $value);
                $value = str_replace("\t", '\\t', $value);
                $value = str_replace("\r", '\\r', $value);
                $value = str_replace("\b", '\\b', $value);
                $value = str_replace("\f", '\\f', $value);
                $value = str_replace('"', '\"', $value);
                
                return $value;
        }
}
?>