XmlEventProvider.java

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package com.sun.jersey.json.impl.reader;

import java.io.IOException;
import java.util.Deque;
import java.util.LinkedList;
import java.util.Queue;
import java.util.Stack;
import java.util.logging.Level;
import java.util.logging.Logger;

import javax.xml.namespace.QName;
import javax.xml.stream.Location;
import javax.xml.stream.XMLStreamException;

import com.sun.jersey.api.json.JSONConfiguration;

import org.codehaus.jackson.JsonLocation;
import org.codehaus.jackson.JsonParser;
import org.codehaus.jackson.JsonToken;

/**
 * Abstract provider for creating {@code JsonXmlEvent} instances from {@code JsonParser}. Extensions of this class should
 * adjust their behaviour according to the JSON notation they are supporting.
 *
 * @author Michal Gajdos (michal.gajdos at oracle.com)
 */
public abstract class XmlEventProvider {

    private static class ProcessingInfo {

        QName name;
        boolean isArray;
        boolean isFirstElement;

        ProcessingInfo(QName name, boolean isArray, boolean isFirstElement) {
            this.name = name;
            this.isArray = isArray;
            this.isFirstElement = isFirstElement;
        }
    }

    /**
     * This wrapper of the {@code JsonParser} allows to peek at the following tokens without actually processing them.
     */
    private static class CachedJsonParser {

        /**
         * JSON parser.
         */
        private final JsonParser parser;
        private final Queue<JsonToken> tokens = new LinkedList<JsonToken>();

        public CachedJsonParser(final JsonParser parser) {
            this.parser = parser;
        }

        public JsonToken nextToken() throws IOException {
            return tokens.isEmpty() ? parser.nextToken() : tokens.poll();
        }

        public JsonToken peekNext() throws IOException {
            final JsonToken jsonToken = parser.nextToken();
            tokens.add(jsonToken);
            return jsonToken;
        }

        public JsonToken peek() throws IOException {
            if (tokens.isEmpty()) {
                tokens.add(parser.nextToken());
            }
            return tokens.peek();
        }

        public JsonToken poll() throws IOException {
            return tokens.poll();
        }

        public void close() throws IOException {
            parser.close();
        }

        public JsonLocation getCurrentLocation() {
            return parser.getCurrentLocation();
        }

        public String getText() throws IOException {
            return parser.getText();
        }

        public String getCurrentName() throws IOException {
            return parser.getCurrentName();
        }

        public boolean hasMoreTokens() throws IOException {
            try {
                return peek() != null;
            } catch (IOException e) {
                return false;
            }
        }
    }

    private static final Logger LOGGER = Logger.getLogger(XmlEventProvider.class.getName());

    private final JSONConfiguration configuration;

    /**
     * JSON parser.
     */
    private final CachedJsonParser parser;

    private final String rootName;

    /**
     * Queue of unprocessed events.
     */
    private final Deque<JsonXmlEvent> eventQueue = new LinkedList<JsonXmlEvent>();

    private final Stack<ProcessingInfo> processingStack = new Stack<ProcessingInfo>();
    
    protected XmlEventProvider(final JsonParser parser, final JSONConfiguration configuration, final String rootName)
            throws XMLStreamException {
        this.parser = new CachedJsonParser(parser);
        this.configuration = configuration;
        this.rootName = rootName;

        try {
            readNext();
        } catch (XMLStreamException ex) {
            LOGGER.log(Level.SEVERE, ex.getMessage(), ex);
            throw new XMLStreamException(ex);
        }
    }

    /**
     * @see com.sun.jersey.json.impl.reader.JsonXmlStreamReader#close()
     */
    void close() throws XMLStreamException {
        eventQueue.clear();
        processingStack.empty();

        try {
            parser.close();
        } catch (IOException ioe) {
            throw new XMLStreamException(ioe);
        }
    }

    /**
     * Creates an {@code EndElementEvent}.
     *
     * @param elementName name of element for which the end element should be created.
     * @param location location of this end element in the JSON stream.
     * @return end element event.
     */
    protected JsonXmlEvent createEndElementEvent(final QName elementName, final Location location) {
        return new EndElementEvent(elementName, location);
    }

    /**
     * Creates an {@code StartElementEvent}.
     *
     * @param elementName name of element for which the start element should be created.
     * @param location location of this start element in the JSON stream.
     * @return start element event.
     */
    protected JsonXmlEvent createStartElementEvent(final QName elementName, final Location location) {
        return new StartElementEvent(elementName, location);
    }

    /**
     * Returns the name of an attribute from the given field name without the leading '@' character if present.
     *
     * @param jsonFieldName field name representing the attribute name.
     * @return the name of an attribute.
     */
    protected String getAttributeName(final String jsonFieldName) {
        return '@' == jsonFieldName.charAt(0) ? jsonFieldName.substring(1) : jsonFieldName;
    }

    /**
     * Returns the attribute qualified name which is determined from the given {@code jsonFieldName} and configuration of the
     * underlying implementation.
     *
     * @param jsonFieldName name of the json field to obtain the qualified name for.
     * @return qualified name of the attribute.
     */
    protected abstract QName getAttributeQName(final String jsonFieldName);
    
    JsonXmlEvent getCurrentNode() {
        return eventQueue.peek();
    }

    /**
     * Returns the element qualified name which is determined from the given {@code jsonFieldName} and configuration of the
     * underlying implementation.
     *
     * @param jsonFieldName name of the json field to obtain the qualified name for.
     * @return qualified name of the element.
     */
    protected abstract QName getElementQName(final String jsonFieldName);

    protected JSONConfiguration getJsonConfiguration() {
        return configuration;
    }

    /**
     * Checks whether the {@code jsonToken} belongs to the group of primitive json values (not an object or an array) and returns
     * the given {@code jsonFieldValue} if the conditions are met. If the {@code jsonFieldValue} does not represents primitive
     * json value an {@code IOException} is thrown.
     *
     * @param jsonToken token to determine whether the given value is of simple json type.
     * @param jsonFieldValue value to be returned if it's one of the simple json types.
     * @return simple json type value.
     * @throws IOException if the given value doesn't belong to the group of primitive json values.
     */
    private String getPrimitiveFieldValue(final JsonToken jsonToken, final String jsonFieldValue) throws IOException {
        if (jsonToken == JsonToken.VALUE_FALSE
                || jsonToken == JsonToken.VALUE_TRUE
                || jsonToken == JsonToken.VALUE_STRING
                || jsonToken == JsonToken.VALUE_NUMBER_FLOAT
                || jsonToken == JsonToken.VALUE_NUMBER_INT
                || jsonToken == JsonToken.VALUE_NULL) {

            return jsonFieldValue;
        }
        
        throw new IOException("Not an XML value, expected primitive value!");
    }

    /**
     * Determines whether the given json field name represents an attribute name.
     *
     * @param jsonFieldName json field name to be examined.
     * @return {@code true} if the given name represents an attribute, {@code false} otherwise.
     */
    protected abstract boolean isAttribute(final String jsonFieldName);

    /**
     * Retrieves and sets attributes for the current element from JSON stream.
     *
     * @throws XMLStreamException if an error occurred during the processing of the JSON stream.
     * @see #processTokens(boolean)
     */
    void processAttributesOfCurrentElement() throws XMLStreamException {
        eventQueue.peek().setAttributes(new LinkedList<JsonXmlEvent.Attribute>());

        processTokens(true);
    }
    
    private JsonXmlEvent processTokens(boolean processAttributes) throws XMLStreamException {
        if (!processAttributes) {
            // get rid of the current event
            eventQueue.poll();
        }

        try {
            while (eventQueue.isEmpty() || processAttributes) {
                while (true) {
                    final JsonToken jsonToken = parser.nextToken();
                    final ProcessingInfo pi = processingStack.isEmpty() ? null : processingStack.peek();

                    if (jsonToken == null) {
                        return getCurrentNode();
                    }

                    switch (jsonToken) {
                        case FIELD_NAME:
                            final String fieldName = parser.getCurrentName();

                            if (isAttribute(fieldName)) {
                                // attribute
                                final QName attributeName = getAttributeQName(fieldName);
                                final String attributeValue = getPrimitiveFieldValue(parser.nextToken(), parser.getText());

                                eventQueue.peek().getAttributes().add(new JsonXmlEvent.Attribute(attributeName, attributeValue));
                            } else {
                                processAttributes = false;

                                // child event
                                if ("$".equals(fieldName)) {
                                    // character event
                                    final String value = getPrimitiveFieldValue(parser.nextToken(), parser.getText());
                                    eventQueue.add(new CharactersEvent(value, new StaxLocation(parser.getCurrentLocation())));
                                } else {
                                    // element event
                                    final QName elementName = getElementQName(fieldName);
                                    final JsonLocation currentLocation = parser.getCurrentLocation();

                                    final boolean isRootEmpty = isEmptyElement(fieldName, true);
                                    if (isRootEmpty) {
                                        eventQueue.add(createStartElementEvent(elementName, new StaxLocation(currentLocation)));
                                        eventQueue.add(createEndElementEvent(elementName, new StaxLocation(currentLocation)));
                                        eventQueue.add(new EndDocumentEvent(new StaxLocation(parser.getCurrentLocation())));
                                    } else {
                                        if (!isEmptyArray() && !isEmptyElement(fieldName, false)) {
                                            eventQueue.add(createStartElementEvent(elementName, new StaxLocation(currentLocation)));
                                            processingStack.add(new ProcessingInfo(elementName, false, true));
                                        }
                                        if (!parser.hasMoreTokens()) {
                                            eventQueue.add(new EndDocumentEvent(new StaxLocation(parser.getCurrentLocation())));
                                        }
                                    }

                                    if (eventQueue.isEmpty()) {
                                        continue;
                                    }

                                    return getCurrentNode();
                                }
                            }
                            break;
                        case START_OBJECT:
                            if (pi == null) {
                                eventQueue.add(new StartDocumentEvent(new StaxLocation(0, 0, 0)));
                                return getCurrentNode();
                            }
                            if (pi.isArray && !pi.isFirstElement) {
                                eventQueue.add(createStartElementEvent(pi.name, new StaxLocation(parser.getCurrentLocation())));
                                return getCurrentNode();
                            } else {
                                pi.isFirstElement = false;
                            }
                            break;
                        case END_OBJECT:
                            processAttributes = false;

                            // end tag
                            eventQueue.add(createEndElementEvent(pi.name, new StaxLocation(parser.getCurrentLocation())));
                            if (!pi.isArray) {
                                processingStack.pop();
                            }
                            if (processingStack.isEmpty()) {
                                eventQueue.add(new EndDocumentEvent(new StaxLocation(parser.getCurrentLocation())));

                                // Eat the last '}' and check whether there is another (unexpected) token.
                                final JsonToken nextToken = parser.nextToken();
                                if ((nextToken != null && nextToken != JsonToken.END_OBJECT)
                                        || parser.peek() != null) {
                                    throw new RuntimeException("Unexpected token: " + parser.getText());
                                }
                            }
                            return getCurrentNode();
                        case VALUE_FALSE:
                        case VALUE_NULL:
                        case VALUE_NUMBER_FLOAT:
                        case VALUE_NUMBER_INT:
                        case VALUE_TRUE:
                        case VALUE_STRING:
                            if (!pi.isFirstElement) {
                                eventQueue.add(createStartElementEvent(pi.name, new StaxLocation(parser.getCurrentLocation())));
                            } else {
                                pi.isFirstElement = false;
                            }
                            if (jsonToken != JsonToken.VALUE_NULL) {
                                eventQueue.add(new CharactersEvent(parser.getText(), new StaxLocation(parser.getCurrentLocation())));
                            }
                            eventQueue.add(new EndElementEvent(pi.name, new StaxLocation(parser.getCurrentLocation())));
                            if (!pi.isArray) {
                                processingStack.pop();
                            }
                            if (processingStack.isEmpty()) {
                                eventQueue.add(new EndDocumentEvent(new StaxLocation(parser.getCurrentLocation())));
                            }
                            processAttributes = false;
                            return getCurrentNode();
                        case START_ARRAY:
                            processingStack.peek().isArray = true;
                            break;
                        case END_ARRAY:
                            processingStack.pop();
                            processAttributes = false;
                            break;
                        default:
                            throw new IllegalStateException("Unknown JSON token: " + jsonToken);
                    }
                }
            }

            return eventQueue.peek();
        } catch (Exception e) {
            throw new XMLStreamException(e);
        }
    }

    /**
     * Checks if the currently processed JSON field is represented as an empty array. If so array tokens are thrown away and no
     * {@code StartElementEvent} should be created.
     *
     * @return {@code true} if next tokens signalize an empty array, {@code false} otherwise.
     * @throws IOException if there is a problem reading next {@code JsonToken}.
     */
    private boolean isEmptyArray() throws IOException {
        final JsonToken jsonToken = parser.peek();

        if (jsonToken == JsonToken.START_ARRAY && parser.peekNext() == JsonToken.END_ARRAY) {
            // throw away parser tokens
            parser.poll();
            parser.poll();

            return true;
        }

        return false;
    }

    private boolean isEmptyElement(final String fieldName, boolean checkRoot) throws IOException {
        if (!checkRoot || (fieldName != null && fieldName.equals(rootName))) {
            final JsonToken jsonToken = parser.peek();

            if (jsonToken == JsonToken.VALUE_NULL) {
                parser.poll();
                return true;
            }
        }

        return false;
    }

    /**
     * Reads and returns next {@code JsonXmlEvent}.
     *
     * @return an instance of {@code JsonXmlEvent}.
     * @throws XMLStreamException if something went wrong.
     */
    JsonXmlEvent readNext() throws XMLStreamException {
        return processTokens(false);
    }
    
}