src/main/java/com/fasterxml/jackson/databind/ext/OptionalHandlerFactory.java

package com.fasterxml.jackson.databind.ext;

import com.fasterxml.jackson.databind.*;
import com.fasterxml.jackson.databind.deser.Deserializers;
import com.fasterxml.jackson.databind.ser.Serializers;
import com.fasterxml.jackson.databind.ser.std.ToStringSerializer;

/**
 * Helper class used for isolating details of handling optional+external types
 * (javax.xml classes) from standard factories that offer them.
 *<p>
 * Note that 2.7 changed handling to slightly less dynamic, to avoid having to
 * traverse class hierarchy, which turned to be a performance issue in
 * certain cases. Since DOM classes are assumed to exist on all Java 1.6
 * environments (yes, even on Android/GAE), this part could be simplified by
 * slightly less dynamic lookups.
 *<p>
 * Also with 2.7 we are supporting JDK 1.7/Java 7 type(s).
 */
public class OptionalHandlerFactory implements java.io.Serializable
{
    private static final long serialVersionUID = 1;

    /* To make 2 main "optional" handler groups (javax.xml.stream)
     * more dynamic, we better only figure out handlers completely dynamically, if and
     * when they are needed. To do this we need to assume package prefixes.
     */
    private final static String PACKAGE_PREFIX_JAVAX_XML = "javax.xml.";

    private final static String SERIALIZERS_FOR_JAVAX_XML = "com.fasterxml.jackson.databind.ext.CoreXMLSerializers";
    private final static String DESERIALIZERS_FOR_JAVAX_XML = "com.fasterxml.jackson.databind.ext.CoreXMLDeserializers";

    // Plus we also have a single serializer for DOM Node:
//    private final static String CLASS_NAME_DOM_NODE = "org.w3c.dom.Node";
//    private final static String CLASS_NAME_DOM_DOCUMENT = "org.w3c.dom.Document";
    private final static String SERIALIZER_FOR_DOM_NODE = "com.fasterxml.jackson.databind.ext.DOMSerializer";
    private final static String DESERIALIZER_FOR_DOM_DOCUMENT = "com.fasterxml.jackson.databind.ext.DOMDeserializer$DocumentDeserializer";
    private final static String DESERIALIZER_FOR_DOM_NODE = "com.fasterxml.jackson.databind.ext.DOMDeserializer$NodeDeserializer";

    private final static String DESERIALIZER_FOR_PATH = "com.fasterxml.jackson.databind.ext.PathDeserializer";

    // // Since 2.7, we will assume DOM classes are always found, both due to JDK 1.6 minimum
    // // and because Android (and presumably GAE) have these classes

    private final static Class<?> CLASS_DOM_NODE;
    private final static Class<?> CLASS_DOM_DOCUMENT;

    static {
        Class<?> doc = null, node = null;
        try {
            node = org.w3c.dom.Node.class;
            doc = org.w3c.dom.Document.class;
        } catch (Exception e) {
            // not optimal but will do
            System.err.println("WARNING: could not load DOM Node and/or Document classes");
        }
        CLASS_DOM_NODE = node;
        CLASS_DOM_DOCUMENT = doc;
    }

    // // But Java7 type(s) may or may not be; dynamic lookup should be fine, still
    // // (note: also assume it comes from JDK so that ClassLoader issues with OSGi
    // // can, I hope, be avoided?)
    
    private final static Class<?> CLASS_JAVA7_PATH;
    static {
        Class<?> cls = null;
        try {
            cls = Class.forName("java.nio.file.Path");
        } catch (Exception e) {
            // not optimal but will do
            System.err.println("WARNING: could not load Java7 Path class");
        }
        CLASS_JAVA7_PATH = cls;
    }
    
    public final static OptionalHandlerFactory instance = new OptionalHandlerFactory();
    
    protected OptionalHandlerFactory() { }

    /*
    /**********************************************************
    /* Public API
    /**********************************************************
     */
    
    public JsonSerializer<?> findSerializer(SerializationConfig config, JavaType type,
            BeanDescription beanDesc)
    {
        final Class<?> rawType = type.getRawClass();

        if ((CLASS_JAVA7_PATH != null) && CLASS_JAVA7_PATH.isAssignableFrom(rawType)) {
            return ToStringSerializer.instance;
        }
        if ((CLASS_DOM_NODE != null) && CLASS_DOM_NODE.isAssignableFrom(rawType)) {
            return (JsonSerializer<?>) instantiate(SERIALIZER_FOR_DOM_NODE);
        }
        String className = rawType.getName();
        String factoryName;
        if (className.startsWith(PACKAGE_PREFIX_JAVAX_XML) || hasSuperClassStartingWith(rawType, PACKAGE_PREFIX_JAVAX_XML)) {
            factoryName = SERIALIZERS_FOR_JAVAX_XML;
        } else {
            return null;
        }

        Object ob = instantiate(factoryName);
        if (ob == null) { // could warn, if we had logging system (j.u.l?)
            return null;
        }
        return ((Serializers) ob).findSerializer(config, type, beanDesc);
    }

    public JsonDeserializer<?> findDeserializer(JavaType type, DeserializationConfig config,
            BeanDescription beanDesc)
        throws JsonMappingException
    {
        final Class<?> rawType = type.getRawClass();

        if ((CLASS_JAVA7_PATH != null) && CLASS_JAVA7_PATH.isAssignableFrom(rawType)) {
            return (JsonDeserializer<?>) instantiate(DESERIALIZER_FOR_PATH);
        }
        if ((CLASS_DOM_NODE != null) && CLASS_DOM_NODE.isAssignableFrom(rawType)) {
            return (JsonDeserializer<?>) instantiate(DESERIALIZER_FOR_DOM_NODE);
        }
        if ((CLASS_DOM_DOCUMENT != null) && CLASS_DOM_DOCUMENT.isAssignableFrom(rawType)) {
            return (JsonDeserializer<?>) instantiate(DESERIALIZER_FOR_DOM_DOCUMENT);
        }
        String className = rawType.getName();
        String factoryName;
        if (className.startsWith(PACKAGE_PREFIX_JAVAX_XML)
                || hasSuperClassStartingWith(rawType, PACKAGE_PREFIX_JAVAX_XML)) {
            factoryName = DESERIALIZERS_FOR_JAVAX_XML;
        } else {
            return null;
        }
        Object ob = instantiate(factoryName);
        if (ob == null) { // could warn, if we had logging system (j.u.l?)
            return null;
        }
        return ((Deserializers) ob).findBeanDeserializer(type, config, beanDesc);
    }
    
    /*
    /**********************************************************
    /* Internal helper methods
    /**********************************************************
     */

    private Object instantiate(String className)
    {
        try {
            return Class.forName(className).newInstance();
        } catch (LinkageError e) { }
        // too many different kinds to enumerate here:
        catch (Exception e) { }
        return null;
    }

    /**
     * Since 2.7 we only need to check for class extension, as all implemented
     * types are classes, not interfaces. This has performance implications for
     * some cases, as we do not need to go over interfaces implemented, just
     * superclasses
     * 
     * @since 2.7
     */
    private boolean hasSuperClassStartingWith(Class<?> rawType, String prefix)
    {
        for (Class<?> supertype = rawType.getSuperclass(); supertype != null; supertype = supertype.getSuperclass()) {
            if (supertype == Object.class) {
                return false;
            }
            if (supertype.getName().startsWith(prefix)) {
                return true;
            }
        }
        return false;
    }
}