JSONHelper.java

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package com.sun.jersey.json.impl;

import java.util.HashMap;
import java.util.Map;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.annotation.XmlRootElement;

/**
 * Helper methods for JSON classes.
 *
 * @author Jakub Podlesak (jakub.podlesak at oracle.com)
 * @author Michal Gajdos (michal.gajdos at oracle.com)
 */
public final class JSONHelper {

    private static JaxbProvider jaxbProvider;

    // just to make clear no instances are meant to be created
    private JSONHelper() {
    }

    /**
     *  calculating local name of an appropriate XML element,
     *  pretty much the same way as it is done by JAXB 2.1 impl
     *  (for situations when we want to pretend the element was present
     *  in an incoming stream amd all we have is the type information)
     *  TODO: work out with JAXB guys a better way of doing it,
     *        probably we could take it from an existing JAXBContext?
     */
    public static String getRootElementName(Class<Object> clazz) {
        XmlRootElement e = clazz.getAnnotation(XmlRootElement.class);
        if (e == null) {
            return getVariableName(clazz.getSimpleName());
        }
        if ("##default".equals(e.name())) {
            return getVariableName(clazz.getSimpleName());
        } else {
            return e.name();
        }
    }

    private static String getVariableName(String baseName) {
        return NameUtil.toMixedCaseName(NameUtil.toWordList(baseName), false);
    }

    public static JaxbProvider getJaxbProvider(final JAXBContext jaxbContext) {
        for (SupportedJaxbProvider provider : SupportedJaxbProvider.values()) {
            try {
                final Class<?> jaxbContextClass = getJaxbContextClass(jaxbContext);

                Class<?> clazz = null;
                if (SupportedJaxbProvider.JAXB_JDK.equals(provider)) {
                    // We can be in OSGi runtime, so try to use system classloader.
                    clazz = ClassLoader.getSystemClassLoader().loadClass(SupportedJaxbProvider.JAXB_JDK.getJaxbContextClassName());
                } else {
                    clazz = Class.forName(provider.getJaxbContextClassName());
                }

                if (clazz.isAssignableFrom(jaxbContextClass)) {
                    return jaxbProvider = provider;
                }
            } catch (ClassNotFoundException e) {
                // Do nothing, try the next provider.
            }
        }
        throw new IllegalStateException("No JAXB provider found for the following JAXB context: "
                + (jaxbContext == null ? null : jaxbContext.getClass()));
    }

    private static Class<?> getJaxbContextClass(final JAXBContext jaxbContext) throws ClassNotFoundException {
        if (jaxbContext != null) {
            return jaxbContext.getClass();
        }

        return ClassLoader.getSystemClassLoader().loadClass(SupportedJaxbProvider.JAXB_JDK.getJaxbContextClassName());
    }

    public static boolean isNaturalNotationEnabled() {
        // JAXB-RI.
        try {
            Class.forName("com.sun.xml.bind.annotation.OverrideAnnotationOf");
            return true;
        } catch (ClassNotFoundException e) {
            if (jaxbProvider == SupportedJaxbProvider.JAXB_RI) {
                return false;
            }
        }

        // JAXB-RI in JDK.
        try {
            ClassLoader.getSystemClassLoader().loadClass("com.sun.xml.internal.bind.annotation.OverrideAnnotationOf");
            return true;
        } catch (ClassNotFoundException e) {
            if (jaxbProvider == SupportedJaxbProvider.JAXB_JDK) {
                return false;
            }
        }

        // If jaxbProvider is null now and later will be resolved either as SupportedJaxbProvider.JAXB_RI or
        // SupportedJaxbProvider.JAXB_JDK the processing of (natural) JSON may throw an exception (because classes mentioned above
        // was not found).
        return jaxbProvider == null || jaxbProvider == SupportedJaxbProvider.MOXY;
    }

    public static Map<String, Object> createPropertiesForJaxbContext(final Map<String, Object> properties) {
        final Map<String, Object> jaxbProperties = new HashMap<String, Object>(properties.size() + 1);
        final String retainReferenceToInfo = "retainReferenceToInfo"; // JAXBContextImpl.RETAIN_REFERENCE_TO_INFO;

        jaxbProperties.putAll(properties);
        jaxbProperties.put(retainReferenceToInfo, Boolean.TRUE);

        return jaxbProperties;
    }

}