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/**
 * Licensed to The Apereo Foundation under one or more contributor license
 * agreements. See the NOTICE file distributed with this work for additional
 * information regarding copyright ownership.
 *
 *
 * The Apereo Foundation licenses this file to you under the Educational
 * Community License, Version 2.0 (the "License"); you may not use this file
 * except in compliance with the License. You may obtain a copy of the License
 * at:
 *
 *   http://opensource.org/licenses/ecl2.txt
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 * License for the specific language governing permissions and limitations under
 * the License.
 *
 */

package org.opencastproject.util;

import java.io.IOException;
import java.io.StringWriter;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.SchemaOutputResolver;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlType;
import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
import javax.xml.transform.Result;
import javax.xml.transform.stream.StreamResult;

/**
 * Provides utility methods for transforming a {@link JAXBContext} into an XML schema.
 */
public final class JaxbXmlSchemaGenerator {

  /** Private constructor to disable creation of new instances. */
  private JaxbXmlSchemaGenerator() {
  }

  /**
   * Builds an xml schema from a JAXBContext.
   *
   * @param jaxbContext
   *          the jaxb context
   * @return the xml as a string
   * @throws IOException
   *           if the JAXBContext can not be transformed into an xml schema
   */
  public static String getXmlSchema(JAXBContext jaxbContext) throws IOException {
    final StringWriter writer = new StringWriter();
    jaxbContext.generateSchema(new SchemaOutputResolver() {
      @Override
      public Result createOutput(String namespaceUri, String suggestedFileName) throws IOException {
        StreamResult streamResult = new StreamResult(writer);
        streamResult.setSystemId("");
        return streamResult;
      }
    });
    return writer.toString();
  }

  /**
   * Builds an xml schema. If the class is not XmlType or XmlRootElement annotated, return null;
   *
   * @param clazz
   *          the jaxb annotated class
   * @return the xml as a string, or null if the class can not be transformed to a schema
   */
  public static String getXmlSchema(Class clazz) {
    if (clazz == null || (!clazz.isAnnotationPresent(XmlType.class) && !clazz.isAnnotationPresent(XmlRootElement.class)
            && !clazz.isAnnotationPresent(XmlJavaTypeAdapter.class))) {
      return null;
    }
    try {
      JAXBContext jaxbContext = JAXBContext.newInstance(clazz);
      return getXmlSchema(jaxbContext);
    } catch (Exception e) {
      return null;
    }
  }

}