uk.ac.ed.inf.ace.Config.java Source code

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Here is the source code for uk.ac.ed.inf.ace.Config.java

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/*
 * Copyright 2012 Daniel Renshaw <d.renshaw@sms.ed.ac.uk>.
 *
 * Licensed under the Apache 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://www.apache.org/licenses/LICENSE-2.0
 *
 * 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 uk.ac.ed.inf.ace;

import com.google.common.base.Preconditions;
import java.io.File;
import java.io.InputStream;
import javax.xml.XMLConstants;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.UnmarshallerHandler;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.sax.SAXResult;
import javax.xml.transform.stream.StreamSource;
import javax.xml.validation.Schema;
import javax.xml.validation.SchemaFactory;
import javax.xml.validation.ValidatorHandler;
import uk.ac.ed.inf.ace.utils.Utilities;

/**
 * @author "Daniel Renshaw" <d.renshaw@sms.ed.ac.uk>
 */
public class Config {

    private static final String DEFAULT_PATH = "config.xml";
    private static final String CONFIG_XSD_RESOURCE_NAME = "config.xsd";

    private Config() {
    }

    public static Engine<?, ?> load(String configPath, String environmentName, String extensionSchemaPath,
            String extensionContextPath) throws Exception {
        configPath = Utilities.ifNull(configPath, DEFAULT_PATH);
        File file = new File(configPath);
        Preconditions.checkState(file.exists(), "Config file missing");
        Schema schema;

        try (InputStream inputStream = uk.ac.ed.inf.ace.config.v1.Engine.class
                .getResourceAsStream(CONFIG_XSD_RESOURCE_NAME)) {
            SchemaFactory schemaFactory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
            StreamSource[] sources;

            if (extensionSchemaPath != null) {
                sources = new StreamSource[] { new StreamSource(inputStream),
                        new StreamSource(new File(extensionSchemaPath)) };
            } else {
                sources = new StreamSource[] { new StreamSource(inputStream) };
            }

            schema = schemaFactory.newSchema(sources);
        }

        ValidatorHandler validatorHandler = schema.newValidatorHandler();
        JAXBContext jaxbContext = JAXBContext
                .newInstance(Utilities.ifNull(extensionContextPath, "") + ":uk.ac.ed.inf.ace.config.v1");
        UnmarshallerHandler unmarshallerHandler = jaxbContext.createUnmarshaller().getUnmarshallerHandler();
        validatorHandler.setContentHandler(unmarshallerHandler);
        TransformerFactory.newInstance().newTransformer().transform(new StreamSource(file),
                new SAXResult(validatorHandler));
        uk.ac.ed.inf.ace.config.v1.EngineBase engineBase = (uk.ac.ed.inf.ace.config.v1.EngineBase) unmarshallerHandler
                .getResult();
        @SuppressWarnings("unchecked")
        Class<? extends Engine<?, ?>> type = (Class<? extends Engine<?, ?>>) Class.forName(engineBase.getType());
        return Utilities.construct(type, new Class[] { engineBase.getClass(), String.class },
                new Object[] { engineBase, environmentName });
    }
}