XmlDecoderFilter.java

/**
 * Licensed to the Austrian Association for Software Tool Integration (AASTI)
 * under one or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information regarding copyright
 * ownership. The AASTI licenses this file to you 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 org.openengsb.core.common.remote;

import java.io.IOException;
import java.io.StringReader;
import java.io.StringWriter;
import java.util.Map;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;

import org.openengsb.core.api.remote.FilterAction;
import org.openengsb.core.api.remote.FilterException;
import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;

import com.google.common.base.Preconditions;

/**
 * This filter takes a {@link String} representing an XML-document and parses it into a {@link Document} The document is
 * passed to the next filter. The resulting document is then printed to a string again and returned. This filter can be
 * used regardless of what Object the XML-document may represent.
 *
 *This filter is intended for incoming ports.
 *
 * <code>
 * <pre>
 *      [XML as String] > Filter > [org.w3c.dom.Document]   > ...
 *                                                             |
 *                                                             v
 *      [XML as String] < Filter < [org.w3c.dom.Document]   < ...
 * </pre>
 * </code>
 */
public class XmlDecoderFilter extends AbstractFilterChainElement<String, String> {

    private FilterAction next;

    @Override
    public String doFilter(String input, Map<String, Object> metadata) throws FilterException {
        Document doc = parseDocument(input);
        Document result = (Document) next.filter(doc, metadata);
        try {
            return writeDocument(result);
        } catch (TransformerException e) {
            throw new FilterException(e);
        }
    }

    @Override
    public void setNext(FilterAction next) {
        checkNextInputAndOutputTypes(next, Document.class, Document.class);
        Preconditions.checkArgument(next.getSupportedInputType().isAssignableFrom(Document.class));
        Preconditions.checkArgument(next.getSupportedOutputType().isAssignableFrom(Document.class));
        this.next = next;
    }

    public static Document parseDocument(String input) {
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        Document doc;
        try {
            DocumentBuilder db = dbf.newDocumentBuilder();
            doc = db.parse(new InputSource(new StringReader(input)));
        } catch (ParserConfigurationException e) {
            throw new FilterException(e);
        } catch (SAXException e) {
            throw new FilterException(e);
        } catch (IOException e) {
            throw new FilterException(e);
        }
        return doc;
    }

    public static String writeDocument(Node input) throws TransformerException {
        Transformer transformer = TransformerFactory.newInstance().newTransformer();
        transformer.setOutputProperty(OutputKeys.INDENT, "yes");
        transformer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", "2");
        StringWriter sw = new StringWriter();

        transformer.transform(new DOMSource(input), new StreamResult(sw));

        return sw.toString();
    }

}