org.opencastproject.oaipmh.harvester.OaiPmhResponse.java Source code

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Here is the source code for org.opencastproject.oaipmh.harvester.OaiPmhResponse.java

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/**
 *  Copyright 2009, 2010 The Regents of the University of California
 *  Licensed 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://www.osedu.org/licenses/ECL-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.opencastproject.oaipmh.harvester;

import org.opencastproject.util.data.Option;
import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;

import static org.apache.commons.lang.StringUtils.trimToNull;
import static org.opencastproject.util.data.Option.option;

/**
 * Base class for all OAI-PMH responses.
 */
public abstract class OaiPmhResponse {
    protected final Document doc;
    protected final XPath xpath;

    public OaiPmhResponse(Document doc) {
        this.doc = doc;
        this.xpath = createXPath();
    }

    /**
     * Create an XPath object suitable for processing OAI-PMH response documents.
     */
    public static XPath createXPath() {
        XPath xPath = XPathFactory.newInstance().newXPath();
        xPath.setNamespaceContext(OaiPmhNamespaceContext.getContext());
        return xPath;
    }

    /**
     * Check if response is an error response.
     */
    public boolean isError() {
        return xpathExists("/oai20:OAI-PMH/oai20:error");
    }

    /**
     * Get the error code if this is an error response.
     */
    public Option<String> getErrorCode() {
        return option(trimToNull(xpathString("/oai20:OAI-PMH/oai20:error/@code")));
    }

    /**
     * Check if this is a "noRecordsMatch" error response.
     */
    public boolean isErrorNoRecordsMatch() {
        return xpathExists("/oai20:OAI-PMH/oai20:error[@code='noRecordsMatch']");
    }

    /**
     * Evaluate the xpath expression against the contained document. The expression must return a string (text).
     */
    protected String xpathString(String expr) {
        try {
            return ((String) xpath.evaluate(expr, doc, XPathConstants.STRING)).trim();
        } catch (XPathExpressionException e) {
            throw new RuntimeException("malformed xpath expression " + expr, e);
        }
    }

    /**
     * Evaluate the xpath expression against the contained document. The expression must return a node.
     */
    protected Node xpathNode(String expr) {
        return xpathNode(xpath, doc, expr);
    }

    public static Node xpathNode(XPath xpath, Node context, String expr) {
        if (expr.startsWith("/"))
            throw new IllegalArgumentException(
                    "an xpath expression that evaluates relative to a given context node "
                            + "must not be absolute, i.e. start with a '/'. In this case the expression is evaluated against the"
                            + "whole document which might not be wanted.");
        try {
            return (Node) xpath.evaluate(expr, context, XPathConstants.NODE);
        } catch (XPathExpressionException e) {
            throw new RuntimeException("malformed xpath expression " + expr, e);
        }
    }

    /**
     * Evaluate the xpath expression against the contained document. The expression must return a node list.
     */
    protected NodeList xpathNodeList(String expr) {
        try {
            return (NodeList) xpath.evaluate(expr, doc, XPathConstants.NODESET);
        } catch (XPathExpressionException e) {
            throw new RuntimeException("malformed xpath expression " + expr, e);
        }
    }

    protected boolean xpathExists(String expr) {
        return xpathNodeList(expr).getLength() > 0;
    }
}