com.twitter.hraven.hadoopJobMonitor.rpc.RestClient.java Source code

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Here is the source code for com.twitter.hraven.hadoopJobMonitor.rpc.RestClient.java

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/*
Copyright 2014 Twitter, Inc.
    
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 com.twitter.hraven.hadoopJobMonitor.rpc;

import java.io.InputStream;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

/**
 * The client to facilitates getting xml over remote restful api
 */
public class RestClient {
    static final Log LOG = LogFactory.getLog(RestClient.class);
    private DefaultHttpClient httpClient = new DefaultHttpClient();
    private static DocumentBuilderFactory docBldrFactory = DocumentBuilderFactory.newInstance();

    public static final ThreadLocal<DocumentBuilder> docBuilder = new ThreadLocal<DocumentBuilder>() {
        @Override
        protected DocumentBuilder initialValue() {
            try {
                return docBldrFactory.newDocumentBuilder();
            } catch (ParserConfigurationException e) {
                LOG.fatal("Error in parsing XML", e);
                return null;
            }
        }
    };

    private final static RestClient SINGLTON = new RestClient();

    /**
     * @return the singlton instance
     */
    public static RestClient getInstance() {
        return SINGLTON;
    }

    public void shutdown() {
        httpClient.getConnectionManager().shutdown();
    }

    /**
     * get an xml from a remote url
     * 
     * @param url
     * @return Document representing xml
     * @throws RestException
     */
    public Document getXml(String url) throws RestException {
        HttpGet getRequest = new HttpGet(url);
        getRequest.addHeader("accept", "application/xml");
        try {
            HttpResponse response = httpClient.execute(getRequest);
            if (response.getStatusLine().getStatusCode() != 200) {
                throw new RuntimeException(
                        "Failed : HTTP error code : " + response.getStatusLine().getStatusCode());
            }
            InputStream xmlStream = response.getEntity().getContent();

            docBuilder.get().reset();
            Document xmlDoc;
            xmlDoc = docBuilder.get().parse(xmlStream);
            // document contains the complete XML as a Tree.
            return xmlDoc;
        } catch (Exception e) {
            throw new RestException(url, e);
        } finally {
            getRequest.releaseConnection();
        }
    }

    public static class RestException extends Exception {
        private static final long serialVersionUID = -6586571654467117663L;

        public RestException(String xmlUrl, Exception orig) {
            super("Error in getting xml at " + xmlUrl, orig);
        }
    }

    /**
     * Used for testing the RestClient
     * 
     * @param args
     * @throws Exception
     */
    public static void main(String[] args) throws Exception {
        Document xmlDoc = RestClient.getInstance()
                .getXml("http://localhost:8080/" + "ws/v1/history/mapreduce/jobs/job_1389724922546_0058/");
        // Iterating through the nodes and extracting the data.
        NodeList nodeList = xmlDoc.getDocumentElement().getChildNodes();
        for (int i = 0; i < nodeList.getLength(); i++) {
            // We have encountered an <employee> tag.
            Node node = nodeList.item(i);
            if (node instanceof Element) {
                System.out.println(node.getNodeName() + " = " + node.getTextContent());
            }
        }
    }
}