org.apache.hawq.pxf.service.FragmentsResponse.java Source code

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Here is the source code for org.apache.hawq.pxf.service.FragmentsResponse.java

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package org.apache.hawq.pxf.service;

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF 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.
 */

import java.io.DataOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.util.List;

import javax.ws.rs.WebApplicationException;
import javax.ws.rs.core.StreamingOutput;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.codehaus.jackson.map.ObjectMapper;

import org.apache.hawq.pxf.api.Fragment;

/**
 * Class for serializing fragments metadata in JSON format. The class implements
 * {@link StreamingOutput} so the serialization will be done in a stream and not
 * in one bulk, this in order to avoid running out of memory when processing a
 * lot of fragments.
 */
public class FragmentsResponse implements StreamingOutput {

    private static final Log Log = LogFactory.getLog(FragmentsResponse.class);

    private List<Fragment> fragments;

    /**
     * Constructs fragments response out of a list of fragments
     *
     * @param fragments fragment list
     */
    public FragmentsResponse(List<Fragment> fragments) {
        this.fragments = fragments;
    }

    /**
     * Serializes a fragments list in JSON, To be used as the result string for
     * HAWQ. An example result is as follows:
     * <code>{"PXFFragments":[{"replicas":
     * ["sdw1.corp.emc.com","sdw3.corp.emc.com","sdw8.corp.emc.com"],
     * "sourceName":"text2.csv", "index":"0","metadata":"&lt;base64 metadata for fragment&gt;",
     * "userData":"&lt;data_specific_to_third_party_fragmenter&gt;"
     * },{"replicas":["sdw2.corp.emc.com","sdw4.corp.emc.com","sdw5.corp.emc.com"
     * ],"sourceName":"text_data.csv","index":"0","metadata":
     * "&lt;base64 metadata for fragment&gt;"
     * ,"userData":"&lt;data_specific_to_third_party_fragmenter&gt;"
     * }]}</code>
     */
    @Override
    public void write(OutputStream output) throws IOException, WebApplicationException {
        DataOutputStream dos = new DataOutputStream(output);
        ObjectMapper mapper = new ObjectMapper();

        dos.write("{\"PXFFragments\":[".getBytes());

        String prefix = "";
        for (Fragment fragment : fragments) {
            StringBuilder result = new StringBuilder();
            /* metaData and userData are automatically converted to Base64 */
            result.append(prefix).append(mapper.writeValueAsString(fragment));
            prefix = ",";
            dos.write(result.toString().getBytes());
        }

        dos.write("]}".getBytes());
    }
}