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From shivzone <...@git.apache.org>
Subject [GitHub] incubator-hawq pull request: HAWQ-577. Updated PXF metadata api to...
Date Tue, 29 Mar 2016 01:36:59 GMT
Github user shivzone commented on a diff in the pull request:

    https://github.com/apache/incubator-hawq/pull/522#discussion_r57661884
  
    --- Diff: pxf/pxf-service/src/main/java/org/apache/hawq/pxf/service/MetadataResponse.java
---
    @@ -0,0 +1,94 @@
    +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.apache.hawq.pxf.api.Metadata;
    +
    +import org.codehaus.jackson.map.ObjectMapper;
    +import org.codehaus.jackson.map.annotate.JsonSerialize.Inclusion;
    +
    +
    +/**
    + * Class for serializing 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 items.
    + */
    +public class MetadataResponse implements StreamingOutput {
    +
    +    private static final Log Log = LogFactory.getLog(MetadataResponse.class);
    +    private static final String METADATA_DEFAULT_RESPONSE = "{\"PXFMetadata\":[]}";
    +
    +    private List<Metadata> metadataList;
    +
    +    /**
    +     * Constructs metadata response out of a metadata list
    +     *
    +     * @param metadataList metadata list
    +     */
    +    public MetadataResponse(List<Metadata> metadataList) {
    +        this.metadataList = metadataList;
    +    }
    +
    +    /**
    +     * Serializes the metadata list in JSON, To be used as the result string for HAWQ.
    +     */
    +    @Override
    +    public void write(OutputStream output) throws IOException,
    +            WebApplicationException {
    +        DataOutputStream dos = new DataOutputStream(output);
    +        ObjectMapper mapper = new ObjectMapper();
    +        mapper.setSerializationInclusion(Inclusion.NON_EMPTY); // ignore empty fields
    +
    +        if(metadataList == null || metadataList.isEmpty()) {
    +            dos.write(METADATA_DEFAULT_RESPONSE.getBytes());
    +            return;
    +        }
    +
    +        dos.write("{\"PXFMetadata\":[".getBytes());
    --- End diff --
    
    What i meant was I wouldn't want to have any coorelation between metadata_default_response
and the header string used in the actual response. I wouldn't mind introducing a separate
constant for the string used in the acutal response but wouldn't use that as part of the default
response


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