co.cask.cdap.logging.gateway.handlers.AbstractJSONCallback.java Source code

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Here is the source code for co.cask.cdap.logging.gateway.handlers.AbstractJSONCallback.java

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/*
 * Copyright  2016 Cask Data, 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 co.cask.cdap.logging.gateway.handlers;

import co.cask.cdap.logging.read.LogEvent;
import co.cask.http.HttpResponder;
import com.google.common.base.Throwables;
import com.google.common.collect.ImmutableMultimap;
import com.google.common.collect.Multimap;
import com.google.gson.Gson;
import org.jboss.netty.handler.codec.http.HttpHeaders;

import java.io.IOException;
import java.nio.CharBuffer;
import java.util.concurrent.atomic.AtomicBoolean;

/**
 * LogReader callback that sends JSON objects.
 */
public abstract class AbstractJSONCallback extends AbstractChunkedCallback {
    protected static final Gson GSON = new Gson();
    private final AtomicBoolean started = new AtomicBoolean();

    AbstractJSONCallback(HttpResponder responder) {
        super(responder);
    }

    @Override
    protected Multimap<String, String> getResponseHeaders() {
        return ImmutableMultimap.of(HttpHeaders.Names.CONTENT_TYPE, "application/json");
    }

    @Override
    public void writeFinal() throws IOException {
        // If an object has been sent already, then simply send closing bracket.
        // If nothing has been sent so far, then send '[]' indicating an empty list
        if (started.get()) {
            encodeSend(CharBuffer.wrap("]"), true);
        } else {
            encodeSend(CharBuffer.wrap("[]"), true);
        }
    }

    @Override
    public void handleEvent(LogEvent logEvent) {
        try {
            // If it is the first logEvent, send an opening bracket.
            // If it is not the first logEvent, send a , to indicate that it is the next element in the list of JSON objects
            if (started.compareAndSet(false, true)) {
                encodeSend(CharBuffer.wrap("["), false);
            } else {
                encodeSend(CharBuffer.wrap(","), false);
            }

            encodeSend(CharBuffer.wrap(GSON.toJson(encodeSend(logEvent))), false);
        } catch (IOException e) {
            // Just propagate the exception, the caller of this Callback should be handling it.
            throw Throwables.propagate(e);
        }
    }

    /**
     * Return a {@link Object} that will be serialized to a JSON string
     */
    protected abstract Object encodeSend(LogEvent logEvent);
}