flume自定义反序列化器deserializer

需求背景：

　　在利用flume进行日志收集的时候，错误信息会将堆栈多行打印，需要将多行信息合并成一行，包装成一个event进行传输。

解决思路：　

　　解决上述需求可以通过自定义拦截器和自定义反序列化器来实现。网上关于自定义拦截器的资料比较多，但考虑到拦截器的定位和使用场景，拦截器不应用于多个event拆分组合，并若flume有并发处理的话，不能保证读取event是顺序的。查阅资料发现，通过自定义flume的反序列化器更加合理和安全。

实现步骤：

　　1：新建一个类，实现 EventDeserializer 接口

　　2： 重写 readEvent()方法或readEvents方法

　　3： 修改flume的配置文件，将sources.deserializer属性设置为自定义类

源码：

　　1:自定义反序列化器 ---> MyLineDeserializer

/**
 * 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
 * <p>
 * http://www.apache.org/licenses/LICENSE-2.0
 * <p>
 * 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.xxx.flume.serializer;

import com.google.common.collect.Lists;
import org.apache.flume.Context;
import org.apache.flume.Event;
import org.apache.flume.annotations.InterfaceAudience;
import org.apache.flume.annotations.InterfaceStability;
import org.apache.flume.event.EventBuilder;
import org.apache.flume.serialization.EventDeserializer;
import org.apache.flume.serialization.ResettableInputStream;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.IOException;
import java.nio.charset.Charset;
import java.util.List;

/**
 * A deserializer that parses text lines from a file.
 */
@InterfaceAudience.Private
@InterfaceStability.Evolving
public class MyLineDeserializer implements EventDeserializer {

    private static final Logger logger = LoggerFactory.getLogger
            (MyLineDeserializer.class);

    private final ResettableInputStream in;
    private final Charset outputCharset;
    private final int maxLineLength;
    private volatile boolean isOpen;

    public static final String OUT_CHARSET_KEY = "outputCharset";
    public static final String CHARSET_DFLT = "UTF-8";

    public static final String MAXLINE_KEY = "maxLineLength";
    public static final int MAXLINE_DFLT = 2048;
    private StringBuffer eventStringBuffer = new StringBuffer();

    MyLineDeserializer(Context context, ResettableInputStream in) {
        this.in = in;
        this.outputCharset = Charset.forName(
                context.getString(OUT_CHARSET_KEY, CHARSET_DFLT));
        this.maxLineLength = context.getInteger(MAXLINE_KEY, MAXLINE_DFLT);
        this.isOpen = true;
    }


    /**
     * Reads a line from a file and returns an event
     *
     * @return Event containing parsed line
     * @throws IOException
     */
    @Override
    public Event readEvent() throws IOException {
        ensureOpen();
        String line = readLine();
        Event event = null;

        while (line != null) {
            //  start with 20 is one timestamp , event end
            if (line.trim().startsWith("20")) {
                event = EventBuilder.withBody(eventStringBuffer.toString(), outputCharset);
                eventStringBuffer.delete(0, eventStringBuffer.length());
            }
            //  add current line push to buffer
            if (line.trim().length() > 0) {
                if (eventStringBuffer.length() > 0) {
                    eventStringBuffer.append(System.lineSeparator()).append(line);
                } else {
                    eventStringBuffer.append(line);
                }
            }
            if (line.trim().startsWith("20")) {
                break;
            }
            line = readLine();
        }

        if (line == null && eventStringBuffer.toString().length() > 0 ){
            event =  EventBuilder.withBody(eventStringBuffer.toString(), outputCharset);
            eventStringBuffer.delete(0, eventStringBuffer.length());
            return event;
        }
        return event;
    }

    /**
     * Batch line read
     *
     * @param numEvents Maximum number of events to return.
     * @return List of events containing read lines
     * @throws IOException
     */
    @Override
    public List<Event> readEvents(int numEvents) throws IOException {
        ensureOpen();
        List<Event> events = Lists.newLinkedList();
        for (int i = 0; i < numEvents; i++) {
            Event event = readEvent();
            if (event != null) {
                events.add(event);
            } else {
                break;
            }
        }
        return events;
    }

    @Override
    public void mark() throws IOException {
        ensureOpen();
        in.mark();
    }

    @Override
    public void reset() throws IOException {
        ensureOpen();
        in.reset();
    }

    @Override
    public void close() throws IOException {
        if (isOpen) {
            reset();
            in.close();
            isOpen = false;
        }
    }

    private void ensureOpen() {
        if (!isOpen) {
            throw new IllegalStateException("Serializer has been closed");
        }
    }

    // TODO: consider not returning a final character that is a high surrogate
    // when truncating
    private String readLine() throws IOException {
        StringBuilder sb = new StringBuilder();
        int c;
        int readChars = 0;
        while ((c = in.readChar()) != -1) {
            readChars++;

            // FIXME: support \r\n
            if (c == '\n') {
                break;
            }

            sb.append((char) c);

            if (readChars >= maxLineLength) {
                logger.warn("Line length exceeds max ({}), truncating line!",
                        maxLineLength);
                break;
            }
        }

        if (readChars > 0) {
            return sb.toString();
        } else {
            return null;
        }
    }

    public static class Builder implements EventDeserializer.Builder {

        @Override
        public MyLineDeserializer build(Context context, ResettableInputStream in) {
            return new MyLineDeserializer(context, in);
        }

    }

}

　　2: flume 配置文件

a1.sources.r1.deserializer =  com.xxx.flume.serializer.MyLineDeserializer$Builder