聊聊BinaryLogFileReader

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序

本文主要研究一下BinaryLogFileReader

BinaryLogFileReader

mysql-binlog-connector-java-0.20.1/src/main/java/com/github/shyiko/mysql/binlog/BinaryLogFileReader.java

public class BinaryLogFileReader implements Closeable {

    public static final byte[] MAGIC_HEADER = new byte[]{(byte) 0xfe, (byte) 0x62, (byte) 0x69, (byte) 0x6e};

    private final ByteArrayInputStream inputStream;
    private final EventDeserializer eventDeserializer;

    public BinaryLogFileReader(File file) throws IOException {
        this(file, new EventDeserializer());
    }

    public BinaryLogFileReader(File file, EventDeserializer eventDeserializer) throws IOException {
        this(file != null ? new BufferedInputStream(new FileInputStream(file)) : null, eventDeserializer);
    }

    public BinaryLogFileReader(InputStream inputStream) throws IOException {
        this(inputStream, new EventDeserializer());
    }

    public BinaryLogFileReader(InputStream inputStream, EventDeserializer eventDeserializer) throws IOException {
        if (inputStream == null) {
            throw new IllegalArgumentException("Input stream cannot be NULL");
        }
        if (eventDeserializer == null) {
            throw new IllegalArgumentException("Event deserializer cannot be NULL");
        }
        this.inputStream = new ByteArrayInputStream(inputStream);
        try {
            byte[] magicHeader = this.inputStream.read(MAGIC_HEADER.length);
            if (!Arrays.equals(magicHeader, MAGIC_HEADER)) {
                throw new IOException("Not a valid binary log");
            }
        } catch (IOException e) {
            try {
                this.inputStream.close();
            } catch (IOException ex) {
                // ignore
            }
            throw e;
        }
        this.eventDeserializer = eventDeserializer;
    }

    /**
     * @return deserialized event or null in case of end-of-stream
     */
    public Event readEvent() throws IOException {
        return eventDeserializer.nextEvent(inputStream);
    }

    @Override
    public void close() throws IOException {
        inputStream.close();
    }

}

• BinaryLogFileReader实现了Closeable接口，其close方法会关闭inputStream；它定义了inputStream、eventDeserializer两个属性，其构造器接收binlog的文件或者inputStream，也允许指定eventDeserializer；其readEvent方法通过eventDeserializer.nextEvent(inputStream)来返回Event，读完的时候返回null

EventDeserializer

mysql-binlog-connector-java-0.20.1/src/main/java/com/github/shyiko/mysql/binlog/event/deserialization/EventDeserializer.java

public class EventDeserializer {

    private final EventHeaderDeserializer eventHeaderDeserializer;
    private final EventDataDeserializer defaultEventDataDeserializer;
    private final Map eventDataDeserializers;

    private EnumSet compatibilitySet = EnumSet.noneOf(CompatibilityMode.class);
    private int checksumLength;

    private final Map tableMapEventByTableId;

    private EventDataDeserializer tableMapEventDataDeserializer;
    private EventDataDeserializer formatDescEventDataDeserializer;

    //......

    public Event nextEvent(ByteArrayInputStream inputStream) throws IOException {
        if (inputStream.peek() == -1) {
            return null;
        }
        EventHeader eventHeader = eventHeaderDeserializer.deserialize(inputStream);
        EventData eventData;
        switch (eventHeader.getEventType()) {
            case FORMAT_DESCRIPTION:
                eventData = deserializeFormatDescriptionEventData(inputStream, eventHeader);
                break;
            case TABLE_MAP:
                eventData = deserializeTableMapEventData(inputStream, eventHeader);
                break;
            default:
                EventDataDeserializer eventDataDeserializer = getEventDataDeserializer(eventHeader.getEventType());
                eventData = deserializeEventData(inputStream, eventHeader, eventDataDeserializer);
        }
        return new Event(eventHeader, eventData);
    }

    //......

}

• EventDeserializer定义了eventHeaderDeserializer、defaultEventDataDeserializer等属性；其nextEvent方法先通过eventHeaderDeserializer.deserialize(inputStream)解析eventHeader，之后根据eventHeader.getEventType()来解析不同的eventData，最后将header及data组装为Event返回

EventHeader

mysql-binlog-connector-java-0.20.1/src/main/java/com/github/shyiko/mysql/binlog/event/EventHeader.java

public interface EventHeader extends Serializable {

    long getTimestamp();
    EventType getEventType();
    long getServerId();
    long getHeaderLength();
    long getDataLength();
}

• EventHeader定义了getTimestamp、getEventType、getServerId、getHeaderLength、getDataLength方法

EventData

mysql-binlog-connector-java-0.20.1/src/main/java/com/github/shyiko/mysql/binlog/event/EventData.java

public interface EventData extends Serializable {
}

• EventData接口继承了Serializable接口

小结

BinaryLogFileReader实现了Closeable接口，其close方法会关闭inputStream；它定义了inputStream、eventDeserializer两个属性，其构造器接收binlog的文件或者inputStream，也允许指定eventDeserializer；其readEvent方法通过eventDeserializer.nextEvent(inputStream)来返回Event，读完的时候返回null

doc

• BinaryLogFileReader

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