canal

canal 是阿里巴巴开源的 MySQL binlog 增量订阅&消费组件

canal 工作原理：

• canal 模拟 MySQL slave 的交互协议，伪装自己为 MySQL slave ，向 MySQL master 发送dump 协议
• MySQL master 收到 dump 请求，开始推送 binary log 给 slave (即 canal )
• canal 解析 binary log 对象(原始为 byte 流)

本文使用的 canal 版本为 v1.1.4

一、canal 安装与配置

安装与配置可以参考：QuickStart，我的 conf/example/instance.properties 配置：

## mysql serverId , v1.0.26+ will autoGen
canal.instance.mysql.slaveId=1234

... ...

canal.instance.master.address=192.168.137.1:3306

... ...

canal.instance.dbUsername=canal
canal.instance.dbPassword=canal
canal.instance.connectionCharset = UTF-8

... ...

二、客户端使用

添加引用：

<dependency>
    <groupId>com.alibaba.otter</groupId>
    <artifactId>canal.client</artifactId>
    <version>1.1.4</version>
</dependency>

代码：

@Component
public class CanalRunner implements CommandLineRunner {

    private static final Logger LOGGER = LoggerFactory.getLogger(CanalRunner.class);

    @Override
    public void run(String... args) throws Exception {

        CanalConnector connector = CanalConnectors.newSingleConnector(
                new InetSocketAddress("192.168.137.101", 11111)
                , "example"
                , "canal", "canal");
        connector.connect();
        connector.subscribe(".*\..*");
        connector.rollback();

        while (true) {
            Message message = connector.getWithoutAck(100); // 获取指定数量的数据
            long batchId = message.getId();
            if (batchId == -1 || message.getEntries().isEmpty()) {
                Thread.sleep(1000);
                continue;
            }

            try {
                printEntries(message.getEntries());
                connector.ack(batchId);// 提交确认，消费成功，通知server删除数据
            } catch (Exception e) {
//                connector.rollback(batchId);// 处理失败, 回滚数据，后续重新获取数据
            }

        }

    }

    private void printEntries(List<CanalEntry.Entry> entries) throws Exception {
        for (CanalEntry.Entry entry : entries) {
            if (entry.getEntryType() != CanalEntry.EntryType.ROWDATA) {
                continue;
            }

            CanalEntry.RowChange rowChange = CanalEntry.RowChange.parseFrom(entry.getStoreValue());

            CanalEntry.EventType eventType = rowChange.getEventType();

            LOGGER.info("数据库名: {}, 数据表名: {}, 事件: {}"
                    , entry.getHeader().getSchemaName(), entry.getHeader().getTableName(), eventType);

            for (CanalEntry.RowData rowData : rowChange.getRowDatasList()) {
                switch (rowChange.getEventType()) {
                    case INSERT:
                        printColumns(rowData.getAfterColumnsList());
                        break;
                    case UPDATE:
                        LOGGER.info("更新前数据：");
                        printColumns(rowData.getBeforeColumnsList());
                        LOGGER.info("更新后数据：");
                        printColumns(rowData.getAfterColumnsList());
                        break;
                    case DELETE:
                        printColumns(rowData.getBeforeColumnsList());
                        break;
                    default:
                        break;
                }
            }
        }
    }

    private void printColumns(List<CanalEntry.Column> columns) {
        Map<String, Object> map = new HashMap<>();
        for(CanalEntry.Column column : columns) {
            map.put(column.getName(), column.getValue());
        }

        ObjectMapper objectMapper = new ObjectMapper();

        try {
            LOGGER.info(objectMapper.writeValueAsString(map));
        } catch (JsonProcessingException e) {
        }
    }
}

CanalConnector 中的参数来自于 /conf/canal.properties：

port	canal.port
destination	canal.destinations
username	canal.instance.tsdb.dbUsername
password	canal.instance.tsdb.dbPassword

参考

1. canal
2. 史上最全的分布式数据同步中间间canal 之入门篇

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