canal环境搭建及基础使用

前段时间有一个实时获取某个表结构数据变动的需求，简单对canal做了个了解，现将当时做demo的过程记录下来。

canal工作原理

1. 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
2. mysql master收到dump请求，开始推送binary log给slave(也就是canal)
3. canal解析binary log对象(原始为byte流)
   

1. 数据库准备

开启 Binlog 写入功能

[mysqld]
log-bin=mysql-bin # 开启 binlog
binlog-format=ROW # 选择 ROW 模式
server_id=1 # 配置 MySQL replaction 需要定义，不要和 canal 的 slaveId 重复

创建canal用户并授权

CREATE USER canal IDENTIFIED BY 'canal';  
GRANT ALL PRIVILEGES ON *.* TO 'canal'@'%' ;
FLUSH PRIVILEGES;

2. canal-server准备

docker大法好，懒人首选。。。。

拉取docker镜像

 docker pull canal/canal-server:v1.1.4

启动canal-server的docker容器

docker run --name canal-server \
-e canal.instance.master.address=127.0.0.1:3306 \
-e canal.instance.dbUsername=canal \
-e canal.instance.dbPassword=canal \
-p 998:11111 \
-d canal/canal-server:v1.1.4

3. 客户端demo代码

pom依赖

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

代码

import com.alibaba.otter.canal.client.CanalConnector;
import com.alibaba.otter.canal.client.CanalConnectors;
import com.alibaba.otter.canal.protocol.CanalEntry;
import com.alibaba.otter.canal.protocol.Message;

import java.net.InetSocketAddress;
import java.util.List;

public class ClientTest {
    public static void main(String args[]) {
        // 创建链接
        CanalConnector connector = CanalConnectors.newSingleConnector(new InetSocketAddress("127.0.0.1",
                998), "example", "", "");
        int batchSize = 1000;
        int emptyCount = 0;
        try {
            connector.connect();
            connector.subscribe(".*\\..*");
            connector.rollback();
            int totalEmptyCount = 120;
            while (emptyCount < totalEmptyCount) {
                Message message = connector.getWithoutAck(batchSize); // 获取指定数量的数据
                long batchId = message.getId();
                int size = message.getEntries().size();
                if (batchId == -1 || size == 0) {
                    emptyCount++;
                    System.out.println("empty count : " + emptyCount);
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                    }
                } else {
                    emptyCount = 0;
                    printEntry(message.getEntries());
                }

                connector.ack(batchId); // 提交确认
            }

            System.out.println("empty too many times, exit");
        } finally {
            connector.disconnect();
        }
    }

    private static void printEntry(List<CanalEntry.Entry> entrys) {
        for (CanalEntry.Entry entry : entrys) {
            if (entry.getEntryType() == CanalEntry.EntryType.TRANSACTIONBEGIN || entry.getEntryType() == CanalEntry.EntryType.TRANSACTIONEND) {
                continue;
            }

            CanalEntry.RowChange rowChage = null;
            try {
                rowChage = CanalEntry.RowChange.parseFrom(entry.getStoreValue());
            } catch (Exception e) {
                throw new RuntimeException("ERROR ## parser of eromanga-event has an error , data:" + entry.toString(),
                        e);
            }

            CanalEntry.EventType eventType = rowChage.getEventType();

            System.out.println(String.format("================&gt; binlog[%s:%s] , name[%s,%s] , eventType : %s",
                    entry.getHeader().getLogfileName(), entry.getHeader().getLogfileOffset(),
                    entry.getHeader().getSchemaName(), entry.getHeader().getTableName(),
                    eventType));

            for (CanalEntry.RowData rowData : rowChage.getRowDatasList()) {
                if (eventType == CanalEntry.EventType.DELETE) {
                    printColumn(rowData.getBeforeColumnsList());
                } else if (eventType == CanalEntry.EventType.INSERT) {
                    printColumn(rowData.getAfterColumnsList());
                } else {
                    System.out.println("-------&gt; before");
                    printColumn(rowData.getBeforeColumnsList());
                    System.out.println("-------&gt; after");
                    printColumn(rowData.getAfterColumnsList());
                }
            }
        }
    }

    private static void printColumn(List<CanalEntry.Column> columns) {
        for (CanalEntry.Column column : columns) {
            System.out.println(column.getName() + " : " + column.getValue() + "    update=" + column.getUpdated());
        }
    }
}

新增、更新、删除数据后日志的打印情况

================> binlog[mysql-bin.000002:6862] , name[panda_big_data,sys_role] , eventType : INSERT
role_id : 3    update=true
role_name : 角色1    update=true
remark :     update=true
dept_id :     update=true
create_time :     update=true
================> binlog[mysql-bin.000002:7098] , name[panda_big_data,sys_role] , eventType : UPDATE
-------> before
role_id : 3    update=false
role_name : 角色1    update=false
remark :     update=false
dept_id :     update=false
create_time :     update=false
-------> after
role_id : 3    update=false
role_name : 角色1    update=false
remark : 2    update=true
dept_id :     update=false
create_time :     update=false
================> binlog[mysql-bin.000002:7356] , name[panda_big_data,sys_role] , eventType : DELETE
role_id : 3    update=false
role_name : 角色1    update=false
remark : 2    update=false
dept_id :     update=false
create_time :     update=false

如打印的日志所示，canal可以获取到数据插入、更新前后、删除前等操作的数据详情，在一些需要了解数据实时变动的场景下，还是很有用的。