SpringCloudAlibaba之Seata
简介
Seata组件是Spring Cloud Alibaba提供的处理分布式事务的组件。那何为分布式事务呢?在微服务环境下,假设有3个服务,A、B、C服务,A的某个方法,方法逻辑是通过OpenFeign调用B服务的方法,再通过OpenFeign调用C服务的方法,最后再执行自身的业务逻辑,对数据库执行操作。那如果在对数据库执行操作时出现异常,此时要进行回滚,即调用B服务的方法和调用C服务的方法中,对数据库的操作,要进行回滚。如果没有分布式事务的介入,B、C服务对数据库的操作是无法回滚的。但有了Seata,这个问题便可得到解决。
四种模式
Seata为我们提供了AT、TCC、SAGA、XA这四种模式,不同模式针对不同的场景需求,提供解决方案。
AT模式:即自动模式,可以解决80%的分布式事务需求,依赖数据库的undo log和redo log。
TCC模式:当某服务操作的数据库是非关系型数据库时,如Redis,就不能用AT模式了,而是使用TCC模式。各服务的逻辑层代码中,编写一组三个方法(prepare、commit、rollback),prepare是无论事务成功与否都要执行的方法,commit是整体事务成功时执行的方法,rollback是整体事务失败时执行的方法
SAGA模式:针对于老项目:编写一个类,当事务失败要进行回滚时,运行这个编写的回滚类。这样子就不用修改原有的代码了。
XA模式:使用较少,强一致性的。
代码示例
首先下载seata:https://github.com/seata/seata/releases
作者这里下载的是1.4.2的windows版本,
下载好后,解压,打开conf文件夹下的registry.conf,
该文件下方还有个config配置,type为file,而这个file指向的是和registry.conf同目录下的file.conf,我们打开编辑它:
如果你用的是mysql8,driverClassName要改成”com.mysql.cj.jdbc.Driver”,url后面要加上”&serverTimezone=Asia/Shanghai”,user、password也要改成自己数据库的用户名和密码。在mysql上建立seata数据库(不叫seata也行,但要和url中的名称保持一致),然后新建3张表,global_table、branch_table、lock_table,sql如下:
-- the table to store GlobalSession data CREATE TABLE IF NOT EXISTS `global_table` ( `xid` VARCHAR(128) NOT NULL, `transaction_id` BIGINT, `status` TINYINT NOT NULL, `application_id` VARCHAR(32), `transaction_service_group` VARCHAR(32), `transaction_name` VARCHAR(128), `timeout` INT, `begin_time` BIGINT, `application_data` VARCHAR(2000), `gmt_create` DATETIME, `gmt_modified` DATETIME, PRIMARY KEY (`xid`), KEY `idx_status_gmt_modified` (`status` , `gmt_modified`), KEY `idx_transaction_id` (`transaction_id`) ) ENGINE = InnoDB DEFAULT CHARSET = utf8mb4; -- the table to store BranchSession data CREATE TABLE IF NOT EXISTS `branch_table` ( `branch_id` BIGINT NOT NULL, `xid` VARCHAR(128) NOT NULL, `transaction_id` BIGINT, `resource_group_id` VARCHAR(32), `resource_id` VARCHAR(256), `branch_type` VARCHAR(8), `status` TINYINT, `client_id` VARCHAR(64), `application_data` VARCHAR(2000), `gmt_create` DATETIME(6), `gmt_modified` DATETIME(6), PRIMARY KEY (`branch_id`), KEY `idx_xid` (`xid`) ) ENGINE = InnoDB DEFAULT CHARSET = utf8mb4; -- the table to store lock data CREATE TABLE IF NOT EXISTS `lock_table` ( `row_key` VARCHAR(128) NOT NULL, `xid` VARCHAR(128), `transaction_id` BIGINT, `branch_id` BIGINT NOT NULL, `resource_id` VARCHAR(256), `table_name` VARCHAR(32), `pk` VARCHAR(36), `status` TINYINT NOT NULL DEFAULT '0' COMMENT '0:locked ,1:rollbacking', `gmt_create` DATETIME, `gmt_modified` DATETIME, PRIMARY KEY (`row_key`), KEY `idx_status` (`status`), KEY `idx_branch_id` (`branch_id`), KEY `idx_xid_and_branch_id` (`xid` , `branch_id`) ) ENGINE = InnoDB DEFAULT CHARSET = utf8mb4;
然后先启动nacos,再启动seata(点击bin目录下的seata-server.bat);如果在nacos的服务列表中,多出来一条数据,说明刚才的配置成功奏效了:
下面我们要新建2个服务模块,订单模块和库存模块;订单模块的某个方法,会通过OpenFeign调用库存模块的方法,这个库存模块的方法会减少库存表的数量1;然后再往自身的订单表新增一条数据。我们首先建立库存模块:
引入依赖:
com.alibaba druid-spring-boot-starter 1.2.8 mysql mysql-connector-java org.mybatis.spring.boot mybatis-spring-boot-starter 2.2.2 org.springframework.boot spring-boot-starter-web com.alibaba.cloud spring-cloud-starter-alibaba-nacos-discovery com.alibaba.cloud spring-cloud-starter-alibaba-seata com.alibaba.cloud spring-cloud-alibaba-dependencies 2.2.6.RELEASE pom import org.springframework.boot spring-boot-dependencies 2.2.6.RELEASE pom import
application.yml的配置:
server: port: 8081 spring: application: name: seata-stock # 不能放在bootstrap.yml中,不然启动报错 datasource: druid: driver-class-name: com.mysql.cj.jdbc.Driver url: jdbc:mysql://127.0.0.1:3306/test?useUnicode=true&characterEncoding=utf-8&allowMultiQueries=true&useSSL=false&serverTimezone=Asia/Shanghai username: root password: 123456 type: com.alibaba.druid.pool.DruidDataSource cloud: nacos: discovery: server-addr: 127.0.0.1:8848 mybatis: # xml文件必须放在src/main/resources下的mapper文件夹下; # 或者xml文件和mapper接口同名、同路径,不需要配置 mapper-locations: classpath*:mapper/*.xml seata: # 事务组名称 tx-service-group: mygroup service: vgroup-mapping: mygroup: default
Controller层:
import com.gs.seatastock.service.StockService; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.RestController; @RestController @RequestMapping("/stock") public class StockController { @Autowired private StockService stockService; @RequestMapping("/desc") public void desc() { stockService.desc(1); } }
Service层:
public interface StockService { void desc(Integer productId); }
import com.gs.seatastock.mapper.StockMapper; import com.gs.seatastock.service.StockService; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Service; @Service public class StockServiceImpl implements StockService { @Autowired private StockMapper stockMapper; public void desc(Integer productId) { stockMapper.stockDesc(productId); } }
mapper层:
import org.apache.ibatis.annotations.Param; public interface StockMapper { Integer stockDesc(@Param("productId") Integer productId); }
xml文件:
update stock set count = count - 1 where product_id = #{productId}
数据库层面,Stock表:
CREATE TABLE `stock` ( `id` int NOT NULL AUTO_INCREMENT, `product_id` int DEFAULT NULL, `count` int DEFAULT NULL, PRIMARY KEY (`id`), UNIQUE KEY `stock_un` (`product_id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb3;
并且插入一条数据:
insert into stock (product_id, count) values(1, 100);
数据库下也要给seata建立一张名为undo_log的表:
CREATE TABLE `undo_log` ( `id` bigint(20) NOT NULL AUTO_INCREMENT, `branch_id` bigint(20) NOT NULL, `xid` varchar(100) NOT NULL, `context` varchar(128) NOT NULL, `rollback_info` longblob NOT NULL, `log_status` int(11) NOT NULL, `log_created` datetime NOT NULL, `log_modified` datetime NOT NULL, PRIMARY KEY (`id`), UNIQUE KEY `ux_undo_log` (`xid`,`branch_id`) ) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;
再建立订单模块,引入依赖:
com.alibaba druid-spring-boot-starter 1.2.8 mysql mysql-connector-java org.mybatis.spring.boot mybatis-spring-boot-starter 2.2.2 org.springframework.boot spring-boot-starter-web com.alibaba.cloud spring-cloud-starter-alibaba-nacos-discovery org.springframework.cloud spring-cloud-starter-openfeign 2.2.6.RELEASE com.alibaba.cloud spring-cloud-starter-alibaba-seata
application.yml的配置:
server: port: 8082 spring: application: name: seata-order # 不能放在bootstrap.yml中,不然启动报错 datasource: druid: driver-class-name: com.mysql.cj.jdbc.Driver url: jdbc:mysql://127.0.0.1:3306/test1?useUnicode=true&characterEncoding=utf-8&allowMultiQueries=true&useSSL=false&serverTimezone=Asia/Shanghai username: root password: 123456 type: com.alibaba.druid.pool.DruidDataSource cloud: nacos: discovery: server-addr: 127.0.0.1:8848 mybatis: # xml文件必须放在src/main/resources下的mapper文件夹下; # 或者xml文件和mapper接口同名、同路径,不需要配置 mapper-locations: classpath*:mapper/*.xml seata: # 事务组名称 tx-service-group: mygroup service: vgroup-mapping: mygroup: default
Controller层(这里有个重要的seata注解:@GlobalTransactional):
import com.gs.seataorder.service.OrderService; import io.seata.spring.annotation.GlobalTransactional; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.RestController; @RestController @RequestMapping("/order") public class OrderController { @Autowired private OrderService orderService; @RequestMapping("/createOrder") @GlobalTransactional public void createOrder() { orderService.createOrder(1); } }
Service层:
public interface OrderService { Integer createOrder(Integer productId); }
import com.gs.seataorder.feign.MyFeignClient; import com.gs.seataorder.mapper.OrderMapper; import com.gs.seataorder.service.OrderService; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Service; @Service public class OrderServiceImpl implements OrderService { @Autowired private MyFeignClient feignClient; @Autowired private OrderMapper mapper; public Integer createOrder(Integer productId) { feignClient.desc(); int i = 1 / 0; return mapper.createOrder(productId); } }
Feign的接口:
import org.springframework.cloud.openfeign.FeignClient; import org.springframework.web.bind.annotation.GetMapping; @FeignClient(value = "seata-stock") public interface MyFeignClient { @GetMapping("/stock/desc") void desc(); }
mapper层:
import org.apache.ibatis.annotations.Param; public interface OrderMapper { Integer createOrder(@Param("productId") Integer productId); }
xml文件:
insert into orderForm(product_id, count) values(#{productId}, 1) on duplicate key update count = count + 1
数据库的orderForm表:
CREATE TABLE `orderform` ( `id` int NOT NULL AUTO_INCREMENT, `product_id` int DEFAULT NULL, `count` int DEFAULT NULL, PRIMARY KEY (`id`), UNIQUE KEY `orderForm_un` (`product_id`) ) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8mb3;
undo_log表也不能少,建表的sql和上面的一样。
打开浏览器去访问:http://localhost:8082/order/createOrder,然后去观察stock表和orderform表;stock表的count字段没有减少,还是100,orderform表没有增加数据,说明此时分布式事务成功了。
以上的代码示例,是基于AT模式的;想要尝试其余模式的,可以参考:
TCC模式:
https://seata.io/zh-cn/blog/integrate-seata-tcc-mode-with-spring-cloud.html
SAGA模式:
https://seata.io/zh-cn/docs/user/saga.html
XA模式:
https://github.com/seata/seata-samples