新建一個Maven項目，最終項目結構如下：
多數據源注入到sqlSessionFactory
POM增加如下依賴：
<!--JSON-->
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-core</artifactId>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.datatype</groupId>
<artifactId>jackson-datatype-joda</artifactId>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.module</groupId>
<artifactId>jackson-module-parameter-names</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-jdbc</artifactId>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
</dependency>
<dependency>
<groupId>com.alibaba</groupId>
<artifactId>druid</artifactId>
<version>1.0.11</version>
</dependency>
<!--mybatis-->
<dependency>
<groupId>org.mybatis.spring.boot</groupId>
<artifactId>mybatis-spring-boot-starter</artifactId>
<version>1.1.1</version>
</dependency>
<!--mapper-->
<dependency>
<groupId>tk.mybatis</groupId>
<artifactId>mapper-spring-boot-starter</artifactId>
<version>1.1.0</version>
</dependency>
<!--pagehelper-->
<dependency>
<groupId>com.github.pagehelper</groupId>
<artifactId>pagehelper-spring-boot-starter</artifactId>
<version>1.1.0</version>
<exclusions>
<exclusion>
<artifactId>mybatis-spring-boot-starter</artifactId>
<groupId>org.mybatis.spring.boot</groupId>
</exclusion>
</exclusions>
</dependency>
這裏需要注意的是：項目是通過擴展mybatis-spring-boot-starter的org.mybatis.spring.boot.autoconfigure.MybatisAutoConfiguration來實現多數據源注入的。在mybatis-spring-boot-starter：1.2.0中，該類取消了默認構造函數，因此本項目依舊使用1.1.0版本。需要關注後續版本是否會重新把擴展開放處理。
之所以依舊使用舊方案，是我個人認爲開放擴展是合理的，相信在未來的版本中會迴歸。
增加主從庫配置(application.yml)
druid:
type: com.alibaba.druid.pool.DruidDataSource master:
url: jdbc:mysql://192.168.249.128:3307/db-test?characterEncoding=UTF-8&autoReconnect=true&zeroDateTimeBehavior=convertToNull&useUnicode=true
driver-class-name: com.mysql.jdbc.Driver
username: root password: root
initial-size: 5
min-idle: 1
max-active: 100
test-on-borrow: true
slave:
url: jdbc:mysql://192.168.249.128:3317/db-test?characterEncoding=UTF-8&autoReconnect=true&zeroDateTimeBehavior=convertToNull&useUnicode=true&characterEncoding=utf-8
driver-class-name: com.mysql.jdbc.Driver
username: root password: root
initial-size: 5
min-idle: 1
max-active: 100
test-on-borrow: true
創建數據源
@Configuration@EnableTransactionManagementpublic class DataSourceConfiguration { @Value("${druid.type}") private Class<? extends DataSource> dataSourceType; @Bean(name = "masterDataSource") @Primary
@ConfigurationProperties(prefix = "druid.master") public DataSource masterDataSource(){ return DataSourceBuilder.create().type(dataSourceType).build();
} @Bean(name = "slaveDataSource") @ConfigurationProperties(prefix = "druid.slave") public DataSource slaveDataSource1(){ return DataSourceBuilder.create().type(dataSourceType).build();
}
}
將多數據源注入到sqlSessionFactory中
前面提到了這裏通過擴展mybatis-spring-boot-starter的org.mybatis.spring.boot.autoconfigure.MybatisAutoConfiguration來實現多數據源注入的
@Configuration@AutoConfigureAfter({DataSourceConfiguration.class})public class MybatisConfiguration extends MybatisAutoConfiguration { private static Log logger = LogFactory.getLog(MybatisConfiguration.class); @Resource(name = "masterDataSource") private DataSource masterDataSource; @Resource(name = "slaveDataSource") private DataSource slaveDataSource; @Bean
public SqlSessionFactory sqlSessionFactory() throws Exception { return super.sqlSessionFactory(roundRobinDataSouceProxy());
} public AbstractRoutingDataSource roundRobinDataSouceProxy(){
ReadWriteSplitRoutingDataSource proxy = new ReadWriteSplitRoutingDataSource();
Map<Object,Object> targetDataResources = new ClassLoaderRepository.SoftHashMap();
targetDataResources.put(DbContextHolder.DbType.MASTER,masterDataSource);
targetDataResources.put(DbContextHolder.DbType.SLAVE,slaveDataSource);
proxy.setDefaultTargetDataSource(masterDataSource);//默認源
proxy.setTargetDataSources(targetDataResources); return proxy;
}
}
實現讀寫分離（多數據源分離）
這裏主要思路如下：
1-將不同的數據源標識記錄在ThreadLocal中
2-通過註解標識出當前的service方法使用哪個庫
3-通過Spring AOP實現攔截註解並注入不同的標識到threadlocal中
4-獲取源的時候通過threadlocal中不同的標識給出不同的sqlSession
標識存放ThreadLocal的實現
public class DbContextHolder { public enum DbType{
MASTER,SLAVE
} private static final ThreadLocal<DbType> contextHolder = new ThreadLocal<>(); public static void setDbType(DbType dbType){ if(dbType==null)throw new NullPointerException();
contextHolder.set(dbType);
} public static DbType getDbType(){ return contextHolder.get()==null?DbType.MASTER:contextHolder.get();
} public static void clearDbType(){
contextHolder.remove();
}
}
註解實現
/**
* 該註解註釋在service方法上，標註爲鏈接slaves庫
* Created by Jason on 2017/3/6.
*/@Target({ElementType.METHOD,ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface ReadOnlyConnection {
}
Spring AOP對註解的攔截
@Aspect@Componentpublic class ReadOnlyConnectionInterceptor implements Ordered { public static final Logger logger = LoggerFactory.getLogger(ReadOnlyConnectionInterceptor.class); @Around("@annotation(readOnlyConnection)") public Object proceed(ProceedingJoinPoint proceedingJoinPoint,ReadOnlyConnection readOnlyConnection) throws Throwable { try {
logger.info("set database connection to read only");
DbContextHolder.setDbType(DbContextHolder.DbType.SLAVE);
Object result = proceedingJoinPoint.proceed(); return result;
}finally {
DbContextHolder.clearDbType();
logger.info("restore database connection");
}
} @Override
public int getOrder() { return 0;
}
}
根據標識獲取不同源
這裏我們通過擴展AbstractRoutingDataSource來獲取不同的源。它是Spring提供的一個可以根據用戶發起的不同請求去轉換不同的數據源，比如根據用戶的不同地區語言選擇不同的數據庫。通過查看源碼可以發現，它是通過determineCurrentLookupKey（）返回的不同key到sqlSessionFactory中獲取不同源（前面已經展示瞭如何在sqlSessionFactory中注入多個源）
public class ReadWriteSplitRoutingDataSource extends AbstractRoutingDataSource { @Override
protected Object determineCurrentLookupKey() { return DbContextHolder.getDbType();
}
}
以上就完成了讀寫分離（多數據源）的配置方案。下面是一個具體的實例
使用方式
Entity
@Table(name = "t_sys_dic_type")public class DicType extends BaseEntity{
String code;
String name;
Integer status;
...
}
Mapper
public interface DicTypeMapper extends BaseMapper<DicType> {
}
Service
@Servicepublic class DicTypeService { @Autowired
private DicTypeMapper dicTypeMapper; @ReadOnlyConnection
public List<DicType> getAll(DicType dicType){ if (dicType.getPage() != null && dicType.getRows() != null) {
PageHelper.startPage(dicType.getPage(), dicType.getRows());
} return dicTypeMapper.selectAll();
}
}
注意這裏的@ReadOnlyConnection註解
Controller
@RestController@RequestMapping("/dictype")public class DicTypeController { @Autowired
private DicTypeService dicTypeService; @RequestMapping(value = "/all") public PageInfo<DicType> getALL(DicType dicType){
List<DicType> dicTypeList = dicTypeService.getAll(dicType); return new PageInfo<>(dicTypeList);
}
}
通過mvn spring-boot:run啓動後
後臺打印出
c.a.d.m.ReadOnlyConnectionInterceptor : set database connection to read only
說明使用了從庫的鏈接獲取數據
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