在spring中有一個AbstractRoutingDataSource抽象類可以實現(xiàn)數(shù)據(jù)源的路由，核心方法是determineTargetDataSource，注釋的大概意思通過determineCurrentLookupKey()確定key，在targetDataSources中通過key檢索對應的數(shù)據(jù)源。

determineCurrentLookupKey()是一個抽象方法，需要我們來實現(xiàn)，返回我們要的key，targetDataSources是一個map，保存數(shù)據(jù)源

我們實現(xiàn)的思路是，項目啟動時就讓spring保存我們所有的數(shù)據(jù)源，通過mybatis的攔截器攔截方法，判斷是應該選擇主數(shù)據(jù)庫還是從數(shù)據(jù)庫然后返回對應的key。

一. 先實現(xiàn)這個數(shù)據(jù)源切換

public class DynamicDataSourceHolder {

    private static final Logger log = LoggerFactory.getLogger(DynamicDataSourceHolder.class);

    private static ThreadLocal<String> dataSourceHolder = new ThreadLocal();

    public static final String master = "master";
    public static final String slave = "slave";


    public static String get() {
        String db = dataSourceHolder.get();
        if(db == null) {
            db = master;
        }

        return db;
    }

    public static void setDBType(String type) {
        log.info("數(shù)據(jù)源類型：{}", type);
        dataSourceHolder.set(type);
    }

    public static void clear() {
        dataSourceHolder.remove();
    }
}

public class DynamicDataSource extends AbstractRoutingDataSource {

    public DynamicDataSource(DataSource defaultTargetDataSource, Map<String, DataSource> targetDataSources) {
        // 調用super方法保存數(shù)據(jù)源
        super.setDefaultTargetDataSource(defaultTargetDataSource);
        super.setTargetDataSources(new HashMap<>(targetDataSources));
        // 啟動時加載
        super.afterPropertiesSet();
    }

    /**
     * 要實現(xiàn)的方法，返回key
     * 通過DynamicDataSourceHolder保存key
     * @return
     */
    @Override
    protected Object determineCurrentLookupKey() {
        return DynamicDataSourceHolder.get();
    }
}

二、實現(xiàn)mybatis攔截器

@Component
@Intercepts({
        @Signature(type = Executor.class, method = "update", args = {MappedStatement.class, Object.class}),
        @Signature(type = Executor.class, method = "query", args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class, })
})
@Slf4j
public class DynamicDataSourceInterceptor implements Interceptor {
    // 正則匹配update等寫語句
    private static final String SQL_REGEX = ".*insert\\u0020.*|.*delete\\u0020.*|.*update\\u0020.*";

    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        // 是否是事務方法
        boolean active = TransactionSynchronizationManager.isActualTransactionActive();
        String lookupKey = DynamicDataSourceHolder.master;
        //非事務
        if(!active) {
            Object[] args = invocation.getArgs();
            // mybatis statment 就是mapper xml文件中的select標簽
            MappedStatement mappedStatements = (MappedStatement) args[0];
            //  SqlCommandType：select、update、insert、delete
            log.info("SqlCommandType:{}", mappedStatements.getSqlCommandType());
            // 可以獲取到sql語句
            log.info("Sql:{}", mappedStatements.getSqlSource().getBoundSql(args[1]).getSql());
            
            /*
            *   如果是select語句
            * */
            if(mappedStatements.getSqlCommandType().equals(SqlCommandType.SELECT)) {
                if(mappedStatements.getId().contains(SelectKeyGenerator.SELECT_KEY_SUFFIX)) {
                    lookupKey = DynamicDataSourceHolder.master;
                } else {
                    lookupKey = DynamicDataSourceHolder.slave;
                }
                // 非select
            }else {
                BoundSql sql = mappedStatements.getSqlSource().getBoundSql(args[1]);
                String sqlStr = sql.getSql().toLowerCase(Locale.CHINA).replaceAll("[\\t\\n\\r]", " ");
                if(sqlStr.matches(SQL_REGEX)) {
                    lookupKey = DynamicDataSourceHolder.master;
                } else {
                    lookupKey = DynamicDataSourceHolder.slave;
                }
            }
            //事務方法走主庫
        } else {
            lookupKey = DynamicDataSourceHolder.master;
        }

        DynamicDataSourceHolder.setDBType(lookupKey);

        return invocation.proceed();
    }

    @Override
    public Object plugin(Object o) {
        if(o instanceof Executor) {
            return Plugin.wrap(o, this);
        } else {
            return o;
        }
    }

    @Override
    public void setProperties(Properties properties) {

    }
}

三、數(shù)據(jù)源配置和配置類

spring:
  datasource:
    druid:
      one:
        url: jdbc:mysql://192.168.1.8:3306/cloud_alibaba_user_center?useUnicode=true&characterEncoding=utf-8&autoReconnect=true&useSSL=false&allowMultiQueries=true&serverTimezone=Asia/Shanghai&nullCatalogMeansCurrent=true
        username: root
        password: LyL@163.com
        driver-class-name: com.mysql.cj.jdbc.Driver
      two:
        url: jdbc:mysql://192.168.1.9:3306/cloud_alibaba_user_center?useUnicode=true&characterEncoding=utf-8&autoReconnect=true&useSSL=false&allowMultiQueries=true&serverTimezone=Asia/Shanghai&nullCatalogMeansCurrent=true
        username: root
        password: LyL@163.com
        driver-class-name: com.mysql.cj.jdbc.Driver

@Configuration
public class DataSourceConfiguration {
 
    @Autowired
    private DynamicDataSourceInterceptor dataSourceInterceptor;
    
    @Bean
    public ConfigurationCustomizer configurationCustomizer() {
        return new ConfigurationCustomizer() {
            @Override
            public void customize(org.apache.ibatis.session.Configuration configuration) {
                configuration.addInterceptor(dataSourceInterceptor);
            }
        };
    }

    @Bean
    @ConfigurationProperties("spring.datasource.druid.one")
    public DataSource masterDataSource(){
        return DruidDataSourceBuilder.create().build();
    }
    @Bean
    @ConfigurationProperties("spring.datasource.druid.two")
    public DataSource slaveDataSource(){
        return DruidDataSourceBuilder.create().build();
    }

 

    @Bean
    @Primary
    public DynamicDataSource dataSource() {
        Map<String, DataSource> targetDataSources = new HashMap<>();
        targetDataSources.put(DynamicDataSourceHolder.master, masterDataSource());
        targetDataSources.put(DynamicDataSourceHolder.slave, slaveDataSource());
        DynamicDataSource dynamicDataSource = new DynamicDataSource(masterDataSource(), targetDataSources);
        return dynamicDataSource;
    }
}

四、啟動類

@SpringBootApplication(exclude = DataSourceAutoConfiguration.class)
@Import({DataSourceConfiguration.class})
@MapperScan(basePackages = "com.yonglong.bookhouse.user.mapper")
public class UserCenterApplication {

    public static void main(String[] args) {
        SpringApplication.run(UserCenterApplication.class, args);
    }
}

測試可用，大家可自行測試，上一篇是mysql主從同步的配置，大家可以單獨修改掉從庫中的數(shù)據(jù)然后查詢看是否為從庫中修改后的數(shù)據(jù)，是就說明大功告成！