基于ThreadLocal来实现动态数据源切换

悠悠 2022-12-17 11:57 293阅读 0赞

如何在程序中做读写分离?

1.直接买阿里云的服务，让它自动帮我们做读写分离，我们客户端还是一个连接的url

2.客户端配置多数据源（主从数据库），然后在程序端通过动态数据源切换来切换数据源，基于ThreadLocal来实现。

关键代码

1.自定义注解(配置要使用哪个数据源)

@Target({ElementType.METHOD, ElementType.TYPE})
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    public @interface DataSource {
    
        /**
         * 数据源key值
         * @return
         */
        String value();
    }

2.threadLocal工具类保存数据源的key

public class DynamicDataSourceContextHolder {
    
        private static final ThreadLocal<String> contextHolder = new ThreadLocal<String>(){
            /**
             * 将 master 数据源的 key作为默认数据源的 key
             * @return
             */
            @Override
            protected String initialValue() {
                return "master";
            }
        };
    
        /**
         * 数据源的 key集合, 用于切换时判断数据源是否存在
         */
        public static List<Object> dataSourceKeys = new ArrayList<>();
    
        /**
         * 切换数据源
         * @param key
         */
        public static void setDataSourceKey(String key){
            contextHolder.set(key);
        }
    
        /**
         * 获取数据源
         * @return
         */
        public static String getDataSourceKey(){
            return contextHolder.get();
        }
    
        /**
         * 重置数据源
         */
        public static void clearDataSourceKey(){
            contextHolder.remove();
        }
    
        /**
         * 判断是否包含数据源
         * @param key
         * @return
         */
        public static boolean containDataSourceKey(String key){
            return dataSourceKeys.contains(key);
        }
    
        /**
         * 添加数据源keys
         * @param keys
         * @return
         */
        public static boolean addDataSourceKeys(Collection<? extends Object> keys){
            return dataSourceKeys.addAll(keys);
        }
    }

3.动态数据源配置类

public class DynamicDataSource extends AbstractRoutingDataSource {
    
    
        @Override
        protected DataSource determineTargetDataSource() {
            return super.determineTargetDataSource();
        }
    
    
        @Override
        protected Object determineCurrentLookupKey() {
            return DynamicDataSourceContextHolder.getDataSourceKey();
        }
    
        public void setDefaultDataSource(Object defaultDataSource){
            super.setDefaultTargetDataSource(defaultDataSource);
        }
    
        public void setDataSources(Map<Object, Object> dataSources){
            super.setTargetDataSources(dataSources);
            DynamicDataSourceContextHolder.addDataSourceKeys(dataSources.keySet());
        }
    }

4.mybatis配置

@Configuration
    @MapperScan(basePackages = {"com.example.demo.mapper"})
    public class MybatisConfig {
    
        @Bean("master")
        @Primary
        @ConfigurationProperties(prefix = "spring.datasource.master")
        public DataSource master(){
            return DataSourceBuilder.create().build();
        }
    
        @Bean("slave")
        @ConfigurationProperties(prefix = "spring.datasource.slave")
        public DataSource slave(){
            return DataSourceBuilder.create().build();
        }
    
        @Bean("dynamicDataSource")
        public DataSource dynamicDataSource(){
            DynamicDataSource dynamicDataSource = new DynamicDataSource();
            Map<Object, Object> dataSourceMap = new HashMap<>(2);
            dataSourceMap.put("master", master());
            dataSourceMap.put("slave", slave());
            dynamicDataSource.setDefaultDataSource(master());
            dynamicDataSource.setDataSources(dataSourceMap);
            return dynamicDataSource;
        }
    
        @Bean
        public SqlSessionFactoryBean sqlSessionFactoryBean() throws Exception{
            SqlSessionFactoryBean sessionFactory = new SqlSessionFactoryBean();
            sessionFactory.setDataSource(dynamicDataSource());
            sessionFactory.setTypeAliasesPackage("com.example.demo.entity");
            PathMatchingResourcePatternResolver resolver = new PathMatchingResourcePatternResolver();
            sessionFactory.setMapperLocations(resolver.getResources("classpath:mapper/*.xml"));
            return sessionFactory;
        }
    
        @Bean
        public PlatformTransactionManager transactionManager(){
            return new DataSourceTransactionManager(dynamicDataSource());
        }
    
    
    }

5.切面拦截设置datasource的key到threadLocal

@Aspect
    @Order(-1)
    @Component
    public class DynamicDataSourceAspect {
    
        @Before("@annotation(dataSource)")
        public void switchDataSource(JoinPoint point, DataSource dataSource){
            if(!DynamicDataSourceContextHolder.containDataSourceKey(dataSource.value())){
                System.out.println("DataSource [{}] doesn't exist, use default DataSource [{}] " + dataSource.value());
            }else {
                DynamicDataSourceContextHolder.setDataSourceKey(dataSource.value());
                System.out.println("Switch DataSource to [" + DynamicDataSourceContextHolder.getDataSourceKey()
                        + "] in Method [" + point.getSignature() + "]");
            }
        }
    
        @After("@annotation(dataSource)")
        public void restoreDataSource(JoinPoint point, DataSource dataSource){
            DynamicDataSourceContextHolder.clearDataSourceKey();
            System.out.println("Restore DataSource to [" + DynamicDataSourceContextHolder.getDataSourceKey()
                    + "] in Method [" + point.getSignature() + "]");
        }
    }