mysql+springBoot支持存储表情

1. 数据库支持utf8mb4

    创建数据库时选择字符集：utf8mb4

2. 表支持utf8mb4

    ```
    DROP TABLE IF EXISTS `mytable`;
    CREATE TABLE `mytable` (
      `uid` bigint(20) NOT NULL, 
      
      PRIMARY KEY (`uid`) 
    ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
    ```

3. SpringBoot hibernate连接池的设置支持utf8mb4

    在配置文件**application-rds.properties**中添加一行：
    ```
    spring.datasource.connectionInitSqls=SET NAMES utf8mb4
    ```

    在**RdsConfiguration.java**中设置连接池的字符集：

    ```
    ...

    import javax.sql.DataSource;
    import java.util.Collections;
    import java.util.Properties;
    import java.util.StringTokenizer;

    @Configuration
    public class RdsConfiguration {

        ...

        @Value("${spring.datasource.connectionInitSqls}")
        private String connectionInitSqls;

        ...

        @Bean(name = "dbDataSource")
        @Qualifier(value = "dbDataSource")

        @Primary
        public DataSource dbDataSource() {
            return dataSource(dburl);
        }

        private DataSource dataSource(String url) {
            DruidDataSource druidDataSource = new DruidDataSource();
            druidDataSource.setUrl(url);
            druidDataSource.setUsername(username);
            druidDataSource.setPassword(password);
            druidDataSource.setInitialSize(initialSize);
            druidDataSource.setMinIdle(minIdle);
            druidDataSource.setMaxActive(maxActive);
            druidDataSource.setMaxWait(maxWait);
            druidDataSource.setTimeBetweenEvictionRunsMillis(timeBetweenEvictionRunsMillis);
            druidDataSource.setMinEvictableIdleTimeMillis(minEvictableIdleTimeMillis);
            druidDataSource.setMaxPoolPreparedStatementPerConnectionSize(maxPoolPreparedStatementPerConnectionSize);
            druidDataSource.setTestWhileIdle(testWhileIdle);
            druidDataSource.setTestOnBorrow(testOnBorrow);
            druidDataSource.setTestOnReturn(testOnReturn);
            druidDataSource.setPoolPreparedStatements(poolPreparedStatements);
            druidDataSource.setValidationQuery(validationQuery);
            //druidDataSource.setFilters(filters);

            // 支持表情
            StringTokenizer tokenizer = new StringTokenizer(connectionInitSqls, ";");
            druidDataSource.setConnectionInitSqls(Collections.list(tokenizer)); //重点设置该参数

            return druidDataSource;
        }

        ...

    ```