DruidDataSourceFactory创建for循环多个数据源，并连接到指定的数据源上

DruidDataSourceFactory是Druid提供的数据源工厂类，可以用于创建并配置Druid数据源。要创建多个数据源，可以使用for循环来重复创建并配置多个Druid数据源，代码示例如下：

import com.alibaba.druid.pool.DruidDataSource;
import com.alibaba.druid.pool.DruidDataSourceFactory;

import java.util.HashMap;
import java.util.Map;
import javax.sql.DataSource;

public class MultiDataSourceUtil {

    private static final String DB_DRIVER_CLASS_NAME = "com.mysql.jdbc.Driver";
    private static final String DB_URL_TEMPLATE = "jdbc:mysql://%s:%s/%s?useUnicode=true&characterEncoding=UTF-8&allowMultiQueries=true&autoReconnect=true&useSSL=false";
    private static final String DB_USER_NAME = "root";
    private static final String DB_PASSWORD = "123456";

    public static Map<String, DataSource> createDataSources() {
        Map<String, DataSource> dataSourceMap = new HashMap<>();

        for (int i = 0; i < 3; i++) {
            String dbName = "db_" + i;
            String url = String.format(DB_URL_TEMPLATE, "localhost", "3306", dbName);
            DruidDataSource dataSource = createDataSource(url);
            dataSourceMap.put(dbName, dataSource);
        }

        return dataSourceMap;
    }

    private static DruidDataSource createDataSource(String url) {
        try {
            DruidDataSource dataSource = (DruidDataSource) DruidDataSourceFactory.createDataSource(getDataSourceProperties(url));
            dataSource.setValidationQuery("SELECT 1");
            dataSource.setTestWhileIdle(true);
            dataSource.setTestOnBorrow(false);
            dataSource.setTestOnReturn(false);
            dataSource.setPoolPreparedStatements(true);
            dataSource.setMaxPoolPreparedStatementPerConnectionSize(20);
            return dataSource;
        } catch (Exception e) {
            throw new RuntimeException("Create data source error", e);
        }
    }

    private static Properties getDataSourceProperties(String url) {
        Properties properties = new Properties();
        properties.setProperty(DruidDataSourceFactory.PROP_DRIVERCLASSNAME, DB_DRIVER_CLASS_NAME);
        properties.setProperty(DruidDataSourceFactory.PROP_URL, url);
        properties.setProperty(DruidDataSourceFactory.PROP_USERNAME, DB_USER_NAME);
        properties.setProperty(DruidDataSourceFactory.PROP_PASSWORD, DB_PASSWORD);
        return properties;
    }
}

在上面的代码中，我们使用for循环创建了3个MySQL数据源，分别对应数据库db_0、db_1、db_2。在createDataSource方法中，我们对Druid数据源进行了一些常用的配置，例如设置连接池大小、开启SQL预编译等。最后，我们将所有的数据源保存到一个Map中，并以数据库名作为key。这样我们就可以根据需要从Map中获取对应的数据源，连接到指定的数据源上进行查询或更新操作。