原来是utf8的字符集，如何批量更改mysql表中字段的字符集为utf8mb4？,数据库报错

"alter table test_str modify column str_desc varchar(500) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;######

JadePool轻松修改MySQL数据库的字符集

import cn.jadepool.sql.Field;
import cn.jadepool.sql.Jade;
import cn.jadepool.sql.Table;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * 修改MySQL数据库字符集
 *
 * @author 上海皆普信息科技有限公司 胡开明
 */
public class ChangeCharset {

    //ALTER SCHEMA `jadepool_dictionary` DEFAULT COLLATE utf8mb4_unicode_ci ;
    //ALTER TABLE `jadepool_dictionary`.`dic_emoji` COLLATE = utf8mb4_unicode_ci ;
    //ALTER TABLE `jadepool_dictionary`.`dic_emoji` CHANGE COLUMN `code` `code` VARCHAR(32) CHARACTER SET 'utf8mb4'  ;
    //ALTER TABLE `fwfw_jiben`.`fwfw_dw` CHARACTER SET = utf8mb4 , COLLATE = DEFAULT ,CHANGE COLUMN `jianjie` `jianjie` TEXT CHARACTER SET 'utf8mb4'  ;

    
    public static void main(String[] args) {
        Jade j = new Jade(getMySQLCon());
        String schema = j.getDb().getCatalog();//数据库的名称
        j.execute("ALTER SCHEMA `" + schema + "` DEFAULT COLLATE utf8mb4_unicode_ci");
        String[] tables = j.getDb().getTableNames();
        for (String tableName : tables) {
            j.execute("ALTER TABLE " + tableName + " COLLATE = utf8mb4_unicode_ci ");
            Table table = j.getDb().getTable(tableName);
            String[] fields = table.getFields();
            for (String fieldName : fields) {
                Field field = j.getDb().getField(tableName, fieldName);
                String typeName = field.getTypeName();
                String size = field.getSize();
                if ("text".equals(typeName)) {
                    j.execute("ALTER TABLE " + tableName + " CHARACTER SET = utf8mb4 , COLLATE = DEFAULT ,CHANGE COLUMN `"+fieldName+"` `"+fieldName+"` TEXT

CHARACTER SET 'utf8mb4' ");
                }
                if ("varchar".equals(typeName)) {
                    j.execute("ALTER TABLE " + tableName + "  CHANGE COLUMN `"+fieldName+"` `"+fieldName+"` VARCHAR("+size+") CHARACTER SET 'utf8mb4'  ");
                }
            }
        }
        j.commit();
    }

    public static synchronized Connection getMySQLCon() {
        Connection con = null;
        String url = "jdbc:mysql://localhost:3306/db_name_xxxxxx?

useOldAliasMetadataBehavior=true&zeroDateTimeBehavior=convertToNull";//useUnicode=true&characterEncoding=utf8mb4&
        String userName = "xxxxxx";
        String password = "xxxxxx";
        try {
            Class.forName("com.mysql.jdbc.Driver");//com.mysql.jdbc.Driver
            con = DriverManager.getConnection(url, userName, password);
        } catch (ClassNotFoundException ex) {
            Logger.getLogger(ChangeCharset.class.getName()).log(Level.SEVERE, null, ex);
        } catch (SQLException ex) {
            Logger.getLogger(ChangeCharset.class.getName()).log(Level.SEVERE, null, ex);
        }
        return con;
    }

}