dbmd应该是DataBaseMetaData类吧
该类getColumns方法定义为
public ResultSet getColumns(String catalog,
String schemaPattern,
String tableNamePattern,
String columnNamePattern)
throws SQLException
第四个参数是 String columnNamePattern - a column name pattern; must match the column name as it is stored in the database
所以%就是某个具体数据库中的某个列名了