JDBC异常：Before start of result set

Exception in thread "main" java.sql.SQLException: Before start of result set

    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1055)

    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:956)

    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:926)

    at com.mysql.jdbc.ResultSetImpl.checkRowPos(ResultSetImpl.java:835)

    at com.mysql.jdbc.ResultSetImpl.getStringInternal(ResultSetImpl.java:5571)

    at com.mysql.jdbc.ResultSetImpl.getString(ResultSetImpl.java:5491)

    at com.mysql.jdbc.ResultSetImpl.getString(ResultSetImpl.java:5531)