struts1 的类型转换器 代码求解释,该怎么解决

public class DateConvert implements Converter {    @Override    public Object convert(Class arg0, Object value) {        if(value==null){            return value;        }        if(value instanceof Date){            return value;        }        Date d=null;        if(value instanceof String){            SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");            try {                d=sdf.parse(value.toString());            } catch (ParseException e) {                // TODO Auto-generated catch block                e.printStackTrace();            }        }        return d;    }}