sql在java使用中的拼接

String sql="select uid,name from user";

Vector gifts = new Vector();
PreparedStatement stmt = null;

ResultSet rst = null;
StringBuffer sql = new StringBuffer(SQL_GET_JIFEN);

GiftForm form = null;
Vector args = new Vector();
try {
???if(!Utilities.changeNull(giftForm.getUserName()).equals("")){
???? sql.append(" AND t3.username like ? ");
????args.add("%"+String.valueOf(giftForm.getUserName())+"%");
???}
???if (!Utilities.changeNull(giftForm.getStartDay()).equals("")
?????&& !Utilities.changeNull(giftForm.getEndDay()).equals("")) {
????sql.append(" AND t2.submitdate >= ? ");
????sql.append(" AND t2.submitdate <= ? ");
????args.add(giftForm.getStartDay());
????args.add(giftForm.getEndDay());
???}

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