已经排查了一小时了，实在是找不出毛病了，一查询就错，Parameter index out of range (1 > number of parameters, which is 0).我看也没少问号啊

public void doGet(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		try {
			req.setCharacterEncoding("UTF-8");
			String command = req.getParameter("command");
			String description = req.getParameter("description");
			req.setAttribute("command", command);
			req.setAttribute("description", description);
			System.out.println(command+description);
			Class.forName("com.mysql.jdbc.Driver");
			Connection ct = DriverManager.getConnection("jdbc:mysql:///wechat?useUnicode=true&characterEncoding=UTF-8",
					"root", "qxqx");
			StringBuilder sql = new StringBuilder(
					"select ID,COMMAND,DESCRIPTION,CONTENT from message where 1=1 ");
			PreparedStatement ps = ct.prepareStatement(sql.toString());
			List<String> paramList = new ArrayList<String>();
			if (command != null && !"".equals(command.trim())) {
				sql.append(" and COMMAND='?' ");
				paramList.add(command);
			}
			if (description != null && !"".equals(description.trim())) {
				sql.append(" and DESCRIPTION like '%' ? '%' ");
				paramList.add(description);
			}
			for (int i = 0; i < paramList.size(); i++) {

				ps.setString(i + 1, paramList.get(i));
			}
			System.out.println(ps.toString());
			ResultSet rs = ps.executeQuery();
			List<Message> messageList = new ArrayList<Message>();

			while (rs.next()) {
				Message message = new Message();
				// 容器里加入的都是引用，不是对象本身，所以后续的set方法依然有用
				messageList.add(message);
				message.setId(rs.getString("ID"));
				message.setCommand(rs.getString("COMMAND"));
				message.setDescription(rs.getString("DESCRIPTION"));
				message.setContent(rs.getString("CONTENT"));
			}
			req.setAttribute("messageList", messageList);
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}

		req.getRequestDispatcher("/WEB-INF/jsp/back/list.jsp").forward(req,
				resp);
	}

还有一个小问题，为什么doPost（）方法用super.doGet（req,resp）会出现405错误，用doPost（req,resp）就可以了

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第一个问题解决了，把PreparedStatement ps = ct.prepareStatement(sql.toString());放到for循环前一行