//未封裝前的servlet類
	protected?void?doGet(HttpServletRequest?req,?HttpServletResponse?resp)
			throws?ServletException,?IOException?{
		try?{
			req.setCharacterEncoding("utf-8");
			String?command?=?req.getParameter("command");
			String?description?=?req.getParameter("description");
			Class.forName("com.mysql.jdbc.Driver");
			Connection?connection?=?DriverManager.getConnection("jdbc:mysql://localhost:3306/micro_message?characterEncoding=utf-8",?"root",
			"root");
			StringBuilder?sql?=?new?StringBuilder("select?ID,COMMAND,DESCRIPTION,CONTENT?from?MESSAGE?where?1=1");
			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);
			}
			PreparedStatement?statement?=?connection.prepareStatement(sql.toString());
			for?(int?i?=?0;?i?<?paramList.size();?i++)?{
			statement.setString(i?+?1,?paramList.get(i));
			}
			ResultSet?resultSet?=?statement.executeQuery();
			List<Message>?messageList?=new?ArrayList<Message>();
			while?(resultSet.next())?{
			Message?message?=?new?Message();
			messageList.add(message);
			message.setId(resultSet.getInt("ID"));
			message.setCommand(resultSet.getString("COMMAND"));
			message.setDescription(resultSet.getString("DESCRIPTION"));
			message.setContent(resultSet.getString("CONTENT"));
			}
			req.setAttribute("messageList",?messageList);
			}?catch?(SQLException?e)?{
			e.printStackTrace();
			}?catch?(ClassNotFoundException?e)?{
				e.printStackTrace();
			}
		
		req.getRequestDispatcher("/WEB-INF/jsp/back/list.jsp").forward(req,?resp);
		
	}
這樣查詢有結(jié)果出現(xiàn)

//封裝后的servlt類
	protected?void?doGet(HttpServletRequest?req,?HttpServletResponse?resp)
			throws?ServletException,?IOException?{
		try?{
			req.setCharacterEncoding("utf-8");
			String?command?=?req.getParameter("command");
			String?description?=?req.getParameter("description");
//			Class.forName("com.mysql.jdbc.Driver");
//			Connection?connection?=?DriverManager.getConnection("jdbc:mysql://localhost:3306/micro_message?characterEncoding=utf-8",?"root",
//			"root");
			Connection?connection=DBUtil.getConnection();
			StringBuilder?sql?=?new?StringBuilder("select?ID,COMMAND,DESCRIPTION,CONTENT?from?MESSAGE?where?1=1");
			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);
			}
			PreparedStatement?statement?=?connection.prepareStatement(sql.toString());
			for?(int?i?=?0;?i?<?paramList.size();?i++)?{
			statement.setString(i?+?1,?paramList.get(i));
			}
			ResultSet?resultSet?=?statement.executeQuery();
			List<Message>?messageList?=new?ArrayList<Message>();
			while?(resultSet.next())?{
			Message?message?=?new?Message();
			messageList.add(message);
			message.setId(resultSet.getInt("ID"));
			message.setCommand(resultSet.getString("COMMAND"));
			message.setDescription(resultSet.getString("DESCRIPTION"));
			message.setContent(resultSet.getString("CONTENT"));
			}
			req.setAttribute("messageList",?messageList);
			}?catch?(SQLException?e)?{
			e.printStackTrace();
			}
		
		req.getRequestDispatcher("/WEB-INF/jsp/back/list.jsp").forward(req,?resp);
		
	}

//DBUtil類
public?class?DBUtil?{

	private?static?final?String?URL="jdbc:mysql://127.0.0.1:3306/micro_message?useUnicode=true&charcterEncoding=utf-8";
	private?static?final?String?USER="root";
	private?static?final?String?PASSWORD="root";
	private?static?Connection?conn=null;
	
	static{
		try?{
			Class.forName("com.mysql.jdbc.Driver");
			conn=DriverManager.getConnection(URL,?USER,?PASSWORD);
		}?catch?(Exception?e)?{
			e.printStackTrace();
		}
		
	}
	public?static?Connection?getConnection(){
		return?conn;
	}
	
	public?static?void?main(String[]?args)?{
		if(conn!=null){
			System.out.println("success");
		}
	}
}
這樣查詢沒有結(jié)果