protected void doGet(HttpServletRequest req, HttpServletResponse resp)

throws ServletException, IOException {

? ? ? ?try {

? ? ?//設置字符編碼

? ? ?req.setCharacterEncoding("UTF-8");

? ? ?//接收頁面的值

? ? ? ? String command =req.getParameter("command");

? ? ? ? String description =req.getParameter("description");?

? ? ? ? //向頁面傳值

? ? ? ? req.setAttribute("command", command);

? ? ? ? req.setAttribute("description", description);

? ? //加載驅動。連接數據庫?

Class.forName("com.mysql.jdbc.Driver");

Connection conn = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/message","root","123123");

//操作數據庫并聲明,用where1=1進行拼裝sql語言

StringBuilder sql =new StringBuilder( "select ID ,COMMAND,DESCRIPTION,CONTENT from MESSAGE where 1=1");

//定義一個集合來暫緩拼接，先拼接好才用到聲明里

List <String> paramList=new ArrayList<String>();

//判斷一個接收的值是不是為空，不為空才拼接

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);

}

//進行聲明

PreparedStatement statement= conn.prepareStatement(sql.toString());

//將拼接好后的sql語言放到集合中

for(int i = 0; i < paramList.size(); i++) {

statement.setString(i + 1, paramList.get(i));

}

//查詢數據庫

ResultSet rs = statement.executeQuery();

//查詢結果放在一個集合中

List<Message> messageList = new ArrayList<Message>();

while(rs.next()) {

System.out.println(messageList);

? Message message = new Message();

messageList.add(message);

message.setId(rs.getInt("ID"));;

message.setCommand(rs.getString("COMMAND"));

message.setDescription(rs.getString("DESCRIPTION"));

message.setContent(rs.getString("CONTENT"));

}

//向頁面傳值

req.setAttribute("messageList",messageList);