protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
try {
req.setCharacterEncoding("utf-8");
//获取jsp页面传递过来的查询关键字
String command=req.getParameter("command");
String description=req.getParameter("description");
req.setAttribute("command", command);
req.setAttribute("description",description);
Class.forName("com.mysql.jdbc.Driver");
Connection conn=DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/micro_message", "root", "root");
//1=1：适用于检索条件不固定情况
//用StringBuffer或者StringBuilder，不要用String。String不会回收
StringBuilder sql=new StringBuilder("SELECT ID,COMMAND,DESCRIPTION,CONTENT FROM message where 1=1");
//定义一个集合，暂时存放关键字
List<String> paramList=new ArrayList<String>();
if(command!=null&&!"".equals(command.trim())){
//精确查询
//添加字符要记得加上必要的空格
sql.append(" and COMMAND=?");
paramList.add(command);
}
if(description!=null&&!"".equals(description.trim())){
//模糊查询（只要包含此内容就可查询）
sql.append(" and DESCRIPTION like '%' ? '%'");
paramList.add(description);
}
PreparedStatement ps=conn.prepareStatement(sql.toString());
//循环语句，获取集合中的值，赋值给ps中的？（问号）
//可以分清两个查询中的哪个查询
for(int i=0;i<paramList.size();i++){
ps.setString(i+1, paramList.get(i));
}
ResultSet rs=ps.executeQuery();
List<Message> messageList=new ArrayList<Message>();
while(rs.next()){
Message message=new Message();
message.setId(rs.getString("ID"));
message.setCommand(rs.getString("COMMAND"));
message.setDescription(rs.getString("DESCRIPTION"));
message.setContent(rs.getString("CONTENT"));
messageList.add(message);
}
//将所有查询信息放入request中，并转到jsp页面
req.setAttribute("messageList", messageList);
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
}
req.getRequestDispatcher("/WEB-INF/jsp/back/list.jsp").forward(req, resp);
}