1. 前臺(tái)jsp，新建一個(gè)下拉控件

<select id="seldvd" onChange="sel_onchange(this)"></select> 

2. js部分，建一個(gè)function方法，利用ajax，指向 'getAllTypes.action' 的servlet部分，獲取傳來的下拉列表的數(shù)據(jù)，動(dòng)態(tài)填充

<span style="white-space:pre"> </span>function loadType(){ <span style="white-space:pre">   </span>$.get(  <span style="white-space:pre">  </span>    'getAllTypes.action', <span style="white-space:pre">   </span>  function(data){ <span style="white-space:pre">   </span>   var $sel = $("#seldvd"); <span style="white-space:pre">     </span> // console.log(data); <span style="white-space:pre">   </span>   for(var i = 0;i<data.length;i++){ <span style="white-space:pre">     </span> <span style="white-space:pre">  </span>$item = $("<option></option>"); //添加option <span style="white-space:pre">     </span> <span style="white-space:pre">  </span>$item.val(data[i].id); //添加option的value ，<span style="line-height: 1.5; white-space: pre-wrap; font-family: Arial, Helvetica, sans-serif;"><span style="font-size:10px;">數(shù)據(jù)庫中用id和type保存的數(shù)據(jù)</span></span> <span style="white-space:pre">     </span> <span style="white-space:pre">  </span>$item.html(data[i].type); //添加option數(shù)據(jù) <span style="white-space:pre">     </span> <span style="white-space:pre">  </span>$sel.append($item); //將option添加進(jìn)select  <span style="white-space:pre">  </span>     }  <span style="white-space:pre">  </span>    },'json'  <span style="white-space:pre">  </span>   ); <span style="white-space:pre"> </span>} 

3. 新建一個(gè)servlet頁面，用來向Ajax返回?cái)?shù)據(jù)

public void doGet(HttpServletRequest request, HttpServletResponse response)       throws ServletException, IOException {     request.setCharacterEncoding("utf-8");     ArrayList<typeInfo> typeList = new ArrayList<typeInfo>();     typeDao td = new typeDao();     typeList = td.getAllTypes();     JSONArray arr = new JSONArray(typeList);//這里導(dǎo)入需要轉(zhuǎn)json數(shù)據(jù)包     String jsString = arr.toString();     //響應(yīng)到客戶端         request.setCharacterEncoding("utf-8");     response.setContentType("text/plain;charset=utf-8");     response.getWriter().print(jsString); //返回下拉列表需要的json格式數(shù)據(jù)   } 

4. 那么問題來了，這個(gè)數(shù)據(jù)來源在哪啊？當(dāng)然在數(shù)據(jù)庫（MySQL）。所以先要寫一個(gè)方法讀取數(shù)據(jù)庫中的數(shù)據(jù)

<strong>typeInfo.java</strong> 

import java.io.Serializable; public class typeInfo implements Serializable {   private int id;   private String type;   public int getId() {     return id;   }   public void setId(int id) {     this.id = id;   }   public String getType() {     return type;   }   public void setType(String type) {     this.type = type;   }   public typeInfo(){   }   public typeInfo(int id, String type) {     this.id = id;     this.type = type;   } }