ajax java 實作自動完成功能

都知道百度建議是用ajax做的，想要做的快速穩定，可複製可移植就不容易了。網路上找了半天，好多都是asp或php的，還有用jquery的，但說明性文件太少，花時間研究不如自己來寫。根據一個pdf文件提供的資料，花了小半天時間，終於實現了。在此與大家分享。 
原理流程圖如下： 

流程圖很明白了，沒什麼要說的，以下貼文程式碼。 
Javascript程式碼： 

var xmlHttpRequest; 
var table; 
var tbody; 
var div; 
var input; 
var curIndex; 
var size; 
var r_userId; 
function createXMLHttpRequest(){ 
if(window.ActiveXObject){ 
xmlHttpRequest = new ActiveXObject("Microsoft.XMLHTTP"); 
}else if(window.XMLHttpRequest){ 
xmlHttpRequest = new XMLHttpRequest(); 
} 
} 
//发送请求 
function findNames(){ 
if(event.keyCode==38||event.keyCode==40){ 
}else{ 
if(input.value.length>0){ 
createXMLHttpRequest(); 
var url = encodeURI(encodeURI("/jforum.html?module=posts&action=findDept&names="+input.value)); 
xmlHttpRequest.open("GET",url,true); 
xmlHttpRequest.onreadystatechange=processMatchResponse; 
xmlHttpRequest.send(null); 
}else{ 
clearNames(); 
} 
} 

} 
function processMatchResponse(){ 
if(xmlHttpRequest.readyState==4){ 
if(xmlHttpRequest.status==200){ 
//alert(xmlHttpRequest.status); 
//var id = xmlHttpRequest.responseXML.getElementsByTagName("id"); 
var dept = xmlHttpRequest.responseXML.getElementsByTagName("dept"); 
var id = xmlHttpRequest.responseXML.getElementsByTagName("id"); 

setNames(dept,id); 

}else{ 
window.alert("您所请求的页面有异常！"); 
} 
} 
} 
function setNames(depts,ids){ 
clearNames(); 
size = depts.length; 
if(size>0){ 
div.style.visibility = "visible"; 
var row,col1,col2,span; 

for(var i = 0;i < size;i++){ 
row = document.createElement("tr"); 
col1 = document.createElement("td"); 
col1.innerText = depts[i].firstChild.data; 
col2 = document.createElement("td"); 
col2.setAttribute("align","right"); 
col2.setAttribute("id","col2"); 
col2.setAttribute("width","5%"); 
span = document.createElement("span"); 
span.innerText = ids[i].firstChild.data; 
span.style.display = "none"; 
col2.appendChild(span); 


row.appendChild(col1); 
row.appendChild(col2); 
row.onmouseout = function(){ 
this.className = &#39;mouseOut&#39;; 
} 
row.onmouseover = function(){ 
clearSelected(); 
this.className = &#39;mouseOver&#39;; 
curIndex = this.rowIndex; 
} 
row.onclick = function(){ 
input.value = this.cells[0].innerText; 
r_userId.value = table.rows[curIndex].cells[1].innerText; 
clearNames(); 
}; 
tbody.appendChild(row); 
} 
row = document.createElement("tr"); 
col2 = document.createElement("td"); 
col1 = document.createElement("td"); 
col2.setAttribute("align","right"); 
link = document.createElement("a"); 
link.href = "javascript:clearNames();"; 
link.innerHTML = "关闭"; 
col1.appendChild(link); 
row.appendChild(col1); 
row.appendChild(col2); 
tbody.appendChild(row); 
} 
} 
function setPosition(){ 
input = document.getElementById("names"); 
r_userId = document.getElementById("r_userId"); 
table = document.getElementById("table"); 
div = document.getElementById("div"); 
tbody = document.getElementById("tbody"); 

div.style.width = input.offsetWidth-2; 
div.style.border = "gray 1px solid"; 
div.style.left = getLeft(input); 
div.style.top = getTop(input)+input.offsetHeight+6; 

curIndex = -1; 
input.focus();//div.style.left+","+div.style.top 
} 
function clearNames(){ 
var ind = tbody.childNodes.length; 
for(i=ind-1;i>=0;i--){ 
tbody.removeChild(tbody.childNodes[i]); 
} 
div.style.visibility="hidden"; 
curIndex = -1; 
} 
function clearSelected(){ 
var ind = tbody.childNodes.length; 
for(var i = ind-1;i>=0;i--){ 
tbody.childNodes[i].className = "mouseOut"; 
} 
} 
function keyDown(){ 
if(div.style.visibility=="visible"){ 
if(event.keyCode ==38){ 
if(curIndex>=0){ 
table.rows[curIndex].className=&#39;mouseOut&#39;; 
curIndex = curIndex-1; 
if(curIndex>=0){ 
table.rows[curIndex].className = &#39;mouseOver&#39;; 
input.value = table.rows[curIndex].cells[0].innerText; 
r_userId.value = table.rows[curIndex].cells[1].innerText; 
} 
} 
} 
if(event.keyCode==40){ 
if(curIndex<size-1){ 
if(curIndex>=0){ 
table.rows[curIndex].className = &#39;mouseOut&#39;; 
} 
curIndex = curIndex+1; 
table.rows[curIndex].className = &#39;mouseOver&#39;; 
input.value = table.rows[curIndex].cells[0].innerText; 
r_userId.value = table.rows[curIndex].cells[1].innerText; 
}else{ 
table.rows[curIndex].className = &#39;mouseOut&#39;; 
curIndex = -1; 
} 
} 
} 
} 
//获取元素的纵坐标 
function getTop(e){ 
var offset=e.offsetTop; 
if(e.offsetParent!=null) offset+=getTop(e.offsetParent); 
return offset; 
} 
//获取元素的横坐标 
function getLeft(e){ 
var offset=e.offsetLeft; 
if(e.offsetParent!=null) offset+=getLeft(e.offsetParent); 
return offset; 
}

程式碼太多，有點亂，沒使用jquery，但更能顯示作者的功底。以下分點闡述： 
1，setPosition()是用來初始化全域所需的各個變量，所以在頁面載入的時候就要先呼叫嘍，例如在body的onload方法，或是其他方式都可以。 
2，findNames()是操作ajax的方法，熟悉ajax的人都可以看明白，裡面最主要的是要對參數進行二次編碼encodeURI()，對應的在後台要進行解碼。 
3，processMatchResponse()是回呼函數，用來處理從後台傳回的數據，這裡交給了setNames()來處理。 
4，setNames中以table方式顯示提示的內容。這裡更多的是JS和node方面的知識。 
5，getTop和getLeft方法是取得文字方塊的絕對位置，相對於瀏覽器左上角的。 
後台java程式碼如下： 

public void findDept() throws IOException{ 
String partDeptName = this.request.getParameter("names"); 
partDeptName = java.net.URLDecoder.decode(partDeptName, "UTF-8"); 
Map<String,String> userMap = DataAccessDriver.getInstance().newUserDAO().getDeptByPart("%" + partDeptName + "%"); 

this.response.setContentType("text/xml;charset=UTF-8"); 
this.response.setHeader("Cache-Control", "no-cache"); 


ServletOutputStream pw = this.response.getOutputStream(); 
OutputStreamWriter out = new OutputStreamWriter(pw,"UTF-8"); 

out.write("<res>"); 
Iterator<Map.Entry<String, String>> it = userMap.entrySet().iterator(); 
while(it.hasNext()){ 
Map.Entry<String, String> entry=(Map.Entry<String,String>)it.next(); 
out.write("<id>"+entry.getKey()+"</id>"); 
out.write("<dept>"+entry.getValue()+"</dept>"); 
} 
out.write("</res>"); 

out.flush(); 
out.close(); 

}

重點： 
1，注意對參數進行解碼。 
2，查詢時視情況進行模糊配對。 
3，回傳資料這裡採用了xml方式，也可以採用json方式。
4，返回的方式這裡採用了 

ServletOutputStream pw = this.response.getOutputStream(); 
OutputStreamWriter out = new OutputStreamWriter(pw,"UTF-8");

這樣的流是受本系統框架的限制，如果使用單純的servlet，可以採用PrintWriter out = response.getWriter();當然out的方法是println()，也可以根據自己框架的情況靈活改變。

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