工程目录结构：
代码：serlvet代码：
@WebServlet("/ajaxServlet")
public class ajaxServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
//得到目标文件路径
String url=request.getServletContext().getRealPath("demo.txt");
File file= new File(url);
//创建输入流
FileInputStream in =new FileInputStream(file);
ServletOutputStream out =response.getOutputStream();
int len=0;
byte[] bs= new byte[1024];
while((len=in.read(bs))>0) {
out.write(bs, 0, len);
}
}
jsp页面：
<html>
<head>
<meta charset="UTF-8">
<title>异步请求</title>
<script type="text/javascript" src="jquery-3.3.1.js"></script>
<script type="text/javascript">
function loadXMLDoc(){
alert("方法运行")
var xmlhttp;
//实例化XMLHTTPRequest对象
if(window.XMLHttpRequest){
//针对ie7+、firefox、chrome等浏览器
xmlhttp=new XMLHttpRequest();
}
else{
//针对ie5、6
xmlhttp=new ActiveXObject("Microsoft.XMLHTTP")
}
xmlhttp.onreadystatechange=function(){
//readystate状态为4（服务器请求完成）并且http的状态码为200(成功)时
if(xmlhttp.readyState==4 && xmlhttp.status==200){
alert(xmlhttp.responseText)
document.getElementById("text").value=xmlhttp.responseText;
}
}
xmlhttp.open("GET",
"${pageContext.request.contextPath}/ajaxServlet?name="
+ window.encodeURIComponent("嘻嘻", "utf-8")
+ "&time=" + new Date().getTime());
xmlhttp.send();
}
</script>
</head>
<body>
点击进行异步请求：<input type="button" value="异步请求" name="btn" id="btn" onclick="loadXMLDoc()"/>
<input type="text" id="text"/>
</body>
</html>
结果图：