在使用ajax的时候，server端处理完相关的逻辑之后，根据操作完的结果，需要给前端展现不同的提示，这种提示可以在前端展示也可以在后端操作，这里我就说说在后端如何给前端发送数据的
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1、前端发送相应的ajax请求
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
<script type="text/javascript" src="../js/jquery-1.4.4.js"></script>
</head>
<script type="text/javascript">
function test(){
var date = new Date();
timestamp = date.getTime();
//alert(timestamp.getTime());
//参数后面加上时间戳是以为ajax机制利用了缓存，如果参数一致就不会再次发送请求了
//前面的../表示路径要在上一个目录，才能发送请求
$.get("../AjaxWrite", { name: "John", time: "2pm",timestamp:timestamp},
//function方法是接受server端传递过来的方法
function(data){
alert(data);
});
}
</script>
<body>
<button onclick="test()">test</button>
<form action="../AjaxWrite">
<input type="submit" value="submit"/>
</form>
</body>
</html>
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2、server端向前端写数据
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package hb.com.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class AjaxWrite extends HttpServlet {
private static final long serialVersionUID = 1L;
public AjaxWrite() {
super();
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doPost(request, response);
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
System.out.println("1");
System.out.println(request.getParameter("name"));
System.out.println(request.getParameter("time"));
PrintWriter pw = response.getWriter();
pw.write("huangbiao");
//server端向前端发送的数据一定 要flush()方法才能被前端接受
pw.flush();
}
}
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3、前端就会显示server端写的数据"huangbiao"弹出
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利用JSP页面或者是HTML页面下载文件的原理
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
<script type="text/javascript" src="../js/jquery-1.4.4.js"></script>
</head>
<script type="text/javascript">
function test(){
var date = new Date();
var timestamp = date.getTime();
alert(timestamp);
$.get("../FileDownload",{"timestamp":timestamp},function(data){
alert(data);
});
}
</script>
<body>
<button onclick="test()">test</button>
<form action="../FileDownload">
<input type="submit" value="submit"/>
</form>
</body>
</html>
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前端触发请求，server端向前端写数据
package hb.com.servlet;
import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class FileDownload extends HttpServlet {
private static final long serialVersionUID = 1L;
public FileDownload() {
super();
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doPost(request, response);
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//写明要下载的文件的大小
int fileLength = 0;
File file = new File("c:\\aaa.xml");
FileInputStream fis = new FileInputStream(file);
fileLength = fis.available();
BufferedInputStream buff = new BufferedInputStream(fis);
response.setContentLength(fileLength);
response.setContentType("application/x-msdownload");
response.setHeader("Content-disposition", "attachment;filename=" + "黄彪.xml");
byte[] b = new byte[1024]; // 相当于我们的缓存
long k = 0; // 该值用于计算当前实际下载了多少字节
// 从response对象中得到输出流,准备下载
OutputStream myout = response.getOutputStream();
// 开始循环下载
while (k < fileLength) {
int j = buff.read(b, 0, 1024);
k += j;
// 将b中的数据写到客户端的内存
myout.write(b, 0, j);
}
// 将写入到客户端的内存的数据,刷新到磁盘
myout.flush();
}
}
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总结：实际上下载问价也是属于server端向前端写数据，只是以文件的方式展现出来，并保存到磁盘上了