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JavaWeb学习记录（一）——response响应头之缓存设置与下载功能的实现

2015-06-30 11:12 851 查看

一、HTTP中常用响应头

Location: http://www.it315.org/index.jsp
Server:apache tomcat

Content-Encoding: gzip

Content-Length: 80

Content-Language: zh-cn

Content-Type: text/html; charset=GB2312

Last-Modified: Tue, 11 Jul 2000 18:23:51 GMT

Refresh: 1;url=http://www.it315.org

Content-Disposition: attachment; filename=aaa.zip

Transfer-Encoding: chunked

Set-Cookie:SS=Q0=5Lb_nQ; path=/search

ETag: W/"7777-1242234904000"

Expires: -1

Cache-Control: no-cache

Pragma: no-cache

Connection: close/Keep-Alive

Date: Tue, 11 Jul 2000 18:23:51 GMT

二、设置缓存信息

　　public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
System.out.println("-----------CacheServlet-------------");
// 设置相应头信息
// 设置缓存时间100秒
// response.setDateHeader("Expires",
// System.currentTimeMillis()+100*1000);
// 禁止使用缓存
// response.setDateHeader("Expires", 0);
// response.setHeader("Cache-Control", "no-cache");
// response.setHeader("Pragma", "no-cache");

response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
out.println("<HTML>");
out.println(" <HEAD><TITLE>A Servlet</TITLE></HEAD>");
out.println(" <BODY>");
// 读取文件
String path = getServletContext().getRealPath("/a.txt");
FileReader reader = new FileReader(new File(path));
char buffer[] = new char[256];
int len = 0;
while ((len = reader.read(buffer)) != -1) {
out.println(new String(buffer, 0, len));
}
reader.close();
out.println(" </BODY>");
out.println("</HTML>");
out.flush();
out.close();
}

/**
* 最后一次修改的时间
*/
@Override
protected long getLastModified(HttpServletRequest req) {
String path = getServletContext().getRealPath("/a.txt");
File file = new File(path);
return file.lastModified();
}

a.txt文件内容：

a.txt在项目中的放置地址：

结果：

三、下载功能源代码如下

public class DownServlet extends HttpServlet {

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String path = request.getServletContext().getRealPath("/down/中国.png");
File file = new File(path);
// 下载的方式打开此操作（指定编码方式，下载文件名与源文件一致）
response.addHeader("Content-Disposition", "attachment;fileName="
+ URLEncoder.encode(file.getName(), "UTF-8"));
OutputStream os = response.getOutputStream();
InputStream is = new FileInputStream(file);
int len = 0;
byte[] buffer = new byte[1024];
while ((len = is.read(buffer)) != -1) {
os.write(buffer, 0, len);
}
is.close();
os.close();
}

public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}

}

本程序中下载文件的地址放置在该项目的如下位置：

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