public class ImageServlet extends HttpServlet {
private final String repository = "/var/images/";
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String filename = request.getParameter("file");
// Security: '..' in the filename will let sneaky users access files
// not in your repository.
filename = filename.replace("..", "");
File file = new File(repository + filename);
if (!file.exists())
throw new FileNotFoundException(file.getAbsolutePath());
response.setHeader("Content-Type", "image/jpeg");
response.setHeader("Content-Length", String.valueOf(file.length()));
response.setHeader("Content-disposition", "attachment;filename=\"" + filename + "\"");
BufferedInputStream bis = new BufferedInputStream(new FileInputStream(file));
BufferedOutputStream bos = new BufferedOutputStream(response.getOutputStream());
byte[] buf = new byte[1024];
while (true) {
int length = bis.read(buf);
if (length == -1)
break;
bos.write(buf, 0, length);
}
bos.flush();
bos.close();
bis.close();
}
}
“contentdisposition:attachment”应该会导致大多数浏览器下载文件而不是显示它,文件名默认为您提供的任何文件。使用这个servlet的方法是让用户调用已经拥有的RPCService,它将文件保存到存储库文件夹中。然后,使用如下url将它们链接或重定向到此servlet
http://your.domain.com/fileServlet?file=myFile.jpg
您可能想做的是将RPC服务中的数据库代码合并到这个servlet中。无需将文件保存在服务器上的任何位置,您可以将数据库结果写入response.getOutputStream()或response.getWriter(),方法与写入文件的方法完全相同,只是结果会直接发送给用户。只要您正确设置了内容头,用户就不会注意到差异。
<servlet>
<servlet-name>ImageServlet</servlet-name>
<servlet-class>
com.package.ImageServlet
</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>ImageServlet</servlet-name>
<url-pattern>/imageServlet</url-pattern>
</servlet-mapping>
现在任何HTTP GET请求
http://your.tomcat.server/webapp/imageServlet
将由ImageServlet.doGet()获取。然后在客户端,您可以创建到文件的普通html链接:
new HTML("<a href='" + GWT.getHostPageBaseURL() + "imageServlet?file=" + filename + "'>download</a>");
……或者,你
能够将其放入ClickHandler(我还没有测试过):
Window.Location.assign(GWT.getHostPageBaseURL() + "imageServlet?file=" + filename);