smartupload组件下载.gif和.swf格式文件时出错，救命啊
exception  

org.apache.jasper.JasperException:   getOutputStream()   has   already   been   called   for   this   response
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:512)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:389)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:314)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:264)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)


root   cause  

java.lang.IllegalStateException:   getOutputStream()   has   already   been   called   for   this   response
org.apache.catalina.connector.Response.getWriter(Response.java:599)
org.apache.catalina.connector.ResponseFacade.getWriter(ResponseFacade.java:195)
org.apache.jasper.runtime.JspWriterImpl.initOut(JspWriterImpl.java:124)
org.apache.jasper.runtime.JspWriterImpl.flushBuffer(JspWriterImpl.java:117)
org.apache.jasper.runtime.PageContextImpl.release(PageContextImpl.java:182)
org.apache.jasper.runtime.JspFactoryImpl.internalReleasePageContext(JspFactoryImpl.java:115)
org.apache.jasper.runtime.JspFactoryImpl.releasePageContext(JspFactoryImpl.java:75)
org.apache.jsp.GRBG.WJZG.download_jsp._jspService(download_jsp.java:176)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:97)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:334)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:314)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:264)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)

其他的文件格式上传下载，没有任何问题。

------解决方案--------------------
getOutputStream() 这个问题是你在操作的过程中有输入也有输出造成的，使用上传下载功能的页面最好是纯JSP代码，不要出现HTML，连空格和回车都不行，%> 与 <%之间也不要有换行和空格，当然 <%与%> 的中间倒是无所谓。
你说只下载gif和.swf时出现问题，那是不是你一下载成功就显示出来了，如果是这样你要把显示的功能放到另一页面，在下载成功后转到这个页面试试
------解决方案--------------------
java.lang.IllegalStateException: getOutputStream() has already been called for this response

楼上说的，也是有可能的。
还有就是，你在servlet里，不要有跳转的语句，不要有out.print等语句。