java - 最佳实践 response.getOutputStream

Question

关于允许用户下载文件的代码的任何评论。

if(fileObject !=null)
response.setHeader("Content-disposition", "attachment; filename=\""+fileObject.getFilename()+"\"");
response.setContentType(fileObject.getFiletype());
response.setContentLength((int)fileObject.getFilesize().intValue());
try {
 if(response !=null && response.getOutputStream() !=null &&fileObject!=null && fileObject.getBinData() !=null ){
    OutputStream out = response.getOutputStream();
    out.write(fileObject.getBinData());
 }


} catch (IOException e) {
    throw new ApplicationRuntimeException(e);
}

大多数时候，我不会低于错误。但是偶尔，我会出错

29 Nov 2010 10:50:41,925 WARN [http-2020-2] - Unable to present exception page: getOutputStream() has already been called for this response
java.lang.IllegalStateException: getOutputStream() has already been called for this response
 at org.apache.catalina.connector.Response.getWriter(Response.java:610)

Answer 1

异常信息很明确:

Unable to present exception page: getOutputStream() has already been called for this response
java.lang.IllegalStateException: getOutputStream() has already been called for this response
at org.apache.catalina.connector.Response.getWriter(Response.java:610)

IOException 被抛出，您将其作为自定义异常重新抛出，这迫使 servletcontainer 显示将为此使用 getWriter() 的异常页面。事实上，您应该让任何 IOException 消失，因为那通常是不归路。

IOException 例如可以在客户端中止请求时在作业期间抛出。最佳做法是自己不在 Servlet API 上捕获 IOException。它已经在 servlet 方法的 throws 子句中声明。

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    FileObject fileObject = getItSomehow();
    if (fileObject != null && fileObject.getBinData() != null) {
        response.setHeader("Content-disposition", "attachment; filename=\"" + fileObject.getFilename() + "\"");
        response.setContentType(fileObject.getFiletype());
        response.setContentLength((int)fileObject.getFilesize().intValue());
        response.getOutputStream().write(fileObject.getBinData());
    } else {
        // ???
    }
}