因此，经过一些额外的研究，我发现输入流甚至不是空的 is.available() 返回0
我的问题不一样。我将上传的图像保存在modeshape存储库中。存储库会话存储在wicket应用程序示例中。因此，只有一个modeshape存储库会话存在。在写入图像时，modeshape会话似乎有问题。因此，我将modeshape会话放在一个同步块中，现在一切正常。

public class MyServlet extends HttpServlet{
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        boolean proceed =true;

        Map<String,String[]> parameters = req.getParameterMap();
        if(parameters!=null){
            //read some parameters which specify the request
        }
        if(proceed) {
            String fileName = req.getHeader("fileName");
            if(!StringUtils.isEmpty(fileName)) {
                InputStream is = req.getInputStream();
                if(is!=null) {
                    //The result of this output is 0 for the first requests only for the last request it is 1
                    System.err.println("Stream size: "+is.available());
                    WicketApplication app=null;
                    try {
                        app = (WicketApplication)Application.get("wicket");
                    } catch (Exception e) {
                        LOG.error("Error while generating WicketApplication object for project "+project.getName(),e);
                    }
                    if(app!=null) {
                        final Session repoSession = app.getRepoSession();
                        synchronized (repoSession) {
                            //write image to repository
                        }
                    }
                }
            }
        }
        //do something....
    }
}