response.sendError出现IllegalStateException

struts2 Dispatcher.sendError

会把异常放到两个属性里

                // WW-1977: Only put errors in the request when code is a 500 error
                if (code == HttpServletResponse.SC_INTERNAL_SERVER_ERROR) {
                    // send a http error response to use the servlet defined error handler
                    // make the exception availible to the web.xml defined error page
                    request.setAttribute("javax.servlet.error.exception", e);

                    // for compatibility
                    request.setAttribute("javax.servlet.jsp.jspException", e);
                }

在设置完属性之后调用

                // send the error response
                response.sendError(code, e.getMessage());

这时，sendError出现IllegalStateException错误

             request.setAttribute("javax.servlet.error.exception", e);

    将会被覆盖变成了IllegalStateException，丢失了原有的异常信息

导致在500页面始终输出的是错误的异常信息

    可以通过获得javax.servlet.jsp.jspException的异常，这个为了兼容老的servlet规范放入的

通常web容器不会覆盖，可以找回丢失的异常