无意间发现Resin的后台报错，奇怪的是sendRedirect的条件根本不成立，也就是不会执行到这行，resin都会报错，而前台JSP却不报错。

原因：在jsp和servlet中，调用sendRedirect()之后，如果没有return，resin中经常抛这个错！此语句前不允许有out.flush()，如果有，也会报错！

如果前面有out.println 或者 out.write 之类的，sendRedirect前也要response.getWriter().close();和out.close();！也就是说要先关闭response的输出，再进行转发！

解决方法：
response.sendRedirect("./index.jsp");
return;//在sendRedirect后面直接return

[11:52:58.796]  java.lang.IllegalStateException: Can't sendRedirect() after data has committed to the client.
[11:52:58.796]   at com.caucho.server.connection.AbstractHttpResponse.sendRedirect(AbstractHttpResponse.java:604)
[11:52:58.796]   at javax.servlet.http.HttpServletResponseWrapper.sendRedirect(HttpServletResponseWrapper.java:109)
[11:52:58.796]   at com.caucho.server.connection.ResponseWrapper.sendRedirect(ResponseWrapper.java:277)
[11:52:58.796]   at com.caucho.server.connection.ResponseAdapter.sendRedirect(ResponseAdapter.java:159)
[11:52:58.796]   at _jsp._simple._post__jsp._jspService(_post__jsp.java:70)
[11:52:58.796]   at com.caucho.jsp.JavaPage.service(JavaPage.java:61)
[11:52:58.796]   at com.caucho.jsp.Page.pageservice(Page.java:587)
[11:52:58.796]   at com.caucho.server.dispatch.PageFilterChain.doFilter(PageFilterChain.java:195)
[11:52:58.796]   at org.tuckey.web.filters.urlrewrite.UrlRewriteFilter.doFilter(UrlRewriteFilter.java:738)
[11:52:58.796]   at com.caucho.server.dispatch.FilterFilterChain.doFilter(FilterFilterChain.java:87)
[11:52:58.796]   at org.javawind.filters.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:29)
[11:52:58.796]   at com.caucho.server.dispatch.FilterFilterChain.doFilter(FilterFilterChain.java:87)
[11:52:58.796]   at com.caucho.server.webapp.WebAppFilterChain.doFilter(WebAppFilterChain.java:187)
[11:52:58.796]   at com.caucho.server.dispatch.ServletInvocation.service(ServletInvocation.java:265)
[11:52:58.796]   at com.caucho.server.hmux.HmuxRequest.handleRequest(HmuxRequest.java:436)
[11:52:58.796]   at com.caucho.server.port.TcpConnection.run(TcpConnection.java:682)
[11:52:58.796]   at com.caucho.util.ThreadPool$Item.runTasks(ThreadPool.java:743)
[11:52:58.796]   at com.caucho.util.ThreadPool$Item.run(ThreadPool.java:662)
[11:52:58.796]   at java.lang.Thread.run(Thread.java:619)