内容简介:某天,将线上的resin容器替换为tomcat.过了一段时间发现有个接口处理失败,提示异常.查看应用日志发现如下的日志:查询相关接口的代码发现,代码对关于302临时跳转的详细解释可以参考
某天,将线上的resin容器替换为tomcat.过了一段时间发现有个接口处理失败,提示异常.查看应用日志发现如下的日志:
Caused by: javax.servlet.ServletException: java.lang.IllegalStateException: Cannot create a session after the response has been committed at org.apache.jsp.WEB_002dINF.content.order.page.error_jsp._jspService(error_jsp.java:293) ~[na:na] at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70) ~[jasper.jar:8.5.12] at javax.servlet.http.HttpServlet.service(HttpServlet.java:742) ~[servlet-api.jar:na] at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:443) ~[jasper.jar:8.5.12] ... 38 common frames omitted
查询相关接口的代码发现,代码对 302
跳转的逻辑处理有问题,具体如下:
@Actions(value = { @Action(value = "dopay", results = {@Result(name = ERROR, location = "/WEB-INF/content/order/page/error.jsp")}), }) @ActionMonitor(value = "pay.doPay") public String doPay() { // 省略代码 String _result = dealWapClient(params); // 问题之所在, 当dealWapClient处理成功时,返回值就是null // 此时,返回ERROR, Struts2会继续执行,渲染错误页面(客户端就能看到错误页面了) // tomcat 能看到, resin下看不到,原因下面分析 if (_result == null) { return ERROR; } // 省略代码 } public String dealWapClient(Map<String, String> params) { // 省略代码 redirect(returnParams, returnUrl); return null; // 省略代码 } }
302跳转解释
关于302临时跳转的详细解释可以参考 HTTP_302 .
也可以参考RFC规范 http://www.ietf.org/rfc/rfc3986.txt
再次就不再赘述.
servletapi对302处理的规定
/** * Sends a temporary redirect response to the client using the * specified redirect location URL and clears the buffer. The buffer will * be replaced with the data set by this method. Calling this method sets the * status code to {@link #SC_FOUND} 302 (Found). * This method can accept relative URLs;the servlet container must convert * the relative URL to an absolute URL * before sending the response to the client. If the location is relative * without a leading '/' the container interprets it as relative to * the current request URI. If the location is relative with a leading * '/' the container interprets it as relative to the servlet container root. * If the location is relative with two leading '/' the container interprets * it as a network-path reference (see * <a href="http://www.ietf.org/rfc/rfc3986.txt"> * RFC 3986: Uniform Resource Identifier (URI): Generic Syntax</a>, section 4.2 * "Relative Reference"). * * <p>If the response has already been committed, this method throws * an IllegalStateException. * After using this method, the response should be considered * to be committed and should not be written to. * * @param location the redirect location URL * @exception IOException If an input or output exception occurs * @exception IllegalStateException If the response was committed or * if a partial URL is given and cannot be converted into a valid URL */ public void sendRedirect(String location) throws IOException;
翻译过来意思就是: 通过该方法告诉客户端临时重定向到一个指定的URL,并且清空缓存区,之前还没有发送到客户端的数据.
并使用该方法设置的数据填充缓存区.
该方法设置http响应的状态码为302.
如果重定向的地址为相对地址,该方法内部会将相对地址转为绝对地址.
如果response已经committed,再次调用该方法会抛出 IllegalStateException
异常.
调用该方法后,response对象的状态应该是 committed
,并且不应该再写入数据.
servlet-api已经详细说明了该方法的用法和需要注意的事项.但是不同的servlet容器在实现机制上可能不尽相同.
项目中发现的问题主要有两个原因:
- 代码有bug.这个是主要原因.
- servlet容器实现不同.
下面就分析下该方法在resin和tomcat中实现的细节:
resin对302的处理
在resin中, HttpServletResponse
接口的实现类是 HttpServletResponseImpl
.代码如下:
abstract public class AbstractCauchoResponse implements CauchoResponse { } public interface CauchoResponse extends HttpServletResponse { } public final class HttpServletResponseImpl extends AbstractCauchoResponse implements CauchoResponse { /** * Sends a redirect to the browser. If the URL is relative, it gets * combined with the current url. * * @param url the possibly relative url to send to the browser */ @Override public void sendRedirect(String url) throws IOException { if (url == null) throw new NullPointerException(); if (isCommitted()) throw new IllegalStateException(L.l("Can't sendRedirect() after data has committed to the client.")); _responseStream.clearBuffer(); // server/10c4 // reset(); resetBuffer(); setStatus(SC_MOVED_TEMPORARILY); String encoding = getCharacterEncoding(); boolean isLatin1 = "iso-8859-1".equals(encoding); String path = encodeAbsoluteRedirect(url); setHeader("Location", path); if (isLatin1) setHeader("Content-Type", "text/html; charset=iso-8859-1"); else setHeader("Content-Type", "text/html; charset=utf-8"); String msg = "The URL has moved <a href=\"" + path + "\">here</a>"; // The data is required for some WAP devices that can't handle an // empty response. if (_writer != null) { _writer.println(msg); } else { ServletOutputStream out = getOutputStream(); out.println(msg); } // closeConnection(); _request.saveSession(); // #503 // 非常重要,这个就是resion和tomcat的不同之处. // 已经关闭了,肯定不能再写入数据. close(); } @Override public void close() throws IOException { // tck - jsp include AbstractHttpResponse response = _response; if (response != null) { response.close(); } } } resin处理`302`方式其实非常简单,步骤如下: 1. 清空缓存区内容并进行重置 2. 设置302状态码 3. 设置`Location` 和 `Content-Type` 响应头 4. 写响应体数据 5. 保存session 6. 关闭连接 整个处理流程非常简单明了. ### tomcat对302的处理 在tomcat中,`HttpServletResponse`接口的实现类是`ResponseFacade`.该类指示一个Facade, 代码如下: ```java ResponseFacade public class ResponseFacade implements HttpServletResponse { @Override public void sendRedirect(String location) throws IOException { if (isCommitted()) { throw new IllegalStateException (sm.getString("coyoteResponse.sendRedirect.ise")); } response.setAppCommitted(true); response.sendRedirect(location); } }
真正的处理由 Response
来进行
public class Response implements HttpServletResponse { /** * Send a temporary redirect to the specified redirect location URL. * * @param location Location URL to redirect to * * @exception IllegalStateException if this response has * already been committed * @exception IOException if an input/output error occurs */ @Override public void sendRedirect(String location) throws IOException { sendRedirect(location, SC_FOUND); } /** * Internal method that allows a redirect to be sent with a status other * than {@link HttpServletResponse#SC_FOUND} (302). No attempt is made to * validate the status code. * * @param location Location URL to redirect to * @param status HTTP status code that will be sent * @throws IOException an IO exception occurred */ public void sendRedirect(String location, int status) throws IOException { if (isCommitted()) { throw new IllegalStateException(sm.getString("coyoteResponse.sendRedirect.ise")); } // Ignore any call from an included servlet if (included) { return; } // 清空缓存区内容并进行重置 resetBuffer(true); // Generate a temporary redirect to the specified location try { String locationUri; // Relative redirects require HTTP/1.1 if (getRequest().getCoyoteRequest().getSupportsRelativeRedirects() && getContext().getUseRelativeRedirects()) { locationUri = location; } else { locationUri = toAbsolute(location); } setStatus(status); setHeader("Location", locationUri); // 这里有个小魔法 if (getContext().getSendRedirectBody()) { PrintWriter writer = getWriter(); writer.print(sm.getString("coyoteResponse.sendRedirect.note", Escape.htmlElementContent(locationUri))); flushBuffer(); } } catch (IllegalArgumentException e) { log.warn(sm.getString("response.sendRedirectFail", location), e); setStatus(SC_NOT_FOUND); } // 设置缓存区的suspended标志位 // 从应用视图的角度看,该响应已经结束了. 但其实连接并没有关闭. setSuspended(true); } }
tomcat处理 302
步骤如下:
Location
tomcat context配置
详细配置项参考: https://tomcat.apache.org/tomcat-7.0-doc/config/context.html
其中和302处理相关的一个配置项为: sendRedirectBody
,文档解释如下:
If true, redirect responses will include a short response body that includes details of the redirect as recommended by RFC 2616. This is disabled by default since including a response body may cause problems for some application component such as compression filters.
根据 RFC 2616 规范,302跳转是可以带有响应体数据的(resin就按规范进行了实现).tomcat默认处理是不带的,原因是可能与其它组件冲突,例如压缩组件.
如果将 sendRedirectBody
的值设为true,则tomcat在处理302时,在写完响应体数据后,会执行缓存区的刷新,客户端能收到对应的响应头数据,完成跳转,且不会应为后续继续写数据导致客户端不能正常跳转.
因为默认是false,导致302响应头数据没有及时发送给客户端,在 sendRedirect
后如果应用发生了异常,则已经设置了的302响应码会被500所替代,客户端不能正常跳转.
###tomcat sendRedirect
后不能跳转的逻辑分析
tomcat处理请求的流程一部分流程如下:
StandardHostValve
-> StandardContextValve
-> StandardWrapperValve
请求入口由 StandardWrapperValve
处理,结束还是需要 StandardHostValve
来处理.
@Override public final void invoke(Request request, Response response) throws IOException, ServletException { // Allocate a servlet instance to process this request try { if (!unavailable) { servlet = wrapper.allocate(); } } catch (UnavailableException e) { } catch (ServletException e) { exception(request, response, e); } catch (Throwable e) { exception(request, response, e); servlet = null; } // 当请求发送异常时, 已经设置的302状态码此时变为500 private void exception(Request request, Response response, Throwable exception) { request.setAttribute(RequestDispatcher.ERROR_EXCEPTION, exception); response.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR); response.setError(); } }
StandardHostValve处理逻辑
@Override public final void invoke(Request request, Response response) throws IOException, ServletException { try { // 省略代码 try { if (!asyncAtStart || asyncDispatching) { context.getPipeline().getFirst().invoke(request, response); } else { // Make sure this request/response is here because an error // report is required. if (!response.isErrorReportRequired()) { throw new IllegalStateException(sm.getString("standardHost.asyncStateError")); } } } catch (Throwable t) { ExceptionUtils.handleThrowable(t); container.getLogger().error("Exception Processing " + request.getRequestURI(), t); // If a new error occurred while trying to report a previous // error allow the original error to be reported. if (!response.isErrorReportRequired()) { request.setAttribute(RequestDispatcher.ERROR_EXCEPTION, t); throwable(request, response, t); } } // 在sendRedirect方法设置的suspended标志位此时又被置为false // 也就是说 response由可以使用了.这就是resin和tomcat设计实现的不同 // Now that the request/response pair is back under container // control lift the suspension so that the error handling can // complete and/or the container can flush any remaining data response.setSuspended(false); Throwable t = (Throwable) request.getAttribute(RequestDispatcher.ERROR_EXCEPTION); // Protect against NPEs if the context was destroyed during a // long running request. if (!context.getState().isAvailable()) { return; } // Look for (and render if found) an application level error page if (response.isErrorReportRequired()) { if (t != null) { throwable(request, response, t); } else { status(request, response); } } if (!request.isAsync() && !asyncAtStart) { context.fireRequestDestroyEvent(request.getRequest()); } } finally { // Access a session (if present) to update last accessed time, based // on a strict interpretation of the specification if (ACCESS_SESSION) { request.getSession(false); } context.unbind(Globals.IS_SECURITY_ENABLED, MY_CLASSLOADER); } }
总结
-
线上替换应用组件,尤其是底层的应用软件需要非常注意.不可全量替换.一定要逐步替换.虽然已经在测试环境,线上灰度替换了一台机器,
但是因为访问量小,导致问题发现的比较晚,直至大批量替换才发现问题.还有就是:同一个规范,但不同的实现细节还是有差异. - 应用开发一定需要遵守API规范,否则会导致奇怪问题的发生.好多人总是说遇到的问题多,踩坑多,那是因为你从来不仔细阅读相关api规范文档或官方文档.不遵守规范导致的问题能叫坑吗?
- 在使用任何一项技术时,优先查询官方文档.不要随手google或baidu.实话说,网上的文章质量参差不齐,难免找到理解错误的文档.
- 养成阅读源代码的习惯,好处不言而喻.如果3年前没有读过tomcat6的源代码,今天排查起来问题就非常困难了.
参考资料
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