JSF 将模板呈现为文本/纯文本

Question

我有一个(可用的)JSF 应用程序。现在我想要使用 JSF 表达式语言扩展不是页面资源的文档(假设是纯文本文档)(因为我需要来自 bean 的状态，这看起来很“自然”)。但我似乎没有完全理解其中的机制......

为了在 web.xml 中处理“*.txt”文件

<servlet-mapping>
    <servlet-name>Faces Servlet</servlet-name>
    <url-pattern>*.xhtml</url-pattern>
</servlet-mapping> 
<servlet-mapping>
    <servlet-name>Faces Servlet</servlet-name>
    <url-pattern>*.txt</url-pattern>
</servlet-mapping>

我添加一个“plain.txt”资源

<f:view contentType="text/plain" xmlns:f="http://java.sun.com/jsf/core" >

hi #{request.contextPath}/

</f:view>

请求

http://myServer/myApp/plain.txt

使用 myfaces 2.1.10 在服务器上出现无限循环失败。将资源重命名为“plain.xhtml”并请求它工作正常。

更新到 myfaces 2.1.17 后(与 2.2.9 相同)，服务“plain.txt”也有效!

问题是:以这种方式使用模板是“最佳实践”还是“意外的副作用”(实际上应该行不通)？有没有更好的方法来实现这样的模板任务？

编辑

经过更多尝试后，它似乎更加奇怪。提供扩展内容似乎随机失败(2.1.17 和 2.2.9)。重新启动后，我在服务器端获得一个资源“res1.txt”的“循环”，但不是资源“res2.txt”的精确副本。也恰好“res1.txt”渲染成功。也许服务器跟踪可以提供一些提示:

首先，有一个很长的“递归”

Mär 09, 2016 5:06:20 PM org.apache.catalina.core.ApplicationDispatcher invoke
SCHWERWIEGEND: Servlet.service() for servlet Faces Servlet threw exception
java.lang.NullPointerException
    at org.apache.myfaces.shared.context.flash.FlashImpl.isKeepMessages(FlashImpl.java:388)
    at org.apache.myfaces.shared.context.flash.FlashImpl._saveMessages(FlashImpl.java:668)
    at org.apache.myfaces.shared.context.flash.FlashImpl.doPostPhaseActions(FlashImpl.java:269)
    at org.apache.myfaces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:254)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:199)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:748)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:486)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:411)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:338)
    at org.apache.myfaces.context.servlet.ServletExternalContextImpl.dispatch(ServletExternalContextImpl.java:369)
    at org.apache.myfaces.view.jsp.JspViewDeclarationLanguage.buildView(JspViewDeclarationLanguage.java:99)
    at org.apache.myfaces.lifecycle.RenderResponseExecutor.execute(RenderResponseExecutor.java:78)
    at org.apache.myfaces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:241)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:199)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:748)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:486)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:411)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:338)
    at org.apache.myfaces.context.servlet.ServletExternalContextImpl.dispatch(ServletExternalContextImpl.java:369)
    at org.apache.myfaces.view.jsp.JspViewDeclarationLanguage.buildView(JspViewDeclarationLanguage.java:99)
    at org.apache.myfaces.lifecycle.RenderResponseExecutor.execute(RenderResponseExecutor.java:78)
    at org.apache.myfaces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:241)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:199)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:748)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:486)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:411)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:338)
    at org.apache.myfaces.context.servlet.ServletExternalContextImpl.dispatch(ServletExternalContextImpl.java:369)
    at org.apache.myfaces.view.jsp.JspViewDeclarationLanguage.buildView(JspViewDeclarationLanguage.java:99)
    at org.apache.myfaces.lifecycle.RenderResponseExecutor.execute(RenderResponseExecutor.java:78)
    at org.apache.myfaces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:241)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:199)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:748)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:486)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:411)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:338)
    at org.apache.myfaces.context.servlet.ServletExternalContextImpl.dispatch(ServletExternalContextImpl.java:369)
    at org.apache.myfaces.view.jsp.JspViewDeclarationLanguage.buildView(JspViewDeclarationLanguage.java:99)
    at org.apache.myfaces.lifecycle.RenderResponseExecutor.execute(RenderResponseExecutor.java:78)
    at org.apache.myfaces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:241)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:199)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:748)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:486)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:411)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:338)
    at org.apache.myfaces.context.servlet.ServletExternalContextImpl.dispatch(ServletExternalContextImpl.java:369)
    at org.apache.myfaces.view.jsp.JspViewDeclarationLanguage.buildView(JspViewDeclarationLanguage.java:99)
    at org.apache.myfaces.lifecycle.RenderResponseExecutor.execute(RenderResponseExecutor.java:78)
    at org.apache.myfaces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:241)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:199)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:748)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:486)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:411)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:338)
    at org.apache.myfaces.context.servlet.ServletExternalContextImpl.dispatch(ServletExternalContextImpl.java:369)
    at org.apache.myfaces.view.jsp.JspViewDeclarationLanguage.buildView(JspViewDeclarationLanguage.java:99)
    at org.apache.myfaces.lifecycle.RenderResponseExecutor.execute(RenderResponseExecutor.java:78)
    at org.apache.myfaces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:241)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:199)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:748)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:486)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:411)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:338)
    at org.apache.myfaces.context.servlet.ServletExternalContextImpl.dispatch(ServletExternalContextImpl.java:369)
    at org.apache.myfaces.view.jsp.JspViewDeclarationLanguage.buildView(JspViewDeclarationLanguage.java:99)
    at org.apache.myfaces.lifecycle.RenderResponseExecutor.execute(RenderResponseExecutor.java:78)
    at org.apache.myfaces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:241)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:199)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:748)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:486)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:411)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:338)
    at org.apache.myfaces.context.servlet.ServletExternalContextImpl.dispatch(ServletExternalContextImpl.java:369)
    at org.apache.myfaces.view.jsp.JspViewDeclarationLanguage.buildView(JspViewDeclarationLanguage.java:99)
    at org.apache.myfaces.lifecycle.RenderResponseExecutor.execute(RenderResponseExecutor.java:78)
    at org.apache.myfaces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:241)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:199)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:505)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:956)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:423)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1079)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:625)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:318)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:745)

这条轨迹不断重复，每次都变得更短，直到它最终走到尽头:

Mär 09, 2016 5:06:20 PM org.apache.catalina.core.StandardWrapperValve invoke
SCHWERWIEGEND: Servlet.service() for servlet [Faces Servlet] in context with path [/cloudsuite-snippets] threw exception
java.lang.NullPointerException
    at org.apache.myfaces.shared.context.flash.FlashImpl.isKeepMessages(FlashImpl.java:388)
    at org.apache.myfaces.shared.context.flash.FlashImpl._saveMessages(FlashImpl.java:668)
    at org.apache.myfaces.shared.context.flash.FlashImpl.doPostPhaseActions(FlashImpl.java:269)
    at org.apache.myfaces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:254)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:199)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:505)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:956)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:423)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1079)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:625)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:318)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:745)

浏览器页面简直是白色的..

编辑二

还有另一个信息:失败并不是真正的不确定性(这会稍微损害我的信仰......)但仍然很奇怪。对于我拥有同名但结尾为“.xhtml”的资源的所有资源，渲染成功。

服务器似乎在内部重定向到“.xhtml”版本，呈现该版本的内容并以“.txt”版本的名称返回它(忽略后者的内容)。这是怎么回事？

Answer 1

The question is: is using templates this way "best practice" or "accidental side effect" (and should not really work)?

它不应该真正起作用。 JSF 作为基于 HTML 表单的 MVC 框架不支持 text/plain内容放在第一位，但只有基于 HTML 的内容，例如 text/html .当在 Mojarra 而不是 MyFaces 上尝试您的用例时(在将 plain.txt 重命名为 plain.xhtml 之后，请参阅下文)，我遇到以下异常:

java.lang.IllegalArgumentException: Unrecognized Content Type.

关于 View 解析，从技术上讲，您应该将 plain.txt 命名为文件为 plain.xhtml并且只添加了 *.txt FacesServlet 的 URL 模式. FacesServlet即在根据 javax.faces.DEFAULT_SUFFIX 重新映射 URL 模式中的任何文件扩展名后定位物理 View 默认为 .xhtml 的上下文参数.当物理文件不存在时，JSF 将从 Facelets View 回退到 JSP View (通过堆栈跟踪中存在 JspViewDeclarationLanguage 来确认)但是作为 plain.jsp也不存在并且 URL 仍然与 FacesServlet 匹配反过来映射它会在无限循环中运行，以徒劳地尝试查找和渲染物理资源。

有关 JSF View 解析的内部工作原理的详尽解释，另请参阅 JSF Facelets: Sometimes I see the URL is .jsf and sometimes .xhtml. Why?关于 dispatch() 上的无限循环，这在技术上又是 JSF 中的一个错误，因为它实际上应该返回 404。

---

Is there a better way to implement such a templating task?

如果唯一的目的是评估 EL 表达式，那么最好使用 JSP servlet 而不是 JSF servlet，并且只使用只读 EL 表达式 ${}而不是可写的 EL 表达式 #{}因为 JSP 不支持它。

最简单的方法是将 servlet 名称更改为 Tomcat 自己的 JSP servlet 之一:jsp (不需要 <servlet> 条目，因为 Tomcat 已经在自己的 /conf/web.xml 中定义了它)。

<servlet-mapping>
    <servlet-name>jsp</servlet-name>
    <url-pattern>*.txt</url-pattern>
</servlet-mapping>

然后修改/plain.txt作为一个 JSP View ，如下所示。注意 ${request}在 JSP 中不存在，它仅作为 ${pageContext} 的属性可用.另见 our EL wiki page .

<%@page contentType="text/plain" %>

hi ${pageContext.request.contextPath}/

至于解析托管 beans，它只是没有发现 JSF @ManagedBean , 但它可以发现 CDI @Named .所以当你install CDI on Tomcat并将感兴趣的托管 bean 重做为 CDI 托管 bean 而不是 JSF 托管 bean，然后它们将可用。

一个不同的替代方案需要更多的工作，但保证跨 servletcontainer 可移植(因为 jsp 的 servlet 名称是 Tomcat 特定的，尽管几乎所有 servletcontainer 都具有相同的“实际”名称)正在使用普通的 vanilla servlet或者甚至是 JAX-RS (RESTful) 资源来完成您想要的任务。将其映射到所需的 URL 模式 /plain.txt ，让它准备好想要的模型，最后转发到一个“真正的”JSP 文件 the usual way .

@WebServlet("/plain.txt")
public class PlainTxtServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.getRequestDispatcher("/WEB-INF/plain.jsp").forward(request, response);
    }

}

并且有一个/WEB-INF/plain.jsp作为物理文件，仍然使用上述 JSP 语法。请注意，它位于 /WEB-INF 内因为您不希望最终用户能够直接请求 /plain.jsp而不是 /plain.txt .

额外的优势是这不一定需要 CDI 来管理 bean，因为您可以像下面这样手动管理 bean:

Bean bean = new Bean();
request.setAttribute("bean", bean);

它将作为 ${bean} 提供在 EL 中。

另见:

• Mixing JSF EL in a JavaScript file
• How to generate JSON response from JSF?