java - JSF 1.2 调用 id *** 组件的操作方法时出错

Question

我正在编写一个教程，其中包括如何创建 Todo JSF 应用程序 link of the tutorial (7. A Todo JSF application) here.

在服务器(tomcat)上运行“Todo.jsp”页面后，我没有在 Controller 构造函数上创建先前创建的预期待办事项列表，当我单击“保存”按钮时，出现以下错误:

Error calling action method of component with id j_id_jsp_1588810359_4:j_id_jsp_1588810359_14

Caused by:

java.lang.NullPointerException - /Todo.jsp(44,3) '#{todoController.save}'java.lang.NullPointerException

我已经在网上搜索过以修复此错误，但没有找到任何有用的信息:(

请询问我是否需要链接任何其他代码行。谢谢...

(编辑)

堆栈跟踪的第一行是:

javax.faces.FacesException: Error calling action method of component with id j_id_jsp_1588810359_4:j_id_jsp_1588810359_14

我使用的 URL 是“http://localhost:8080/de.vogella.jsf.todo/faces/Todo.jsp”

我的“web.xml”是:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
  <display-name>de.vogella.jsf.todo</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
    <servlet-name>FacesServlet</servlet-name>
    <servlet-class>javax.faces.webapp.FacesServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>FacesServlet</servlet-name>
    <url-pattern>/faces/*</url-pattern>
  </servlet-mapping>
  <context-param>
    <param-name>javax.servlet.jsp.jstl.fmt.localizationContext</param-name>
    <param-value>resources.application</param-value>
  </context-param>
  <context-param>
    <description>State saving method: 'client' or 'server' (=default). See JSF Specification 2.5.2</description>
    <param-name>javax.faces.STATE_SAVING_METHOD</param-name>
    <param-value>client</param-value>
  </context-param>
  <context-param>
    <description>
    This parameter tells MyFaces if javascript code should be allowed in
    the rendered HTML output.
    If javascript is allowed, command_link anchors will have javascript code
    that submits the corresponding form.
    If javascript is not allowed, the state saving info and nested parameters
    will be added as url parameters.
    Default is 'true'</description>
    <param-name>org.apache.myfaces.ALLOW_JAVASCRIPT</param-name>
    <param-value>true</param-value>
  </context-param>
  <context-param>
    <description>
    If true, rendered HTML code will be formatted, so that it is 'human-readable'
    i.e. additional line separators and whitespace will be written, that do not
    influence the HTML code.
    Default is 'true'</description>
    <param-name>org.apache.myfaces.PRETTY_HTML</param-name>
    <param-value>true</param-value>
  </context-param>
  <context-param>
    <param-name>org.apache.myfaces.DETECT_JAVASCRIPT</param-name>
    <param-value>false</param-value>
  </context-param>
  <context-param>
    <description>
    If true, a javascript function will be rendered that is able to restore the
    former vertical scroll on every request. Convenient feature if you have pages
    with long lists and you do not want the browser page to always jump to the top
    if you trigger a link or button action that stays on the same page.
    Default is 'false'
</description>
    <param-name>org.apache.myfaces.AUTO_SCROLL</param-name>
    <param-value>true</param-value>
  </context-param>
  <servlet>
    <servlet-name>faces</servlet-name>
    <servlet-class>org.apache.myfaces.webapp.MyFacesServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>faces</servlet-name>
    <url-pattern>*.jsf</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>faces</servlet-name>
    <url-pattern>*.faces</url-pattern>
  </servlet-mapping>
  <listener>
    <listener-class>org.apache.myfaces.webapp.StartupServletContextListener</listener-class>
  </listener>
</web-app>

Answer 1

您的待办事项 Controller 为空。您是否按照教程中的说明注册了它？

7.4. Register your managed beans