Question

我正在做一个教程，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，我没有预先在控制器构造函数上创建的todos列表，当我点击“保存”按钮时，我有以下错误：

调用id为j_id_jsp_1588810359_4的组件的操作方法时出错：j_id_jsp_1588810359_14

引起：

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

我已经在网上搜索以修复错误，但我没有找到任何有用的信息:(

请问我是否必须链接任何其他代码行。谢谢......

（适用编辑）

stacktrace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

我使用的网址是“http：// localhost：8080 / de.vogella.jsf.todo / faces / Todo.jsp”

和我的“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

你的todocontroller是null。您是否按照教程中的说明进行了注册？

7.4。注册您的托管bean

JSF 1.2错误调用id为***的组件的动作方法

1 个答案: