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Question

我有一個關於在JSF中使用el-tag的奇怪問題。我有以下的依賴幾乎是空的項目：

<dependency> 
     <groupId>javax.el</groupId> 
     <artifactId>el-api</artifactId> 
     <version>2.2</version> 
     <scope>compile</scope> 
    </dependency> 
    <dependency> 
     <groupId>org.glassfish.web</groupId> 
     <artifactId>el-impl</artifactId> 
     <version>2.2</version> 
     <scope>runtime</scope> 
    </dependency> 
    <dependency> 
     <groupId>com.sun.faces</groupId> 
     <artifactId>jsf-api</artifactId> 
     <version>2.2.4</version> 
    </dependency> 
    <dependency> 
     <groupId>com.sun.faces</groupId> 
     <artifactId>jsf-impl</artifactId> 
     <version>2.2.4</version> 
    </dependency> 

    <dependency> 
     <groupId>javax.servlet</groupId> 
     <artifactId>servlet-api</artifactId> 
     <version>2.5</version> 
     <scope>provided</scope> 
    </dependency> 

    <dependency> 
     <groupId>javax.servlet</groupId> 
     <artifactId>jstl</artifactId> 
     <version>1.2</version> 
    </dependency> 

    <dependency> 
     <groupId>org.primefaces</groupId> 
     <artifactId>primefaces</artifactId> 
     <version>4.0</version> 
    </dependency> 
    <dependency> 
     <groupId>org.primefaces.themes</groupId> 
     <artifactId>cupertino</artifactId> 
     <version>1.0.10</version> 
    </dependency> 
    <dependency> 
     <groupId>org.primefaces.themes</groupId> 
     <artifactId>all-themes</artifactId> 
     <version>1.0.10</version> 
    </dependency> 

而且我有一個bean，它開始像這樣：

import javax.faces.bean.ManagedBean; 
import javax.faces.bean.ApplicationScoped; 

@ManagedBean(name = "requester") 
@ApplicationScoped 
public class UserBean implements Serializable { 
    public String getRequestIdentificator() { 
     return requestIdentificator; 
    } 

    public void setRequestIdentificator(String requestIdentificator) { 
     this.requestIdentificator = requestIdentificator; 
    } 

和web.xml看起來是這樣的：

<web-app version="3.0" 
     xmlns="http://java.sun.com/xml/ns/javaee" 
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
     xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" 
     id="DAS_ID"> 

    <display-name>DAS</display-name> 

    <context-param> 
     <param-name>org.apache.myfaces.EXPRESSION_FACTORY</param-name> 
     <param-value>com.sun.el.ExpressionFactoryImpl</param-value> 
    </context-param> 
    <context-param> 
     <param-name>com.sun.faces.expressionFactory</param-name> 
     <param-value>com.sun.el.ExpressionFactoryImpl</param-value> 
    </context-param> 
    <context-param> 
     <description>Parameter required by Mojarra 2.0</description> 
     <param-name>com.sun.faces.allowTextChildren</param-name> 
     <param-value>true</param-value> 
    </context-param> 
    <context-param> 
     <param-name>javax.faces.VALIDATE_EMPTY_FIELDS</param-name> 
     <param-value>true</param-value> 
    </context-param> 

    <context-param> 
     <description> 
      Tell the runtime where we are in the project development 
      lifecycle. Valid values are: 
      Development, UnitTest, SystemTest, or Production. 
      The runtime will display helpful hints to correct common mistakes 
      when the value is Development. 
     </description> 
     <param-name>javax.faces.PROJECT_STAGE</param-name> 
     <param-value>Development</param-value> 
    </context-param> 

    <!-- Faces Servlet --> 
    <servlet> 
     <servlet-name>Faces Servlet</servlet-name> 
     <servlet-class>javax.faces.webapp.FacesServlet</servlet-class> 
     <load-on-startup>1</load-on-startup> 
    </servlet> 

    <servlet-mapping> 
     <servlet-name>Faces Servlet</servlet-name> 
     <url-pattern>/faces/*</url-pattern> 
    </servlet-mapping> 

    <welcome-file-list> 
     <welcome-file>faces/main.xhtml</welcome-file> 
    </welcome-file-list> 

</web-app> 

不幸的是，每次，像<p:commandButton value="Request" action="#{requester.requestData}" />這樣的東西被稱爲，這個結果

SEVERE: javax.el.PropertyNotFoundException: /main.xhtml @19,100 value="#{requester.requestIdentificator}": Target Unreachable, identifier 'requester' 
resolved to null 

我已經搜索了錯誤，常見的錯誤是例如總結在這裏：Target Unreachable, identifier resolved to null，但沒有一個適用。此外，NetBeans能夠對我所做的每件事都使用代碼完成功能（我也嘗試了除requestIdentificator之外的其他功能） - 因此，代碼似乎寫得完全正確。 Bean接縫永遠不會被初始化（所以在構造函數中的日誌不會被調用），但根據例如https://stackoverflow.com/a/11013290/2096209，沒有必要在JSF 2.x（我使用2.1）中的faces-config中註冊Bean，這樣就不會成爲問題。

我正在使用mvn tomcat7運行一切：運行。有沒有人提示如何解決這個問題？

Answer 1

I使用javax.faces.bean軟件包時，經常會遇到同樣的問題。嘗試導入的

import javax.faces.bean.ApplicationScoped; 

代替作爲@ManagedBean註釋使用@Named

import javax.inject.Named; 
import javax.enterprise.context.ApplicationScoped; 

@Named("requester") 
@ApplicationScoped 
public class UserBean implements Serializable { 

然後生成並重新部署

import javax.enterprise.context.ApplicationScoped; 

代替。看看是否有幫助

Answer 2

問題是，我試着用mvn tomcat7運行它：運行。如果我把這個戰爭複製到一個普通的tomcat7實例中，它就會起作用，而且，如果我使用mvn tomcat7運行它：run-war。似乎是一個maven-tomcat插件的bug。