Question

这是我的第一个项目。我有主页面，当我点击一个链接时，参数（“id_action”）的值在bean中为null。这是Managed Bean的代码：

 @ManagedBean(eager=true)
 @ApplicationScoped
 public class LessonController implements Serializable {  
 private ArrayList <Lesson> lessons;
 private String content ="";
 private String name ="";

 public LessonController() {
     fillLessonAll();
 }
 private void fillLessonAll() {
    Connection conn = null;
    Statement stmt = null;
    ResultSet rs = null;
    lessons = new ArrayList <Lesson> ();
    try {
         conn = DataBase.getConnection();
         stmt = conn.createStatement();
         rs = stmt.executeQuery("select * from lessons");
        while(rs.next()){
            Lesson lesson = new Lesson();
            lesson.setName(rs.getString("name"));
            lesson.setLesson(rs.getString("lesson"));
            lesson.setId(rs.getInt("idlessons"));
            lessons.add(lesson);
        }
    }catch (SQLException ex){
          Logger.getLogger(DataBase.class.getName()).log(Level.SEVERE,null,ex);
    } finally {
        try {
            if(conn!=null) conn.close();
            if(stmt!=null) stmt.close();
            if(rs!=null) rs.close();
        } catch (SQLException ex) {
              Logger.getLogger(LessonController.class.getName()).log(Level.SEVERE, null, ex);
        }
    }   
 } 
 public ArrayList<Lesson> getLessonList (){
     return lessons;
 }
     public void findId() {
     Map <String,String> params = FacesContext.getCurrentInstance().getExternalContext().getInitParameterMap();
    name = params.get("id_action");
    for(Lesson less : lessons) {
        if(less.getName().equals(name)) content = less.getLesson();
    }
 }
 public String getContent() {
     return content;
 }
 }

这是 main.xhtml

  <html xmlns="http://www.w3.org/1999/xhtml"
  xmlns:f="http://java.sun.com/jsf/core"
  xmlns:ui="http://java.sun.com/jsf/facelets"
  xmlns:h="http://java.sun.com/jsf/html"

  >

 <h:head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
    <title>Facelets Template</title>
    <h:outputStylesheet library="css" name="main.css"/>
    <h:outputStylesheet library="css" name="leftmen3"/>
 </h:head>

 <h:body>
    <ui:composition template="/templates/lesson_template.xhtml">
        <ui:define name="content">
            <div class="content">

                <h:outputText value="#{lessonController.content}" /> 

            </div>
        </ui:define>
    </ui:composition>

</h:body>

</html>

这是 lesson_template.xhtml

 <html xmlns="http://www.w3.org/1999/xhtml"
  xmlns:ui="http://java.sun.com/jsf/facelets"
  xmlns:h="http://java.sun.com/jsf/html"  
  xmlns:f="http://java.sun.com/jsf/core">

<h:head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
    <title>Facelets Template</title>
    <h:outputStylesheet library="css" name="main.css"/>
</h:head>
<h:body>
    <div>
        <ui:insert name="leftmenu">
            <ui:include src="../templates/leftmenu.xhtml"></ui:include>
        </ui:insert>
        <ui:insert name="content">
            <ui:include src="../templates/content.xhtml"></ui:include>
        </ui:insert>
    </div>
 </h:body>

 </html>

这是 leftmenu.xhtml

 <ui:composition>
        <h:dataTable value="#{lessonController.lessonList}" var="less" >
            <h:column>
                <h:form>
                    <h:commandLink action="#{lessonController.findId()}" value="#{less.name}">
                        <f:param name="id_action" value="#{less.name}"></f:param>
                    </h:commandLink>
                </h:form>

            </h:column>
        </h:dataTable>  

    </ui:composition>

faces-config 很简单：

 <?xml version='1.0' encoding='UTF-8'?>
 <faces-config version="2.1"
          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-facesconfig_2_1.xsd">
 <application>
 <resource-bundle>
    <base-name>messages</base-name>
    <var>msg</var>
</resource-bundle>
</application>
</faces-config>

Answer 1

我在LessonController课程中发现了一个错误！

需要：

Map params = FacesContext.getCurrentInstance（）。getExternalContext（）。getRequestParameterMap（）;

代替： Map params = FacesContext.getCurrentInstance（）。getExternalContext（）。getInitParameterMap（）

现在它正在运作。

f：param向bean返回“null”

1 个答案: