为什么托管 Bean 列表在 sessionscoped 中包含空元素？答案

【问题标题】：Why Managed Bean List becomes including null elements in sessionscoped?为什么托管 Bean 列表在 sessionscoped 中包含空元素？
【发布时间】：2014-12-06 01:05:52
【问题描述】：

我想获取有关联系人的一些信息并将它们显示在表格中。我使用了两个以PersonalContact 和BusinessContact 命名的托管bean 和一个以Contact 命名的抽象类，包括firstName、lastName、ID、email 和mphone 派生自的属性。另外，一个将bean添加到arraylist的通用类。我把BusinessContact 作为一个bean，把tableBusiness 作为一个表和泛型类AddressBook 放在这里，个人文件与它们平行。

从屏幕获取的输入被分配给bean的属性，但是当bean转到Arraylist要添加时，其内容变为空。这是为什么？是关于范围的吗？

这是我的豆子：

import javax.faces.bean.ManagedBean;
import javax.faces.bean.ViewScoped;

@ManagedBean
@ViewScoped
public class BusinessContact extends Contact{
    private String companyName,workPhone;

    public BusinessContact() {}

    public BusinessContact(String companyName, String workPhone, String ID, String firstName, String lastName, String email, String mphone) {
        super(ID, firstName, lastName, email, mphone);
        this.companyName = companyName;
        this.workPhone = workPhone;
    }


    /**
     * Creates a new instance of BusinessContact
     */
    public String getCompanyName() {
        return companyName;
    }

    public void setCompanyName(String companyName) {
        this.companyName = companyName;
    }

    public String getWorkPhone() {
        return workPhone;
    }

    public void setWorkPhone(String workPhone) {
        this.workPhone = workPhone;
    }        
}

这是我的business.xhtml：

<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org   /TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
  xmlns:h="http://xmlns.jcp.org/jsf/html"
  xmlns:f="http://xmlns.jcp.org/jsf/core"
  xmlns:ui="http://xmlns.jcp.org/jsf/facelets">
 <h:head>
    <title>Contact</title>
 </h:head>
 <h:body>
    <h:form>
    <h:panelGrid columns="2"> 
     First Name:
     <h:inputText id="firstName" required="true" 
                  requiredMessage="Can not be blank" value="#{businessContact.firstName}">
     </h:inputText>
     ID:
     <h:inputText id="id" required="true" 
                  requiredMessage="Can not be blank" value="#{businessContact.ID}">
     </h:inputText>
     Last Name:
     <h:inputText id="lastName" required="true" 
                  requiredMessage="Can not be blank" value="#{businessContact.lastName}">
     </h:inputText>

     E-mail:
     <h:inputText id="email" required="true" 
                  requiredMessage="Can not be blank" value="#{businessContact.email}">
     </h:inputText>
     Mobile Phone:
     <h:inputText id="mphone" required="true" 
                  requiredMessage="Can not be blank" value="#{businessContact.mphone}">
     </h:inputText>
     Company Name:
     <h:inputText id="companyName" required="true" 
                  requiredMessage="Can not be blank" value="#{businessContact.companyName}">
     </h:inputText>
     Work Phone:
     <h:inputText id="workPhone" required="true" 
                  requiredMessage="Can not be blank" value="#{businessContact.workPhone}">
     </h:inputText>

    </h:panelGrid>

    <h:commandButton  value="Add" id="add" action="#{addressBook.add(BusinessContact)}"></h:commandButton>

    <h:commandButton  value="Delete" id="delete" action="#{addressBook.remove(BusinessContact)}"></h:commandButton>
    <h:outputLink id="t" value="tableBusiness.xhtml"> Click see the table</h:outputLink>
    <ui:debug hotkey="k" rendered="true"/>
  </h:form>
</h:body>

这是我将 bean 放入数组列表的通用类：

import java.util.ArrayList;
import javax.faces.bean.ManagedBean;
import javax.faces.bean.SessionScoped;

@ManagedBean
@SessionScoped
public class AddressBook <T extends Contact> {
    private ArrayList<T> list = new ArrayList<T>();
    T clas;

    public ArrayList<T> getList() {
        return list;
    }

    public void setList(ArrayList<T> list) {
        this.list = list;
    }

    public void add(T obj) { 
        this.clas=obj;
        //System.out.println(obj.getFirstName()+" ");
        list.add(obj);

    }
    public void remove(T obj)
    {
       list.remove(obj);
    }
    /**
     * Creates a new instance of AddressBook
     */
    public AddressBook() {}        
}

最后，这个 xhmtl 用于在表格中显示数组列表：

<html xmlns="http://www.w3.org/1999/xhtml"
  xmlns:h="http://xmlns.jcp.org/jsf/html"
  xmlns:f="http://xmlns.jcp.org/jsf/core">
<h:head>

</h:head>
<h:body>
    <h:form>
        "#{businessContact.firstName}"
       <h:dataTable value="#{addressBook.list}" var="BusinessContact">
        <h:column>
                <f:facet name="header">
                    First Name
                </f:facet>
            <h:outputText value="#{businessContact.firstName}">
            </h:outputText>
        </h:column>
            <h:column>
                <f:facet name="header">
                    Last Name
                </f:facet>
                #{businessContact.lastName}
            </h:column>
            <h:column>
                <f:facet name="header">
                  Mobile Phone
                </f:facet>
                #{businessContact.mphone}
            </h:column> 
            <h:column>
                <f:facet name="header">
                  E-mail
                </f:facet>
                #{businessContact.email}
            </h:column>  
            <h:column>
                <f:facet name="header">
                  Company Name
                </f:facet>
                #{businessContact.companyName}
            </h:column>  
            <h:column>
                <f:facet name="header">
                  Work Phone
                </f:facet>
                #{businessContact.workPhone}
            </h:column>  
      </h:dataTable>
    </h:form>
</h:body>
</html>

【问题讨论】：

标签： jsf primefaces

【解决方案1】：

您正在命名var="BusinessContact"，但尝试将其用作"businessContact"

改变这一行

<h:dataTable value="#{addressBook.list}" var="BusinessContact">

到这里

<h:dataTable value="#{addressBook.list}" var="businessContact">

【讨论】：

对不起，它不起作用。我修复了一些东西，但结果是arraylist的整个对象变成了最后添加的对象。