错误：javax.el.PropertyNotFoundException：目标无法到达，“null”返回 null [重复]答案

【问题标题】：Error : javax.el.PropertyNotFoundException: Target Unreachable, 'null' returned null [duplicate]错误：javax.el.PropertyNotFoundException：目标无法到达，“null”返回 null [重复]
【发布时间】：2014-10-24 10:27:45
【问题描述】：

当我运行我的 JSF 页面时，我在下面遇到了这个错误。

javax.el.PropertyNotFoundException: Target Unreachable, 'null' returned null..

警告：/createStaff.xhtml @33,125 value="#{staffBean.staff.firstName}"：目标不可达，'null' 返回 null javax.el.PropertyNotFoundException: /createStaff.xhtml @33,125 value="#{staffBean.staff.firstName}"：目标无法到达， “空”返回空

我不明白为什么我在使用 value="#{staffBean.staff.firstName}" 时会遇到错误。当我使用上面的 value="#{staffBean.userName}" 和 value="#{staffBean.passWord}" 时没有问题。

这是我的 createStaff.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:p="http://primefaces.org/ui">
    <h:head>
        <title>Create Staff</title>
    </h:head>
    <h:body>
        <f:view>
            <h:form>
                <p:panel id ="panel" header="Staff Creation">
                    <p:messages id="msgs" />
                    <h:panelGrid columns="3" columnClasses="label, value">
                        <h:outputText value="Username: *" />
                        <p:inputText id="username" value="#{staffBean.userName}"   required="true" label="Username">
                        </p:inputText>
                        <p:message for="username" />

                        <h:outputLabel for="pwd1" value="Password 1: *" />
                        <p:password id="pwd1" value="#{staffBean.passWord}" match="pwd2" label="Password 1" required="true" feedback="true" />
                        <p:message for="pwd1" />

                        <h:outputLabel for="pwd2" value="Password 2: *" />
                        <p:password id="pwd2" value="#{staffBean.passWord}" label="Password 2" required="true" feedback="true" />
                        <p:message for="pwd2" />

                        <h:outputText value="First name: *" />
                        <p:inputText id="firstname" value="#{staffBean.staff.firstName}"   required="true" label="Username">
                        </p:inputText>
                        <p:message for="firstname" />

                        <h:outputText value="Last name: *" />
                        <p:inputText id="lastname" value="#{staffBean.staff.lastName}"   required="true" label="Username">
                        </p:inputText>
                        <p:message for="lastname" />

                        <h:outputText value="Last name: *" />
                        <p:selectOneRadio id="genderconsole" value="#{staffBean.staff.gender}" required="true">
                            <f:selectItem itemLabel="Male" itemValue="Male" />
                            <f:selectItem itemLabel="Female" itemValue="Female" />

                        </p:selectOneRadio>
                        <p:message for="genderconsole" />


                        <p:commandButton value="Create Staff" 
                                         id="ajax" 

                                         update="panel">

                        </p:commandButton>
                    </h:panelGrid>
                </p:panel>
            </h:form>
        </f:view>
    </h:body>
</html>

这是我的 StaffBean.java

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package managedbean;

import entities.Staff;
import java.io.IOException;
import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;
import javax.ejb.EJB;
import javax.enterprise.context.SessionScoped;
import javax.faces.FacesException;
import javax.faces.application.FacesMessage;
import javax.faces.context.ExternalContext;
import javax.faces.context.FacesContext;
import javax.faces.view.ViewScoped;
import javax.inject.Named;
import sessionBean.staffSessionBeanLocal;


@Named(value = "staffBean")
@SessionScoped
//@ViewScoped
public class StaffBean implements Serializable {

    @EJB
    private staffSessionBeanLocal staffSession;
    private String userName;
    private String passWord;
    private String loginStatus;
    private Staff staff;

...........
////Code removed

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public String getPassWord() {
        return passWord;
    }

    public void setPassWord(String passWord) {
        this.passWord = passWord;
    }

    public String getLoginStatus() {
        return loginStatus;
    }

    public void setLoginStatus(String loginStatus) {
        this.loginStatus = loginStatus;
    }

    public Staff getStaff() {
        return staff;
    }

    public void setStaff(Staff staff) {
        this.staff = staff;
    }

}

这是我的员工实体。

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */

package entities;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.ManyToMany;


@Entity
public class Staff extends User implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
    private String imageURL;
    @ManyToMany(cascade = {CascadeType.ALL}, fetch = FetchType.EAGER)
    private List<Roles> roles = new ArrayList<Roles>();

    @Override
    public Long getId() {
        return id;
    }

    @Override
    public void setId(Long id) {
        this.id = id;
    }

    @Override
    public int hashCode() {
        int hash = 0;
        hash += (id != null ? id.hashCode() : 0);
        return hash;
    }

    @Override
    public boolean equals(Object object) {
        // TODO: Warning - this method won't work in the case the id fields are not set
        if (!(object instanceof Staff)) {
            return false;
        }
        Staff other = (Staff) object;
        if ((this.id == null && other.id != null) || (this.id != null && !this.id.equals(other.id))) {
            return false;
        }
        return true;
    }

    @Override
    public String toString() {
        return "entities.Staff[ id=" + id + " ]";
    }

    public String getImageURL() {
        return imageURL;
    }

    public void setImageURL(String imageURL) {
        this.imageURL = imageURL;
    }

    public List<Roles> getRoles() {
        return roles;
    }

    public void setRoles(List<Roles> roles) {
        this.roles = roles;
    }

}

这是我的 User 类，Staff 类从它扩展而来。

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */

package entities;

import java.io.Serializable;
import java.sql.Timestamp;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.MappedSuperclass;


@MappedSuperclass
public class User implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
    private String password;
    private Timestamp joinDate;
    private String userType;
    private String gender;
    private String email;
    private String contactNo;
    private String firstName;
    private String lastName;
    private Timestamp dOB;
    private String address;
    private String accountStatus;
    private int numOfFailLogin;
    private String maritalStatus;
    private String activationCode;


    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    @Override
    public int hashCode() {
        int hash = 0;
        hash += (id != null ? id.hashCode() : 0);
        return hash;
    }

    @Override
    public boolean equals(Object object) {
        // TODO: Warning - this method won't work in the case the id fields are not set
        if (!(object instanceof User)) {
            return false;
        }
        User other = (User) object;
        if ((this.id == null && other.id != null) || (this.id != null && !this.id.equals(other.id))) {
            return false;
        }
        return true;
    }

    @Override
    public String toString() {
        return "entities.User[ id=" + id + " ]";
    }


    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public Timestamp getJoinDate() {
        return joinDate;
    }

    public void setJoinDate(Timestamp joinDate) {
        this.joinDate = joinDate;
    }

    public String getUserType() {
        return userType;
    }

    public void setUserType(String userType) {
        this.userType = userType;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getContactNo() {
        return contactNo;
    }

    public void setContactNo(String contactNo) {
        this.contactNo = contactNo;
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public Timestamp getdOB() {
        return dOB;
    }

    public void setdOB(Timestamp dOB) {
        this.dOB = dOB;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public String getAccountStatus() {
        return accountStatus;
    }

    public void setAccountStatus(String accountStatus) {
        this.accountStatus = accountStatus;
    }

    public String getMaritalStatus() {
        return maritalStatus;
    }

    public void setMaritalStatus(String maritalStatus) {
        this.maritalStatus = maritalStatus;
    }

    public int getNumOfFailLogin() {
        return numOfFailLogin;
    }

    public void setNumOfFailLogin(int numOfFailLogin) {
        this.numOfFailLogin = numOfFailLogin;
    }

    public String getActivationCode() {
        return activationCode;
    }

    public void setActivationCode(String activationCode) {
        this.activationCode = activationCode;
    }

}

【问题讨论】：

标签： jsf el propertynotfoundexception

【解决方案1】：

您的实体staff 中没有属性firstName

更新：

看起来你的staffobject 是空添加：

@PostConstruct
public void init() {
    staff = new Stuff();
}

【讨论】：

您好。我的用户实体中有 firstName 属性。员工扩展用户类。知道问题可能出在哪里吗？
@LawrenceWong 更新了我的答案。
谢谢！我的代码现在可以工作了。
我做了很多东西，我知道这是问题所在，但在这一点上我忘记了，浪费了很多时间，直到我到达这里。没有初始化对象是我的错误。

【解决方案2】：

错误提示当访问“firstName”时，无法访问。所以“工作人员”还没有建成。

向您的托管 bean 添加一个方法，这将解决问题。

@PostConstruct
public void init() {
    staff= new Staff ();
}

为了更好地理解为什么你应该这样做而不是不

职员职员 = new Staff();

JSF - what is the difference between @PostConstruct and direct method call from constructor?

【讨论】：

感谢您的链接。现在阅读。