java jsp获取每个选定项目的列表

Question

我的目标是获取所选公司所有员工的列表。 正如您在问题末尾的 jsp 文件中看到的那样，我收到错误消息：

 {IndirectList: not instantiated}

您能帮我获取每个选定公司的所有员工列表吗？

公司.java

package analysis.data;
import java.io.Serializable;
import java.lang.Integer;
import java.lang.String;
import java.util.List;

import javax.persistence.*;

/**
 * Entity implementation class for Entity: Company
 *
 */
@Entity
public class Company implements Serializable {

    @Id
    @GeneratedValue
    private Integer id;

    @Column(unique=true, nullable=false) 
    private String lastname;

    @OneToMany(mappedBy="company", fetch=FetchType.LAZY)    // LAZY = fetch when needed, EAGER = fetch immediately
    private List<Employee> employees;

    private static final long serialVersionUID = 1L;

    public Company() {
        super();
    }   
    public Integer getId() {
        return this.id;
    }

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

    public String getLastname() {
        return this.lastname;
    }

    public void setLastname(String lastname) {
        this.lastname = lastname.toUpperCase();
    }

    public List<Employee> getEmployees() {
        return this.employees;
    }   
}

Employee.java

package analysis.data;
import java.io.Serializable;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToOne;

/**
 * Entity implementation class for Entity: Company
 *
 */
@Entity
public class Employee implements Serializable {

    @Id
    @GeneratedValue
    private Integer id;

    @Column(nullable=false) 
    private String firstname;

    @Column(nullable=false)
    private String lastname;    

    @ManyToOne
    private Company company;

    private static final long serialVersionUID = 1L;

    public Employee() {
        super();
        //nbAbsences = 0;
    }  

    public Integer getId() {
        return this.id;
    }

    public void setId(Integer id) {
        this.id = id;
    }   
    public String getFirstname() {
        return this.firstname;
    }

    public void setFirstname(String firstname) {
        this.firstname = firstname;
    }   
    public String getLastname() {
        return this.lastname;
    }

    public void setLastname(String lastname) {
        this.lastname = lastname;
    }

    public Company getCompany() {
        return this.company;
    }

    public void setCompany(Company company) {
        this.company = company;
        if (!company.getEmployees().contains(this)) {
            company.getEmployees().add(this);
        }
    }

    @Override
    public String toString() {
        return "[" + this.getId() + "] " + this.getFirstname() + " " + this.getLastname();
    }
}

在我的 controller.java 中

    public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {

....

        } else if (methode.equals("get") && action.equals("/detailsCompany")) {
            doDetailsCompany(request, response);
....

    private void doDetailsCompany(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        int id = Integer.valueOf(request.getParameter("id"));
        Company company = CompanyDAO.retrieveById(id);
        request.setAttribute("company", company);       
        loadJSP(urlDetailsCompany, request, response);
    }
....

在我的 CompanyDAO.java 中

public class CompanyDAO {

...

    public static Company retrieveById(int id) {            
            EntityManager em = GestionFactory.factory.createEntityManager();
            Company company = em.find(Company.class, id);
            em.close();
            return company;
        }

...

    public static List<Company> getAll() {
        EntityManager em = GestionFactory.factory.createEntityManager();
        Query q = em.createQuery("SELECT c FROM Company c");
        @SuppressWarnings("unchecked")
        List<Company> listCompany = q.getResultList();      
        return listCompany;
    }
}

在这里我选择公司名称（id）被重定向到 detailsCompany 以查看该公司的所有员工：

<jsp:useBean id="companys" type="java.util.List<analysis.data.Company>" scope="request"/>

    <table>
        <tr>
            <th>Company Name</th>
            <th>Number of employees</th>
            <th>Employees</th>
        </tr>
    <% for (Company company : companys) {%>
        <tr>
            <td><%=company.getNom()%></td>
            <td><%=company.getEmployees().size()%></td>
            <td><a href="<%= getServletContext().getContextPath()%>/do/detailsCompany?id=<%=company.getId()%>">See the list</a></td>
        </tr>
    <% } %>
    </table>

最后在我的detailsCompany.jsp JSP 文件中，我不知道如何提取每个所选公司的员工列表。

<jsp:useBean id="company" type="java.util.List<analysis.data.Company>" scope="request"/>

<p>Company : <%=company.getEmployees()%></p>

我明白了 {IndirectList：未实例化} 而不是员工名单。 我不确定我的代码这样做是否正确。

Answer 1

问题出在

`<%=company.getEmployees()%>`

getEmployees() 返回一个 List 对象，因此 JSP 调用它的 toString 函数，导致消息“IndirectList：未实例化”

如果您希望打印员工详细信息（即其 toString 方法的等价性），您可能希望执行以下操作：

`<p>Company : <% List<Employee> employees = company.getEmployees();
    for(i=0;i<employees.size();i++)%> 
        <%= employees.get(i);%>
</p>
`

您可能还想添加一些换行符来分隔各种员工记录。