创建 h:selectOneMenu 时出现 java.util.ConcurrentModificationException

Question

我正在尝试创建一个 h:selectOneMenu

我收到了许多错误，但最新的一个在主题行中。我已经为此工作了一段时间，但我无法让它发挥作用。

请帮忙

JPA：

package com.homework.jpa

import java.io.Serializable;
import javax.persistence.*;
import java.math.BigDecimal;
import java.util.List;


/**
 * The persistent class for the GRIDMASTER database table.
 * 
 */
@Entity
@NamedQuery(name="Gridmaster.findAll", query="SELECT g FROM Gridmaster g")
public class Gridmaster implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    private long gridid;

    @Column(name="\"PROGRAM\"")
    private String program;

    public Gridmaster() {
    }

    public long getGridid() {
        return this.gridid;
    }

    public void setGridid(long gridid) {
        this.gridid = gridid;
    }


    public String getProgram() {
        return this.program;
    }

    public void setProgram(String program) {
        this.program = program;
    }
}

EJB：

import com.homework.jpa.*;

import java.util.List;

@Stateless
public class GridMasterBean {

    @PersistenceContext
    private EntityManager em;

        public List<Gridmaster> getDisplayGridList() {
            return em.createQuery("FROM Gridmaster m", Gridmaster.class).getResultList();
}

支持 bean：

@ManagedBean
public class gridMaster_backing {
    private static final String String = null;
    @EJB
    private GridMasterBean ejb;
    private List gridList = new ArrayList();    
    public String pickedGrid;

    public String getPickedGrid() {
        return pickedGrid;
    }

    public void setPickedgrid(String pickedGrid) {
        this.pickedGrid = pickedGrid;
    }

    public void setGridList(List gridList) {
        this.gridList = gridList;
    }

    public List getGridList() {
        // produces List of Grids
        gridList.clear();
        List gridList = ejb.getDisplayGridList();
            Iterator it  = gridList.iterator();
            while(it.hasNext()){
                 Gridmaster programCodes  = (Gridmaster)it.next();
                 SelectItem sItem = new SelectItem();
                 //Long GridId = Gridmaster.getGridid();

                 //String progName = programCodes.getDescription() + " -- " + programCodes.getProgramCode();
                 sItem.setLabel(program);
                 sItem.setValue(gridid);
                 gridList.add(sItem);
             }          
        return gridList; 
        }
    }

xhtml:

<h:selectOneMenu value="#{gridMaster_backing.pickedGrid}">
            <f:selectItems value="#{gridMaster_backing.gridList}" />

        </h:selectOneMenu>

Answer 1

问题是gridList.add(sItem)。您正在尝试在迭代列表时添加到列表中。而是使用索引迭代列表。然后在索引处添加。请务必在添加 at index 时相应地更新迭代器变量。