arraylist上的并发修改

Question

public static void removeData(ServiceRequest r) {
    readData();
    ArrayList<ServiceRequest> targets = new ArrayList<ServiceRequest>();
    for (ServiceRequest s : serviceQueue) {  
    //ConcurrentModification Exception triggered on previous line
        if ( 
            s.getClient().getSms() == r.getClient().getSms() && 
            s.getTech().getName().equals(r.getTech().getName()) && 
            s.getDate().equals(r.getDate())) {
                JOptionPane.showMessageDialog(null, s.getClient().getSms() + "'s Service Request with " + s.getTech().getName() + " on " + s.getDate().toString() + " has been removed!");
                targets.add(s);
                System.out.print("targetted"); }
    }
    if (targets.isEmpty()) { System.out.print("*"); }
    else { 
        System.out.print("removed");
        serviceQueue.removeAll(targets); 
        writeData(); }
}
public static void addData(ServiceRequest r) {
    readData();
    removeData(r);
    if (r.getClient().getStatus().equals("MEMBER") || r.getClient().getStatus().equals("ALISTER")) {
        serviceQueue.add(r); } 
    else if (r.getClient().getStatus().equals("BANNED") || r.getClient().getStatus().equals("UNKNOWN")) {
        JOptionPane.showMessageDialog(null, "New Request failed: " + r.getClient().getSms() + " is " + r.getClient().getStatus() + "!", "ERROR: " + r.getClient().getSms(), JOptionPane.WARNING_MESSAGE);
    }
    else {
        int response = JOptionPane.showConfirmDialog(null, r.getClient().getSms() + " is " + r.getClient().getStatus() + "...", "Manually Overide?", JOptionPane.OK_CANCEL_OPTION);
        if (response == JOptionPane.OK_OPTION) {
            serviceQueue.add(r); }
    }
    writeData(); }

public static void readData() {
    try {
        Boolean complete = false;
        FileReader reader = new FileReader(f);
        ObjectInputStream in = xstream.createObjectInputStream(reader);
        serviceQueue.clear();
        while(complete != true) {   
            ServiceRequest test = (ServiceRequest)in.readObject();      
            if(test != null && test.getDate().isAfter(LocalDate.now().minusDays(180))) { 
                serviceQueue.add(test); }
                else { complete = true; }
        }
        in.close(); } 
    catch (IOException | ClassNotFoundException e) { e.printStackTrace(); } 
}
public static void writeData() {
    if(serviceQueue.isEmpty()) { serviceQueue.add(new ServiceRequest()); }
    try {
        FileWriter writer = new FileWriter(f);
        ObjectOutputStream out = xstream.createObjectOutputStream(writer);
        for(ServiceRequest r : serviceQueue) { out.writeObject(r); }
        out.writeObject(null);
        out.close(); }
    catch (IOException e) { e.printStackTrace(); }
}

编辑

这些更改导致并发mod每次触发而不是断断续续地触发，我想这意味着删除代码更好，但现在错误在it.remove()；触发

public static void removeData(ServiceRequest r) {
    readData();
    for(Iterator<ServiceRequest> it = serviceQueue.iterator(); it.hasNext();) {
        ServiceRequest s = it.next();
        if ( 
            s.getClient().getSms() == r.getClient().getSms() && 
            s.getTech().getName().equals(r.getTech().getName()) && 
            s.getDate().equals(r.getDate())) {
                JOptionPane.showMessageDialog(null, s.getClient().getSms() + "'s Service Request with " + s.getTech().getName() + " on " + s.getDate().toString() + " has been removed!");
                it.remove();  //Triggers here (line 195)
                System.out.print("targetted"); }
    }
    writeData(); }

线程“awt-eventqueue-0”java.util.concurrentModificatio中的异常nException at java.util.arrayList$itr.checkforcoModification(arrayList.java:901)at java.util.arrayList$itr.next(arrayList.java:851)at data.serviceRequest.removeData(serviceRequest.java:195)at data.serviceRequest.addData(serviceRequest.java:209)<...>

编辑经过更多的搜索，我已经将for循环切换到：

        Iterator<ServiceRequest> it = serviceQueue.iterator();
        while(it.hasNext()) {

又回到了间歇性触发。我的意思是，当我第一次尝试导入数据时（removeData方法是从addData方法触发的），它会触发并发mod异常，但下一次尝试时，它会推过失败并转移到另一个文件。我知道有很多这些并发的mod问题，但我没有找到任何对我的情况有帮助的东西，所以链接到其他答案是非常受欢迎的...

Answer 1

这不是怎么做的，在遍历列表时删除元素，您使用迭代器。像这样：

List<ServiceRequest> targets = new ArrayList<ServiceRequest>();
for(Iterator<ServiceRequest> it = targets.iterator(); it.hasNext();) {
    ServiceRequest currentServReq = it.next();
    if(someCondition) {
        it.remove();
    }
}

如果只有一个线程，则不会以这种方式获得ConcurrentModificationException。

如果代码中涉及多个线程，则仍可能获得ConcurrentModificationException。解决这个问题的一种方法是使用collections.synchronizedCollection（...）因此，您将获得一个不会产生ConcurrentModificationException的同步集合。但是，您的代码可能会变得非常慢。