我试图附加到对象的hashmap，但read方法的输出即使在附加之后也保持不变（第一次和第二次称为read方法）。我在网上搜索了关于追加objectoutputstream的内容，根据答案我覆盖了 writeStreamHeader 子类中的方法 AppendableObjectOutputStream ，但对我不起作用。

public class MapObject {
public static void main(String args[]) {
    new MapObject();
}
public MapObject() {
    output1();       //createing objectOutputStream
    read();          //first time called read method    //output 15  20  14  12
    output2();       //appending to objectOutputStream
    read();          //second time called read method    //output 15  20  14  12
}
public void output1() {
    Map<Integer, List<Integer>> listMap = new HashMap<>();
    listMap.put(1, new ArrayList<>());
    listMap.get(1).add(15);
    listMap.get(1).add(20);
    listMap.put(2, new ArrayList<>());
    listMap.get(2).add(14);
    listMap.get(2).add(12);
    try {
        ObjectOutputStream objectOutputStream = new ObjectOutputStream(new BufferedOutputStream(new FileOutputStream(new File("map"))));
        objectOutputStream.writeObject(listMap);
        objectOutputStream.flush();
        objectOutputStream.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
}
public void output2() {
    Map<Integer, List<Integer>> listMap = new HashMap<>();
    listMap.put(1, new ArrayList<>());
    listMap.get(1).add(11);
    listMap.get(1).add(12);
    listMap.put(2, new ArrayList<>());
    listMap.get(2).add(21);
    listMap.get(2).add(22);
    try {
        AppendableObjectOutputStream appendableObjectOutputStream = new AppendableObjectOutputStream(new BufferedOutputStream(new FileOutputStream(new File("map"), true)));
        appendableObjectOutputStream.writeObject(listMap);
        appendableObjectOutputStream.flush();
        appendableObjectOutputStream.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
}
public void read() {
    ObjectInputStream objectInputStream = null;
    try {
        objectInputStream = new ObjectInputStream(new BufferedInputStream(new FileInputStream(new File("map"))));
        Map<Integer, List<Integer>> listMap = (Map<Integer, List<Integer>>) objectInputStream.readObject();
        listMap.values().forEach(v1 -> {
            v1.forEach(System.out::println);
        });
    } catch (IOException e) {
        e.printStackTrace();
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    }}
}

我发现objectoutputstream类的子类如下所示。

public class AppendableObjectOutputStream extends ObjectOutputStream {
public AppendableObjectOutputStream(OutputStream out) throws IOException {
    super(out);
}
@Override
protected void writeStreamHeader() throws IOException {
}}

对不起，英语不好。