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当从JSON(Gson)反序列化时,如何初始化PropertyChangeSupport?

propertychangesupport json-deserialization gson java

codenamezero · 技术社区 · 7 年前

PropertyChangeSupport ,但当我从json字符串反序列化时,变量 propertyChangeSupport null ,尽管我用一个 new PropertyChangeSupport(this) 在默认构造函数中。如何使用Gson正确初始化或反序列化它?

public class Blah implements BlahInterface {
    private PropertyChangeSupport propertyChangeSupport;

    protected int id;
    protected BlahType type;

    public Blah() {
        propertyChangeSupport = new PropertyChangeSupport(this);
    }

    public int getId() {
        return id;
    }

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

    public BlahType getType() {
        return type;
    }

    public void setType(BlahType type) {
        this.type = type;
    }

    public void addPropertyChangeListener(PropertyChangeListener listener) {
        this.propertyChangeSupport.addPropertyChangeListener(listener);
    }

    public PropertyChangeListener[] getPropertyChangeListeners() {
        return this.propertyChangeSupport.getPropertyChangeListeners();
    }
}

new PropertyChangeSupport(this); 直接在一开始,也是不可能的。我有点想避免手动创建一个函数,例如 initializePropertyChangeSupport() 然后在反序列化后手动调用,因为这有点难看。

我想做的是:

JsonArray ja = json.get("blahs").getAsJsonArray();
ja.forEach(item -> {
    Blah blah = BlahInterface.Parse(item.toString());
    // But here I can't addPropertyChangeListener because propertyChangeSupport is null
    // vvvvvvvvvvvv
    blah.addPropertyChangeListener(new PropertyChangeListener() {

        @Override
        public void propertyChange(PropertyChangeEvent evt) {
            BlahState state = (BlahState) evt.getNewValue();
            Logger.debug("Property had been updated, " + state.toString());
        }
    });
});

这是我的json解析函数:

@SuppressWarnings("unchecked")
public static <T extends Blah> T Parse(String json) {
    Gson gson = new Gson();

    Blah t = new Blah(gson.fromJson(json, Blah.class));
    switch (t.getType()) {
        case blahone:
            return (T) gson.fromJson(json, BlahOne.class);
        default:
            return (T) t;
    }
};

1 回复 | 直到 7 年前

codenamezero 7 年前

这个问题的解决方案是实现 InstanceCreator<T> createInstance 函数,该函数依次返回具有 PropertyChangeSupport

public class Blah implements InstanceCreator<Blah> {
    private final transient PropertyChangeSupport pcs = new PropertyChangeSupport(this);

    ...

    public void addPropertyChangeListener(PropertyChangeListener listener) {
        this.pcs.addPropertyChangeListener(listener);
    }

    public void removePropertyChangeListener(PropertyChangeListener listener) {
        this.pcs.removePropertyChangeListener(listener);
    }

    @Override
    public Blah createInstance(Type type) {
        return new Blah();
    }   
}

注意:瞬态关键字在 pcs 只是为了让Gson在序列化期间跳过它,否则Gson将引发异常。