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Java对象引用问题?

builder-pattern object-reference builder java

1

SourceVisor · 技术社区 · 7 年前

public class Payload{

    private Map<String, Object> map;

    public static Payload INSTANCE = new Payload();

    private Payload(){
        map = new HashMap<>();
    }

    public Payload put(String key, Object value){
        map.put(key, value);
        return this;
    }

    public Map<String, Object> getMap(){
        return map;
    }
}

public class AjaxRequestBinder {

    private String url;
    private String method;
    private Map<String, Object> data;
    private String dataType;

    public AjaxRequestBinder(String url, String method, Payload payload, AjaxDataType dataType) {
        this.url = url;
        this.method = method;
        this.data = payload != null ? payload.getMap() : Payload.INSTANCE.getMap();
        this.dataType = dataType != null ? dataType.name() : AjaxDataType.html.name();
    }
    //... getters() & setters()
}

public List<AjaxRequestBinder> getSampleAjaxBinders() throws Exception {
    List<AjaxRequestBinder> requestBinders = new ArrayList<>();
    requestBinders.add(new AjaxRequestBinder(getEndpointURL(ServiceModule.CAT), HttpMethod.GET.name(), null, AjaxDataType.json));
    requestBinders.add(new AjaxRequestBinder(getEndpointURL(ServiceModule.DOG), HttpMethod.GET.name(), null, AjaxDataType.json));
    requestBinders.add(new AjaxRequestBinder(getEndpointURL(ServiceModule.CHICKEN), HttpMethod.GET.name(), null, AjaxDataType.json));
    requestBinders.add(new AjaxRequestBinder(getEndpointURL(ServiceModule.GOAT), HttpMethod.GET.name(), null, AjaxDataType.json));
    requestBinders.add(new AjaxRequestBinder(getEndpointURL(ServiceModule.RABBIT), HttpMethod.POST.name(), buildPayload(ServiceModule.RABBIT, HttpMethod.POST), AjaxDataType.json));
    return requestBinders;
}

public Payload buildPayload(ServiceModule module, HttpMethod httpMethod) throws Exception {
    Payload payload = Payload.INSTANCE;
    module = module != null ? module : ServiceModule.NONE;

    if(httpMethod.equals(HttpMethod.POST)){

        switch(module){
            case CAT:{
                // Do nothing
            }break;
            case DOG:{
                // Do nothing
            }break;
            case CHICKEN:{
                // Do nothing
            }break;
            case GOAT:{
                // Do nothing
            }break;
            case RABBIT:{
                payload.put("color", "white").put("action", "hops");
            }break;
        }
    }else{
        throw new NotYetImplementedException();
    }
    return payload;
}

getSampleAjaxBinders() 调用时,它返回一个 AjaxRequestBinder 每个人都拥有的对象;

data = {"color":"white", "action":"hops"}

然而,这仅适用于最后添加的项目。所有之前添加的项目都应该简单地具有 data = {} buildPayload(ServiceModule module, HttpMethod httpMethod)

谁能给我解释一下,是什么导致了这里出现的这个奇怪的物体参照问题;

1 回复 | 直到 7 年前

1

4

Sergey Kalinichenko 7 年前

Payload ,正好设置为 RABBIT

你的 buildPayload payload 设置为共享实例:

Payload payload = Payload.INSTANCE;

同时,当你经过的时候 null 有效载荷至 AjaxRequestBinder 构造函数,构造函数使用相同的 Payload.INSTANCE

this.data = payload != null ? payload.getMap() : Payload.INSTANCE.getMap();

你可以通过制作构造函数public并在中创建新实例 有效载荷 用于以下情况: 提供给 AjaxRequestBinder 建造商:

public static final Payload INSTANCE = new Payload();
// Add this line to Payload
public static final Payload EMPTY = new Payload();
...
// Use EMPTY payload when the caller does not supply an actual one:
this.data = payload != null ? payload.getMap() : Payload.EMPTY.getMap();

构建有效负载