Java:数据同步问题

Question

我的Java程序向客户端的API发出请求，客户端API将在不规则的时间间隔上返回一个键值对(即不是每5秒/10秒，有时是1秒或5秒)。

我已经将自己的代码( HashMap )插入到客户端API代码中，以存储所有的键值对。

我的目标是运行下面标记为“！”的代码一旦Hashmap条件匹配。我不是Java数据同步方面的专家。注意，Thread.Sleep(3000)不能工作，因为键值对是在不规则的时间间隔上更新的。此外，同一键的值也会随着时间的推移而变化。我试着运行下面的程序，它立即通过标记为“！”的代码块运行，这不是我想要实现的。

解决这个问题最有效的办法是什么？

Class Testing{
    public static void main(String[] args){
        // connect to API...
        ClientAPI clientAPI = new ClientAPI();
        clientAPI.connect();

        // make a request to retrieve an update of a HashMap
        clientAPI.requestHashMapUpdate();

        // !!! execute the following block of code only if hashmap contains a specific key value pair, i.e. key1, 1 
        // if hashmap does not contain key or the key-value pair do not match , then wait until the key-value pair are matched and run the code
        if(clientAPI.getMyHashMap().containsKey("key1")){
            if(clientAPI.getMyHashMap().get("key1") == 1){
                    System.out.println("Print Me only if key and value are matched !!!!!!!!");
            }
        }

    }
}


Class ClientAPI{
    private HashMap<String,Integer> myHashMap;
    
    // Constructor
    public clientAPI(){
            myHashMap = new HashMap<String,Integer>();
    }

    // callback function of API's requestHashMapUpdate method
    public void updateHashMapKeyValuePair(String key, int value){
        System.out.println("Key:" + key + ", Value: " + value);
        // code i wrote to update hashmap with key value pair returned from API
        myHashMap.put(key,value);
    }

    // my code to retrieve the latest snapshot of myHashMap
    public HashMap<String,Integer> getMyHashMap(){
        return myHashMap;
    }

}

Answer 1

重写客户端API (如果未关闭扩展)：

class MyClientAPI extends ClientAPI {
    ...
    @Override
    public void updateHashMapKeyValuePair(String key, int value) {
        super.updateHashMapKeyValuePair(key, value);
        if("key1".equals(key) && 1 == value)
            System.out.println("Print Me only if key and value are matched !!!!!!!!");
    }
    ...
}

只需检查每一个新值就行了。

要使用它，只需改变

ClientAPI clientAPI = new MyClientAPI();

解决此问题的另一种方法是为ClientAPI类提供注册侦听器的能力。

interface UpdateHashMapKeyValuePairListener {
    void digestUpdate(String key, int value);
}

class ClientAPI {
    ...
    private List<UpdateHashMapKeyValuePairListener> listeners = new ArrayList();
    ...
    public void registerUpdateListener(UpdateHashMapKeyValuePairListener u) {
        listeners.add(u);
    }
    ...
    public void updateHashMapKeyValuePair(final String key, final int value) {
        listeners.forEach(u -> u.digestUpdate(key, value));
        ...
    }
    ...
}

然后，任何想知道什么时候有新值进入的人，只要实现这个接口就可以了。

...
clientAPI.registerUpdateListener((key, value) -> {
    if("key1".equals(key) && 1 == value)
        System.out.println("Print Me only if key and value are matched !!!!!!!!");
});
clientAPI.connect();
...

Answer 2

每次更新HashMap时检查它的内容。为此，您可以在Testing类中注册侦听器，以便每次在ClientAPI类中更新HashMap时触发侦听器。

首先定义侦听器的功能接口：

 @FunctionalInterface
  public interface OnUpdateMapListener {
      void onUpdateMap(Map<String, Integer> map);
  }

然后在ClientAPI中添加侦听器

 public class ClientAPI {
        private HashMap<String, Integer> myHashMap;
        private OnUpdateMapListener onUpdateMapListener;

定义onMapUpdate方法以在ClientAPI中传递侦听器的主体

public void onMapUpdate(OnUpdateMapListener onUpdateMapListener) {
        this.onUpdateMapListener = onUpdateMapListener;
}

并在HashMap更新时在updateHashMapKeyValuePair中触发侦听器

public void updateHashMapKeyValuePair(String key, int value) {
  System.out.println("Key:" + key + ", Value: " + value);
  // code i wrote to update hashmap with key value pair returned from API
   myHashMap.put(key, value);
   onUpdateMapListener.onUpdateMap(myHashMap);
 }

在main方法中，注册侦听器并检查映射内容。每当ClientAPI在updateHashMapKeyValuePair方法中接收到新的Map内容时，都会触发这一点：

clientAPI.onMapUpdate(stringIntegerHashMap -> {
      // !!! the following code is executed every time the hashMap is updated
       if (clientAPI.getMyHashMap().containsKey("key1")) {
           if (clientAPI.getMyHashMap().get("key1") == 1) {
             System.out.println("Print Me only if key and value are matched !!!!!!!!");
           }
      }
});

ClientAPI类：

public class ClientAPI {
    private HashMap<String, Integer> myHashMap;

    private OnUpdateMapListener onUpdateMapListener;

    // Constructor
    public ClientAPI() {
        myHashMap = new HashMap<String, Integer>();
    }

    // callback function of API's requestHashMapUpdate method
    public void updateHashMapKeyValuePair(String key, int value) {
        System.out.println("Key:" + key + ", Value: " + value);
        // code i wrote to update hashmap with key value pair returned from API
        myHashMap.put(key, value);
        onUpdateMapListener.onUpdateMap(myHashMap);
    }

    // my code to retrieve the latest snapshot of myHashMap
    public HashMap<String, Integer> getMyHashMap() {
        return myHashMap;
    }

    public void requestHashMapUpdate() {
      //.....
    }

    public void onMapUpdate(OnUpdateMapListener onUpdateMapListener) {
        this.onUpdateMapListener = onUpdateMapListener;
    }
}

Testing类：

 public static void main(String[] args) {
      // connect to API...
        ClientAPI clientAPI = new ClientAPI();
        clientAPI.connect();

        // make a request to retrieve an update of a HashMap
       clientAPI.requestHashMapUpdate();

        clientAPI.onMapUpdate(stringIntegerHashMap -> {
            // !!! the following code is executed every time the hashMap is updated
            if (clientAPI.getMyHashMap().containsKey("key1")) {
                if (clientAPI.getMyHashMap().get("key1") == 1) {
                    System.out.println("Print Me only if key and value are matched !!!!!!!!");
                }
            }
        });

        clientAPI.updateHashMapKeyValuePair("key1", 1);
        clientAPI.updateHashMapKeyValuePair("key1", 2);
    }

结果：

Key:key1, Value: 1
Print Me only if key and value are matched !!!!!!!!
Key:key1, Value: 2