Java: 数据同步问题

Question

我的 Java 程序向客户端的 API 发出请求，客户端的 API 将 return 键值对 不规则 时间间隔（即不是每 5 秒/10 秒，有时是 1 秒或 5 秒）。

并且我已将我自己的代码 HashMap 插入到客户端 API 代码中以存储所有键值对。

我的目标是运行下面标有“!!!”的代码一旦 Hashmap 条件匹配。我不是 Java 数据同步方面的专家。请注意，Thread.Sleep(3000) 将不起作用，因为键值对会以不规则的时间间隔更新。而且，同一个键的值也会随着时间发生变化。我尝试了下面的运行程序，它立即运行通过标有“!!!”的代码块，这不是我想要实现的。

解决这个问题最有效的解决方案是什么？

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

覆盖你的客户端API（如果它没有关闭扩展）：

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 !!!!!!!!");
    }
    ...
}

然后简单地检查每个新出现的值。

要使用它，只需更改

ClientAPI clientAPI = new MyClientAPI();

解决此问题的另一种方法是为您的 ClientAPI class 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));
        ...
    }
    ...
}

那么，谁想知道什么时候有新值进入，只要实现这个接口即可，例如

...
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

每次更新都要检查HashMap的内容。为此，您可以在 Testing class 中注册一个侦听器，以便在 ClientAPI class.

中每次更新 HashMap 时触发

首先为监听器定义功能接口：

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

然后在ClientAPI

中添加监听器

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

定义onMapUpdate方法以在ClientAPI中传递监听器的正文:

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

并在 updateHashMapKeyValuePair

中的 HashMap 更新时触发侦听器

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方法中注册监听器并检查地图内容。这将在每次 ClientAPI 在 updateHashMapKeyValuePair 方法中接收新的地图内容时触发：

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 class:

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 class:

 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

Java: 数据同步问题

Java: data synchronization issue

java

volatile

data-synchronization