应用服务器中的Java并发

Question

I have a small web application with CRUD operations. For the data, I can't use a db, so I must store it in a map or similar data structure. Based on the requirement, I need two maps to store and access the data, and I have to make sure they are in sync with each other. Now, the question, what is the preferred way to make crud operations on the two maps on in a multi threaded environment making sure they are in consistent state. Is there a better approach or pattern to avoid locking and synchronization?

Thanks

Answer 1

I believe there has to be some synchronization involved. You can try the following approach. First of all use a ConcurrentHashMap for both of your maps. Then encapsulate both your maps in an object that will have synchronized methods to ensure your data is in a consistent state. The following is an example:

public class ParentMap {
   private ConcurrentHashMap<String, Object> map1 = new ConcurrentHashMap<>();
   private ConcurrentHashMap<String, Object> map2 = new ConcurrentHashMap<>();

   public synchronized void add(Object objectToAdd) {
      // Add to map1 
      // Add to map2
   }

   public synchronized void update(String key, Object object) {
      // Update the object based on the key on both maps (following the rules of your application)
   }

   public synchronized void delete(String key) {
      // Delete in both maps following the rules of your application
   }

   public Object get(String key) {
      // Use the rules of your application to read
   }
}

Ensure that there is only one ParentMap object in your application. You may use the Singleton Pattern for this.