A SimpleDataStore详解编程语言

import java.util.HashMap; 
import java.util.Map; 
import java.util.concurrent.ConcurrentHashMap; 
import java.util.concurrent.ConcurrentMap;

public interface DataStore { 
 
    /** 
     * return a snapshot value of componentName 
     */ 
    Map<String,Object> get(String componentName); 
 
    Object get(String componentName, String key); 
 
    void put(String componentName, String key, Object value); 
 
    void remove(String componentName, String key); 
 
}

public class SimpleDataStore implements DataStore { 
 
    // <组件类名或标识, <数据名, 数据值>> 
    private ConcurrentMap<String, ConcurrentMap<String, Object>> data = 
        new ConcurrentHashMap<String, ConcurrentMap<String,Object>>(); 
 
    public Map<String, Object> get(String componentName) { 
        ConcurrentMap<String, Object> value = data.get(componentName); 
        if(value == null) return new HashMap<String, Object>(); 
 
        return new HashMap<String, Object>(value); 
    } 
 
    public Object get(String componentName, String key) { 
        if (!data.containsKey(componentName)) { 
            return null; 
        } 
        return data.get(componentName).get(key); 
    } 
 
    public void put(String componentName, String key, Object value) { 
        Map<String, Object> componentData = data.get(componentName); 
        if(null == componentData) { 
            data.putIfAbsent(componentName, new ConcurrentHashMap<String, Object>()); 
            componentData = data.get(componentName); 
        } 
        componentData.put(key, value); 
    } 
 
    public void remove(String componentName, String key) { 
        if (!data.containsKey(componentName)) { 
            return; 
        } 
        data.get(componentName).remove(key); 
    } 
 
}