JAVAutil。在Java中将映射转换为ConcurrentMap时发生并发错误

Question

我有一个Map<String,Object>要转换成ConcurrentMap<String,Object>

    Map<String,Object> testMap = new HashMap<String,Object>();
    testMap.put("test", null); //This null causing issues in conversion
    testMap.put("test2","123");
    testMap.put("test3",234);
    ConcurrentMap<String,Object> concMap = new ConcurrentHashMap<>(testMap);

我得到一个空指针异常。如果我复制到一个新的HashMap<String,Object>

    Map<String,Object> testMap = new HashMap<String,Object>();
    testMap.put("test", null);
    testMap.put("test2","123");
    testMap.put("test3",234);
    Map<String,Object> concMap = new HashMap<>(testMap);

我没有任何错误。没有NullPointerException有没有安全的方法从Map<String,Object>到ConcurrentMap<String,Object>

Answer 1

在documentation for ^{}中：

Like Hashtable but unlike HashMap, this class does not allow null to be used as a key or value.

至于其他ConcurrentMaps，the only other implementation ^{}, does not allow null either

Answer 2

如果您查看ConcurrentHashMap的源代码，就会发现它不允许空键或空值-

java.util.concurrent.ConcurrentHashMap#putVal

/** Implementation for put and putIfAbsent */
final V putVal(K key, V value, boolean onlyIfAbsent) {
    if (key == null || value == null) throw new NullPointerException();