map - Hazelcast IMap.get() 抛出 HazelcastSerializationException，但 IMap.put() 工作正常

Question

我有一个在 VM 上运行的 Hazelcast 服务器实例。数据应该存储在 MAP<Integer, User> ，其中User类如下:

public class User implements com.hazelcast.nio.serialization.DataSerializable{
    private Integer id;
    private String name;
    private String nick;
    private Boolean sex;

    //getters & setters

    @Override
    public void writeData(ObjectDataOutput out) throws IOException{
        out.writeInt(id.intValue());
        out.writeUTF(name);
        out.writeUTF(nick);
        out.writeBoolean(sex);
    }

    @Override
    public void readData(ObjectDataInput in) throws IOException{       
        id = (Integer) in.readInt();
        name = in.readUTF();
        nick = in.readUTF();
        sex = in.readBoolean();
    }

我使用客户端实例连接到此服务器并尝试将对象添加到该 map :

    System.out.println("Map Size: " + map.size());
    map.put(1, user);
    System.out.println("Map Size: " + map.size());

    System.out.println(map.containsKey(1) ? "yes":"no");
    System.out.println(map.containsValue(user) ? "yes":"no");
    User queried = (User) map.get(1);    /*this is line 64*/

    System.out.println(queried.toString());

上面的代码给了我以下控制台输出:

    Map Size: 0
    Map Size: 1
    yes
    yes

还有以下 User queried = (User) map.get(1); 行的异常:

Problem while reading DataSerializable, namespace: 0, id: 0, class: com.blabla.User, exception: com.blabla.User.<init>()

这里有什么问题？为什么我无法读取刚刚放入 Map 的数据？

以下是异常详情:

com.hazelcast.nio.serialization.DataSerializer.read(DataSerializer.java:114)
    com.hazelcast.nio.serialization.DataSerializer.read(DataSerializer.java:36)
    com.hazelcast.nio.serialization.StreamSerializerAdapter.read(StreamSerializerAdapter.java:59)
    com.hazelcast.nio.serialization.SerializationServiceImpl.toObject(SerializationServiceImpl.java:218)
    com.hazelcast.client.spi.impl.ClientClusterServiceImpl._sendAndReceive(ClientClusterServiceImpl.java:172)
    com.hazelcast.client.spi.impl.ClientClusterServiceImpl.sendAndReceive(ClientClusterServiceImpl.java:137)
    com.hazelcast.client.spi.impl.ClientInvocationServiceImpl.invokeOnTarget(ClientInvocationServiceImpl.java:42)
    com.hazelcast.client.spi.impl.ClientInvocationServiceImpl.invokeOnKeyOwner(ClientInvocationServiceImpl.java:53)
    com.hazelcast.client.proxy.ClientMapProxy.invoke(ClientMapProxy.java:492)
    com.hazelcast.client.proxy.ClientMapProxy.get(ClientMapProxy.java:83)
    com.blabla.HazelcastFactory.insertUser(HazelcastFactory.java:64)

java.lang.NoSuchMethodException: com.dileky.User.<init>()
    java.lang.Class.getConstructor0(Class.java:2800)
    java.lang.Class.getDeclaredConstructor(Class.java:2043)
    com.hazelcast.nio.ClassLoaderUtil.newInstance(ClassLoaderUtil.java:54)
    com.hazelcast.nio.ClassLoaderUtil.newInstance(ClassLoaderUtil.java:50)
    com.hazelcast.nio.serialization.DataSerializer.read(DataSerializer.java:103)
    com.hazelcast.nio.serialization.DataSerializer.read(DataSerializer.java:36)
    com.hazelcast.nio.serialization.StreamSerializerAdapter.read(StreamSerializerAdapter.java:59)
    com.hazelcast.nio.serialization.SerializationServiceImpl.toObject(SerializationServiceImpl.java:218)
    com.hazelcast.client.spi.impl.ClientClusterServiceImpl._sendAndReceive(ClientClusterServiceImpl.java:172)
    com.hazelcast.client.spi.impl.ClientClusterServiceImpl.sendAndReceive(ClientClusterServiceImpl.java:137)
    com.hazelcast.client.spi.impl.ClientInvocationServiceImpl.invokeOnTarget(ClientInvocationServiceImpl.java:42)
    com.hazelcast.client.spi.impl.ClientInvocationServiceImpl.invokeOnKeyOwner(ClientInvocationServiceImpl.java:53)
    com.hazelcast.client.proxy.ClientMapProxy.invoke(ClientMapProxy.java:492)
    com.hazelcast.client.proxy.ClientMapProxy.get(ClientMapProxy.java:83)
    com.blabla.HazelcastFactory.insertUser(HazelcastFactory.java:64)

Answer 1

从堆栈跟踪看来，您的类没有默认构造函数(没有参数的构造函数)。如果您定义了带有参数集的构造函数，则编译器不会自动创建默认构造函数，您必须显式定义它。或者，您的类或构造函数可能不是公共(public)范围的，而是包私有(private)或私有(private)的。

public class User {

  // Fields

  public User() {
  }

  // Getters / Setters
}