Question

我在VM上运行了Hazelcast服务器实例。数据应该存储在MAP<Integer, User>中，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映射：

    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());

上面的代码为我提供了以下控制台输出：

    Map Size: 0
    Map Size: 1
    yes
    yes

以下行User queried = (User) map.get(1);的例外：

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

这是什么问题？为什么我无法读取我刚才放在地图中的数据？

以下是例外情况：

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，您的类似乎没有默认构造函数（没有参数的构造函数）。如果已使用参数集定义了构造函数，则编译器不会自动创建默认构造函数，您必须明确定义它。或者，您的类或构造函数可能不是公共作用域，而是包私有或私有。

public class User {

  // Fields

  public User() {
  }

  // Getters / Setters
}

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

1 个答案: