Jackson：无法反序列化 START_OBJECT 令牌中的 Number 实例

我的 GWT 服务返回LinkedList<VisualData>。就是这样VisualData looks:

import javax.xml.bind.annotation.XmlRootElement;
import com.google.gwt.user.client.rpc.IsSerializable;

@XmlRootElement
public class VisualData implements IsSerializable {
    private Number value;
    private long timestamp;

    public VisualData() {
    }

    public VisualData(Number value, long timestamp) {
        this.value = value;
        this.timestamp = timestamp;
    }

    public long getTimestamp() {
        return timestamp;
    }

    public Number getValue() {
        return value;
    }

    public void setTimestamp(long timestamp) {
        this.timestamp = timestamp;
    }

    public void setValue(Number value) {
        this.value = value;
    }
}

我得到以下与字段相关的异常private Number value.

SEVERE: The exception contained within MappableContainerException could not be mapped to a response, re-throwing to the HTTP container
org.codehaus.jackson.map.JsonMappingException: Can not deserialize instance of java.lang.Number out of START_OBJECT token
at [Source: org.apache.catalina.connector.CoyoteInputStream@a0eb51; line: 1, column: 29] (through reference chain: org.jage.charts.client.VisualData["value"])

当我改变时private Number value to private Object value，我得到的所有 getter 和 setter：

SEVERE: WebModule[/AgECharts]Exception while dispatching incoming RPC call
com.google.gwt.user.client.rpc.SerializationException: Type 'org.jage.charts.client.VisualData' was not included in the set of types which can be serialized by this SerializationPolicy or its Class object could not be loaded. For security purposes, this type will not be serialized.: instance = Value:{@type=xs:int, $=6}, timestamp:1360240281439
at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serialize(ServerSerializationStreamWriter.java:619)

第二种情况很清楚，Object类不可序列化。但为什么我得到Can not deserialize instance of java.lang.Number out of START_OBJECT token?

如果不为您的对象提供额外的类型信息，您将无法将数据反序列化到该对象中。value场地。这是因为Number类是抽象的，不能被实例化。将字段更改为Object不会有帮助，因为该类上没有杰克逊无法将数据反序列化到的可编辑字段。

您应该将该字段更改为该字段的具体实现之一Number class (Integer, Long, Double etc).