java - 为什么在我使用 hibernate 时这个类应该实现 java.io.Serializable？

Question

此异常仅在使用 Tweet Class 时发生。我找不到应该使用 Serializable 的原因。我自己在 GeneticMessage.hbm.xml 中进行了映射。 Tweet 类中的所有类型(long 和 Date)都是 Hibernate 中的基本类型(我认为是)。

其实只要在Exception中提到的为Tweet实现Serializable就可以解决问题。但我还是想知道原因。

方法

Domain domain = (Domain) objects[0];Query q = session.createQuery("FROM PreprocessedMessage WHERE domain = ?");q.setEntity(0, domain);return q.list(); // this line

Exception:

java.lang.ClassCastException: idv.petrie.prtm.model.Tweet cannot be cast to java.io.Serializable    org.hibernate.type.CollectionType.getKeyOfOwner(CollectionType.java:381)    org.hibernate.type.CollectionType.resolve(CollectionType.java:425)    org.hibernate.engine.TwoPhaseLoad.initializeEntity(TwoPhaseLoad.java:139)    org.hibernate.loader.Loader.initializeEntitiesAndCollections(Loader.java:982)    org.hibernate.loader.Loader.doQuery(Loader.java:857)    org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:274)    org.hibernate.loader.Loader.doList(Loader.java:2533)    org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2276)    org.hibernate.loader.Loader.list(Loader.java:2271)    org.hibernate.loader.hql.QueryLoader.list(QueryLoader.java:452)    org.hibernate.hql.ast.QueryTranslatorImpl.list(QueryTranslatorImpl.java:363)    org.hibernate.engine.query.HQLQueryPlan.performList(HQLQueryPlan.java:196)    org.hibernate.impl.SessionImpl.list(SessionImpl.java:1268)    org.hibernate.impl.QueryImpl.list(QueryImpl.java:102)    idv.petrie.prtm.model.helper.PreprocessedMessageHelper$3.execute(PreprocessedMessageHelper.java:66)    idv.petrie.prtm.util.ModelHelper.execute(ModelHelper.java:36)    idv.petrie.prtm.model.helper.PreprocessedMessageHelper.findMessageByDomain(PreprocessedMessageHelper.java:69)    idv.petrie.prtm.servlet.MessageEvaluationServlet.doGet(MessageEvaluationServlet.java:44)    javax.servlet.http.HttpServlet.service(HttpServlet.java:621)    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

PreprocessedMessage.java

package idv.petrie.prtm.model;import java.util.Collection;import java.util.HashSet;import java.util.Set;public class PreprocessedMessage extends GeneticMessage {    private GeneticMessage message;    private Set dependencies;    private Set tokens;    public PreprocessedMessage() {        super();    }    public PreprocessedMessage(GeneticMessage message, String content) {        this();        this.setMessage(message);        this.setContent(content);        this.setDomain(message.getDomain());    }    public PreprocessedMessage(GeneticMessage message) {        this(message, message.getContent());    }    public PreprocessedMessage(GeneticMessage message,            Set dependencies) {        this(message);        this.dependencies = dependencies;    }    public static Collection convertToCollection(            Collection messages) {        Collection result = new HashSet();        for (GeneticMessage message : messages) {            result.add(new PreprocessedMessage(message));        }        return result;    }    public void setMessage(GeneticMessage message) {        this.message = message;    }    public GeneticMessage getMessage() {        return message;    }    public Set getDependencies() {        return dependencies;    }    public void setDependencies(Set dependencies) {        for (Dependency d : dependencies) {            d.setMessage(this);        }        this.dependencies = dependencies;    }    public Collection getTokens() {        return tokens;    }    public void setTokens(Set tokens) {        for (Token t : tokens) {            t.setMessage(this);        }        this.tokens = tokens;    }}

Tweet.java

package idv.petrie.prtm.model;import java.util.Date;public class Tweet extends GeneticMessage {    private long tweetId;    private Date createdAt;    private long fromUserId;    public Tweet() {        super();    }    public Tweet(String content) {        this();        setContent(content);    }    public Date getCreatedAt() {        return createdAt;    }    public void setCreatedAt(Date createdAt) {        this.createdAt = createdAt;    }    public long getFromUserId() {        return fromUserId;    }    public void setFromUserId(long fromUserId) {        this.fromUserId = fromUserId;    }    public void setTweetId(long tweetId) {        this.tweetId = tweetId;    }    public long getTweetId() {        return tweetId;    }}

GeneticMessage.java

package idv.petrie.prtm.model;import java.util.Date;public class GeneticMessage implements Comparable {    public enum Status {        NEW(0), PREPROCESSED(1);        private int id;        private Status(int id) {            this.id = id;        }        public int getId() {            return id;        }    }    private long id;    private Date modifiedAt;    private String content;    private Status status;    private Domain domain;    public GeneticMessage() {        setModifiedAt();        setStatus(Status.NEW);    }    public long getId() {        return id;    }    public void setId(long id) {        this.id = id;    }    public String getContent() {        return content;    }    public void setContent(String content) {        this.content = content;    }    public void setModifiedAt() {        this.modifiedAt = new Date();    }    public Date getModifiedAt() {        return modifiedAt;    }    public void setStatus(Status status) {        this.status = status;    }    public Status getStatus() {        return status;    }    public void setDomain(Domain domain) {        this.domain = domain;    }    public Domain getDomain() {        return domain;    }    public int compareTo(GeneticMessage o) {        String content = this.getContent();        String anotherContent = o.getContent();        return content.compareTo(anotherContent);    }    public void setModifiedAt(Date modifiedAt) {        this.modifiedAt = modifiedAt;    }}

GeneticMessage.hbm.xml

<code>
<?xml version="1.0" encoding="utf-8"?> 
<!DOCTYPE hibernate-mapping 
 PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>

    <typedef class="idv.petrie.prtm.model.GeneticMessage.Status"
        name="Status">
        <param name="enumClassName">idv.petrie.prtm.model.GeneticMessage.Status</param>
        <param name="identifierMethod">getId</param>
    </typedef>

    <class name="idv.petrie.prtm.model.GeneticMessage">
        <id name="id">
            <generator class="native" />
        </id>
        <property name="modifiedAt" />
        <property name="content" />
        <property name="status" />
        <many-to-one name="domain" class="idv.petrie.prtm.model.Domain"
            cascade="all" outer-join="true" />

        <joined-subclass name="idv.petrie.prtm.model.PreprocessedMessage">
            <key />
            <many-to-one name="message" class="idv.petrie.prtm.model.GeneticMessage"
                outer-join="true" />
            <set name="dependencies" cascade="save-update" inverse="true">
                <key property-ref="message" />
                <one-to-many class="idv.petrie.prtm.model.Dependency" />
            </set>
            <set name="tokens" cascade="save-update" inverse="true">
                <key property-ref="message" />
                <one-to-many class="idv.petrie.prtm.model.Token" />
            </set>
        </joined-subclass>

        <joined-subclass name="idv.petrie.prtm.model.Tweet">
            <key />
            <property name="tweetId" unique="true" />
            <property name="createdAt" />
            <property name="fromUserId" />
        </joined-subclass>
    </class>
</hibernate-mapping>
</code>

Answer 1

这个问题已经过去了 6 年，但对于那些偶然发现这个问题的人来说，这是我的 5 美分:

tweetId 可能不是 Tweet 的主键，这就是为什么它是唯一的类这需要是可序列化的。它被报告为 Hibernate 中的错误。 (https://hibernate.atlassian.net/browse/HHH-7668)。

总结:如果你想在 Hibernate 对象之间建立关系，只需使用主键作为链接列。否则，使链接的对象可序列化，这样也可以。 :-)