Java XStream删除集合中不需要的字段

我有一个对象“角色”，它可以包含几个“特权”，它们也是对象。现在，当我尝试用Xstream序列化角色时，我的xml如下所示：

  <role>
    <roleName>Administrator</roleName>
    <privileges class="org.hibernate.collection.PersistentSet">
      <set>
        <privilege>
          <privilegeId>1001</privilegeId>
          <privilegeName>Admin Privilege</privilegeName>
          <privilegeKey>Admin</privilegeKey>
        </privilege>
      </set>
      <initialized>true</initialized>
      <owner class="role" reference="../.."/>
      <cachedSize>-1</cachedSize>
      <rolemodel.valueobject.Role.privileges</role>
      <key class="int">3</key>
      <dirty>false</dirty>
      <storedSnapshot class="map">
        <entry>
          <privilege reference="../../../set/privilege"/>
          <privilege reference="../../../set/privilege"/>
        </entry>
      </storedSnapshot>
    </privileges>
  </role>

  <role>
    <roleName>Administrator</roleName>
    <privileges>
          <privilegeId>1001</privilegeId>
          <privilegeName>Admin Privilege</privilegeName>
          <privilegeKey>Admin</privilegeKey>
    </privileges>
  </role>

以及它产生的xml：

  <role>
    <roleId>3</roleId>
    <roleName>Web Administrator</roleName>
    <privileges>
      <privilege>Web Access</privilege>
    </privileges>
  </role>

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  <role>
    <roleId>3</roleId>
    <roleName>Web Administrator</roleName>
    <privileges>
      <privilege>Web Access</privilege>
    </privileges>
  </role>