Deserialization throwing ClassNotFoundException for object in object

Question

I'm trying to serialize and deserialize an object, which has a Liferay User object in it (which basically it's a UserImpl). The serialization/deserialization occurs in the API library which is used in other projects.

This is my object:

public class ObjectDTO implements Serializable {

    private static final long serialVersionUID = 1927888580878066482L;

    private User user;
    private String string1;
    private String string2;

    public ObjectDTO() {
    }

        //getters, setters  

}

The method where the serialization/deserialization occurs:

            ByteArrayOutputStream bos = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(bos);
        oos.writeObject(obj);

        byte[] bytes = bos.toByteArray();

        oos.close();
        bos.close();

        ByteArrayInputStream bis = new ByteArrayInputStream(bytes);
        ObjectInputStream ois = new ObjectInputStream(bis);

        Object o = ois.readObject();

        ois.close();
        bis.close();

        return o;

The serialization works, and in a few line I make the deserialization, and this does not work. It throws a ClassNotFoundException for UserImpl:

java.lang.ClassNotFoundException: com.liferay.portal.model.impl.UserImpl
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1645)
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1491)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:247)
at java.io.ObjectInputStream.resolveClass(ObjectInputStream.java:604)
at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1575)
at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1496)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1732)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1329)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1947)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1871)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1753)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1329)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:351)
at com.sample.services.service.ClpSerializer.translateOutputGeneric(ClpSerializer.java:431)
at com.sample.services.service.ClpSerializer.translateOutput(ClpSerializer.java:490)
at com.sample.services.service.EntityServiceClp.getEntityByUserId(EntityServiceClp.java:62)
at com.sample.services.service.EntityServiceUtil.getEntityByUserId(EntityServiceUtil.java:45)
at com.sample.portlet.Portlet.showPortlet(Portlet.java:57)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:176)
at org.springframework.web.portlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:358)
at org.springframework.web.portlet.mvc.annotation.AnnotationMethodHandlerAdapter.doHandle(AnnotationMethodHandlerAdapter.java:345)
at org.springframework.web.portlet.mvc.annotation.AnnotationMethodHandlerAdapter.handleRender(AnnotationMethodHandlerAdapter.java:288)
at org.springframework.web.portlet.DispatcherPortlet.doRenderService(DispatcherPortlet.java:734)
at org.springframework.web.portlet.FrameworkPortlet.processRequest(FrameworkPortlet.java:522)
at org.springframework.web.portlet.FrameworkPortlet.doDispatch(FrameworkPortlet.java:470)
at javax.portlet.GenericPortlet.render(GenericPortlet.java:233)
at com.liferay.portlet.FilterChainImpl.doFilter(FilterChainImpl.java:101)
at com.liferay.portal.kernel.portlet.PortletFilterUtil.doFilter(PortletFilterUtil.java:64)
at com.liferay.portal.kernel.servlet.PortletServlet.service(PortletServlet.java:92)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:646)
at org.apache.catalina.core.ApplicationDispatcher.doInclude(ApplicationDispatcher.java:551)
at org.apache.catalina.core.ApplicationDispatcher.include(ApplicationDispatcher.java:488)
at com.liferay.portlet.InvokerPortletImpl.invoke(InvokerPortletImpl.java:639)
at com.liferay.portlet.InvokerPortletImpl.invokeRender(InvokerPortletImpl.java:724)
at com.liferay.portlet.InvokerPortletImpl.render(InvokerPortletImpl.java:426)
at org.apache.jsp.html.portal.render_005fportlet_jsp._jspService(render_005fportlet_jsp.java:1387)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:377)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:646)
at org.apache.catalina.core.ApplicationDispatcher.doInclude(ApplicationDispatcher.java:551)
at org.apache.catalina.core.ApplicationDispatcher.include(ApplicationDispatcher.java:488)
at com.liferay.portal.util.PortalImpl.renderPortlet(PortalImpl.java:3859)
at com.liferay.portal.util.PortalUtil.renderPortlet(PortalUtil.java:1222)
at com.liferay.portlet.layoutconfiguration.util.RuntimePortletUtil.processPortlet(RuntimePortletUtil.java:160)
at com.liferay.portlet.layoutconfiguration.util.RuntimePortletUtil.processPortlet(RuntimePortletUtil.java:94)
at com.liferay.portlet.layoutconfiguration.util.RuntimePortletUtil.processTemplate(RuntimePortletUtil.java:256)
at com.liferay.portlet.layoutconfiguration.util.RuntimePortletUtil.processTemplate(RuntimePortletUtil.java:181)
at org.apache.jsp.html.portal.layout.view.portlet_jsp._jspService(portlet_jsp.java:761)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:377)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:646)
at org.apache.catalina.core.ApplicationDispatcher.doInclude(ApplicationDispatcher.java:551)
at org.apache.catalina.core.ApplicationDispatcher.include(ApplicationDispatcher.java:488)
at com.liferay.portal.action.LayoutAction.includeLayoutContent(LayoutAction.java:364)
at com.liferay.portal.action.LayoutAction.processLayout(LayoutAction.java:623)
at com.liferay.portal.action.LayoutAction.execute(LayoutAction.java:232)
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:431)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:236)
at com.liferay.portal.struts.PortalRequestProcessor.process(PortalRequestProcessor.java:154)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)
at org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:414)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
at com.liferay.portal.servlet.MainServlet.callParentService(MainServlet.java:520)
at com.liferay.portal.servlet.MainServlet.service(MainServlet.java:497)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:126)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:126)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.servlet.filters.strip.StripFilter.processFilter(StripFilter.java:309)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:123)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.servlet.filters.themepreview.ThemePreviewFilter.processFilter(ThemePreviewFilter.java:88)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:123)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.servlet.filters.gzip.GZipFilter.processFilter(GZipFilter.java:121)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:123)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.servlet.filters.secure.SecureFilter.processFilter(SecureFilter.java:182)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:123)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.servlet.filters.autologin.AutoLoginFilter.processFilter(AutoLoginFilter.java:239)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:123)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:646)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:436)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:374)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:302)
at com.liferay.portal.servlet.FriendlyURLServlet.service(FriendlyURLServlet.java:134)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:126)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:126)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.servlet.filters.strip.StripFilter.processFilter(StripFilter.java:261)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:123)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.servlet.filters.themepreview.ThemePreviewFilter.processFilter(ThemePreviewFilter.java:88)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:123)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.servlet.filters.gzip.GZipFilter.processFilter(GZipFilter.java:110)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:123)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.servlet.filters.secure.SecureFilter.processFilter(SecureFilter.java:182)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:123)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.servlet.filters.i18n.I18nFilter.processFilter(I18nFilter.java:222)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:123)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:126)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:126)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:126)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.servlet.filters.autologin.AutoLoginFilter.processFilter(AutoLoginFilter.java:239)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:123)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:646)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:436)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:374)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:302)
at com.liferay.portal.servlet.filters.virtualhost.VirtualHostFilter.processFilter(VirtualHostFilter.java:280)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:123)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.servlet.filters.absoluteredirects.AbsoluteRedirectsFilter.processFilter(AbsoluteRedirectsFilter.java:85)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:123)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:126)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:126)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.tuckey.web.filters.urlrewrite.UrlRewriteFilter.doFilter(UrlRewriteFilter.java:738)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:126)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.servlet.filters.threadlocal.ThreadLocalFilter.processFilter(ThreadLocalFilter.java:52)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:123)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.liferay.portal.kernel.servlet.BaseFilter.processFilter(BaseFilter.java:196)
at com.liferay.portal.kernel.servlet.BaseFilter.doFilter(BaseFilter.java:126)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:470)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:857)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
at java.lang.Thread.run(Thread.java:619)

Any ideas or leads about this one?

Answer 1

Looks like User is an interface and you are using UserImpl as implementation class for this interface, UserImpl should also be implementing interface Serializable if that needs to be serialized.

Additionally, in case you wish not to serialize a member you can declare it transient.

Cheers !!

Answer 2

The interface User is contained in portal-service.jar, which is on the global classpath. The implementation class, UserImpl is in portal-impl.jar which is in Liferay's webapplication's local classpath (e.g. in WEB-INF/lib) and you cannot get at it. I'd say you shouldn't rely on serializing this object - after all, you would never know if you can deserialize it again.

Rather have purely the userid in your own serialized object and fetch it again from database when you need to deserialize.

This is the way Liferay's servicebuilder makes objects available to all webapplications, despite the implementation of services and objects living purely within one application.

If you're tempted to add portal-impl.jar to your own application's classpath: It will not work! You'll run into all kinds of other issues, unrelated to the problem you're trying to solve. You'll need to find a different solution for the underlying problem.