Question

我有一个servlet，我想通过UrlConnection一些对象。当我测试它时，它工作正常。当我传递Java本机对象（String，File ..）时。但是当我尝试传递自己的Object（我自己的类的实例）时，Object通过ObjectOutputStream正确地发送到Servlet，但是当我想在servlet端恢复对象时，它不起作用。它抛出了我的课没有找到的异常。

我在项目中有MyObject类，其中applet加载并发送到servlet，然后我的servlet包中也有MyObject类...所以我必须放置MyObject上班吗？

这是我的applet代码，它通过MyObject

将URLConnection实例发送到servlet

  URLConnection con = null;
        ObjectOutputStream outputToServlet = null;
        ObjectInputStream inputFromServlet = null;
        MyObject my = new MyObject("200");
//open Url connection
        con = CommunicationAgent.openConnectionWithServlet(CommunicationAgent.setUrlForServletConnection());
        con.setDefaultUseCaches(false);
        con.setDoOutput(true);
        con.setDoInput(true);

// creating ObjectOutputStream
        try {
            outputToServlet = new ObjectOutputStream(con.getOutputStream());
        } catch (IOException ex) {
            Logger.getLogger(SoundAppletSimpleVersion.class.getName()).log(Level.SEVERE, null, ex);
        }

//Send MyObject instance to server      
        try {
            outputToServlet.writeObject(my);

        } catch (IOException ex) {
            Logger.getLogger(SoundAppletSimpleVersion.class.getName()).log(Level.SEVERE, null, ex);
        }

这是来自我的servlet的代码，从请求对象轻松获取流，然后我想将传入的对象复制到servlet中的MyObject实例。这是一个问题，抛出异常

ObjectInputStream input = new ObjectInputStream(request.getInputStream());
        MyObject my = null;
        try {
            my = (MyObject) input.readObject();
        } catch (ClassNotFoundException ex) {
            Logger.getLogger(Servlet.class.getName()).log(Level.SEVERE, null, ex);
            System.out.print("nepovedlo se precist objekt");
        }

Tomcat抛出异常

INFO: Reloading Context with name [/Rozhlas_jsf] is completed
XII 04, 2012 3:43:22 DOP. Servlets.Servlet processRequest
SEVERE: null
java.lang.ClassNotFoundException: SoundApplet.MyObject
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1711)
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1556)
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Class.java:264)
    at java.io.ObjectInputStream.resolveClass(ObjectInputStream.java:622)
    at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1593)
    at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1514)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1750)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1347)
    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:369)
    at Servlets.Servlet.processRequest(Servlet.java:42)
    at Servlets.Servlet.doPost(Servlet.java:120)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:641)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:225)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:169)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:927)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:999)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:565)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:307)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
    at java.lang.Thread.run(Thread.java:722)

来自Javaconsole

network: Connecting http://localhost:8084/Rozhlas_jsf/Servlet with proxy=DIRECT
XII 04, 2012 3:44:26 DOP. SoundApplet.SoundAppletSimpleVersion jButton8ActionPerformed
SEVERE: null
java.io.IOException: Server returned HTTP response code: 500 for URL: http://localhost:8084/Rozhlas_jsf/Servlet
    at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source)
    at SoundApplet.SoundAppletSimpleVersion.jButton8ActionPerformed(SoundAppletSimpleVersion.java:708)
    at SoundApplet.SoundAppletSimpleVersion.access$1000(SoundAppletSimpleVersion.java:27)
    at SoundApplet.SoundAppletSimpleVersion$12.actionPerformed(SoundAppletSimpleVersion.java:371)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
    at java.awt.Component.processMouseEvent(Unknown Source)
    at javax.swing.JComponent.processMouseEvent(Unknown Source)
    at java.awt.Component.processEvent(Unknown Source)
    at java.awt.Container.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$000(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)

Exception in thread "AWT-EventQueue-3" java.lang.NullPointerException
    at SoundApplet.SoundAppletSimpleVersion.jButton8ActionPerformed(SoundAppletSimpleVersion.java:717)
    at SoundApplet.SoundAppletSimpleVersion.access$1000(SoundAppletSimpleVersion.java:27)
    at SoundApplet.SoundAppletSimpleVersion$12.actionPerformed(SoundAppletSimpleVersion.java:371)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
    at java.awt.Component.processMouseEvent(Unknown Source)
    at javax.swing.JComponent.processMouseEvent(Unknown Source)
    at java.awt.Component.processEvent(Unknown Source)
    at java.awt.Container.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$000(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)

我想问题在于放置我的课程。我必须做些什么来正确地工作？我需要在servlet中接收MyObject实例，然后在servlet中与他一起工作。它适用于本机Java对象，因为Java无法在MyObject中找到SoundApplet.MyObject类。

在这种情况下，Java如何使用类。例如，当我发送FIle对象时，当我在servlet Java中收到它时，使用哪个类。来自我的Applet中的库的File类或来自projectwith servlet的库中的File类，或者它无关紧要？我真的很困惑这个问题，请尝试解释我和帮助。

这是MyObject类实际放置在web项目中已编译的SoundApplet.jar中的图像。 enter image description here

Answer 1

来自The Apache Tomcat 5.5 Servlet/JSP Container: Quick Start：

..

对于必须在所有Web应用程序中共享的类和资源，请将解压缩的类和资源放在$CATALINA_BASE/shared/classes下，或将包含这些类和资源的JAR文件放在$CATALINA_BASE/shared/lib下。

因此，如果SoundApplet.MyObject位于Jar（我推荐）中，请将其放在lib目录中。如果它不在Jar中，请将类文件放在classes/SoundApplet目录中。另外，包名称应为alllowercase，例如soundapplet。

另请注意，该类必须至少在 2个单独的位置，以供servlet和applet使用。上面概述了服务器类路径，但是applet（或者更确切地说是JVM）无法访问这些路径。

将自定义对象从applet传递到servlet

1 个答案: