将自定义对象从 applet 传递到 servlet

【问题标题】：Passing custom Objects from applet to servlet将自定义对象从 applet 传递到 servlet
【发布时间】：2012-11-21 15:23:12
【问题描述】：

我有一个 servlet，我想通过 UrlConnection 一些对象。当我测试它时，它工作得很好。当我传递 Java 原生对象时（String、File..）。但是当我尝试传递我自己的Object（我自己的类的实例）时，对象通过ObjectOutputStream 正确发送到Servlet，但是当我想在servlet 端恢复对象时它不起作用。它会抛出未找到我的类的异常。

我在带有小程序的项目中有MyObject 类，它被加载并发送到servlet，然后我的servlet 包中也有MyObject 类...所以我必须将MyObject 类放在哪里才能工作？

这是我通过URLConnection 发送MyObject 实例到servlet 的小程序代码

  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，然后我想将传入对象复制到 servlet 中的 MyObject 实例。这是一个问题并抛出异常

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)

从 Java 控制台

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)

我想问题在于安排我的课程。我必须做什么才能正确工作？我需要将 MyObject 实例接收到 servlet 中，然后在 servlet 中与他一起工作。它适用于本机 Java 对象，为什么 Java 无法在 SoundApplet.MyObject 中找到 MyObject 类。

在这种情况下，Java 如何处理类。例如，当发送 FIle 对象时，当我在 servlet Java 中收到它时，使用哪个类。 File 我的 Applet 中的库中的类或 File 带有 servlet 的项目中的库中的类，或者没关系？我对这个问题真的很困惑，请尝试向我解释并提供帮助。

这是 MyObject 类真正放置在 Web 项目中已编译的 SoundApplet.jar 中的图像。

【问题讨论】：

    标签： java servlets applet classnotfoundexception urlconnection


    【解决方案1】：

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

    • ..
    • 对于必须在所有 Web 应用程序之间共享的类和资源，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 在 Jar 中（我推荐），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。顺便说一句，包名应该是alllowercase，例如soundapplet.

    另请注意，该类需要位于至少 2 个不同的位置，以供 servlet 和 applet 使用。上面列出了服务器类路径，但小程序（或者更确切地说是 JVM）无法访问这些路径中的任何一个。

    【讨论】：

    • 我将我的 SoundApplet.jar 添加到了我的 Web 应用程序的 /WEB-INF/lib/SoundApplet.jar 中，并且我从 Tomcat 中得到了这个异常：SEVERE: Servlet.service() for servlet [Servlet] in带有路径 [/Rozhlas_jsf] 的上下文抛出异常 java.lang.ClassCastException: SoundApplet.MyObject cannot be cast to Servlets.MyObject
    • 为了尽快获得更好的帮助，请发布SSCCE（servlet 和 applet 代码）。
    • 好吧，我试着做简单的例子，我想在这里做什么，你有两个项目。一个是 Applet 项目，接下来是我的 Web 项目。这是链接link 你能运行吗？ @安德鲁汤普森
    • 我已经尝试了所有文件夹来放置我的 Applet.jar 文件，但找不到我的类 :-(
    • “你能运行它吗？” 我不打算尝试下载 5 兆的应用程序，构建它并运行它。
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