java - 将自定义对象从 applet 传递到 servlet

标签 java servlets applet classnotfoundexception urlconnection

我有一个 servlet，我想通过 UrlConnection 传递一些对象。当我测试它时，效果很好。当我传递 Java native 对象(String、File..)时。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。它抛出异常，表示找不到我的类。

我在带有小程序的项目中有 MyObject 类，该类被加载并发送到 servlet，然后我的 servlet 包中也有 MyObject 类...那么我必须在哪里放置 MyObject 类才能工作？

这是我的小程序代码，它通过 URLConnection 将 MyObject 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);
        }

这是我的 servlet 中的代码，可以轻松地从请求对象获取流，然后我想将传入对象复制到 servlet 中的 MyObject 实例。这里有一个问题，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)

以及来自 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)

我猜问题出在我的类(class)安排上。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 native Java 对象，为什么 Java 无法在 SoundApplet.MyObject 中找到 MyObject 类。

在本例中 Java 如何与类一起工作。例如，当发送 FIle 对象时，当我在 servlet Java 中接收它时，使用 Which 类。我的 Applet 中的库中的 File 类或带有 servlet 的项目中的库中的 File 类还是不重要？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 类实际放置在 Web 项目中已编译的 SoundApplet.jar 中的图像。 enter image description here

最佳答案

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

  • ..
  • For classes and resources that must be shared across all web applications, place unpacked classes and resources under $CATALINA_BASE/shared/classes, or place JAR files containing those classes and resources under $CATALINA_BASE/shared/lib.

因此，如果 SoundApplet.MyObject 位于 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，包名称应该是alllowercase，例如soundapplet。

另请注意，该类需要至少位于2 个不同的位置才能被servlet 和applet 使用。上面概述了服务器类路径，但是小程序(或者更确切地说 JVM)无法访问这些路径中的任何一个。

关于java - 将自定义对象从 applet 传递到 servlet，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/13695487/

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