Java Applet可在IDE中使用，但不能在浏览器中使用

Question

因此，我创建了一个简单的游戏，不久前就开始运行。 但是，最近，当我尝试在任何浏览器中运行它时，它只是给了我NullPointerException。 线程堆栈如下：

cache: Initialize resource manager: com.sun.deploy.cache.ResourceProviderImpl@18a270a
security: property package.access value sun.,com.sun.xml.internal.,com.sun.imageio.,com.sun.istack.internal.,com.sun.jmx.,com.sun.proxy.,com.sun.org.apache.bcel.internal.,com.sun.org.apache.regexp.internal.,com.sun.org.apache.xerces.internal.,com.sun.org.apache.xpath.internal.,com.sun.org.apache.xalan.internal.extensions.,com.sun.org.apache.xalan.internal.lib.,com.sun.org.apache.xalan.internal.res.,com.sun.org.apache.xalan.internal.templates.,com.sun.org.apache.xalan.internal.utils.,com.sun.org.apache.xalan.internal.xslt.,com.sun.org.apache.xalan.internal.xsltc.cmdline.,com.sun.org.apache.xalan.internal.xsltc.compiler.,com.sun.org.apache.xalan.internal.xsltc.trax.,com.sun.org.apache.xalan.internal.xsltc.util.,com.sun.org.apache.xml.internal.res.,com.sun.org.apache.xml.internal.serializer.utils.,com.sun.org.apache.xml.internal.utils.,com.sun.org.apache.xml.internal.security.,com.sun.org.glassfish.,org.jcp.xml.dsig.internal.,com.sun.java.accessibility.
security: property package.access new value sun.,com.sun.xml.internal.,com.sun.imageio.,com.sun.istack.internal.,com.sun.jmx.,com.sun.proxy.,com.sun.org.apache.bcel.internal.,com.sun.org.apache.regexp.internal.,com.sun.org.apache.xerces.internal.,com.sun.org.apache.xpath.internal.,com.sun.org.apache.xalan.internal.extensions.,com.sun.org.apache.xalan.internal.lib.,com.sun.org.apache.xalan.internal.res.,com.sun.org.apache.xalan.internal.templates.,com.sun.org.apache.xalan.internal.utils.,com.sun.org.apache.xalan.internal.xslt.,com.sun.org.apache.xalan.internal.xsltc.cmdline.,com.sun.org.apache.xalan.internal.xsltc.compiler.,com.sun.org.apache.xalan.internal.xsltc.trax.,com.sun.org.apache.xalan.internal.xsltc.util.,com.sun.org.apache.xml.internal.res.,com.sun.org.apache.xml.internal.serializer.utils.,com.sun.org.apache.xml.internal.utils.,com.sun.org.apache.xml.internal.security.,com.sun.org.glassfish.,org.jcp.xml.dsig.internal.,com.sun.java.accessibility.,com.sun.javaws,com.sun.deploy,com.sun.jnlp
security: property package.definition value sun.,com.sun.xml.internal.,com.sun.imageio.,com.sun.istack.internal.,com.sun.jmx.,com.sun.proxy.,com.sun.org.apache.bcel.internal.,com.sun.org.apache.regexp.internal.,com.sun.org.apache.xerces.internal.,com.sun.org.apache.xpath.internal.,com.sun.org.apache.xalan.internal.extensions.,com.sun.org.apache.xalan.internal.lib.,com.sun.org.apache.xalan.internal.res.,com.sun.org.apache.xalan.internal.templates.,com.sun.org.apache.xalan.internal.utils.,com.sun.org.apache.xalan.internal.xslt.,com.sun.org.apache.xalan.internal.xsltc.cmdline.,com.sun.org.apache.xalan.internal.xsltc.compiler.,com.sun.org.apache.xalan.internal.xsltc.trax.,com.sun.org.apache.xalan.internal.xsltc.util.,com.sun.org.apache.xml.internal.res.,com.sun.org.apache.xml.internal.serializer.utils.,com.sun.org.apache.xml.internal.utils.,com.sun.org.apache.xml.internal.security.,com.sun.org.glassfish.,org.jcp.xml.dsig.internal.,com.sun.java.accessibility.
security: property package.definition new value sun.,com.sun.xml.internal.,com.sun.imageio.,com.sun.istack.internal.,com.sun.jmx.,com.sun.proxy.,com.sun.org.apache.bcel.internal.,com.sun.org.apache.regexp.internal.,com.sun.org.apache.xerces.internal.,com.sun.org.apache.xpath.internal.,com.sun.org.apache.xalan.internal.extensions.,com.sun.org.apache.xalan.internal.lib.,com.sun.org.apache.xalan.internal.res.,com.sun.org.apache.xalan.internal.templates.,com.sun.org.apache.xalan.internal.utils.,com.sun.org.apache.xalan.internal.xslt.,com.sun.org.apache.xalan.internal.xsltc.cmdline.,com.sun.org.apache.xalan.internal.xsltc.compiler.,com.sun.org.apache.xalan.internal.xsltc.trax.,com.sun.org.apache.xalan.internal.xsltc.util.,com.sun.org.apache.xml.internal.res.,com.sun.org.apache.xml.internal.serializer.utils.,com.sun.org.apache.xml.internal.utils.,com.sun.org.apache.xml.internal.security.,com.sun.org.glassfish.,org.jcp.xml.dsig.internal.,com.sun.java.accessibility.,com.sun.javaws,com.sun.deploy,com.sun.jnlp
security: property package.access value sun.,com.sun.xml.internal.,com.sun.imageio.,com.sun.istack.internal.,com.sun.jmx.,com.sun.proxy.,com.sun.org.apache.bcel.internal.,com.sun.org.apache.regexp.internal.,com.sun.org.apache.xerces.internal.,com.sun.org.apache.xpath.internal.,com.sun.org.apache.xalan.internal.extensions.,com.sun.org.apache.xalan.internal.lib.,com.sun.org.apache.xalan.internal.res.,com.sun.org.apache.xalan.internal.templates.,com.sun.org.apache.xalan.internal.utils.,com.sun.org.apache.xalan.internal.xslt.,com.sun.org.apache.xalan.internal.xsltc.cmdline.,com.sun.org.apache.xalan.internal.xsltc.compiler.,com.sun.org.apache.xalan.internal.xsltc.trax.,com.sun.org.apache.xalan.internal.xsltc.util.,com.sun.org.apache.xml.internal.res.,com.sun.org.apache.xml.internal.serializer.utils.,com.sun.org.apache.xml.internal.utils.,com.sun.org.apache.xml.internal.security.,com.sun.org.glassfish.,org.jcp.xml.dsig.internal.,com.sun.java.accessibility.,com.sun.javaws,com.sun.deploy,com.sun.jnlp
security: property package.access new value sun.,com.sun.xml.internal.,com.sun.imageio.,com.sun.istack.internal.,com.sun.jmx.,com.sun.proxy.,com.sun.org.apache.bcel.internal.,com.sun.org.apache.regexp.internal.,com.sun.org.apache.xerces.internal.,com.sun.org.apache.xpath.internal.,com.sun.org.apache.xalan.internal.extensions.,com.sun.org.apache.xalan.internal.lib.,com.sun.org.apache.xalan.internal.res.,com.sun.org.apache.xalan.internal.templates.,com.sun.org.apache.xalan.internal.utils.,com.sun.org.apache.xalan.internal.xslt.,com.sun.org.apache.xalan.internal.xsltc.cmdline.,com.sun.org.apache.xalan.internal.xsltc.compiler.,com.sun.org.apache.xalan.internal.xsltc.trax.,com.sun.org.apache.xalan.internal.xsltc.util.,com.sun.org.apache.xml.internal.res.,com.sun.org.apache.xml.internal.serializer.utils.,com.sun.org.apache.xml.internal.utils.,com.sun.org.apache.xml.internal.security.,com.sun.org.glassfish.,org.jcp.xml.dsig.internal.,com.sun.java.accessibility.,com.sun.javaws,com.sun.deploy,com.sun.jnlp,org.mozilla.jss
security: property package.definition value sun.,com.sun.xml.internal.,com.sun.imageio.,com.sun.istack.internal.,com.sun.jmx.,com.sun.proxy.,com.sun.org.apache.bcel.internal.,com.sun.org.apache.regexp.internal.,com.sun.org.apache.xerces.internal.,com.sun.org.apache.xpath.internal.,com.sun.org.apache.xalan.internal.extensions.,com.sun.org.apache.xalan.internal.lib.,com.sun.org.apache.xalan.internal.res.,com.sun.org.apache.xalan.internal.templates.,com.sun.org.apache.xalan.internal.utils.,com.sun.org.apache.xalan.internal.xslt.,com.sun.org.apache.xalan.internal.xsltc.cmdline.,com.sun.org.apache.xalan.internal.xsltc.compiler.,com.sun.org.apache.xalan.internal.xsltc.trax.,com.sun.org.apache.xalan.internal.xsltc.util.,com.sun.org.apache.xml.internal.res.,com.sun.org.apache.xml.internal.serializer.utils.,com.sun.org.apache.xml.internal.utils.,com.sun.org.apache.xml.internal.security.,com.sun.org.glassfish.,org.jcp.xml.dsig.internal.,com.sun.java.accessibility.,com.sun.javaws,com.sun.deploy,com.sun.jnlp
security: property package.definition new value sun.,com.sun.xml.internal.,com.sun.imageio.,com.sun.istack.internal.,com.sun.jmx.,com.sun.proxy.,com.sun.org.apache.bcel.internal.,com.sun.org.apache.regexp.internal.,com.sun.org.apache.xerces.internal.,com.sun.org.apache.xpath.internal.,com.sun.org.apache.xalan.internal.extensions.,com.sun.org.apache.xalan.internal.lib.,com.sun.org.apache.xalan.internal.res.,com.sun.org.apache.xalan.internal.templates.,com.sun.org.apache.xalan.internal.utils.,com.sun.org.apache.xalan.internal.xslt.,com.sun.org.apache.xalan.internal.xsltc.cmdline.,com.sun.org.apache.xalan.internal.xsltc.compiler.,com.sun.org.apache.xalan.internal.xsltc.trax.,com.sun.org.apache.xalan.internal.xsltc.util.,com.sun.org.apache.xml.internal.res.,com.sun.org.apache.xml.internal.serializer.utils.,com.sun.org.apache.xml.internal.utils.,com.sun.org.apache.xml.internal.security.,com.sun.org.glassfish.,org.jcp.xml.dsig.internal.,com.sun.java.accessibility.,com.sun.javaws,com.sun.deploy,com.sun.jnlp,org.mozilla.jss
security: property package.access value sun.,com.sun.xml.internal.,com.sun.imageio.,com.sun.istack.internal.,com.sun.jmx.,com.sun.proxy.,com.sun.org.apache.bcel.internal.,com.sun.org.apache.regexp.internal.,com.sun.org.apache.xerces.internal.,com.sun.org.apache.xpath.internal.,com.sun.org.apache.xalan.internal.extensions.,com.sun.org.apache.xalan.internal.lib.,com.sun.org.apache.xalan.internal.res.,com.sun.org.apache.xalan.internal.templates.,com.sun.org.apache.xalan.internal.utils.,com.sun.org.apache.xalan.internal.xslt.,com.sun.org.apache.xalan.internal.xsltc.cmdline.,com.sun.org.apache.xalan.internal.xsltc.compiler.,com.sun.org.apache.xalan.internal.xsltc.trax.,com.sun.org.apache.xalan.internal.xsltc.util.,com.sun.org.apache.xml.internal.res.,com.sun.org.apache.xml.internal.serializer.utils.,com.sun.org.apache.xml.internal.utils.,com.sun.org.apache.xml.internal.security.,com.sun.org.glassfish.,org.jcp.xml.dsig.internal.,com.sun.java.accessibility.,com.sun.javaws,com.sun.deploy,com.sun.jnlp,org.mozilla.jss
security: property package.access new value sun.,com.sun.xml.internal.,com.sun.imageio.,com.sun.istack.internal.,com.sun.jmx.,com.sun.proxy.,com.sun.org.apache.bcel.internal.,com.sun.org.apache.regexp.internal.,com.sun.org.apache.xerces.internal.,com.sun.org.apache.xpath.internal.,com.sun.org.apache.xalan.internal.extensions.,com.sun.org.apache.xalan.internal.lib.,com.sun.org.apache.xalan.internal.res.,com.sun.org.apache.xalan.internal.templates.,com.sun.org.apache.xalan.internal.utils.,com.sun.org.apache.xalan.internal.xslt.,com.sun.org.apache.xalan.internal.xsltc.cmdline.,com.sun.org.apache.xalan.internal.xsltc.compiler.,com.sun.org.apache.xalan.internal.xsltc.trax.,com.sun.org.apache.xalan.internal.xsltc.util.,com.sun.org.apache.xml.internal.res.,com.sun.org.apache.xml.internal.serializer.utils.,com.sun.org.apache.xml.internal.utils.,com.sun.org.apache.xml.internal.security.,com.sun.org.glassfish.,org.jcp.xml.dsig.internal.,com.sun.java.accessibility.,com.sun.javaws,com.sun.deploy,com.sun.jnlp,org.mozilla.jss,com.sun.browser,com.sun.glass,com.sun.javafx,com.sun.media.jfxmedia,com.sun.media.jfxmediaimpl,com.sun.openpisces,com.sun.prism,com.sun.scenario,com.sun.t2k,com.sun.webpane,com.sun.pisces,com.sun.webkit
security: property package.definition value sun.,com.sun.xml.internal.,com.sun.imageio.,com.sun.istack.internal.,com.sun.jmx.,com.sun.proxy.,com.sun.org.apache.bcel.internal.,com.sun.org.apache.regexp.internal.,com.sun.org.apache.xerces.internal.,com.sun.org.apache.xpath.internal.,com.sun.org.apache.xalan.internal.extensions.,com.sun.org.apache.xalan.internal.lib.,com.sun.org.apache.xalan.internal.res.,com.sun.org.apache.xalan.internal.templates.,com.sun.org.apache.xalan.internal.utils.,com.sun.org.apache.xalan.internal.xslt.,com.sun.org.apache.xalan.internal.xsltc.cmdline.,com.sun.org.apache.xalan.internal.xsltc.compiler.,com.sun.org.apache.xalan.internal.xsltc.trax.,com.sun.org.apache.xalan.internal.xsltc.util.,com.sun.org.apache.xml.internal.res.,com.sun.org.apache.xml.internal.serializer.utils.,com.sun.org.apache.xml.internal.utils.,com.sun.org.apache.xml.internal.security.,com.sun.org.glassfish.,org.jcp.xml.dsig.internal.,com.sun.java.accessibility.,com.sun.javaws,com.sun.deploy,com.sun.jnlp,org.mozilla.jss
security: property package.definition new value sun.,com.sun.xml.internal.,com.sun.imageio.,com.sun.istack.internal.,com.sun.jmx.,com.sun.proxy.,com.sun.org.apache.bcel.internal.,com.sun.org.apache.regexp.internal.,com.sun.org.apache.xerces.internal.,com.sun.org.apache.xpath.internal.,com.sun.org.apache.xalan.internal.extensions.,com.sun.org.apache.xalan.internal.lib.,com.sun.org.apache.xalan.internal.res.,com.sun.org.apache.xalan.internal.templates.,com.sun.org.apache.xalan.internal.utils.,com.sun.org.apache.xalan.internal.xslt.,com.sun.org.apache.xalan.internal.xsltc.cmdline.,com.sun.org.apache.xalan.internal.xsltc.compiler.,com.sun.org.apache.xalan.internal.xsltc.trax.,com.sun.org.apache.xalan.internal.xsltc.util.,com.sun.org.apache.xml.internal.res.,com.sun.org.apache.xml.internal.serializer.utils.,com.sun.org.apache.xml.internal.utils.,com.sun.org.apache.xml.internal.security.,com.sun.org.glassfish.,org.jcp.xml.dsig.internal.,com.sun.java.accessibility.,com.sun.javaws,com.sun.deploy,com.sun.jnlp,org.mozilla.jss,com.sun.browser,com.sun.glass,com.sun.javafx,com.sun.media.jfxmedia,com.sun.media.jfxmediaimpl,com.sun.openpisces,com.sun.prism,com.sun.scenario,com.sun.t2k,com.sun.webpane,com.sun.pisces,com.sun.webkit
basic: Added progress listener: sun.plugin.util.ProgressMonitorAdapter@13b7c28
network: Cache entry not found [url: file:////files5.ad.lake.stark.k12.oh.us/shd/2015/15TROYERJONATHAN/Documents/Computer%20Science/Game/GUI.class, version: null]
network: Cache entry not found [url: file:////files5.ad.lake.stark.k12.oh.us/shd/2015/15TROYERJONATHAN/Documents/Computer%20Science/Game/, version: null]
security: Accessing keys and certificate in Mozilla user profile: null
network: Created version ID: 1.7.0.25
network: Created version ID: 1.7.0.25
security: SSV validation: running: 1.7.0_25, requested: null, range: null
network: Created version ID: 1.7.0.25
network: Created version ID: 1.7.0.25
security: continue with running version
network: Cache entry not found [url: file:////files5.ad.lake.stark.k12.oh.us/shd/2015/15TROYERJONATHAN/Documents/Computer%20Science/Game/ColorPanel.class, version: null]
basic: Applet loaded.
basic: Applet resized and added to parent container
basic: PERF: AppletExecutionRunnable - applet.init() BEGIN ; jvmLaunch dt 216867 us, pluginInit dt 217500 us, TotalTime: 434367 us
java.lang.NullPointerException
    at GUI.init(GUI.java:70)
    at com.sun.deploy.uitoolkit.impl.awt.AWTAppletAdapter.init(Unknown Source)
    at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
basic: Removed progress listener: sun.plugin.util.ProgressMonitorAdapter@13b7c28
security: Reset deny session certificate store

这是错误所在（至少据我所知）：

URL url=getCodeBase();
String u=url.toString();

当在JCreator中运行该applet时，它运行良好，但在任何浏览器或Adobe Dreamweaver中均不能运行。 我不知道任何线程堆栈意味着什么。 如果有人可以解释，那将非常有帮助。 如果您想要代码（很长又很乱），请给我发送电子邮件至spidermaninja@gmail.com。

Answer 1

我想GUI是您的applet类的名称。 （顺便说一句，如果您定义了它的包 ，那会很好，但它不会影响此问题）

从传输的跟踪中的stacktrace中，我还可以假设问题中的两行代码是69行和70行。

因此，我可以假设getCodeBase()返回null以便以下行自动导致NullPointerException （NPE）。 从Java 7更新25开始，当applet从本地文件系统运行时， getCodeBase()返回null。

因此，您应该检查getCodeBase（）返回的值是否为null，以便您的代码如下所示：

String u = "Some default value";
URL url=getCodeBase();
if(url != null) {
    u=url.toString();
}