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  • Java:在按钮单击事件中输出到服务器时出错

Java:在按钮单击事件中输出到服务器时出错

java javafx

Java:在按钮单击事件中输出到服务器时出错,java,javafx,Java,Javafx,Java有一个问题，我不能使用button click事件通过输出流发送任何类型的数据，因为它会给我一个NullPointerException。如果在button click事件之外使用，这段代码可以很好地工作，但是当我在这个特定部分中尝试它时，它将捕获该异常。 如果有人能发现我的错误，如果可能的话，能解释一下发生了什么，这样我就不会一次又一次地犯同样的错误，我会很感激的 代码： 例外情况： "C:\Program Files\Java\jdk1.8.0_151\bin\java" "-jav

Java有一个问题，我不能使用button click事件通过输出流发送任何类型的数据，因为它会给我一个NullPointerException。如果在button click事件之外使用，这段代码可以很好地工作，但是当我在这个特定部分中尝试它时，它将捕获该异常。 如果有人能发现我的错误，如果可能的话，能解释一下发生了什么，这样我就不会一次又一次地犯同样的错误，我会很感激的

代码：

例外情况：

"C:\Program Files\Java\jdk1.8.0_151\bin\java" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2017.3.2\lib\idea_rt.jar=51005:C:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2017.3.2\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_151\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\rt.jar;C:\Users\vasco\IdeaProjects\Learning\out\production\Learning" sample.Main
C:\Users\vasco
Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1774)
    at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1657)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
    at javafx.event.Event.fireEvent(Event.java:198)
    at javafx.scene.Node.fireEvent(Node.java:8413)
    at javafx.scene.control.Button.fire(Button.java:185)
    at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:182)
    at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:96)
    at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:89)
    at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
    at javafx.event.Event.fireEvent(Event.java:198)
    at javafx.scene.Scene$MouseHandler.process(Scene.java:3757)
    at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3485)
    at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
    at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2494)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:381)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:295)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$353(GlassViewEventHandler.java:417)
    at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:416)
    at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
    at com.sun.glass.ui.View.notifyMouse(View.java:937)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.lambda$null$147(WinApplication.java:177)
    at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
    at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1769)
    ... 52 more
Caused by: java.lang.NullPointerException
    at sample.Main.actionPerformed(Main.java:94)
    ... 62 more
首先，如果（！userField.getText（）.isEmpty（））或（！passwordField.getText（）.isEmpty（））如果（！passwordField.getText（）.isEmpty（）），则会导致或可能导致
NullPointerException
错误。这是因为
isEmpty（）
函数可能返回
null
。相反，如果（！userField.getText（）.equals（“”））使用
if
和
if（！passwordField.getText（）.equals（“”）
，尽管速度稍慢，但您知道它永远不会返回空值，如图所示

异常的另一个原因可能是套接字变量的初始化，replace
os=newdataoutputstream（socket.getOutputStream（））
for
os=newdataoutputstream（新套接字（“您的IP地址”，int-port））

作为旁注，不要使用
sendBytes（“”）函数，使用
sendUTF（“”）
它还有以下好处：


    

  • 空字节“\u0000”是以2字节格式而不是1字节格式编码的，因此编码的字符串永远不会嵌入空字节
    • 

  • 仅使用1字节、2字节和3字节格式
    • 

  • 以代理项对的形式表示
    • 



如果有帮助，请选择“作为答案”，如果您有问题或它仍然不起作用，请告诉我，我会解决它。
您能在这里发布完整的异常消息吗？我编辑了帖子并添加了它哪一行是第94行？这是os=writebytes。如果我删除此代码并将其放在其他不使用按钮事件的地方，它就会工作。我也试着把它放在一个空白处，并通过那个事件调用这个空白，结果是一样的。嗯，我不认为这是因为isEmpty语句，否则它不会通过那个部分，但是我改变了它，因为它可能在某个时候给我一个错误。我还犯了一个错误，第94行实际上是os=new DataOutputStream。。。而这条线就是给予的NullPointerException@VascoFerreira所以问题可能出在Socket变量中，你能发布Socket变量的初始化和声明吗？我发现了问题，变量没有被声明为静态的。我的愚蠢举动。感谢您的帮助：）@VascoFerreira请检查它现在是否纠正了您的问题（尽管您已经解决了它，将变量更改为静态），以及它是否选择它作为答案。

"C:\Program Files\Java\jdk1.8.0_151\bin\java" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2017.3.2\lib\idea_rt.jar=51005:C:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2017.3.2\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_151\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_151\jre\lib\rt.jar;C:\Users\vasco\IdeaProjects\Learning\out\production\Learning" sample.Main
C:\Users\vasco
Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1774)
    at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1657)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
    at javafx.event.Event.fireEvent(Event.java:198)
    at javafx.scene.Node.fireEvent(Node.java:8413)
    at javafx.scene.control.Button.fire(Button.java:185)
    at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:182)
    at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:96)
    at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:89)
    at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
    at javafx.event.Event.fireEvent(Event.java:198)
    at javafx.scene.Scene$MouseHandler.process(Scene.java:3757)
    at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3485)
    at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
    at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2494)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:381)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:295)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$353(GlassViewEventHandler.java:417)
    at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:416)
    at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
    at com.sun.glass.ui.View.notifyMouse(View.java:937)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.lambda$null$147(WinApplication.java:177)
    at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
    at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1769)
    ... 52 more
Caused by: java.lang.NullPointerException
    at sample.Main.actionPerformed(Main.java:94)
    ... 62 more