为什么我的PrintWriter在我尝试写入时会抛出异常?
我有一个简单的ChatClient将数据发送到服务器。为了使聊天客户端发送数据,我创建了一个Socket,使用PrintWriter创建socket.getOutputStream(),然后执行writer.println(“”)。出于某种原因,我得到了一个很大的例外。我看了类似的例外,很多人都说要更新java。但是我的Mac上有最新版本。是因为我有Leopard,还是它是我的劣质编程?请看一下。为什么我的PrintWriter在我尝试写入时会抛出异常?
private void setUpNetworking() {
try {
**sock = new Socket("127.0.0.1", 65534);**
InputStreamReader streamReader = new InputStreamReader(sock.getInputStream());
reader = new BufferedReader(streamReader);
**writer = new PrintWriter(sock.getOutputStream());**
System.out.println("made connection... everything here works");
}
catch (IOException ex) {
ex.printStackTrace();
System.out.println("setup fail, but i didn't get this");
}
}
public class SendButtonListener implements ActionListener{
public void actionPerformed (ActionEvent ev){
try {
**writer.println(entertext.getText());**
**writer.flush();**
System.out.println("PROBLEM IS RIGHT HERE!!!");
}
catch (Exception ex) {
ex.printStackTrace();
System.out.println("i get a exception. HELP");
}
这里是我的例外:
java.lang.NullPointerException
at SimpleChatClient$SendButtonListener.actionPerformed(SimpleChatClient.java:52)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1882)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2202)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:420)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:258)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:246)
at java.awt.Component.processMouseEvent(Component.java:5617)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3129)
at java.awt.Component.processEvent(Component.java:5382)
at java.awt.Container.processEvent(Container.java:2010)
at java.awt.Component.dispatchEventImpl(Component.java:4083)
at java.awt.Container.dispatchEventImpl(Container.java:2068)
at java.awt.Component.dispatchEvent(Component.java:3918)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4256)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3936)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3866)
at java.awt.Container.dispatchEventImpl(Container.java:2054)
at java.awt.Window.dispatchEventImpl(Window.java:1801)
at java.awt.Component.dispatchEvent(Component.java:3918)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:501)
at java.awt.EventQueue.access$000(EventQueue.java:80)
at java.awt.EventQueue$1.run(EventQueue.java:462)
at java.awt.EventQueue$1.run(EventQueue.java:461)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:84)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:95)
at java.awt.EventQueue$2.run(EventQueue.java:476)
at java.awt.EventQueue$2.run(EventQueue.java:475)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:84)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:473)
at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:269)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:190)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:184)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:176)
**at java.awt.EventDispatchThread.run(EventDispatchThread.java:110)**
我不知道这意味着什么。请帮忙。
从您的堆栈跟踪和笔记,这听起来当您在SendButtonListener
的actionPerformed
方法调用
writer.println(entertext.getText());
一样,无论是writer
enterText
为空。
哪一个是空的,它如何得到这种方式在代码中是不清楚的,但你应该能够通过调试器或日志记录找出它。
所以我查了我的代码,事实证明,当我打印时,writer是空的。我是否给它赋值,如果是这样,怎么样?感谢您的建议。 – 2011-04-17 16:42:51
你已经在你的setupNetworking方法中获得了代码,它应该或多或少地用于创建作者,但是你需要确保在你需要发送之前调用它。你也应该确保在使用它之后正确地关闭它,并且如果有异常它会被关闭。 – 2011-04-17 17:02:01
下面是如何调试这一点 - 无论是:
- 放在一个单独的
println
打印,可能是零,它具有异常 - 之前或者在调试器中运行它每一件事情(Eclipse提供一个,例如),看看变量的值,当你得到该行
Chekc线52 of.SimpleChatClient是,一些有ir.null
或者'writer'或者'entertext'都是null。使用调试器/ SOP知道哪一个。 – Nishant 2011-04-17 16:01:38