用示例关闭 Java 中的通道异常
原文:https://www . geeksforgeeks . org/closedchannelexception-in-Java-with-examples/
当在关闭的通道或对尝试的操作关闭的通道上尝试输入/输出操作时，调用类 ClosedChannelException。也就是说，如果引发此异常，并不意味着通道完全关闭，而是对尝试的操作关闭。
语法:
public class ClosedChannelException
extends IOException
ClosedChannelException 的层次结构如下:
现在让我们先看看这个类的构造函数细节，然后再来看它的方法。
| constructors | describe | | --- | --- | | 闭合通道异常() | An instance of the class is constructed. |现在让我们讨论从 Throwable 类继承的方法。它们以表格形式描述如下:
| way | describe | | --- | --- | | [Add suppressed (throws exceptions)](https://www.geeksforgeeks.org/throwable-addsuppressed-method-in-java-with-examples/?ref=rp) | Add this exception to the suppressed exception in order to schedule this exception. | | [【充质痕迹()](https://www.geeksforgeeks.org/throwable-fillinstacktrace-method-in-java/) | Record the current state information of the stack frame of the current thread in this Throwable object, and fill in the execution stack trace. | | [get case()](https://www.geeksforgeeks.org/throwable-getcause-method-in-java-with-examples/?ref=rp) | If the reason is unknown, return the reason or null of the Throwable. | | [获取本地化消息()](https://www.geeksforgeeks.org/throwable-getlocalizedmessage-method-in-java-with-examples/) | Returns the localized description of this Throwable. Subclasses can override descriptions. If the subclass does not override this method, the result will be the same as that of getMessage (). | | [getMessage()](https://www.geeksforgeeks.org/throwable-getmessage-method-in-java-with-examples/?ref=rp) | Returns the detailed message description of this Throwable. | | [getStackTrace（）](https://www.geeksforgeeks.org/throwable-getstacktrace-method-in-java-with-examples/) | Returns an array of stack trace elements, each element representing a stack frame. Allows access to stack trace information printed by printStackTrace (). | | [getSuppressed()](https://www.geeksforgeeks.org/throwable-getsuppressed-method-in-java-with-examples/?ref=rp) | | | [T0】 init cause | Initialize this throwable reason with a given value. | | [打印堆栈跟踪()](https://www.geeksforgeeks.org/throwable-printstacktrace-method-in-java-with-examples/?ref=rp) | Print this Throwable and its backtracking on the error output stream. | | [打印堆栈跟踪(打印流)](https://www.geeksforgeeks.org/throwable-printstacktrace-method-in-java-with-examples/?ref=rp) | Print this Throwable and its backtracking on the specified print stream. | | [打印堆栈跟踪(PrintWriter s)](https://www.geeksforgeeks.org/throwable-printstacktrace-method-in-java-with-examples/?ref=rp) | Print this Throwable and its backtracking to the specified print writer. | | [设置堆栈跟踪(堆栈跟踪元素[]堆栈跟踪)](https://www.geeksforgeeks.org/throwable-setstacktrace-method-in-java-with-examples/?ref=rp) | Set the stack trace element of this Throwable. It is designed for remote procedure call framework and advanced systems, and allows clients to override the default stack trace. | | [toString()](https://www.geeksforgeeks.org/throwable-tostring-method-in-java-with-examples/?ref=rp) | Returns a brief description of the Throwable in the format: the class name of the object: the result of calling getLocalizedMessage () of the object. If getLocalizedMessage () returns null, only the class name is returned. |注意: 这个指的是方法被调用的上下文中的对象。
实现:我们本质上是要创建一个通道，关闭它，然后尝试在关闭的通道上执行读操作。这将触发关闭通道异常。步骤如下:
- 我们将创建一个 RandomAccessFile 类的实例，以“读写”模式从您的系统中打开一个文本文件。
- 现在我们使用文件通道类创建一个打开文件的通道。
- 之后，我们使用 ByteBuffer 类创建一个缓冲区来从该通道读取字节数据。
- 此外，字符集类，我们将编码方案定义为“US-ASCII”。
- 最后，在我们开始读取这个文件之前，我们关闭通道。
因此，当在此通道上尝试读取操作时，将引发 ClosedChannelException。我们在 catch 块中捕获异常，您可以在其中添加任何特定于您的需求的异常处理，这里我们只打印一条消息。
例
Java 语言(一种计算机语言，尤用于创建网站)
// Java Program to Illustraye Working of
// ClosedChannelException
// Importing required classes
// Input output classes
import java.io.IOException;
import java.io.RandomAccessFile;
// Classes from java.nio package
import java.nio.ByteBuffer;
import java.nio.channels.ClosedChannelException;
import java.nio.channels.FileChannel;
import java.nio.charset.Charset;
// Main class
// For ClosedChannelException
public class GFG {
// Main driver method
public static void main(String args[])
throws IOException
{
// Try block to check for exceptions
try {
// Open a file in your system using the
// RandomAccessFile class Custom local directory
// on machine
RandomAccessFile randomAccessFile
= new RandomAccessFile(
"D:/Documents/textDoc.txt", "rw");
// Now creating a channel using the FileChannel
// class to the file opened using the
// RandomAccessFile class
FileChannel fileChannel
= randomAccessFile.getChannel();
// Create a buffer to read bytes from the
// channel using the ByteBuffer class
ByteBuffer byteBuffer
= ByteBuffer.allocate(512);
Charset charset = Charset.forName("US-ASCII");
// Close the file channel
// We do this so the exception is thrown
fileChannel.close();
// Try to read from the fileChannel which is now
// closed
while (fileChannel.read(byteBuffer) > 0) {
byteBuffer.rewind();
System.out.print(
charset.decode(byteBuffer));
byteBuffer.flip();
}
// Closing the connections to free up memory
// resources using close() method
randomAccessFile.close();
}
// Catch block to handle the exceptions
// Handling Application specific Exception
catch (ClosedChannelException e) {
// Print message if exception is occured
System.out.println(
"ClosedChannelException has occurred");
}
}
}
输出:
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