FileChannel类的简单用法-优快云博客

本文通过三个示例展示了如何使用 Java NIO 进行文件读写操作，包括直接写入字节到文件、复制文件及使用 transferTo 方法进行高效文件传输。

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清单一：

 
  importjava.io.*; 
 importjava.nio.*; 
 importjava.nio.channels.*; 
 publicclassGetChannel 
{
 privatestaticfinalintBSIZE=1024; 
 publicstaticvoidmain(String[]args)throwsIOException 
{
 FileChannelfc=newFileOutputStream("data.txt").getChannel(); 
 fc.write(ByteBuffer.wrap("sometxt".getBytes()));//write()Writesasequenceofbytesto  
 //thischannelfromthegivenbuffer  
fc.close();
 fc=newRandomAccessFile("data.txt","rw").getChannel(); 
 fc.position(fc.size());//abstractFileChannelposition(longnewPosition)  
 //Setsthischannel'sfileposition.  
 fc.write(ByteBuffer.wrap("somemore".getBytes())); 
fc.close();
 fc=newFileInputStream("data.txt").getChannel(); 
 ByteBufferbf=ByteBuffer.allocate(BSIZE);//staticByteBufferallocate(intcapacity)  
 //Allocatesanewbytebuffer.  
 //一旦调用read（）来告知FileChannel向ByteBuffer存储字节，就必须调用缓冲器上的filp（），  
 //让它做好别人存储字节的准备（是的，他是有点拙劣，但请记住他是很拙劣的，但却适于获取大速度）  
 //  
 fc.read(bf);//Readsasequenceofbytesfromthischannelintothegivenbuffer  
bf.flip();
 while(bf.hasRemaining()) 
 System.out.print((char)bf.get()); 
}
}
 

清单二：

 
  //Copyingafileusingchannelsandbuffers;  
 importjava.io.*; 
 importjava.nio.*; 
 importjava.nio.channels.*; 
 publicclassChannelCopy 
{
 privatestaticfinalintBSIZE=1024; 
 publicstaticvoidmain(String[]args)throwsIOException 
{
 if(args.length!=2) 
{
 System.out.println("argument:sourcefiledestfile"); 
 System.exit(1); 
}
FileChannel
 in=newFileInputStream(args[0]).getChannel(), 
 out=newFileOutputStream(args[1]).getChannel(); 
ByteBufferbb=ByteBuffer.allocate(BSIZE);
 while(in.read(bb)!=-1) 
{
bb.flip();
out.write(bb);
 bb.clear();//prepareforreading;清空缓冲区；  
}
}
}
 

清单三

 
  importjava.io.*; 
 importjava.nio.*; 
 importjava.nio.channels.*; 
 publicclassTransferTo 
{
 publicstaticvoidmain(String[]args)throwsIOException 
{
 if(args.length!=2) 
{
 System.out.println("argument:sourcefiledestfile"); 
 System.exit(1); 
}
FileChannel
 in=newFileInputStream(args[0]).getChannel(), 
 out=newFileOutputStream(args[1]).getChannel(); 
 //abstractlongtransferTo(longposition,longcount,WritableByteChanneltarget)  
 //Transfersbytesfromthischannel'sfiletothegivenwritablebytechannel.  
 in.transferTo(0,in.size(),out); 
 //or  
 //usingout  
 //abstractlongtransferFrom(ReadableByteChannelsrc,longposition,longcount)  
 //Transfersbytesintothischannel'sfilefromthegivenreadablebytechannel.  
 //out.transferFrom(in,0,in.size());  
}
}
 