Java中如何高效的读取大文件

读取文件行的标准方式是在内存中读取，Guava 和Apache Commons IO都提供了如下所示快速读取文件行的方法：

Files.readLines(new File(path), Charsets.UTF_8)FileUtils.readLines(new File(path))

这种方法带来的问题是文件的所有行都被存放在内存中，当文件足够大时很快就会导致程序抛出OutOfMemoryError 异常。

import java.io.File

import java.io.FileInputStream

import java.io.FileNotFoundException

import java.io.FileOutputStream

import java.io.IOException

import java.nio.ByteBuffer

import java.nio.channels.FileChannel

public class ReadWriteCompare

{

public static void main(String[] args) throws IOException

{

FileInputStream fileInputStream = new FileInputStream("f:"+ File.separator +"IBM e-Mentor Program Kickoff Night 1105.pdf")

FileOutputStream fileOutputStream = new FileOutputStream("f:" + File.separator + "test.pdf")

FileChannel inChannel = fileInputStream.getChannel()

FileChannel outChannel= fileOutputStream.getChannel()

ByteBuffer byteBuffer = ByteBuffer.allocate(1024)

//Direct Buffer的效率会更高。

// ByteBuffer byteBuffer = ByteBuffer.allocateDirect(1024)

long start = System.currentTimeMillis()

while(true)

{

int eof = inChannel.read(byteBuffer)

if(eof == -1 ) break

byteBuffer.flip()

outChannel.write(byteBuffer)

byteBuffer.clear()

}

System.out.println("spending : " + (System.currentTimeMillis()-start))

inChannel.close()

outChannel.close()

}

}

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