Java NIO通道之間的數據傳輸


在Java NIO中,可以非常頻繁地將數據從一個通道傳輸到另一個通道。批量傳輸文件數據是非常普遍的,因爲幾個優化方法已經添加到FileChannel類中,使其更有效率。

通道之間的數據傳輸在FileChannel類中的兩種方法是:

  • FileChannel.transferTo()方法
  • FileChannel.transferFrom()方法

FileChannel.transferTo()方法

transferTo()方法用來從FileChannel到其他通道的數據傳輸。

下面來看一下transferTo()方法的例子:

public abstract class Channel extends AbstractChannel  
{    
   public abstract long transferTo (long position, long count, WritableByteChannel target);  
}

FileChannel.transferFrom()方法

transferFrom()方法允許從源通道到FileChannel的數據傳輸。

下面來看看transferFrom()方法的例子:

public abstract class Channel extends AbstractChannel  
{    
    public abstract long transferFrom (ReadableByteChannel src, long position, long count);  
}

基本通道到通道數據傳輸示例

下面來看看從4個不同文件讀取文件內容的簡單示例,並將它們的組合輸出寫入第五個文件:

package com.yiibai;

import java.io.File;
import java.io.FileOutputStream;
import java.io.FileInputStream;
import java.nio.channels.WritableByteChannel;
import java.nio.channels.FileChannel;

public class TransferDemo {
    public static void main(String[] argv) throws Exception {
        String relativelyPath = System.getProperty("user.dir");
        // Path of Input files
        String[] iF = new String[] { relativelyPath + "/input1.txt", relativelyPath + "/input2.txt",
                relativelyPath + "/input3.txt", relativelyPath + "/input4.txt" };
        // Path of Output file and contents will be written in this file
        String oF = relativelyPath + "/combine_output.txt";
        // Acquired the channel for output file
        FileOutputStream output = new FileOutputStream(new File(oF));
        WritableByteChannel targetChannel = output.getChannel();
        for (int j = 0; j < iF.length; j++) {
            // Get the channel for input files
            FileInputStream input = new FileInputStream(iF[j]);
            FileChannel inputChannel = input.getChannel();

            // The data is tranfer from input channel to output channel
            inputChannel.transferTo(0, inputChannel.size(), targetChannel);

            // close an input channel
            inputChannel.close();
            input.close();
        }
        // close the target channel
        targetChannel.close();
        output.close();
        System.out.println("All jobs done...");
    }
}

在上述程序中,將4個不同的文件(即input1.txtinput2.txtinput3.txtinput4.txt)的內容讀取並將其組合的輸出寫入第五個文件,即:combine_output.txt文件的中。combine_output.txt文件的內容如下 -

this is content from input1.txt
this is content from input2.txt
this is content from input3.txt
this is content from input4.txt