Java NIO分散/聚集或向量I/O

在Java NIO中，通道提供了稱為分散/聚集或向量I/O的重要功能。 這是一種簡(jiǎn)單但功能強(qiáng)大的技術(shù)，通過(guò)這種技術(shù)，使用單個(gè)write()函數(shù)將字節(jié)從一組緩沖區(qū)寫入流，并且可以使用單個(gè)read()函數(shù)將字節(jié)從流讀取到一組緩沖區(qū)中。

Java NIO已經(jīng)內(nèi)置了分散/聚集支持。它可以用于從頻道讀取和寫入頻道。

分散讀取

“分散讀取”用于將數(shù)據(jù)從單個(gè)通道讀取多個(gè)緩沖區(qū)中的數(shù)據(jù)。

下面來(lái)看看分散原理的說(shuō)明：

下面是執(zhí)行分射讀取操作的代碼示例：

public interface ScatteringByteChannel extends ReadableByteChannel  
{  
    public long read (ByteBuffer [] argv) throws IOException;  
    public long read (ByteBuffer [] argv, int length, int offset) throws IOException;  
}

聚集寫入

“聚集寫入”用于將數(shù)據(jù)從多個(gè)緩沖區(qū)寫入單個(gè)通道。

下面來(lái)看看聚集原則的簡(jiǎn)單說(shuō)明：

下面來(lái)看看看執(zhí)行聚集寫入操作的代碼示例：

public interface GatheringByteChannel extends WritableByteChannel  
{  
    public long write(ByteBuffer[] argv) throws IOException;  
    public long write(ByteBuffer[] argv, int length, int offset) throws IOException;  
}

基本散點(diǎn)/聚集示例

下面來(lái)看看兩個(gè)緩沖區(qū)的簡(jiǎn)單例子。 第一個(gè)緩沖區(qū)保存隨機(jī)數(shù)，第二個(gè)緩沖區(qū)使用分散/聚集機(jī)制保存寫入的數(shù)據(jù)：

package com.yiibai;

import java.io.FileOutputStream;
import java.io.FileInputStream;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.ScatteringByteChannel;
import java.nio.channels.GatheringByteChannel;

public class ScatterGatherIO {
    public static void main(String params[]) {
        String data = "Scattering and Gathering example shown in yiibai.com";
        gatherBytes(data);
        scatterBytes();
    }

    /*
     * gatherBytes() is used for reading the bytes from the buffers and write it
     * to a file channel.
     */
    public static void gatherBytes(String data) {
        String relativelyPath = System.getProperty("user.dir");
        // The First Buffer is used for holding a random number
        ByteBuffer buffer1 = ByteBuffer.allocate(8);
        // The Second Buffer is used for holding a data that we want to write
        ByteBuffer buffer2 = ByteBuffer.allocate(400);
        buffer1.asIntBuffer().put(420);
        buffer2.asCharBuffer().put(data);
        GatheringByteChannel gatherer = createChannelInstance(relativelyPath+"/testout.txt", true);
        // Write the data into file
        try {
            gatherer.write(new ByteBuffer[] { buffer1, buffer2 });
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    /*
     * scatterBytes() is used for reading the bytes from a file channel into a
     * set of buffers.
     */
    public static void scatterBytes() {
        String relativelyPath = System.getProperty("user.dir");
        // The First Buffer is used for holding a random number
        ByteBuffer buffer1 = ByteBuffer.allocate(8);
        // The Second Buffer is used for holding a data that we want to write
        ByteBuffer buffer2 = ByteBuffer.allocate(400);
        ScatteringByteChannel scatter = createChannelInstance(relativelyPath+"/testout.txt", false);
        // Reading a data from the channel
        try {
            scatter.read(new ByteBuffer[] { buffer1, buffer2 });
        } catch (Exception e) {
            e.printStackTrace();
        }
        // Read the two buffers seperately
        buffer1.rewind();
        buffer2.rewind();

        int bufferOne = buffer1.asIntBuffer().get();
        String bufferTwo = buffer2.asCharBuffer().toString();
        // Verification of content
        System.out.println(bufferOne);
        System.out.println(bufferTwo);
    }

    public static FileChannel createChannelInstance(String file, boolean isOutput) {
        FileChannel FChannel = null;
        try {
            if (isOutput) {
                FChannel = new FileOutputStream(file).getChannel();
            } else {
                FChannel = new FileInputStream(file).getChannel();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return FChannel;
    }
}

在上述程序中，第一個(gè)緩沖區(qū)在控制臺(tái)上打印隨機(jī)輸出，第二個(gè)緩沖區(qū)在控制臺(tái)上打印“Scattering and Gathering example shown in yiibai.com”。

它還用“Scattering and Gathering example shown in yiibai.com”替換testout.txt文件的內(nèi)容。

420
Scattering and Gathering example shown in yiibai.com