JAVA NIO的BufferByte与Channel DEMO实例

最新推荐文章于 2021-12-17 22:19:37 发布

天义tianyi

最新推荐文章于 2021-12-17 22:19:37 发布

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分类专栏： java 文章标签： java NIO

本文链接：https://blog.youkuaiyun.com/tianyijavaoracle/article/details/41479085

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本文介绍使用Java NIO进行文件数据的读写操作，并通过对比传统IO与NIO性能，展示了NIO在处理大量数据时的高效优势。

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package nio;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.channels.FileChannel;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
/**
<strong><span style="font-size:24px;color:#ff0000;"> * 实现功能，从一个文件读取数据输出到另一个文件</span></strong>
 * @author Administrator
 *
 */
public class Test2 {

	public static void main(String[] args) {

		try {

			FileInputStream fin = new FileInputStream("F://e.txt");
			
			FileChannel fc = fin.getChannel();
			
			ByteBuffer byteBuffer = ByteBuffer.allocate(1024);

			FileOutputStream fos = new FileOutputStream("F://t.txt");
			
			FileChannel foc = fos.getChannel();

			while (true) {
				byteBuffer.clear();
				int len = fc.read(byteBuffer);
				if (len == -1) {
					break;
				}
				byteBuffer.flip();
				foc.write(byteBuffer);
				byteBuffer.flip();
				System.out.println(decode(byteBuffer));
			}
			foc.close();
			fc.close();

		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

	public static String decode(ByteBuffer sendBuffer) {// ByteBuffer read
														// String
		Charset cs = Charset.forName("utf-8");
		byte[] bs = new byte[sendBuffer.limit()];
		sendBuffer.get(bs);
		
		return new String(bs, cs);
		// return new String(sendBuffer.array(),cs);
	}
}

package nio;


import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
<strong><span style="font-size:24px;color:#ff0000;">//输入格式化数据</span></strong>

public class Test7 {


<span style="white-space:pre">	</span>public static void main(String[] args) throws Exception {
<span style="white-space:pre">		</span>ByteBuffer bookBuf = ByteBuffer.wrap("java".getBytes("utf-8"));
<span style="white-space:pre">		</span>ByteBuffer autBuf = ByteBuffer.wrap("tianyi".getBytes("utf-8"));
<span style="white-space:pre">		</span>int booklen = bookBuf.limit();
<span style="white-space:pre">		</span>int authlen = autBuf.limit();
<span style="white-space:pre">		</span>System.out.println(booklen + " " + authlen);
<span style="white-space:pre">		</span>ByteBuffer[] bufs = new ByteBuffer[] { bookBuf, autBuf };
<span style="white-space:pre">		</span>File file = new File("F://t1.txt");
<span style="white-space:pre">		</span>if (!file.exists()) {
<span style="white-space:pre">			</span>file.createNewFile();
<span style="white-space:pre">		</span>}
<span style="white-space:pre">		</span>// FileOutputStream fos = new FileOutputStream(file);
<span style="white-space:pre">		</span>// FileChannel fc = fos.getChannel();
<span style="white-space:pre">		</span>// fc.write(bufs);
<span style="white-space:pre">		</span>// fos.close();


<span style="white-space:pre">		</span>ByteBuffer b1 = ByteBuffer.allocate(23);
<span style="white-space:pre">		</span>ByteBuffer b2 = ByteBuffer.allocate(9);


<span style="white-space:pre">		</span>bufs = new ByteBuffer[] { b1, b2 };


<span style="white-space:pre">		</span>FileInputStream fis = new FileInputStream(file);
<span style="white-space:pre">		</span>FileChannel fc = fis.getChannel();


<span style="white-space:pre">		</span>fc.read(bufs);


<span style="white-space:pre">		</span>String bookname = new String(bufs[0].array(), "utf-8");
<span style="white-space:pre">		</span>String autname = new String(bufs[1].array(), "utf-8");


<span style="white-space:pre">		</span>System.out.println(bookname + autname);


<span style="white-space:pre">	</span>}
}

package nio;
//传统IO与NIO性能测试对比

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;


public class Test8 {
<span style="white-space:pre">	</span>static int numOfInts = 8000000;


<span style="white-space:pre">	</span>public static void main(String[] args) throws Exception {
<span style="white-space:pre">		</span>System.out.println("传统IO");
<span style="white-space:pre">		</span>ioTest1();
<span style="white-space:pre">		</span>System.out.println("NIO");
<span style="white-space:pre">		</span>ioTest2();
<span style="white-space:pre">	</span>}


<span style="white-space:pre">	</span>public static void ioTest2() throws Exception {
<span style="white-space:pre">		</span>// NIO
<span style="white-space:pre">		</span>long start = System.currentTimeMillis();
<span style="white-space:pre">		</span>FileOutputStream fout = new FileOutputStream(new File("F://ctio.txt"));
<span style="white-space:pre">		</span>FileChannel fc = fout.getChannel();
<span style="white-space:pre">		</span>ByteBuffer byteBuffer = ByteBuffer.allocate(numOfInts * 4);
<span style="white-space:pre">			</span>for (int i = 0; i < numOfInts; i++) {
<span style="white-space:pre">			</span>byteBuffer.put(int2byte(i));
<span style="white-space:pre">		</span>}
<span style="white-space:pre">			</span>long mid = System.currentTimeMillis();
<span style="white-space:pre">			</span>System.out.println((mid - start) );
<span style="white-space:pre">		</span>
<span style="white-space:pre">		</span>byteBuffer.flip();
<span style="white-space:pre">		</span>fc.write(byteBuffer);
<span style="white-space:pre">		</span>  mid = System.currentTimeMillis();
<span style="white-space:pre">		</span>System.out.println((mid - start) );


<span style="white-space:pre">		</span>FileInputStream fin = new FileInputStream(new File("F://ctio.txt"));
<span style="white-space:pre">		</span>FileChannel fic = fin.getChannel();


<span style="white-space:pre">		</span>byteBuffer = ByteBuffer.allocate(numOfInts * 4);


<span style="white-space:pre">		</span>fic.read(byteBuffer);
<span style="white-space:pre">		</span>fic.close();


<span style="white-space:pre">		</span>byteBuffer.flip();
<span style="white-space:pre">		</span>while ((byteBuffer.hasRemaining())) {
<span style="white-space:pre">			</span>byteBuffer.get();


<span style="white-space:pre">		</span>}
<span style="white-space:pre">		</span>long end = System.currentTimeMillis();
<span style="white-space:pre">		</span>System.out.println((end - mid) );
<span style="white-space:pre">	</span>}


<span style="white-space:pre">	</span>/** 32位int转byte[] */
<span style="white-space:pre">	</span>public static byte[] int2byte(int res) {
<span style="white-space:pre">		</span>byte[] targets = new byte[4];
<span style="white-space:pre">		</span>targets[0] = (byte) (res & 0xff);// 最低位
<span style="white-space:pre">		</span>targets[1] = (byte) ((res >> 8) & 0xff);// 次低位
<span style="white-space:pre">		</span>targets[2] = (byte) ((res >> 16) & 0xff);// 次高位
<span style="white-space:pre">		</span>targets[3] = (byte) (res >>> 24);// 最高位,无符号右移。
<span style="white-space:pre">		</span>return targets;
<span style="white-space:pre">	</span>}


<span style="white-space:pre">	</span>/**
<span style="white-space:pre">	</span> * 将长度为2的byte数组转换为16位int
<span style="white-space:pre">	</span> * 
<span style="white-space:pre">	</span> * @param res
<span style="white-space:pre">	</span> *            byte[]
<span style="white-space:pre">	</span> * @return int
<span style="white-space:pre">	</span> * */
<span style="white-space:pre">	</span>public static int byte2int(byte b1, byte b2, byte b3, byte b4) {
<span style="white-space:pre">		</span>// res = InversionByte(res);
<span style="white-space:pre">		</span>// 一个byte数据左移24位变成0x??000000，再右移8位变成0x00??0000
<span style="white-space:pre">		</span>int targets = (b1 & 0xff) << 24 | ((b2 & 0xff) << 16)
<span style="white-space:pre">				</span>| ((b3 & 0xff) << 8) | (b4 & 0xff); // | 表示安位或
<span style="white-space:pre">		</span>return targets;
<span style="white-space:pre">	</span>}


<span style="white-space:pre">	</span>public static void ioTest1() throws Exception {
<span style="white-space:pre">		</span>// 传统IO
<span style="white-space:pre">		</span>long start = System.currentTimeMillis();
<span style="white-space:pre">		</span>DataOutputStream dos = new DataOutputStream(new BufferedOutputStream(
<span style="white-space:pre">				</span>new FileOutputStream(new File("F://ctio.txt"))));


<span style="white-space:pre">		</span>for (int i = 0; i < numOfInts; i++) {
<span style="white-space:pre">			</span>dos.writeInt(i);
<span style="white-space:pre">		</span>}
<span style="white-space:pre">		</span>if (dos != null) {
<span style="white-space:pre">			</span>dos.close();
<span style="white-space:pre">		</span>}
<span style="white-space:pre">		</span>long mid = System.currentTimeMillis();
<span style="white-space:pre">		</span>System.out.println((mid - start) );
<span style="white-space:pre">		</span>DataInputStream dis = new DataInputStream(new BufferedInputStream(
<span style="white-space:pre">				</span>new FileInputStream(new File("F://ctio.txt"))));


<span style="white-space:pre">		</span>for (int i = 0; i < numOfInts; i++) {
<span style="white-space:pre">			</span>dis.readInt();
<span style="white-space:pre">		</span>}
<span style="white-space:pre">		</span>if (dis != null) {
<span style="white-space:pre">			</span>dis.close();
<span style="white-space:pre">		</span>}


<span style="white-space:pre">		</span>long end = System.currentTimeMillis();
<span style="white-space:pre">		</span>System.out.println((end - mid) );
<span style="white-space:pre">	</span>}
}