Java I/O NIO学习

2022-11-23 13:48:56

给出一个学习的链接讲的很全。。

http://ifeve.com/java-nio-all/

上边的是中文翻译的这里是原地址：
http://tutorials.jenkov.com/java-nio/overview.html

Channel：

FileChannel
DatagramChannel
SocketChannel
ServerSocketChannel

Buffer：

ByteBuffer
CharBuffer
DoubleBuffer
FloatBuffer
IntBuffer
LongBuffer
ShortBuffer
Mappedyteuffer

Selector:

利用Channel与Buffer对文件的读写

import java.io.BufferedInputStream;

import java.io.BufferedReader;

import java.io.File;

import java.io.FileInputStream;

import java.io.FileNotFoundException;

import java.io.FileReader;

import java.io.FileWriter;

import java.io.FilenameFilter;

import java.io.IOException;

import java.io.InputStream;

import java.io.InputStreamReader;

import java.io.OutputStream;

import java.io.PrintStream;

import java.io.PrintWriter;

import java.io.ObjectInputStream.GetField;

import java.io.RandomAccessFile;

import java.lang.ref.PhantomReference;

import java.lang.ref.Reference;

import java.lang.ref.ReferenceQueue;

import java.lang.ref.SoftReference;

import java.lang.ref.WeakReference;

import java.nio.ByteBuffer;

import java.nio.CharBuffer;

import java.nio.channels.FileChannel;

import java.util.ArrayList;

import java.util.Arrays;

import java.util.Collection;

import java.util.Collections;

import java.util.HashSet;

import java.util.Iterator;

import java.util.LinkedList;

import java.util.List;

import java.util.Set;

import java.util.regex.Pattern;

public class Test{

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

		RandomAccessFile accessFile = new RandomAccessFile(new File("/home/estar/Test/a.java"), "rw");

		//获得文件通道

		FileChannel fileChannel = accessFile.getChannel();

		//分配缓冲区

		ByteBuffer bf = ByteBuffer.allocate(1024);

		//首先判断一下是否有数据可读

		int byteReads = fileChannel.read(bf);

		//如果缓冲区里有数据

		while (byteReads != -1){

			System.out.println("byteReads : " +  byteReads);

			//切换到读模式

			bf.flip();

			//读position 到 limit之间的数据

			while (bf.hasRemaining()) {

				System.out.println((char)bf.get());

			}

			//清空读出来的数据

			bf.clear();

			//重新读取

			byteReads = fileChannel.read(bf);

		}

		//写入数据之前首先清空一下缓冲区

		bf.clear();

		//放入数据

		bf.put("AAHJKHJK".getBytes());

		//将position置0

		bf.flip();

		fileChannel.write(bf);

		fileChannel.write(ByteBuffer.wrap("nixing".getBytes()));

	}

}

实现两个文件内容的复制：

 FileChannel

			in = new FileInputStream("/home/estar/Test/a.java").getChannel(),

			out = new FileOutputStream("/home/estar/Test/b.java").getChannel();

	   ByteBuffer buf = ByteBuffer.allocate(1024);

	   while ((in.read(buf)) != -1){

		   buf.flip();

		   out.write(buf);

		   buf.clear();

	   }

内存映射文件：

MapByteBuffer的与普通I/O的比较

import java.io.BufferedInputStream;

import java.io.BufferedOutputStream;

import java.io.BufferedReader;

import java.io.DataInputStream;

import java.io.DataOutputStream;

import java.io.File;

import java.io.FileInputStream;

import java.io.FileNotFoundException;

import java.io.FileOutputStream;

import java.io.FileReader;

import java.io.FileWriter;

import java.io.FilenameFilter;

import java.io.IOException;

import java.io.InputStream;

import java.io.InputStreamReader;

import java.io.OutputStream;

import java.io.PrintStream;

import java.io.PrintWriter;

import java.io.ObjectInputStream.GetField;

import java.io.RandomAccessFile;

import java.lang.ref.PhantomReference;

import java.lang.ref.Reference;

import java.lang.ref.ReferenceQueue;

import java.lang.ref.SoftReference;

import java.lang.ref.WeakReference;

import java.nio.ByteBuffer;

import java.nio.CharBuffer;

import java.nio.IntBuffer;

import java.nio.channels.FileChannel;

import java.util.ArrayList;

import java.util.Arrays;

import java.util.Collection;

import java.util.Collections;

import java.util.HashSet;

import java.util.Iterator;

import java.util.LinkedList;

import java.util.List;

import java.util.Set;

import java.util.regex.Pattern;

import javax.xml.datatype.Duration;

/*

 * 尽管旧的I/O在用nio实现后性能有所提高， 但是“映射文件访问”往往可以更加显著地加快速度

 */

public class Test {

	public static int numOfInts = 400000;

	//抽象类提供模板方法

	public abstract static class Tester {

		String name;

		public Tester(String name) {

			this.name = name;

		}

		//模板方法

		public void runTest() {

			System.out.print("test  : " + name + " : ");

			long start = System.nanoTime();

			test();

			long end = System.nanoTime();

			double duration = (end - start) / 1.0e9;

			System.out.format("%.2f\n", duration);

		}

		public abstract void test();

	}

	public static Tester[] tests = { 

		/*

		 * 匿名内部类提供模板的具体实现

		 */

		new Tester("Stream Write:") {

		@Override

		public void test() {

			try {

				DataOutputStream dos = new DataOutputStream(

						new BufferedOutputStream(new FileOutputStream(new File(

								"tmp.tmp"))));

				for (int i = 0; i < numOfInts; ++i) {

					dos.writeInt(i);

				}

				dos.close();

			} catch (IOException e) {

				// TODO Auto-generated catch block

				e.printStackTrace();

			}

		}

	}, new Tester("Mapped Write:") {

		@Override

		public void test() {

			try {

				FileChannel fchinal = new RandomAccessFile("tmp.tmp", "rw")

						.getChannel();

				try {

					IntBuffer intBuffer = fchinal.map(

							FileChannel.MapMode.READ_WRITE, 0, fchinal.size())

							.asIntBuffer();

					for (int i = 0; i < numOfInts; ++i) {

						intBuffer.put(i);

					}

					fchinal.close();

				} catch (IOException e) {

					// TODO Auto-generated catch block

					e.printStackTrace();

				}

			} catch (FileNotFoundException e) {

				// TODO Auto-generated catch block

				e.printStackTrace();

			}

		}

	}, new Tester("Stream Read") {

		@Override

		public void test() {

			try {

				DataInputStream dis = new DataInputStream(new BufferedInputStream(

						new FileInputStream(new File("tmp.tmp"))));

				for (int i = 0; i < numOfInts; ++i) {

					dis.readInt();

				}

				dis.close();

			} catch (Exception e) {

				// TODO Auto-generated catch block

				e.printStackTrace();

			}

		}

	},new Tester("Map Read") {

		@Override

		public void test() {

			FileChannel fChannel;

			try {

				fChannel = new RandomAccessFile("tmp.tmp", "rw").getChannel();

			    IntBuffer intBuffer = fChannel.map(FileChannel.MapMode.READ_WRITE, 0, fChannel.size()).asIntBuffer();

			    for (int i = 0; i < numOfInts; ++i) {

			    	intBuffer.get();

			    }

			    fChannel.close();

			} catch (Exception e) {

				// TODO Auto-generated catch block

				e.printStackTrace();

			}

		}

	},

	new Tester("Stream Read/Write") {

		@Override

		public void test() {

			RandomAccessFile raf;

			try {

				raf = new RandomAccessFile("tmp.tmp", "rw");

				raf.writeInt(1);

				for(int i = 0; i < numOfInts; ++i){

					raf.seek(raf.length() - 4);

					raf.writeInt(raf.readInt());

				}

				raf.close();

			} catch (Exception e) {

				// TODO Auto-generated catch block

				e.printStackTrace();

			}

		}

	},

	new Tester("Map Read/Write") {

		@Override

		public void test() {

			FileChannel fChannel;

			try {

				fChannel = new RandomAccessFile("tmp.tmp", "rw").getChannel();

				IntBuffer intBuffer = fChannel.map(FileChannel.MapMode.READ_WRITE, 0, fChannel.size()).asIntBuffer();

				intBuffer.put(1);

				for (int i = 1; i <= numOfInts; ++i) {

					intBuffer.put(intBuffer.get(i - 1));

				}

			} catch (Exception e) {

				// TODO Auto-generated catch block

				e.printStackTrace();

			}

		}

	}

	};

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

		for (Tester tester : tests) {

			tester.runTest();

		}

	}

}

输出：

test  : Stream Write: : 0.06

test  : Mapped Write: : 0.01

test  : Stream Read : 0.06

test  : Map Read : 0.01

test  : Stream Read/Write : 3.43

test  : Map Read/Write : 0.01

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