Java I/O NIO学习

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