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0bf.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:") {@Overridepublic 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 blocke.printStackTrace();}}}, new Tester("Mapped Write:") {@Overridepublic 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 blocke.printStackTrace();}} catch (FileNotFoundException e) {// TODO Auto-generated catch blocke.printStackTrace();}}}, new Tester("Stream Read") {@Overridepublic 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 blocke.printStackTrace();}}},new Tester("Map Read") {@Overridepublic 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 blocke.printStackTrace();}}},new Tester("Stream Read/Write") {@Overridepublic 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 blocke.printStackTrace();}}},new Tester("Map Read/Write") {@Overridepublic 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 blocke.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