第18章 java I/O系统（3）

18.10 新I/O

新I/O速度的提高来自于所使用的结构更接近于操作系统执行I/O的方式：通道和缓冲器。我们并没有字节和通道交互；我们只是和缓冲器交互。并把缓冲器派送到通道。通道要么从缓冲器获得数据，要么向缓冲器发送数据。

唯一直接与通道交互的缓冲器是ByteBuffer。

package com.thinkinjava.chapter18.part10;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;

public class GetChannel {
    private  static final int BSIZE = 1024;
    
    @SuppressWarnings("resource")
    public static void main(String[] args) throws Exception {
        
        //写一个文件
        FileChannel fc = new FileOutputStream("src/com/thinkinjava/chapter18/part10/data.txt").getChannel();
        fc.write(ByteBuffer.wrap("Some text ".getBytes()));
        fc.close();
        
        //在文件的末尾追加字符
        fc = new RandomAccessFile("src/com/thinkinjava/chapter18/part10/data.txt", "rw").getChannel();
        fc.position(fc.size());
        fc.write(ByteBuffer.wrap("Some more".getBytes()));
        fc.close();
        
        //读文件
        fc = new FileInputStream("src/com/thinkinjava/chapter18/part10/data.txt").getChannel();
        //对于只读访问，我们必须显示地使用静态的allocate()方法类分配ByteBuffer。
        ByteBuffer buff = ByteBuffer.allocate(BSIZE);
        fc.read(buff);
        //一旦调用read()来告知FileChannel向ByteBuffer存储字节，就必须调用缓冲器上的额flip()
        buff.flip();
        
        while(buff.hasRemaining())
            System.out.print((char)buff.get());
        
        
    }
    
}

package com.thinkinjava.chapter18.part10;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;

public class ChannelCopy {
    
    private static final int BSIZE = 1024;
    
    
    @SuppressWarnings("resource")
    public static void main(String[] args) throws IOException {
        
        args = new String[]{"src/com/thinkinjava/chapter18/part10/data.txt","src/com/thinkinjava/chapter18/part10/data1.txt"};
        
        if(args.length != 2){
            System.out.println("arguments: sourcefile destfile");
            System.exit(1);
        }
        
        FileChannel in = new FileInputStream(args[0]).getChannel(),
        out = new FileOutputStream(args[1]).getChannel();
        
        ByteBuffer buffer = ByteBuffer.allocate(BSIZE);
        
        while(in.read(buffer) != -1){
            buffer.flip();//准备写操作
            out.write(buffer);
            buffer.clear();//准备读操作
        }
        
        
        
        
        
    }
    
    
}

package com.thinkinjava.chapter18.part10;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.channels.FileChannel;

public class TransferTo {

    @SuppressWarnings("resource")
    public static void main(String[] args) throws IOException {

        args = new String[] { "src/com/thinkinjava/chapter18/part10/data.txt",
                "src/com/thinkinjava/chapter18/part10/data2.txt" };

        if (args.length != 2) {
            System.out.println("arguments: sourcefile destfile");
            System.exit(1);
        }

        FileChannel in = new FileInputStream(args[0]).getChannel(), out = new FileOutputStream(
                args[1]).getChannel();

        //transferTo()和transferFrom()则允许将一个通道和另一个通道直接相连
        in.transferTo(0, in.size(), out);
        // out.transferFrom(in, 0, in.size());

    }

}

18.10.1 转换数据

package com.thinkinjava.chapter18.part10;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.charset.Charset;

public class BufferToText {
    
    private static final int BISZE = 1024;
    
    //缓冲容器容纳的是普通的字节，为了把他们转换成字符，我们要在输入它们的时候对其进行编码，
    //要么在将其从缓冲器输出时对他们呢进行解码
    @SuppressWarnings("resource")
    public static void main(String[] args) throws Exception {
        
        FileChannel fc = new FileOutputStream("src/com/thinkinjava/chapter18/part10/data2.txt").getChannel();
        
        fc.write(ByteBuffer.wrap("Some text".getBytes()));
        fc.close();
        
        fc = new FileInputStream("src/com/thinkinjava/chapter18/part10/data2.txt").getChannel();
        ByteBuffer buffer = ByteBuffer.allocate(BISZE);
        fc.read(buffer);
        buffer.flip();
        
        //没有效果
        System.out.println(buffer.asCharBuffer());
        //用系统自带的字符集解码
        buffer.rewind();
        String encoding = System.getProperty("file.encoding");
        
        System.out.println("Decoded using "+encoding+":"+Charset.forName(encoding).decode(buffer));
        
        fc = new FileOutputStream("src/com/thinkinjava/chapter18/part10/data2.txt").getChannel();
        
        fc.write(ByteBuffer.wrap("Some text".getBytes("UTF-16BE")));
        fc.close();
        
        //不再重新读入
        fc = new FileInputStream("src/com/thinkinjava/chapter18/part10/data2.txt").getChannel();
        buffer.clear();
        fc.read(buffer);
        buffer.flip();
        System.out.println(buffer.asCharBuffer());
        
        //
        fc = new FileOutputStream("src/com/thinkinjava/chapter18/part10/data2.txt").getChannel();
        buffer = ByteBuffer.allocate(24);
        buffer.asCharBuffer().put("Some text");
        fc.write(buffer);
        fc.close();
        
        //读取和显示
        fc = new FileInputStream("src/com/thinkinjava/chapter18/part10/data2.txt").getChannel();
        buffer.clear();
        fc.read(buffer);
        buffer.flip();
        System.out.println(buffer.asCharBuffer());
        
        
    }
    
}

获得系统字符集

package com.thinkinjava.chapter18.part10;

import java.nio.charset.Charset;
import java.util.Iterator;
import java.util.SortedMap;

public class AvaiableCharSets {
    public static void main(String[] args) {
        
        SortedMap<String, Charset> charSets = Charset.availableCharsets();
        
        Iterator<String> it = charSets.keySet().iterator();
        
        while(it.hasNext()){
            
            String csName = it.next();
            System.out.print(csName);
            
            Iterator<String> aliases = charSets.get(csName).aliases().iterator();
            
            if(aliases.hasNext())
                System.out.print(":");
            while(aliases.hasNext()){
                System.out.print(aliases.next());
                if(aliases.hasNext())
                    System.out.print(";");
            }
            System.out.println("");
        }
        
    }
}

18.10.2 获取基本类型

package com.thinkinjava.chapter18.part10;

import java.nio.ByteBuffer;

public class GetData {
        
    private static final int BSIZE = 1024;
    
    public static void main(String[] args) {
        
        
        ByteBuffer bb = ByteBuffer.allocate(BSIZE);//分配容量
        
        int i = 0;
        while(i++<bb.limit())
            if(bb.get() != 0)
                print("nonzero");
        print("i = "+i);
        print();
        bb.rewind();
        
        
        //存储和读取char array
        bb.asCharBuffer().put("Howdy!");
        char c;
        while((c = bb.getChar()) != 0)
            printnb(c+" ");
        print();
        bb.rewind();
        
        //存储和读取short型
        bb.asShortBuffer().put((short)471142);
        print(bb.getInt());
        bb.rewind();
        
        //存储和读取int
        bb.asIntBuffer().put(99471142);
        print(bb.getInt());
        bb.rewind();
        
        //存储和读取long
        bb.asLongBuffer().put(99471142);
        print(bb.getLong());
        bb.rewind();
        
        
        //存储和读取float
        bb.asFloatBuffer().put(99471142);
        print(bb.getFloat());
        bb.rewind();
        
        //存储和读取double
        bb.asDoubleBuffer().put(99471142);
        print(bb.getDouble());
        bb.rewind();
        
        
        
        
        
        
        
        
        
        
        
        
    }

    private static void printnb(Object obj) {
        System.out.print(String.valueOf(obj));
    }

    private static void print(Object obj) {
        System.out.print(String.valueOf(obj));
        System.out.println();
    }
    private static void print() {
        System.out.println();
    }
    
    
    
    
}

18.10.3 视图缓冲器

package com.thinkinjava.chapter18.part10;

import java.nio.ByteBuffer;
import java.nio.IntBuffer;

public class IntBufferDemo {
    
    private static final int BSIZE = 1024;
    
    public static void main(String[] args) {
        
        ByteBuffer bb = ByteBuffer.allocate(BSIZE);
        IntBuffer ib = bb.asIntBuffer();
        
        ib.put(new int[]{11,42,47,99,143,811,1016});
        
        System.out.println(ib.get(3));
        
        ib.put(3,1811);
        
        ib.flip();
        while(ib.hasRemaining()){
            int i = ib.get();
            System.out.println(i);
        }
        
        
        
        
        
        
    }
    
}

package com.thinkinjava.chapter18.part10;

import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.DoubleBuffer;
import java.nio.FloatBuffer;
import java.nio.IntBuffer;
import java.nio.LongBuffer;
import java.nio.ShortBuffer;

public class ViewBuffers {
    
    public static void main(String[] args) {
        
        ByteBuffer bb = ByteBuffer.wrap(new byte[]{0,0,0,0,0,0,0,'a'});
        bb.rewind();

        //byte 
        System.out.print("Byte Buffer ");
        while(bb.hasRemaining())
            System.out.print(bb.position()+"->"+bb.get()+",");//Byte Buffer 0->0,1->0,2->0,3->0,4->0,5->0,6->0,7->97,
        System.out.println();
        
        //Char
        CharBuffer cb = ((ByteBuffer)bb.rewind()).asCharBuffer();
        System.out.print("Char Buffer ");
        while(cb.hasRemaining())
            System.out.print(cb.position()+"->"+cb.get()+",");//Char Buffer 0-> ,1-> ,2-> ,3->a
        System.out.println();
        
        //float 
        FloatBuffer fb = ((ByteBuffer)bb.rewind()).asFloatBuffer();
        System.out.print("Float Buffer ");
        while(fb.hasRemaining())
            System.out.print(fb.position()+"->"+fb.get()+",");//Float Buffer 0->0.0,1->1.36E-43,
        System.out.println();
        
        //int 
        IntBuffer ib = ((ByteBuffer)bb.rewind()).asIntBuffer();
        System.out.print("Int Buffer ");
        while(ib.hasRemaining())
            System.out.print(ib.position()+"->"+ib.get()+",");//Int Buffer 0->0,1->97,
        System.out.println();
        
        
        //long 
        LongBuffer lb = ((ByteBuffer)bb.rewind()).asLongBuffer();
        System.out.print("Long Buffer ");
        while(lb.hasRemaining())
            System.out.print(lb.position()+"->"+lb.get()+",");//Long Buffer 0->97,
        System.out.println();
        
        //short 
        ShortBuffer sb = ((ByteBuffer)bb.rewind()).asShortBuffer();
        System.out.print("Short Buffer ");
        while(sb.hasRemaining())
            System.out.print(sb.position()+"->"+sb.get()+",");//Short Buffer 0->0,1->0,2->0,3->97,
        System.out.println();
        
        //double 
        DoubleBuffer db = ((ByteBuffer)bb.rewind()).asDoubleBuffer();
        System.out.print("Double Buffer ");
        while(db.hasRemaining())
            System.out.print(db.position()+"->"+db.get()+",");//Double Buffer 0->4.8E-322,
        System.out.println();
        
    }
    
}

package com.thinkinjava.chapter18.part10;

import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.util.Arrays;

public class Endians {
    
    public static void main(String[] args) {
        
        ByteBuffer bb = ByteBuffer.wrap(new byte[12]);
        bb.asCharBuffer().put("abcdef");
        
        System.out.println(Arrays.toString(bb.array()));
        bb.rewind();

        bb.order(ByteOrder.BIG_ENDIAN);
        bb.asCharBuffer().put("abcdef");
        System.out.println(Arrays.toString(bb.array()));
        bb.rewind();
        
        bb.order(ByteOrder.LITTLE_ENDIAN);
        bb.asCharBuffer().put("abcdef");
        System.out.println(Arrays.toString(bb.array()));
        
        
    }
    
}

感觉只是介绍api用法，不写了。。。。