2020.8.1

学习内容:

1、RandomAccessFile随机访问文件

RandomAccessFile可以随机读写文件,随机读写文件就是说可以任意访问文件的位置，这是其他流所不能操纵的。RandomAccessFile 类包含一个记录指针，用于标识当前流的读写位置，这个位置可以向前移动，也可以向后移动。RandomAccessFile包含两个方法来操作文件记录指针。

long getFilePoint():记录文件指针的当前位置。
void seek(long pos):将文件记录指针定位到pos位置。

RandomAccessFile类的构造函数如下。

public，RandomAccessFile (File file,String mode)throws FileNotFoundException
public RandomAccessFile (String name,String mode)throws FileNotFoundException

在 RandomAccessFile中读写文件有四种模式如表所示

 示例：使用RandomAccessFile随机读写文件

import java. io. IOException; 
import java. io. RandomAccessFile;
public class RandomAccessFileDemo
  public static void main (String[] args) throws IOException {
    //创建对象
    RandomAccessFile acf =new RandomAccessFile ("D: /Hello.txt", "rw");
    //写byte数组
     byte[] b = "Hello Java! !".getBytes() ;
     acf.write(b) ;
    //设置偏移量
   acf.seek(6) ;
   System. out. println("pointer="+acf .getFilePointer()) ;
   byte[] b2="C++" .getBytes() ;
   acf.write (b2) ;
   int len=-1;
   byte[] buf=new byte [1024] ;
   //将偏移量设置成第一个位置
   acf .seek(0) ;
   System. out. println ("pointer "+acf .getFilePointer());
   while( (len=acf . read (buf)) !=-1) {
       String s =new String (buf,0, len) ;
       System. out.println(s) ;
   }
 }
}

综合实例：

package helloworld;
import java.io.*;
public class IOUtils {
    public static void main(String[] args) {
        byte[] ary= {41,4,-2,(byte)0xfe,(byte)0xff};
        for(int b:ary) {
            b&=0xff;
            if(b<=0xf)
                System.out.print("0");
            System.out.print(Integer.toHexString(b)+" ");
        }
        System.out.println();
    }
    public static byte[] read(String file) {
        try {
            InputStream in=new FileInputStream(file);
            byte[] buf=new byte[in.available()];
            in.read(buf);
            in.close();
            return buf;
        }catch(IOException e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        }
    }
    public static Object deepCopy(Object obj) {
        try {
            ByteArrayOutputStream buf=new ByteArrayOutputStream();
            ObjectOutputStream oos=new ObjectOutputStream(buf);
            oos.writeObject(obj);
            oos.close();
            byte[] ary=buf.toByteArray();
            ObjectInputStream ois=new ObjectInputStream(new ByteArrayInputStream(ary));
            Object o=ois.readObject();
            ois.close();
            return o;
        }catch(Exception e) {
            throw new RuntimeException(e);
        }
    }
    public static void cp(File from,File to) {
        try {
            InputStream in=new FileInputStream(from);
            OutputStream out=new FileOutputStream(to);
            byte[] buf=new byte[1024];
            int n;
            while((n=in.read(buf))!=-1) {
                out.write(buf,0,n);
            }
            in.close();
            out.close();
        }catch(IOException e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        }
    }
    public static void cpl(File from,File to) {
        try {
            InputStream in=new FileInputStream(from);
            OutputStream out=new FileOutputStream(to);
            int b;
            while((b=in.read())!=-1) {
                out.write(b);
            }
            in.close();
            out.close();
        }catch(IOException e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        }
    }
    public static void cp(String from,String to) {
        cp(new File(from),new File(to));
    }
    /**将文件按照16进制形式打印到控制台，每16个byte为一行*/
    public static void print(File file) {
        try {
            InputStream in=new FileInputStream(file);
            int b;
            int i=1;
            while((b=in.read())!=-1) {
                if(b<=0xf)
                    System.out.print("0");
                System.out.print(Integer.toHexString(b)+" ");
                if(i++%16==0) {
                    System.out.println();
                }
            }
            System.out.println();
            in.close();
        }catch(IOException e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        }
    }
    public static void print(String file) {
        print(new File(file));
    }
    public static void split(String file,int size) {
        try {
            if(size<=0) {
                throw new IllegalArgumentException("搞啥呀！");
            }
            int idx=0;
            InputStream in=new BufferedInputStream(new FileInputStream(file));
            OutputStream out=new BufferedOutputStream(new FileOutputStream(file+"."+idx++));
            int b;
            int count=0;
            while((b=in.read())!=-1) {
                out.write(b);
                count++;
                if(count%(size*1024)==0) {
                    out.close();
                    out=new BufferedOutputStream(new FileOutputStream(file+"."+idx++));
                }
            }
            in.close();
            out.close();
        }catch(IOException e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        }
    }
    public static void join(String file) {
        try {
            String filename=file.substring(0,file.lastIndexOf("."));
            String num=file.substring(file.lastIndexOf(".")+1);
            int idx=Integer.parseInt(num);
            OutputStream out=new FileOutputStream(filename);
            File f=new File(filename+"."+idx++);
            while(f.exists()) {
                InputStream in=new FileInputStream(f);
                cp(in,out);
                in.close();
                f=new File(filename+"."+idx++);
            }
            out.close();
        }catch(IOException e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        }
    }
    public static void cp(InputStream in,OutputStream out) throws IOException{
        byte[] buf=new byte[1024*512];
        int count;
        while((count=in.read(buf))!=-1) {
            out.write(buf,0,count);
        }
        out.flush();
    }
}