java常用的文件读写操作

jopen 4年前

现在算算已经做java开发两年了,回过头想想还真是挺不容易的,java的东西是比较复杂但是如果基础功扎实的话能力的提升就很快,这次特别整理了点有关文件操作的常用代码和大家分享

1.文件的读取(普通方式)

(1)第一种方法

    File f=new File("d:"+File.separator+"test.txt");        InputStream in=new FileInputStream(f);        byte[] b=new byte[(int)f.length()];        int len=0;        int temp=0;        while((temp=in.read())!=-1){               b[len]=(byte)temp;               len++;        }        System.out.println(new String(b,0,len,"GBK"));        in.close();  
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这种方法貌似用的比较多一点

(2)第二种方法

    File f=new File("d:"+File.separator+"test.txt");        InputStream in=new FileInputStream(f);        byte[] b=new byte[1024];        int len=0;        while((len=in.read(b))!=-1){            System.out.println(new String(b,0,len,"GBK"));         }        in.close();  
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2.文件读取(内存映射方式)
    File f=new File("d:"+File.separator+"test.txt");        FileInputStream in=new FileInputStream(f);        FileChannel chan=in.getChannel();        MappedByteBuffer buf=chan.map(FileChannel.MapMode.READ_ONLY, 0, f.length());        byte[] b=new byte[(int)f.length()];        int len=0;        while(buf.hasRemaining()){           b[len]=buf.get();            len++;         }        chan.close();        in.close();        System.out.println(new String(b,0,len,"GBK"));  
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这种方式的效率是最好的,速度也是最快的,因为程序直接操作的是内存

 

3.文件复制(边读边写)操作

(1)比较常用的方式

 
package org.lxh;        import java.io.File;    import java.io.FileInputStream;    import java.io.FileOutputStream;    import java.io.InputStream;    import java.io.OutputStream;        public class ReadAndWrite {            public static void main(String[] args) throws Exception {            File f=new File("d:"+File.separator+"test.txt");            InputStream in=new FileInputStream(f);            OutputStream out=new FileOutputStream("e:"+File.separator+"test.txt");            int temp=0;            while((temp=in.read())!=-1){                out.write(temp);            }            out.close();            in.close();        }        } 

(2)使用内存映射的实现
package org.lxh;        import java.io.File;    import java.io.FileInputStream;    import java.io.FileOutputStream;    import java.nio.ByteBuffer;    import java.nio.channels.FileChannel;    public class ReadAndWrite2 {           public static void main(String[] args) throws Exception {        File f=new File("d:"+File.separator+"test.txt");        FileInputStream in=new FileInputStream(f);        FileOutputStream out=new FileOutputStream("e:"+File.separator+"test.txt");            FileChannel fin=in.getChannel();            FileChannel fout=out.getChannel();            //开辟缓冲            ByteBuffer buf=ByteBuffer.allocate(1024);            while((fin.read(buf))!=-1){                //重设缓冲区                buf.flip();                //输出缓冲区                fout.write(buf);                //清空缓冲区                buf.clear();            }            fin.close();            fout.close();            in.close();            out.close();        }        }  
</div> </div> 来自:http://blog.csdn.net/smartcodekm/article/details/25914785