读文件java

转自：http://hi.baidu.com/0_net/blog/item/8566fc2bb730c293033bf63e.html

一.获得控制台用户输入的信息

    public String getInputMessage() throws IOException...{
        System.out.println("请输入您的命令∶");
        byte buffer[]=new byte[1024];
        int count=System.in.read(buffer);
        char[] ch=new char[count-2];//最后两位为结束符，删去不要
        for(int i=0;i<count-2;i++)
            ch[i]=(char)buffer[i];
        String str=new String(ch);
        return str;
    }
    可以返回用户输入的信息，不足之处在于不支持中文输入，有待进一步改进。

    二.复制文件
    1.以文件流的方式复制文件

    public void copyFile(String src,String dest) throwsIOException...{
        FileInputStream in=new FileInputStream(src);
        File file=new File(dest);
        if(!file.exists())
            file.createNewFile();
        FileOutputStream out=new FileOutputStream(file);
        int c;
        byte buffer[]=new byte[1024];
        while((c=in.read(buffer))!=-1)...{
            for(int i=0;i<c;i++)
                out.write(buffer[i]);        
        }
        in.close();
        out.close();
    }
    该方法经过测试，支持中文处理，并且可以复制多种类型，比如txt，xml，jpg，doc等多种格式

    三.写文件

    1.利用PrintStream写文件

    public void PrintStreamDemo()...{
        try ...{
            FileOutputStream out=new FileOutputStream("D:/test.txt");
            PrintStream p=new PrintStream(out);
            for(int i=0;i<10;i++)
                p.println("This is "+i+" line");
        } catch (FileNotFoundException e) ...{
            e.printStackTrace();
        }
    }
    2.利用StringBuffer写文件
public void StringBufferDemo() throws IOException......{
        File file=new File("/root/sms.log");
        if(!file.exists())
            file.createNewFile();
        FileOutputStream out=newFileOutputStream(file,true);        
        for(int i=0;i<10000;i++)......{
            StringBuffer sb=new StringBuffer();
            sb.append("这是第"+i+"行:前面介绍的各种方法都不关用,为什么总是奇怪的问题 ");
            out.write(sb.toString().getBytes("utf-8"));
        }        
        out.close();
    }
    该方法可以设定使用何种编码，有效解决中文问题。
四.文件重命名
    
    public void renameFile(String path,String oldname,Stringnewname)...{
        if(!oldname.equals(newname))...{//新的文件名和以前文件名不同时,才有必要进行重命名
            File oldfile=new File(path+"/"+oldname);
            File newfile=new File(path+"/"+newname);
            if(newfile.exists())//若在该目录下已经有一个文件和新文件名相同，则不允许重命名
                System.out.println(newname+"已经存在！");
            else...{
                oldfile.renameTo(newfile);
            }
        }         
    }

  五.转移文件目录
    转移文件目录不等同于复制文件，复制文件是复制后两个目录都存在该文件，而转移文件目录则是转移后，只有新目录中存在该文件。
    
    public void changeDirectory(String filename,String oldpath,Stringnewpath,boolean cover)...{
        if(!oldpath.equals(newpath))...{
            File oldfile=new File(oldpath+"/"+filename);
            File newfile=new File(newpath+"/"+filename);
            if(newfile.exists())...{//若在待转移目录下，已经存在待转移文件
                if(cover)//覆盖
                    oldfile.renameTo(newfile);
                else
                    System.out.println("在新目录下已经存在："+filename);
            }
            else...{
                oldfile.renameTo(newfile);
            }
        }       
    }
    六.读文件
    1.利用FileInputStream读取文件
    
    public String FileInputStreamDemo(String path) throwsIOException...{
        File file=new File(path);
        if(!file.exists()||file.isDirectory())
            throw new FileNotFoundException();
        FileInputStream fis=new FileInputStream(file);
        byte[] buf = new byte[1024];
        StringBuffer sb=new StringBuffer();
        while((fis.read(buf))!=-1)...{
            sb.append(newString(buf));    
            buf=new byte[1024];//重新生成，避免和上次读取的数据重复
        }
        return sb.toString();
    }
2.利用BufferedReader读取

    在IO操作，利用BufferedReader和BufferedWriter效率会更高一点

    
    public String BufferedReaderDemo(String path) throwsIOException...{
        File file=new File(path);
        if(!file.exists()||file.isDirectory())
            throw new FileNotFoundException();
        BufferedReader br=new BufferedReader(new FileReader(file));
        String temp=null;
        StringBuffer sb=new StringBuffer();
        temp=br.readLine();
        while(temp!=null)...{
            sb.append(temp+" ");
            temp=br.readLine();
        }
        return sb.toString();
    }

    3.利用dom4j读取xml文件

    
    public Document readXml(String path) throws DocumentException,IOException...{
        File file=new File(path);
        BufferedReader bufferedreader = new BufferedReader(newFileReader(file));
        SAXReader saxreader = new SAXReader();
        Document document = (Document)saxreader.read(bufferedreader);
        bufferedreader.close();
        return document;
    }
    七.创建文件(文件夹)

1.创建文件夹  
    public void createDir(String path)...{
        File dir=new File(path);
        if(!dir.exists())
            dir.mkdir();
    }
2.创建新文件
    public void createFile(String path,String filename) throwsIOException...{
        File file=new File(path+"/"+filename);
        if(!file.exists())
            file.createNewFile();
    }
    八.删除文件(目录)
1.删除文件     
    public void delFile(String path,String filename)...{
        File file=new File(path+"/"+filename);
        if(file.exists()&&file.isFile())
            file.delete();
    }
2.删除目录
要利用File类的delete()方法删除目录时，必须保证该目录下没有文件或者子目录，否则删除失败，因此在实际应用中，我们要删除目录，必须利用递归删除该目录下的所有子目录和文件，然后再删除该目录。  
    public void delDir(String path)...{
        File dir=new File(path);
        if(dir.exists())...{
            File[] tmp=dir.listFiles();
            for(int i=0;i<tmp.length;i++)...{
                if(tmp[i].isDirectory())...{
                    delDir(path+"/"+tmp[i].getName());
                }
                else...{
                    tmp[i].delete();
                }
            }
            dir.delete();
        }
    }

使用NIO的FileChannel和ByteBuffer高效读取文件

2009-11-08 14:18

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;

public class ReadWriteCompare
{

public static void main(String[] args) throws IOException
{
FileInputStream fileInputStream = new FileInputStream("f:"+ File.separator +"IBM e-Mentor Program Kickoff Night 1105.pdf");
FileOutputStream fileOutputStream = new FileOutputStream("f:" + File.separator + "test.pdf");
   FileChannel inChannel = fileInputStream.getChannel();
FileChannel outChannel= fileOutputStream.getChannel();

ByteBuffer byteBuffer = ByteBuffer.allocate(1024);

   //Direct Buffer的效率会更高。
//   ByteBuffer byteBuffer = ByteBuffer.allocateDirect(1024);     

   long start = System.currentTimeMillis();
while(true)
{
int eof = inChannel.read(byteBuffer);
if(eof == -1 ) break;
byteBuffer.flip();
    outChannel.write(byteBuffer);
byteBuffer.clear();
}
System.out.println("spending : " + (System.currentTimeMillis()-start));
inChannel.close();
outChannel.close();
}

}