读取Java文件到byte数组的三种方式

import java.io.BufferedInputStream;  
import java.io.ByteArrayOutputStream;  
import java.io.File;  
import java.io.FileInputStream;  
import java.io.FileNotFoundException;  
import java.io.IOException;  
import java.io.RandomAccessFile;  
import java.nio.ByteBuffer;  
import java.nio.MappedByteBuffer;  
import java.nio.channels.FileChannel;  
import java.nio.channels.FileChannel.MapMode;  
  
  
public class FileUtils {  
  
    /** 
     * the traditional io way  
     * @param filename 
     * @return 
     * @throws IOException 
     */  
    public static byte[] toByteArray(String filename) throws IOException{  
          
        File f = new File(filename);  
        if(!f.exists()){  
            throw new FileNotFoundException(filename);  
        }  
  
        ByteArrayOutputStream bos = new ByteArrayOutputStream((int)f.length());  
        BufferedInputStream in = null;  
        try{  
            in = new BufferedInputStream(new FileInputStream(f));  
            int buf_size = 1024;  
            byte[] buffer = new byte[buf_size];  
            int len = 0;  
            while(-1 != (len = in.read(buffer,0,buf_size))){  
                bos.write(buffer,0,len);  
            }  
            return bos.toByteArray();  
        }catch (IOException e) {  
            e.printStackTrace();  
            throw e;  
        }finally{  
            try{  
                in.close();  
            }catch (IOException e) {  
                e.printStackTrace();  
            }  
            bos.close();  
        }  
    }  
      
      
    /** 
     * NIO way 
     * @param filename 
     * @return 
     * @throws IOException 
     */  
    public static byte[] toByteArray2(String filename)throws IOException{  
          
        File f = new File(filename);  
        if(!f.exists()){  
            throw new FileNotFoundException(filename);  
        }  
          
        FileChannel channel = null;  
        FileInputStream fs = null;  
        try{  
            fs = new FileInputStream(f);  
            channel = fs.getChannel();  
            ByteBuffer byteBuffer = ByteBuffer.allocate((int)channel.size());  
            while((channel.read(byteBuffer)) > 0){  
                // do nothing  
//              System.out.println("reading");  
            }  
            return byteBuffer.array();  
        }catch (IOException e) {  
            e.printStackTrace();  
            throw e;  
        }finally{  
            try{  
                channel.close();  
            }catch (IOException e) {  
                e.printStackTrace();  
            }  
            try{  
                fs.close();  
            }catch (IOException e) {  
                e.printStackTrace();  
            }  
        }  
    }  
      
      
    /** 
     * Mapped File  way 
     * MappedByteBuffer 可以在处理大文件时，提升性能 
     * @param filename 
     * @return 
     * @throws IOException 
     */  
    public static byte[] toByteArray3(String filename)throws IOException{  
          
        FileChannel fc = null;  
        try{  
            fc = new RandomAccessFile(filename,"r").getChannel();  
            MappedByteBuffer byteBuffer = fc.map(MapMode.READ_ONLY, 0, fc.size()).load();  
            System.out.println(byteBuffer.isLoaded());  
            byte[] result = new byte[(int)fc.size()];  
            if (byteBuffer.remaining() > 0) {  
//              System.out.println("remain");  
                byteBuffer.get(result, 0, byteBuffer.remaining());  
            }  
            return result;  
        }catch (IOException e) {  
            e.printStackTrace();  
            throw e;  
        }finally{  
            try{  
                fc.close();  
            }catch (IOException e) {  
                e.printStackTrace();  
            }  
        }  
    }  
}