读取Java文件到byte数组的三种方式

原文链接：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();
             }
         }
     }
 }