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读取Java文件到byte数组的三种方法(总结)

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读取Java文件到byte数组的三种方法(总结) 。

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package zs;
 
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 {
     public byte [] getContent(String filePath) throws IOException {
         File file = new File(filePath);
         long fileSize = file.length();
         if (fileSize > Integer.MAX_VALUE) {
             System.out.println( "file too big..." );
             return null ;
         }
         FileInputStream fi = new FileInputStream(file);
         byte [] buffer = new byte [( int ) fileSize];
         int offset = 0 ;
         int numRead = 0 ;
         while (offset < buffer.length
         && (numRead = fi.read(buffer, offset, buffer.length - offset)) >= 0 ) {
             offset += numRead;
         }
         // 确保所有数据均被读取
         if (offset != buffer.length) {
         throw new IOException( "Could not completely read file "
                     + file.getName());
         }
         fi.close();
         return buffer;
     }
 
     /**
      * 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();
             }
         }
     }
}

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