读取Java文件到byte数组的三种方式

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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();}}}}
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