读取Java文件到byte数组的三种方法(总结)

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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