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();
			}
		}
	}
}

 

评论

1 楼 jiiming 2014-05-26  

在第一个方法里面，第39行返回的时候，流是否需要关闭一下？