java---------------byte[]--------------操作

本文主要是介绍java---------------byte[]--------------操作，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

其他在java层创建数据：

 byte[] buffer = new byte[200];  
        for(int i=0;i<200;i+=10)
        buffer[i]=(byte)i;

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读取Java文件到byte数组的三种方式  （http://sharewind.iteye.com/blog/1582869）

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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