How to use memory Mapping to process large Files in Java
本篇内容介绍了"Java中如何用内存映射处理大文件"的有关知识，在实际案例的操作过程中，不少人都会遇到这样的困境，接下来就让小编带领大家学习一下如何处理这些情况吧!希望大家仔细阅读，能够学有所成!
package test; import java.io.BufferedInputStream; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.IOException; import java.io.RandomAccessFile; import java.nio.MappedByteBuffer; import java.nio.channels.FileChannel; public class Test { public static void main(String[] args) { try { FileInputStream fis=new FileInputStream("/home/tobacco/test/res.txt"); int sum=0; int n; long t1=System.currentTimeMillis(); try { while((n=fis.read())>=0){ sum+=n; } } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } long t=System.currentTimeMillis()-t1; System.out.println("sum:"+sum+" time:"+t); } catch (FileNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } try { FileInputStream fis=new FileInputStream("/home/tobacco/test/res.txt"); BufferedInputStream bis=new BufferedInputStream(fis); int sum=0; int n; long t1=System.currentTimeMillis(); try { while((n=bis.read())>=0){ sum+=n; } } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } long t=System.currentTimeMillis()-t1; System.out.println("sum:"+sum+" time:"+t); } catch (FileNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } MappedByteBuffer buffer=null; try { buffer=new RandomAccessFile("/home/tobacco/test/res.txt","rw").getChannel().map(FileChannel.MapMode.READ_WRITE, 0, 1253244); int sum=0; int n; long t1=System.currentTimeMillis(); for(int i=0;i=0){ //sum+=n; } } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } long t=System.currentTimeMillis()-t1; System.out.println("sum:"+sum+" time:"+t); } catch (FileNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } try { FileInputStream fis=new FileInputStream("/home/tobacco/test/res.txt"); BufferedInputStream bis=new BufferedInputStream(fis); int sum=0; int n; long t1=System.currentTimeMillis(); try { while((n=bis.read())>=0){ //sum+=n; } } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } long t=System.currentTimeMillis()-t1; System.out.println("sum:"+sum+" time:"+t); } catch (FileNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } MappedByteBuffer buffer=null; try { buffer=new RandomAccessFile("/home/tobacco/test/res.txt","rw").getChannel().map(FileChannel.MapMode.READ_WRITE, 0, 1253244); int sum=0; int n; long t1=System.currentTimeMillis(); for(int i=0;i
