java io 流 效率

这几天在给公司查询一段代码的效率问题，我之前也大概在javaeye上问过就是关于我blog里 lucene索引文档的pdf,word,xls时的效率问题，今天又查了查感觉还是代码上的问题，于是又改了些代码，发现效率又很大的提高，所以把io 流效率的问题又仔细研究了下，留个笔记

import java.io.*;

public class IOTest {

public static void main(String[] args){

             IOTest io = new IOTest();

             try{

             long startTime = System.currentTimeMillis();

             io.readWrite("c:/temp/1.txt","c:/temp/2.txt");    

             long endTime = System.currentTimeMillis();

             System.out.println("Time taken for reading and writing using default behaviour : "

                                                           + (endTime - startTime) + " milli seconds" );

 

             long startTime1 = System.currentTimeMillis();

             io.readWriteBuffer("c:/temp/1.txt","c:/temp/2.txt");           

             long endTime1 = System.currentTimeMillis();

             System.out.println("Time taken for reading and writing using buffered streams : "

                                                           + (endTime1 - startTime1) + " milli seconds" );

 

             long startTime2 = System.currentTimeMillis();

             io.readWriteArray("c:/temp/1.txt","c:/temp/2.txt");             

             long endTime2 = System.currentTimeMillis();

             System.out.println("Time taken for reading and writing using custom buffering : "

                                                           + (endTime2 - startTime2) + " milli seconds" );

             }catch(IOException e){ e.printStackTrace();}

}

public static void readWrite(String fileFrom, String fileTo) throws IOException{

             InputStream in = null;

             OutputStream out = null;

             try{

                          in = new FileInputStream(fileFrom);

                          out = new FileOutputStream(fileTo);

                          while(true){

                                          int bytedata = in.read();

                                          if(bytedata == -1)

                                          break;

                                          out.write(bytedata);

                          }

             }

             finally{

              if(in != null)

                          in.close();

              if(out !=null)

                          out.close();

             }

}

public static void readWriteBuffer(String fileFrom, String fileTo) throws IOException{

             InputStream inBuffer = null;

             OutputStream outBuffer = null;

             try{

                          InputStream in = new FileInputStream(fileFrom);

                          inBuffer = new BufferedInputStream(in);

                          OutputStream out = new FileOutputStream(fileTo);

                          outBuffer = new BufferedOutputStream(out);

                          while(true){

                                          int bytedata = inBuffer.read();

                                          if(bytedata == -1)

                                          break;

                                          out.write(bytedata);

                          }

             }

             finally{

              if(inBuffer != null)

                          inBuffer.close();

              if(outBuffer !=null)

                          outBuffer.close();

             }

}          

public static void readWriteArray(String fileFrom, String fileTo) throws IOException{

             InputStream in = null;

             OutputStream out = null;

             try{

                          in = new FileInputStream(fileFrom);

                          out = new FileOutputStream(fileTo);

                          int availableLength = in.available();

                          byte[] totalBytes = new byte[availableLength];

                          int bytedata = in.read(totalBytes);

                          out.write(totalBytes);

                            

             }

             finally{

              if(in != null)

                          in.close();

              if(out !=null)

                          out.close();

             }

}          

}

Time taken for reading and writing using default behavior : 660 milli seconds

Time taken for reading and writing using buffered streams : 270 milli seconds

Time taken for reading and writing using custom buffering : 0 milli seconds

结果表明最后一种还最快的

评论

2 楼 xifo 2009-06-06  

应该还有更合理的处理方式：

public static void readWriteCustom(String from, String to) throws IOException{

		InputStream in = new FileInputStream(from);
		OutputStream out = new FileOutputStream(to);
		try {
			byte[] bytes = new byte[128*1024];
			int len;
			while ((len = in.read(bytes)) > 0) {
				out.write(bytes, 0, len);
			}
		}finally {
			if (in != null)in.close();
			if (out != null)out.close();
		}
	}

这是比较典型的流对象处理方式，通常不受内存限制，并且性能比楼主最后一种方式更好，经测试，复制一个3.25M的文件，时间可以减少到最后一种方式的一半。

1 楼 jenkinv 2007-07-30  

一般情况下，，内存与时间是矛盾体。时间下来了，内存上去了。
当然，读一个小小文件，内存也大不到哪去。
你提供的这个方法，速度倒是很理想。受教了，谢谢！