java读写文件摘抄

java IO以追加方式写文件FileWrite
文章分类:Java编程 
package com.demo.test; 

import java.io.BufferedWriter; 
import java.io.File; 
import java.io.FileWriter; 
import java.io.IOException; 

public class WriteFile { 
/** 
* fileName文件名不带扩展名 
* content写入内容 
* head CSV表头 
* @param fileName 
* @param content 
* @param head 
*/ 
public static void write(String fileName, String content, String head) { 
String dirPath = null; 
File dirFile = null; 
File file = null; 
FileWriter fw=null; 
BufferedWriter bw=null; 
try { 
dirPath = System.getProperty("user.dir") + File.separator 
+ "N2510data"; 
dirFile = new File(dirPath); 
if(!dirFile.exists()){ 
dirFile.mkdirs(); 
System.out.println(dirFile.getAbsolutePath()+"N2510data文件夹创建成功..."); 
} 
file = new File(dirFile, fileName + ".csv"); 
if (file.exists()) { 
if (file.length() > 1024 * 100) { 
File destFile = new File(dirFile, fileName + "-"+ System.currentTimeMillis() + ".csv"); 
file.renameTo(destFile); 
WriteFile.createFileAndWriteHead(file, head); 
} 
}else{ 
WriteFile.createFileAndWriteHead(file, head); 
} 
fw = new FileWriter(file, true); 
bw = new BufferedWriter(fw); 
bw.write(content); 
bw.newLine(); 
bw.flush(); 
bw.close(); 

} catch (IOException e) { 
e.printStackTrace(); 
}finally{ 
bw=null; 
fw=null; 
} 

} 

/** 
* 创建文件并写入表头 
* @param file 
* @param head 
*/ 
public static void createFileAndWriteHead(File file, String head) { 
FileWriter fw=null; 
BufferedWriter bw=null; 
try { 
if (!file.exists()) { 
if (file.createNewFile()) { 
fw = new FileWriter(file, true); 
bw = new BufferedWriter(fw); 
bw.write(head); 
bw.newLine(); 
bw.flush(); 
bw.close(); 
} else { 
System.out.println("When you create file has error..."); 
} 
} 
} catch (IOException e) { 
e.printStackTrace(); 
}finally{ 
bw=null; 
fw=null; 
} 
} 

public static void main(String args[]) { 
while (true) { 
int i = 0; 
WriteFile.write("ff", "1000000000000000000000000000000000000", 
"001,002,003"); 
i++; 
if (i > 100000) { 
break; 
} 
} 
} 

} 

import java.io.BufferedOutputStream;    
import java.io.File;    
import java.io.FileOutputStream;    
import java.io.FileWriter;    
import java.nio.ByteBuffer;    
import java.nio.channels.FileChannel;    
   
/**   
 * 测试各种写文件的方法性能。   
 *    
 * @author 老紫竹 JAVA世纪网(java2000.net)   
 *    
 */   
public class T {    
   
  public static void main(String[] args) {    
    FileOutputStream out = null;    
    FileOutputStream outSTr = null;    
    BufferedOutputStream Buff = null;    
    FileWriter fw = null;    
    int count = 1000000;// 写文件行数    
    try {    
      byte[] bs = "测试java 文件操作\r\n".getBytes();    
      out = new FileOutputStream(new File("C:/add.txt"));    
      long begin = System.currentTimeMillis();    
      for (int i = 0; i < count; i++) {    
        out.write(bs);    
      }    
      out.close();    
      long end = System.currentTimeMillis();    
      System.out.println("FileOutputStream执行耗时:" + (end - begin) + " 豪秒");    
   
      outSTr = new FileOutputStream(new File("C:/add0.txt"));    
      Buff = new BufferedOutputStream(outSTr);    
      long begin0 = System.currentTimeMillis();    
      for (int i = 0; i < count; i++) {    
        Buff.write(bs);    
      }    
      Buff.flush();    
      Buff.close();    
      long end0 = System.currentTimeMillis();    
      System.out.println("BufferedOutputStream执行耗时:" + (end0 - begin0) + " 豪秒");    
   
      fw = new FileWriter("C:/add2.txt");    
      long begin3 = System.currentTimeMillis();    
      for (int i = 0; i < count; i++) {    
        fw.write("测试java 文件操作\r\n");    
      }    
      fw.flush();    
      fw.close();    
      long end3 = System.currentTimeMillis();    
      System.out.println("FileWriter执行耗时:" + (end3 - begin3) + " 豪秒");    
   
      long begin4 = System.currentTimeMillis();    
      String path = "C:/add3.txt";    
      ByteBuffer bb = ByteBuffer.wrap(bs);    
      FileChannel out2 = new FileOutputStream(path).getChannel();    
      for (int i = 0; i < count; i++) {    
        out2.write(bb);    
        bb.rewind();    
      }    
   
      out2.close();    
      long end4 = System.currentTimeMillis();    
      System.out.println("FileChannel执行耗时:" + (end4 - begin4) + " 豪秒");    
    } catch (Exception e) {    
      e.printStackTrace();    
    } finally {    
      try {    
        fw.close();    
        Buff.close();    
        outSTr.close();    
        out.close();    
      } catch (Exception e) {    
        e.printStackTrace();    
      }    
    }    
  }    
}  

在我的笔记本上，运行结果如下 

FileOutputStream执行耗时:4891 豪秒 

BufferedOutputStream执行耗时:78 豪秒 

FileWriter执行耗时:438 豪秒 

FileChannel执行耗时:2812 豪秒 

当然最终生成的文件都是正确的 

总结： 

BufferedOutputStream 由于有缓冲，性能明显好 

FileOutputStream 性能最差，因为其每次都写入字节。 

FileWriter 性能很一般 

FileChannel使用了nio,但如果没有缓冲，必能太指望性能了