前言

众所周知，Java中有多种针对文件的操作类，以面向字节流和字符流可分为两大类，这里以写入为例：

面向字节流的：FileOutputStream 和 BufferedOutputStream

面向字符流的：FileWriter 和 BufferedWriter

近年来发展出New I/O ，也叫NIO，里面又包装了两个类：NewOutputStream 和 NewBufferedWriter

现在，我们建立测试程序，比较这些类写入文件的性能。

机器配置

Processor Name: Intel Core i7

Processor Speed: 2.2 GHz

Number of Processors: 1

Total Number of Cores: 4

L2 Cache (per Core): 256 KB

L3 Cache: 6 MB

Memory: 16 GB

测试程序

纵向比较：几种文件操作类向文件中写入相同行数的内容(每行内容均为“写入文件Datan”)，比较其耗费时间

横向比较：对于同一个文件操作类，比较写入不同行数内容情况下所耗费时间；本文以2的次方指数级增长行数

1 importjava.io.File;2 importjava.io.FileOutputStream;3 import java.io.*;4 importjava.nio.file.Files;5 importjava.nio.file.Paths;6

7 public classtestFileIO {8

9 public static void testDriver () throwsIOException {10 int maxlineNum = 100000001;//写入文件的最大行数

11 int startlineNum = 1;//写入文件的行数

12 int Multiplying = 2;//行数增长倍率

13

14 long begin = 0L;15 long end = 0L;16

17 //将时间统计写入文件Result.txt中

18 FileWriter fileWriter = new FileWriter("./Result.txt", true);19 BufferedWriter bufferedWriter = newBufferedWriter(fileWriter);20

21 System.out.println("Test FileOutputStream begin.");22 for (int lineNum = startlineNum; lineNum < maxlineNum; lineNum *=Multiplying) {23 begin =System.currentTimeMillis();24 testFileOutputStream(lineNum);25 end =System.currentTimeMillis();26 long timeElapse_FileOutputStream = end -begin;27 bufferedWriter.write(String.valueOf(timeElapse_FileOutputStream)+"t");28 }29 System.out.println("Test FileOutputStream end.n");30

31 System.out.println("Test BufferedOutputStream begin.");32 bufferedWriter.write("n");33 for (int lineNum = startlineNum; lineNum < maxlineNum; lineNum *=Multiplying) {34 begin =System.currentTimeMillis();35 testBufferedOutputStream(lineNum);36 end =System.currentTimeMillis();37 long timeElapse_BufferedOutputStream = end -begin;38 bufferedWriter.write(String.valueOf(timeElapse_BufferedOutputStream)+"t");39 }40 System.out.println("Test BufferedOutputStream end.n");41

42 System.out.println("Test FileWriter begin.");43 bufferedWriter.write("n");44 for (int lineNum = startlineNum; lineNum < maxlineNum; lineNum *=Multiplying) {45 begin =System.currentTimeMillis();46 testFileWriter(lineNum);47 end =System.currentTimeMillis();48 long timeElapse_FileWriter = end -begin;49 bufferedWriter.write(String.valueOf(timeElapse_FileWriter)+"t");50 }51 System.out.println("Test FileWriter end.n");52

53 System.out.println("Test BufferedWriter begin.");54 bufferedWriter.write("n");55 for (int lineNum = startlineNum; lineNum < maxlineNum; lineNum *=Multiplying) {56 begin =System.currentTimeMillis();57 testBufferedWriter(lineNum);58 end =System.currentTimeMillis();59 long timeElapse_BufferedWriter = end -begin;60 bufferedWriter.write(String.valueOf(timeElapse_BufferedWriter)+"t");61 }62 System.out.println("Test BufferedWriter end.n");63

64 System.out.println("Test NewOutputStream begin.");65 bufferedWriter.write("n");66 for (int lineNum = startlineNum; lineNum < maxlineNum; lineNum *=Multiplying) {67 begin =System.currentTimeMillis();68 testNewOutputStream(lineNum);69 end =System.currentTimeMillis();70 long timeElapse_NewOutputStream = end -begin;71 bufferedWriter.write(String.valueOf(timeElapse_NewOutputStream)+"t");72 }73 System.out.println("Test NewOutputStream end.n");74

75 System.out.println("Test NewBufferedWriter begin.");76 bufferedWriter.write("n");77 for (int lineNum = startlineNum; lineNum < maxlineNum; lineNum *=Multiplying) {78 begin =System.currentTimeMillis();79 testNewBufferedWriter(lineNum);80 end =System.currentTimeMillis();81 long timeElapse_NewBufferedWriter = end -begin;82 bufferedWriter.write(String.valueOf(timeElapse_NewBufferedWriter)+"t");83 }84 System.out.println("Test NewOutputStream end.n");85

86 bufferedWriter.close();87 }88

89 /************************** I/O *****************************/

90 //面向字节

91 public static void testFileOutputStream (int lineNum) throwsIOException {92 FileOutputStream fileOutputStream = new FileOutputStream(new File("./testFileOutputStream.txt"));93 while (--lineNum > 0) {94 fileOutputStream.write("写入文件Datan".getBytes());95 }96 fileOutputStream.close();97 }98

99 public static void testBufferedOutputStream (int lineNum) throwsIOException {100 FileOutputStream fileOutputStream = new FileOutputStream(new File("./testBufferedOutputStream.txt"));101 BufferedOutputStream bufferedOutputStream = newBufferedOutputStream(fileOutputStream);102 while (--lineNum > 0) {103 bufferedOutputStream.write("写入文件Datan".getBytes());104 }105 bufferedOutputStream.close();106 }107

108 //面向字符

109 public static void testFileWriter (int lineNum) throwsIOException {110 FileWriter fileWriter = new FileWriter("./testFileWriter.txt");111 while (--lineNum > 0) {112 fileWriter.write("写入文件Datan");113 }114 fileWriter.close();115 }116

117 public static void testBufferedWriter (int lineNum) throwsIOException {118 FileWriter fileWriter = new FileWriter("./testBufferedWriter.txt");119 BufferedWriter bufferedWriter = newBufferedWriter(fileWriter);120 while (--lineNum > 0) {121 bufferedWriter.write("写入文件Datan");122 }123 bufferedWriter.close();124 }125

126

127 /************************** NIO ****************************/

128 public static void testNewOutputStream (int lineNum) throwsIOException {129 OutputStream outputStream = Files.newOutputStream(Paths.get("./testNewOutputStream.txt"));130 while (--lineNum > 0) {131 outputStream.write("写入文件Datan".getBytes());132 }133 outputStream.close();134 }135

136 public static void testNewBufferedWriter (int lineNum) throwsIOException {137 BufferedWriter newBufferedReader = Files.newBufferedWriter(Paths.get("./testNewBufferedWriter.txt"));138 while (--lineNum > 0) {139 newBufferedReader.write("写入文件Datan");140 }141 newBufferedReader.close();142 }143

144

145 public static void main (String[] args) throwsIOException {146 //多次测试时可清空result.txt文件

147 FileWriter fileWriter = new FileWriter("./Result.txt");148 testDriver();149 }150 }

测试结果

从上图可以看出，写入行数超过20W以上时，FileOutputStream和NewOutputStream耗费时间远远超出其他4个类。为了清晰，让我们放大其他4个类的图：

可以看出，这4个类中，BufferWriter和NewBufferedWriter所耗费时间更少，但总体差别不是很大。

让我们再来看看，写入26W行数据以下时的情况：

可以看出，在数据量较小的情况下，这4个类所耗费时间的差异并不是很大，在更小的数据量下，它们的效率几乎没有差别。

后记

从以上分析可知(注意横坐标写入行数是指数级增加的)，各个类的时间复杂度大致为O(1/kn)，其中不同的类的k不同，导致了最终巨大的差异。

这里只给出了测试结果，并未分析其底层实现原理，欢迎评论区留言。

另外，我没有在其他机器测试，有兴趣的小伙伴可以将自己的测试结果发出来，共同进步^_^

附件

本次测试数据结果(若看不清，可以下载到本地看)