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Java文件操作类效率对比

2018-08-26 17:19:36来源：博客园阅读 ()

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Data\n”），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 import java.io.File;
  2 import java.io.FileOutputStream;
  3 import java.io.*;
  4 import java.nio.file.Files;
  5 import java.nio.file.Paths;
  6 
  7 public class testFileIO {
  8 
  9     public static void testDriver () throws IOException {
 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 = new BufferedWriter(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) throws IOException {
 92         FileOutputStream fileOutputStream = new FileOutputStream(new File("./testFileOutputStream.txt"));
 93         while (--lineNum > 0) {
 94             fileOutputStream.write("写入文件Data\n".getBytes());
 95         }
 96         fileOutputStream.close();
 97     }
 98 
 99     public static void testBufferedOutputStream (int lineNum) throws IOException {
100         FileOutputStream fileOutputStream = new FileOutputStream(new File("./testBufferedOutputStream.txt"));
101         BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(fileOutputStream);
102         while (--lineNum > 0) {
103             bufferedOutputStream.write("写入文件Data\n".getBytes());
104         }
105         bufferedOutputStream.close();
106     }
107 
108     //面向字符
109     public static void testFileWriter (int lineNum) throws IOException {
110         FileWriter fileWriter = new FileWriter("./testFileWriter.txt");
111         while (--lineNum > 0) {
112             fileWriter.write("写入文件Data\n");
113         }
114         fileWriter.close();
115     }
116 
117     public static void testBufferedWriter (int lineNum) throws IOException {
118         FileWriter fileWriter = new FileWriter("./testBufferedWriter.txt");
119         BufferedWriter bufferedWriter = new BufferedWriter(fileWriter);
120         while (--lineNum > 0) {
121             bufferedWriter.write("写入文件Data\n");
122         }
123         bufferedWriter.close();
124     }
125 
126 
127     /************************** NIO ****************************/
128     public static void testNewOutputStream (int lineNum) throws IOException {
129         OutputStream outputStream = Files.newOutputStream(Paths.get("./testNewOutputStream.txt"));
130         while (--lineNum > 0) {
131             outputStream.write("写入文件Data\n".getBytes());
132         }
133         outputStream.close();
134     }
135 
136     public static void testNewBufferedWriter (int lineNum) throws IOException {
137         BufferedWriter newBufferedReader = Files.newBufferedWriter(Paths.get("./testNewBufferedWriter.txt"));
138         while (--lineNum > 0) {
139             newBufferedReader.write("写入文件Data\n");
140         }
141         newBufferedReader.close();
142     }
143 
144 
145     public static void main (String[] args) throws IOException {
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(k)，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，可以将浏览器字体放大，或下载到本地看)

~~~~~~~~~~~~~~~~~~~~~分割线~~~~~~~~~~~~~~~~~~~~~~~

评论区小伙伴“ andorxor”提出：

XXXOutputStream是用来写二进制的，你把字符串转换成字节数组再写自然就慢了，主要慢在转换的过程。

因此，将程序修改，提前把字符和字节内容都准备好，再次验证。新程序如下：

  1 import java.io.File;
  2 import java.io.FileOutputStream;
  3 import java.io.*;
  4 import java.nio.file.Files;
  5 import java.nio.file.Paths;
  6 
  7 public class testFileIO {
  8 
  9 
 10     public static void testDriver () throws IOException {
 11         int maxlineNum = 100000001;//写入文件的最大行数
 12         int startlineNum = 1;//写入文件的行数
 13         int Multiplying = 2;//行数增长倍率
 14 
 15         String contentChars = "写入文件Data\n";//每行的内容（字符流）
 16         byte[] contentBytes = "写入文件Data\n".getBytes();//每行的内容（字节流）
 17 
 18         long begin = 0L;
 19         long end = 0L;
 20 
 21         //将时间统计写入文件Result.txt中
 22         FileWriter fileWriter = new FileWriter("./Result.txt", true);
 23         BufferedWriter bufferedWriter = new BufferedWriter(fileWriter);
 24 
 25         System.out.println("Test FileOutputStream begin.");
 26         for (int lineNum = startlineNum; lineNum < maxlineNum; lineNum *= Multiplying) {
 27             begin = System.currentTimeMillis();
 28             testFileOutputStream(lineNum,contentBytes);
 29             end = System.currentTimeMillis();
 30             long timeElapse_FileOutputStream = end - begin;
 31             bufferedWriter.write(String.valueOf(timeElapse_FileOutputStream)+"\t");
 32         }
 33         System.out.println("Test FileOutputStream end.\n");
 34 
 35         System.out.println("Test BufferedOutputStream begin.");
 36         bufferedWriter.write("\n");
 37         for (int lineNum = startlineNum; lineNum < maxlineNum; lineNum *= Multiplying) {
 38             begin = System.currentTimeMillis();
 39             testBufferedOutputStream(lineNum,contentBytes);
 40             end = System.currentTimeMillis();
 41             long timeElapse_BufferedOutputStream = end - begin;
 42             bufferedWriter.write(String.valueOf(timeElapse_BufferedOutputStream)+"\t");
 43         }
 44         System.out.println("Test BufferedOutputStream end.\n");
 45 
 46         System.out.println("Test FileWriter begin.");
 47         bufferedWriter.write("\n");
 48         for (int lineNum = startlineNum; lineNum < maxlineNum; lineNum *= Multiplying) {
 49             begin = System.currentTimeMillis();
 50             testFileWriter(lineNum,contentChars);
 51             end = System.currentTimeMillis();
 52             long timeElapse_FileWriter = end - begin;
 53             bufferedWriter.write(String.valueOf(timeElapse_FileWriter)+"\t");
 54         }
 55         System.out.println("Test FileWriter end.\n");
 56 
 57         System.out.println("Test BufferedWriter begin.");
 58         bufferedWriter.write("\n");
 59         for (int lineNum = startlineNum; lineNum < maxlineNum; lineNum *= Multiplying) {
 60             begin = System.currentTimeMillis();
 61             testBufferedWriter(lineNum,contentChars);
 62             end = System.currentTimeMillis();
 63             long timeElapse_BufferedWriter = end - begin;
 64             bufferedWriter.write(String.valueOf(timeElapse_BufferedWriter)+"\t");
 65         }
 66         System.out.println("Test BufferedWriter end.\n");
 67 
 68         System.out.println("Test NewOutputStream begin.");
 69         bufferedWriter.write("\n");
 70         for (int lineNum = startlineNum; lineNum < maxlineNum; lineNum *= Multiplying) {
 71             begin = System.currentTimeMillis();
 72             testNewOutputStream(lineNum,contentBytes);
 73             end = System.currentTimeMillis();
 74             long timeElapse_NewOutputStream = end - begin;
 75             bufferedWriter.write(String.valueOf(timeElapse_NewOutputStream)+"\t");
 76         }
 77         System.out.println("Test NewOutputStream end.\n");
 78 
 79         System.out.println("Test NewBufferedWriter begin.");
 80         bufferedWriter.write("\n");
 81         for (int lineNum = startlineNum; lineNum < maxlineNum; lineNum *= Multiplying) {
 82             begin = System.currentTimeMillis();
 83             testNewBufferedWriter(lineNum,contentChars);
 84             end = System.currentTimeMillis();
 85             long timeElapse_NewBufferedWriter = end - begin;
 86             bufferedWriter.write(String.valueOf(timeElapse_NewBufferedWriter)+"\t");
 87         }
 88         System.out.println("Test NewOutputStream end.\n");
 89 
 90         bufferedWriter.close();
 91     }
 92 
 93     /************************** I/O *****************************/
 94     //面向字节
 95     public static void testFileOutputStream (int lineNum, byte[] content) throws IOException {
 96         FileOutputStream fileOutputStream = new FileOutputStream(new File("./testFileOutputStream.txt"));
 97         while (--lineNum > 0) {
 98             fileOutputStream.write(content);
 99         }
100         fileOutputStream.close();
101     }
102 
103     public static void testBufferedOutputStream (int lineNum, byte[] content) throws IOException {
104         FileOutputStream fileOutputStream = new FileOutputStream(new File("./testBufferedOutputStream.txt"));
105         BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(fileOutputStream);
106         while (--lineNum > 0) {
107             bufferedOutputStream.write(content);
108         }
109         bufferedOutputStream.close();
110     }
111 
112     //面向字符
113     public static void testFileWriter (int lineNum, String content) throws IOException {
114         FileWriter fileWriter = new FileWriter("./testFileWriter.txt");
115         while (--lineNum > 0) {
116             fileWriter.write(content);
117         }
118         fileWriter.close();
119     }
120 
121     public static void testBufferedWriter (int lineNum, String content) throws IOException {
122         FileWriter fileWriter = new FileWriter("./testBufferedWriter.txt");
123         BufferedWriter bufferedWriter = new BufferedWriter(fileWriter);
124         while (--lineNum > 0) {
125             bufferedWriter.write(content);
126         }
127         bufferedWriter.close();
128     }
129 
130 
131     /************************** NIO ****************************/
132     public static void testNewOutputStream (int lineNum, byte[] content) throws IOException {
133         OutputStream outputStream = Files.newOutputStream(Paths.get("./testNewOutputStream.txt"));
134         while (--lineNum > 0) {
135             outputStream.write(content);
136         }
137         outputStream.close();
138     }
139 
140     public static void testNewBufferedWriter (int lineNum,String content) throws IOException {
141         BufferedWriter newBufferedReader = Files.newBufferedWriter(Paths.get("./testNewBufferedWriter.txt"));
142         while (--lineNum > 0) {
143             newBufferedReader.write(content);
144         }
145         newBufferedReader.close();
146     }
147 
148 
149     public static void main (String[] args) throws IOException {
150         //多次测试时可清空result.txt文件
151         FileWriter fileWriter = new FileWriter("./Result.txt");
152         testDriver();
153     }
154 }