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。
import java.io.File;
import java.io.FileOutputStream;
import java.io.*;
import java.nio.file.Files;
import java.nio.file.Paths;
public class testFileIO {
public static void testDriver () throws IOException {
int maxlineNum = 100000001;//写入文件的最大行数
int startlineNum = 1;//写入文件的行数
int Multiplying = 2;//行数增长倍率
long begin = 0L;
long end = 0L;
//将时间统计写入文件Result.txt中
FileWriter fileWriter = new FileWriter("./Result.txt", true);
BufferedWriter bufferedWriter = new BufferedWriter(fileWriter);
System.out.println("Test FileOutputStream begin.");
for (int lineNum = startlineNum; lineNum < maxlineNum; lineNum *= Multiplying) {
begin = System.currentTimeMillis();
testFileOutputStream(lineNum);
end = System.currentTimeMillis();
long timeElapse_FileOutputStream = end - begin;
bufferedWriter.write(String.valueOf(timeElapse_FileOutputStream)+"\t");
}
System.out.println("Test FileOutputStream end.\n");
System.out.println("Test BufferedOutputStream begin.");
bufferedWriter.write("\n");
for (int lineNum = startlineNum; lineNum < maxlineNum; lineNum *= Multiplying) {
begin = System.currentTimeMillis();
testBufferedOutputStream(lineNum);
end = System.currentTimeMillis();
long timeElapse_BufferedOutputStream = end - begin;
bufferedWriter.write(String.valueOf(timeElapse_BufferedOutputStream)+"\t");
}
System.out.println("Test BufferedOutputStream end.\n");
System.out.println("Test FileWriter begin.");
bufferedWriter.write("\n");
for (int lineNum = startlineNum; lineNum < maxlineNum; lineNum *= Multiplying) {
begin = System.currentTimeMillis();
testFileWriter(lineNum);
end = System.currentTimeMillis();
long timeElapse_FileWriter = end - begin;
bufferedWriter.write(String.valueOf(timeElapse_FileWriter)+"\t");
}
System.out.println("Test FileWriter end.\n");
System.out.println("Test BufferedWriter begin.");
bufferedWriter.write("\n");
for (int lineNum = startlineNum; lineNum < maxlineNum; lineNum *= Multiplying) {
begin = System.currentTimeMillis();
testBufferedWriter(lineNum);
end = System.currentTimeMillis();
long timeElapse_BufferedWriter = end - begin;
bufferedWriter.write(String.valueOf(timeElapse_BufferedWriter)+"\t");
}
System.out.println("Test BufferedWriter end.\n");
System.out.println("Test NewOutputStream begin.");
bufferedWriter.write("\n");
for (int lineNum = startlineNum; lineNum < maxlineNum; lineNum *= Multiplying) {
begin = System.currentTimeMillis();
testNewOutputStream(lineNum);
end = System.currentTimeMillis();
long timeElapse_NewOutputStream = end - begin;
bufferedWriter.write(String.valueOf(timeElapse_NewOutputStream)+"\t");
}
System.out.println("Test NewOutputStream end.\n");
System.out.println("Test NewBufferedWriter begin.");
bufferedWriter.write("\n");
for (int lineNum = startlineNum; lineNum < maxlineNum; lineNum *= Multiplying) {
begin = System.currentTimeMillis();
testNewBufferedWriter(lineNum);
end = System.currentTimeMillis();
long timeElapse_NewBufferedWriter = end - begin;
bufferedWriter.write(String.valueOf(timeElapse_NewBufferedWriter)+"\t");
}
System.out.println("Test NewOutputStream end.\n");
bufferedWriter.close();
}
/************************** I/O *****************************/
//面向字节
public static void testFileOutputStream (int lineNum) throws IOException {
FileOutputStream fileOutputStream = new FileOutputStream(new File("./testFileOutputStream.txt"));
while (--lineNum > 0) {
fileOutputStream.write("写入文件Data\n".getBytes());
}
fileOutputStream.close();
}
public static void testBufferedOutputStream (int lineNum) throws IOException {
FileOutputStream fileOutputStream = new FileOutputStream(new File("./testBufferedOutputStream.txt"));
BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(fileOutputStream);
while (--lineNum > 0) {
bufferedOutputStream.write("写入文件Data\n".getBytes());
}
bufferedOutputStream.close();
}
//面向字符
public static void testFileWriter (int lineNum) throws IOException {
FileWriter fileWriter = new FileWriter("./testFileWriter.txt");
while (--lineNum > 0) {
fileWriter.write("写入文件Data\n");
}
fileWriter.close();
}
public static void testBufferedWriter (int lineNum) throws IOException {
FileWriter fileWriter = new FileWriter("./testBufferedWriter.txt");
BufferedWriter bufferedWriter = new BufferedWriter(fileWriter);
while (--lineNum > 0) {
bufferedWriter.write("写入文件Data\n");
}
bufferedWriter.close();
}
/************************** NIO ****************************/
public static void testNewOutputStream (int lineNum) throws IOException {
OutputStream outputStream = Files.newOutputStream(Paths.get("./testNewOutputStream.txt"));
while (--lineNum > 0) {
outputStream.write("写入文件Data\n".getBytes());
}
outputStream.close();
}
public static void testNewBufferedWriter (int lineNum) throws IOException {
BufferedWriter newBufferedReader = Files.newBufferedWriter(Paths.get("./testNewBufferedWriter.txt"));
while (--lineNum > 0) {
newBufferedReader.write("写入文件Data\n");
}
newBufferedReader.close();
}
public static void main (String[] args) throws IOException {
//多次测试时可清空result.txt文件
FileWriter fileWriter = new FileWriter("./Result.txt");
testDriver();
}
}
测试结果，如图所示：
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：
import java.io.File;
import java.io.FileOutputStream;
import java.io.*;
import java.nio.file.Files;
import java.nio.file.Paths;
public class testFileIO {
public static void testDriver () throws IOException {
int maxlineNum = 100000001;//写入文件的最大行数
int startlineNum = 1;//写入文件的行数
int Multiplying = 2;//行数增长倍率
String contentChars = "写入文件Data\n";//每行的内容（字符流）
byte[] contentBytes = "写入文件Data\n".getBytes();//每行的内容（字节流）
long begin = 0L;
long end = 0L;
//将时间统计写入文件Result.txt中
FileWriter fileWriter = new FileWriter("./Result.txt", true);
BufferedWriter bufferedWriter = new BufferedWriter(fileWriter);
System.out.println("Test FileOutputStream begin.");
for (int lineNum = startlineNum; lineNum < maxlineNum; lineNum *= Multiplying) {
begin = System.currentTimeMillis();
testFileOutputStream(lineNum,contentBytes);
end = System.currentTimeMillis();
long timeElapse_FileOutputStream = end - begin;
bufferedWriter.write(String.valueOf(timeElapse_FileOutputStream)+"\t");
}
System.out.println("Test FileOutputStream end.\n");
System.out.println("Test BufferedOutputStream begin.");
bufferedWriter.write("\n");
for (int lineNum = startlineNum; lineNum < maxlineNum; lineNum *= Multiplying) {
begin = System.currentTimeMillis();
testBufferedOutputStream(lineNum,contentBytes);
end = System.currentTimeMillis();
long timeElapse_BufferedOutputStream = end - begin;
bufferedWriter.write(String.valueOf(timeElapse_BufferedOutputStream)+"\t");
}
System.out.println("Test BufferedOutputStream end.\n");
System.out.println("Test FileWriter begin.");
bufferedWriter.write("\n");
for (int lineNum = startlineNum; lineNum < maxlineNum; lineNum *= Multiplying) {
begin = System.currentTimeMillis();
testFileWriter(lineNum,contentChars);
end = System.currentTimeMillis();
long timeElapse_FileWriter = end - begin;
bufferedWriter.write(String.valueOf(timeElapse_FileWriter)+"\t");
}
System.out.println("Test FileWriter end.\n");
System.out.println("Test BufferedWriter begin.");
bufferedWriter.write("\n");
for (int lineNum = startlineNum; lineNum < maxlineNum; lineNum *= Multiplying) {
begin = System.currentTimeMillis();
testBufferedWriter(lineNum,contentChars);
end = System.currentTimeMillis();
long timeElapse_BufferedWriter = end - begin;
bufferedWriter.write(String.valueOf(timeElapse_BufferedWriter)+"\t");
}
System.out.println("Test BufferedWriter end.\n");
System.out.println("Test NewOutputStream begin.");
bufferedWriter.write("\n");
for (int lineNum = startlineNum; lineNum < maxlineNum; lineNum *= Multiplying) {
begin = System.currentTimeMillis();
testNewOutputStream(lineNum,contentBytes);
end = System.currentTimeMillis();
long timeElapse_NewOutputStream = end - begin;
bufferedWriter.write(String.valueOf(timeElapse_NewOutputStream)+"\t");
}
System.out.println("Test NewOutputStream end.\n");
System.out.println("Test NewBufferedWriter begin.");
bufferedWriter.write("\n");
for (int lineNum = startlineNum; lineNum < maxlineNum; lineNum *= Multiplying) {
begin = System.currentTimeMillis();
testNewBufferedWriter(lineNum,contentChars);
end = System.currentTimeMillis();
long timeElapse_NewBufferedWriter = end - begin;
bufferedWriter.write(String.valueOf(timeElapse_NewBufferedWriter)+"\t");
}
System.out.println("Test NewOutputStream end.\n");
bufferedWriter.close();
}
/************************** I/O *****************************/
//面向字节
public static void testFileOutputStream (int lineNum, byte[] content) throws IOException {
FileOutputStream fileOutputStream = new FileOutputStream(new File("./testFileOutputStream.txt"));
while (--lineNum > 0) {
fileOutputStream.write(content);
}
fileOutputStream.close();
}
public static void testBufferedOutputStream (int lineNum, byte[] content) throws IOException {
FileOutputStream fileOutputStream = new FileOutputStream(new File("./testBufferedOutputStream.txt"));
BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(fileOutputStream);
while (--lineNum > 0) {
bufferedOutputStream.write(content);
}
bufferedOutputStream.close();
}
//面向字符
public static void testFileWriter (int lineNum, String content) throws IOException {
FileWriter fileWriter = new FileWriter("./testFileWriter.txt");
while (--lineNum > 0) {
fileWriter.write(content);
}
fileWriter.close();
}
public static void testBufferedWriter (int lineNum, String content) throws IOException {
FileWriter fileWriter = new FileWriter("./testBufferedWriter.txt");
BufferedWriter bufferedWriter = new BufferedWriter(fileWriter);
while (--lineNum > 0) {
bufferedWriter.write(content);
}
bufferedWriter.close();
}
/************************** NIO ****************************/
public static void testNewOutputStream (int lineNum, byte[] content) throws IOException {
OutputStream outputStream = Files.newOutputStream(Paths.get("./testNewOutputStream.txt"));
while (--lineNum > 0) {
outputStream.write(content);
}
outputStream.close();
}
public static void testNewBufferedWriter (int lineNum,String content) throws IOException {
BufferedWriter newBufferedReader = Files.newBufferedWriter(Paths.get("./testNewBufferedWriter.txt"));
while (--lineNum > 0) {
newBufferedReader.write(content);
}
newBufferedReader.close();
}
public static void main (String[] args) throws IOException {
//多次测试时可清空result.txt文件
FileWriter fileWriter = new FileWriter("./Result.txt");
testDriver();
}
}
结果如图所示：
可以看出和前面的案例几乎没有差异（图就不画了）。
所以XXXOutputStream效率低的原因并不是字符串转换成字节数组，而是其本身的实现方式所致。
公众号：javafirst
作者：xiaoxi666
https://www.cnblogs.com/xiaoxi666/p/9531893.html
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