在测试各种加密文件大小时,我应该测量下面代码的运行时间。但是我认为我使用的方法只是输出CPU的当前定时器而不是程序的运行时间。这是要实现的代码,但我认为我没有做对
long startTime = System.nanoTime();
// call function
obj.callFunction();
long endTime = System.nanoTime();
long timeDifference = endTime - startTime;
这是我的实际程序。我应该如何修改计时器代码以反射(reflect)程序的实际运行时间而不是系统时钟?谢谢!
import javax.crypto.Cipher;
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import javax.crypto.CipherInputStream;
import javax.crypto.CipherOutputStream;
import javax.crypto.spec.SecretKeySpec;
public class AESJava {
public static void main(String[] args) {
// returns the current value of the system timer, in nanoseconds
System.out.print("time in nanoseconds = ");
System.out.println(System.nanoTime());
try {
BufferedReader br = new BufferedReader(new FileReader("key.txt"));
String key = br.readLine();
br.close();
FileInputStream fis = new FileInputStream("original.txt");
FileOutputStream fos = new FileOutputStream("encrypted.txt");
encrypt(key, fis, fos);
FileInputStream fis2 = new FileInputStream("encrypted.txt");
FileOutputStream fos2 = new FileOutputStream("decrypted.txt");
decrypt(key, fis2, fos2);
} catch (Throwable e) {
e.printStackTrace();
}
}
public static void encrypt(String key, InputStream is, OutputStream os) throws Throwable {
encryptOrDecrypt(key, Cipher.ENCRYPT_MODE, is, os);
}
public static void decrypt(String key, InputStream is, OutputStream os) throws Throwable {
encryptOrDecrypt(key, Cipher.DECRYPT_MODE, is, os);
}
public static void encryptOrDecrypt(String key, int mode, InputStream is, OutputStream os) throws Throwable {
SecretKeySpec dks = new SecretKeySpec(key.getBytes(),"AES");
Cipher cipher = Cipher.getInstance("AES");
if (mode == Cipher.ENCRYPT_MODE) {
cipher.init(Cipher.ENCRYPT_MODE, dks);
CipherInputStream cis = new CipherInputStream(is, cipher);
doCopy(cis, os);
} else if (mode == Cipher.DECRYPT_MODE) {
cipher.init(Cipher.DECRYPT_MODE, dks);
CipherOutputStream cos = new CipherOutputStream(os, cipher);
doCopy(is, cos);
}
}
public static void doCopy(InputStream is, OutputStream os) throws IOException {
byte[] bytes = new byte[128];
int numBytes;
while ((numBytes = is.read(bytes)) != -1) {
os.write(bytes, 0, numBytes);
}
os.flush();
os.close();
is.close();
}
}
最佳答案
我很困惑,因为你的第一件事是绝对正确的,但是你的主要方法并没有按照你写的去做。它只打印 CPU 时间(自纪元以来),不计算实际的挂钟时间。更改程序的最简单方法是创建一个方法(函数)来执行您的主要方法所做的事情,然后只需插入初始部分即可。以下是摘录:
private static void doMain(){
try {
BufferedReader br = new BufferedReader(new FileReader("key.txt"));
String key = br.readLine();
br.close();
FileInputStream fis = new FileInputStream("original.txt");
FileOutputStream fos = new FileOutputStream("encrypted.txt");
encrypt(key, fis, fos);
FileInputStream fis2 = new FileInputStream("encrypted.txt");
FileOutputStream fos2 = new FileOutputStream("decrypted.txt");
decrypt(key, fis2, fos2);
} catch (Throwable e) {
e.printStackTrace();
}
}
那么您的主要方法就是:
public static void main(String ...args){
long startTime = System.nanoTime();
// call function
doMain();
long endTime = System.nanoTime();
long timeDifference = endTime - startTime;
}
计算平均时间的更好方法是多次执行此操作(需要纳秒精度的单次运行不会非常准确)。所以你可以这样做:
public static void main(String ...args){
long startTime = System.nanoTime();
// call function
for(int i = 0; i < NUM; ++i)
doMain();
long endTime = System.nanoTime();
long timeDifference = endTime - startTime;
double avgTime = (double)timeDifference / (double)NUM;
}
尽管这可能不准确,但我会强烈提醒您。在尝试计时时需要注意两件事:1) 操作系统是否会假设数据已经在 RAM 中,以及 2) 体系结构是否会假设数据已经在缓存中。如果你运行这么多次,你可能会以 RAM 的速度运行,而不是以读/写磁盘的速度运行。要真正获得平均速度,您需要确保操作系统必须读取/写入磁盘(这可能需要许多中间“虚拟”读取/写入)。
关于java - 以纳秒为单位衡量程序的运行时间,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/22652351/