package com.youai.test;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
public class TestRandom {
    public static void main(String[] args) throws NoSuchAlgorithmException {
        System.out.println("start.....");
        long start = System.currentTimeMillis();
        SecureRandom random = SecureRandom.getInstanceStrong();
        for(int i = 0; i < 100; i++) {
            System.out.println("第" + i + "個隨機數(shù).");
            random.nextInt(10000);
        }
        System.out.println("finish...time/ms:" + (System.currentTimeMillis() - start));
    }
}

jstack -l <你的java進程>

// name of the pure random file (also used for setSeed())
private static final String NAME_RANDOM = "/dev/random";
// name of the pseudo random file
private static final String NAME_URANDOM = "/dev/urandom";
private static RandomIO initIO(final Variant v) {
    return AccessController.doPrivileged(
        new PrivilegedAction<RandomIO>() {
            @Override
            public RandomIO run() {
                File seedFile;
                File nextFile;
                switch(v) {
                //...忽略中間代碼
                case BLOCKING: // blocking狀態(tài)下從/dev/random文件中讀取
                    seedFile = new File(NAME_RANDOM);
                    nextFile = new File(NAME_RANDOM);
                    break;
                case NONBLOCKING: // unblocking狀態(tài)下從/dev/urandom文件中讀取數(shù)據(jù)
                    seedFile = new File(NAME_URANDOM);
                    nextFile = new File(NAME_URANDOM);
                    break;
               	//...忽略中間代碼
                try {
                    return new RandomIO(seedFile, nextFile);
                } catch (Exception e) {
                    return null;
                }
            }
    });
}
// constructor, called only once from initIO()
private RandomIO(File seedFile, File nextFile) throws IOException {
    this.seedFile = seedFile;
    seedIn = new FileInputStream(seedFile);
    nextIn = new FileInputStream(nextFile);
    nextBuffer = new byte[BUFFER_SIZE];
}
private void ensureBufferValid() throws IOException {
     long time = System.currentTimeMillis();
     if ((buffered > 0) && (time - lastRead < MAX_BUFFER_TIME)) {
         return;
     }
     lastRead = time;
     readFully(nextIn, nextBuffer);
     buffered = nextBuffer.length;
}

import java.io.FileInputStream;
import java.io.IOException;
public class TestReadUrandom {
    public static void main(String[] args) throws IOException {
        System.out.println("start.....");
        for(int i = 0; i < 100; i++) {
            System.out.println("第" + i + "次讀取隨機數(shù)");
            FileInputStream inputStream = new FileInputStream("/dev/random");
            byte[] buf = new byte[32];
            inputStream.read(buf, 0, buf.length);
        }
    }
}

#include <stdio.h>
#include <fcntl.h>
int main() {
    int randnum = 0;
    int fd = open("/dev/random", O_RDONLY);
    if(fd == -1) {
        printf("open error.\n");
        return 1;
    }
    int i = 0;
    for(i = 0; i < 100; i++) {
        read(fd, (char *)&randnum, sizeof(int));
        printf("random number = %d\n", randnum);
    }
    close(fd);
    return 0;
}

#include <windows.h>
JNIEXPORT jbyteArray JNICALL Java_sun_security_mscapi_PRNG_generateSeed
  (JNIEnv *env, jclass clazz, jint length, jbyteArray seed)
{
	//省略不關鍵代碼...
	else if (length > 0) {
            pbData = new BYTE[length];
            if (::CryptGenRandom(  // 此處通過調(diào)用windows提供的apiCryptGenRandom獲取隨機數(shù)
                hCryptProv,
                length,
                pbData) == FALSE) {
                ThrowException(env, PROVIDER_EXCEPTION, GetLastError());
                __leave;
            }
            result = env->NewByteArray(length);
            env->SetByteArrayRegion(result, 0, length, (jbyte*) pbData);
        }
  //省略不關鍵代碼...
}