bytes[] 到数字类型的转换是个经常用到的代码,解决方式也不止一种，最近需要将bytes[]转为long,有机会深入了解了一下，此文做个总结。 java代码实现 如果不想借助任何已经有的类，完全可以自己实现这段代码，如下：
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/** * 将字节数组转为long<br> * 如果input为null,或offset指定的剩余数组长度不足8字节则抛出异常 * @param input * @param offset 起始偏移量 * @param littleEndian 输入数组是否小端模式 * @return */ public static long longFrom8Bytes(byte[] input, int offset, boolean littleEndian){ long value=0; // 循环读取每个字节通过移位运算完成long的8个字节拼装 for(int count=0;count<8;++count){ int shift=(littleEndian?count:(7-count))<<3; value |=((long)0xff<< shift) & ((long)input[offset+count] << shift); } return value; } |
借助java.nio.ByteBuffer实现 java.nio.ByteBuffer 本身就有getLong,getInt,getFloat….方法,只要将byte[]转换为ByteBuffer就可以实现所有primitive类型的数据读取,参见javadoc。
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/** * 利用 {@link java.nio.ByteBuffer}实现byte[]转long * @param input * @param offset * @param littleEndian 输入数组是否小端模式 * @return */ public static long bytesToLong(byte[] input, int offset, boolean littleEndian) { // 将byte[] 封装为 ByteBuffer ByteBuffer buffer = ByteBuffer.wrap(input,offset,8); if(littleEndian){ // ByteBuffer.order(ByteOrder) 方法指定字节序,即大小端模式(BIG_ENDIAN/LITTLE_ENDIAN) // ByteBuffer 默认为大端(BIG_ENDIAN)模式 buffer.order(ByteOrder.LITTLE_ENDIAN); } return buffer.getLong(); } |
借助java.io.DataInputStream实现 java.io.DataInputStream 同样提供了readLong,readLong,readLong….方法,只要将byte[]转换为DataInputStream就可以实现所有primitive类型的数据读取,参见javadoc。 完整测试代码 下面的Junit 测试代码计算String 的MD5校验码(16 bytes),然后使用上述方式分别将16 bytes转换为2个long(大端模式)然后以16进制模式输出结果,以验证三种方式一致性。
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package net.gdface.facelog; import java.io.ByteArrayInputStream; import java.io.DataInputStream; import java.io.IOException; import java.nio.ByteBuffer; import java.nio.ByteOrder; import java.security.MessageDigest; import java.security.NoSuchAlgorithmException; import org.junit.Test; public class TestSerialVersionUID { /** * 生成MD5校验码 * * @param source * @return */ static public byte[] getMD5(byte[] source) { if (null==source) return null; try { MessageDigest md = MessageDigest.getInstance("MD5"); return md.digest(source); } catch (NoSuchAlgorithmException e) { e.printStackTrace(); } return null; } /** * 将16位byte[] 转换为32位的HEX格式的字符串String * * @param buffer * @return */ static public String toHex(byte buffer[]) { if (null==buffer) return null; StringBuffer sb = new StringBuffer(buffer.length * 2); for (int i = 0; i < buffer.length; i++) { sb.append(Character.forDigit((buffer[i] & 240) >> 4, 16)); sb.append(Character.forDigit(buffer[i] & 15, 16)); } return sb.toString(); } /** * 将字节数组转为long<br> * 如果input为null,或offset指定的剩余数组长度不足8字节则抛出异常 * @param input * @param offset 起始偏移量 * @param littleEndian 输入数组是否小端模式 * @return */ public static long longFrom8Bytes(byte[] input, int offset, boolean littleEndian){ if(offset <0 || offset+8>input.length) throw new IllegalArgumentException(String.format("less than 8 bytes from index %d is insufficient for long",offset)); long value=0; for(int count=0;count<8;++count){ int shift=(littleEndian?count:(7-count))<<3; value |=((long)0xff<< shift) & ((long)input[offset+count] << shift); } return value; } /** * 利用 {@link java.nio.ByteBuffer}实现byte[]转long * @param input * @param offset * @param littleEndian 输入数组是否小端模式 * @return */ public static long bytesToLong(byte[] input, int offset, boolean littleEndian) { if(offset <0 || offset+8>input.length) throw new IllegalArgumentException(String.format("less than 8 bytes from index %d is insufficient for long",offset)); ByteBuffer buffer = ByteBuffer.wrap(input,offset,8); if(littleEndian){ // ByteBuffer.order(ByteOrder) 方法指定字节序,即大小端模式(BIG_ENDIAN/LITTLE_ENDIAN) // ByteBuffer 默认为大端(BIG_ENDIAN)模式 buffer.order(ByteOrder.LITTLE_ENDIAN); } return buffer.getLong(); } @Test public void test() throws IOException { String input="net.gdface.facelog.dborm.person.FlPersonBeanBase"; byte[] md5 = getMD5(input.getBytes()); System.out.printf("md5 [%s]\n",toHex(md5)); // 三种方式运算结果对比验证 DataInputStream dataInput = new DataInputStream(new ByteArrayInputStream(md5)); long l1 = dataInput.readLong(); long l2 = dataInput.readLong(); System.out.printf("l1=0x%x l2=0x%x,DataInputStream\n", l1,l2); long ln1 = bytesToLong(md5,0, false); long ln2 = bytesToLong(md5,8, false); System.out.printf("ln1=0x%x ln2=0x%x,ByteBuffer\n", ln1,ln2); long ll1 = longFrom8Bytes(md5,0, false); long ll2 = longFrom8Bytes(md5,8, false); System.out.printf("ll1=0x%x ll2=0x%x\n", ll1,ll2); } } |
输出结果 md5 [39627933ceeebf2740e1f822921f5837] l1=0x39627933ceeebf27 l2=0x40e1f822921f5837,DataInputStream ln1=0x39627933ceeebf27 ln2=0x40e1f822921f5837,,ByteBuffer ll1=0x39627933ceeebf27 ll2=0x40e1f822921f5837 参考资料 《Java 中 byte、byte 数组和 int、long 之间的转换》 from:https://blog.csdn.net/10km/article/details/77435659
View Details第一种：饿汉模式（线程安全）
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public class Single2 { private static Single2 instance = new Single2(); private Single2(){ System.out.println("Single2: " + System.nanoTime()); } public static Single2 getInstance(){ return instance; } } |
第二种：懒汉模式 （如果方法没有synchronized，则线程不安全）
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public class Single3 { private static Single3 instance = null; private Single3(){ System.out.println("Single3: " + System.nanoTime()); } public static synchronized Single3 getInstance(){ if(instance == null){ instance = new Single3(); } return instance; } } |
第三种：懒汉模式改良版（线程安全，使用了double-check，即check-加锁-check，目的是为了减少同步的开销）
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public class Single4 { private volatile static Single4 instance = null; private Single4(){ System.out.println("Single4: " + System.nanoTime()); } public static Single4 getInstance(){ if(instance == null){ synchronized (Single4.class) { if(instance == null){ instance = new Single4(); } } } return instance; } } |
第四种：利用私有的内部工厂类（线程安全，内部类也可以换成内部接口，不过工厂类变量的作用域要改为public了。）
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public class Singleton { private Singleton(){ System.out.println("Singleton: " + System.nanoTime()); } public static Singleton getInstance(){ return SingletonFactory.singletonInstance; } private static class SingletonFactory{ private static Singleton singletonInstance = new Singleton(); } } |
from:https://my.oschina.net/yangchunlian/blog/1607947
View Details在同步块中调用 wait() 和 notify()方法，如果阻塞，通过循环来测试等待条件。请参考答案中的示例代码。 【生产者】
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import java.util.Vector; import java.util.logging.Level; import java.util.logging.Logger; public class Producer implements Runnable { private final Vector sharedQueue; private final int SIZE; public Producer(Vector sharedQueue, int size) { this.sharedQueue = sharedQueue; this.SIZE = size; } @Override public void run() { // 生产数据 for (int i = 0; i < 7; i++) { System.out.println("Produced:" + i); try { produce(i); } catch (InterruptedException ex) { Logger.getLogger(Producer.class.getName()).log(Level.SEVERE, null, ex); } } } private void produce(int i) throws InterruptedException { // wait if queue is full while (sharedQueue.size() == SIZE) { synchronized (sharedQueue) { System.out.println("Queue is full " + Thread.currentThread().getName() + " is waiting , size: " + sharedQueue.size()); sharedQueue.wait(); } } // producing element and notify consumers synchronized (sharedQueue) { sharedQueue.add(i); sharedQueue.notifyAll(); } } } |
【消费者】
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import java.util.Vector; import java.util.logging.Level; import java.util.logging.Logger; public class Consumer implements Runnable { private final Vector sharedQueue; private final int SIZE; public Consumer(Vector sharedQueue, int size) { this.sharedQueue = sharedQueue; this.SIZE = size; } @Override public void run() { // 消费数据 while (true) { try { System.out.println("Consumer: " + consume()); Thread.sleep(50); } catch (InterruptedException ex) { Logger.getLogger(Consumer.class.getName()).log(Level.SEVERE, null, ex); } } } private int consume() throws InterruptedException { // wait if queue is empty while (sharedQueue.isEmpty()) { synchronized (sharedQueue) { System.out.println("Queue is empty " + Thread.currentThread().getName() + " is waiting , size: " + sharedQueue.size()); sharedQueue.wait(); } } //otherwise consume element and notify waiting producer synchronized (sharedQueue) { sharedQueue.notifyAll(); return (Integer) sharedQueue.remove(0); } } } |
【测试函数】
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import java.util.Vector; public class ProducerConsumerSolution { public static void main(String[] args) { Vector sharedQueue = new Vector(); int size = 4; Thread prodThread = new Thread(new Producer(sharedQueue, size), "Producer"); Thread consThread = new Thread(new Consumer(sharedQueue, size), "Consumer"); prodThread.start(); consThread.start(); } } |
运行结果：
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Produced:0 Queue is empty Consumer is waiting , size: 0 Produced:1 Consumer: 0 Produced:2 Produced:3 Produced:4 Produced:5 Queue is full Producer is waiting , size: 4 Consumer: 1 Produced:6 Queue is full Producer is waiting , size: 4 Consumer: 2 Consumer: 3 Consumer: 4 Consumer: 5 Consumer: 6 Queue is empty Consumer is waiting , size: 0 |
from:https://www.cnblogs.com/xbq8080/p/10371214.html
View Details