JAVA----util常用类,1字符串转日期，2格式化类Format，3Random，4MD5,5Base64

util常用类

1. 字符串转日期

1.1 Date/Calendar

String dateStr = "2020-01-01 10:00:00";
jdk1.8之前与时间 日期相关的类型有2个   java.util.Date    java.util.Calendar

Date() 
Date(long date)   将毫秒数转换成Date对象
       
long getTime()  
    
 private static void demo() {
        Date date = new Date();
        System.out.println(date);//Thu May 20 14:52:13 CST 2021
​
        //获得当前时间毫秒数
        //System.out.println(System.currentTimeMillis());
​
        Date date1 = new Date(System.currentTimeMillis());
        System.out.println(date1.getTime());
    }    

 

 

Calendar：
  private static void demo1() {
        //创建日历对象
        Calendar calendar = Calendar.getInstance();
        System.out.println(calendar);
​
        //get(int field)
        System.out.println(calendar.get(Calendar.YEAR));
        System.out.println(calendar.get(Calendar.MONTH) + 1);
        System.out.println(calendar.get(Calendar.DATE));
        System.out.println(calendar.get(Calendar.DAY_OF_MONTH));
​
        //获得今天是周几:  7
        String[] week = {"7", "1", "2", "3", "4", "5", "6"};
        System.out.println(calendar.get(Calendar.DAY_OF_WEEK));//5 第五天  星期四
        System.out.println(week[calendar.get(Calendar.DAY_OF_WEEK) - 1]);
​
        System.out.println("-----------------------");
        //修改时间  2021-4  set
        //calendar.set(Calendar.MONTH,Calendar.APRIL);
        //calendar.set(Calendar.DAY_OF_MONTH,calendar.get(Calendar.DAY_OF_MONTH)+10);
        calendar.add(Calendar.DAY_OF_MONTH, 10);
        System.out.println(calendar.get(Calendar.YEAR));
        System.out.println(calendar.get(Calendar.MONTH) + 1);
        System.out.println(calendar.get(Calendar.DATE));
​
        //calendar.set(2019,Calendar.JANUARY,10,12,30,30);
        //day+10
        
        //获得一个月份的最大的天数:  31  30  28/29
        System.out.println(calendar.getActualMaximum(Calendar.DATE));
    }      

 

1.2 LocalDate/LocalDateTime

线程安全  值不可变的
java.time.*
LocalDate： 年-月-日
LocalDateTime     年-月-日 时分秒
DateTimeFormatter: 格式化1.8+     

 

 private static void userRegister1() {
        Scanner input = new Scanner(System.in);
        System.out.println("录入name:");
        String name = input.nextLine();
        System.out.println("录入birthday:");
        String birthday = input.nextLine();
​
        UserInfo1 userInfo1 = new UserInfo1();
        userInfo1.setName(name);
        //需要将String转LocalDate
        //userInfo1.setBirthday(LocalDate.parse(birthday));
        userInfo1.setBirthday(LocalDate.parse(birthday,DateTimeFormatter.ofPattern("yyyy年MM月dd")));
        userInfo1.setCreateTime(LocalDateTime.now());//获得当前系统的时间  new Date()
​
        System.out.println(userInfo1);
​
    }

 

private static void testLocalDateTime() {
        LocalDateTime now = LocalDateTime.now();
        System.out.println(now.toString());//2021-05-20T16:02:34.623
​
        LocalDateTime localDateTime = LocalDateTime.of(2019, Month.APRIL, 20, 12, 30, 30);
        System.out.println(localDateTime);//2019-10-20T12:30:30
​
        //求间隔天数
        long until = Math.abs(now.until(localDateTime, ChronoUnit.HOURS));
        System.out.println(until);
​
        //get   ChronoField
//        System.out.println(now.get(ChronoField.YEAR));
//        System.out.println(now.getYear());
​
        //修改  plus/minus  +10
        // ChronoUnit
//        now = now.plus(Duration.of(10,ChronoUnit.DAYS));
//        System.out.println(now);
​
//        now = now.minus(10, ChronoUnit.DAYS);
//        System.out.println(now);
​
        LocalDate now1 = LocalDate.now();
        System.out.println(now1);
        LocalDate localDate = LocalDate.of(2021,Month.APRIL,1);
        Period period = localDate.until(now1);
        System.out.println(period.toString());
        //get
        System.out.println(period.getYears());
        System.out.println(period.getMonths());
        System.out.println(period.getDays());
​
​
    }

 

 

2. 格式化类Format

1. DateFormat

使用子类: SimpleDateFormat 线程不安全的类

常用构造:
  SimpleDateFormat(String pattern) 
      
常用方法:
  Date   parse(String dateStr)  将字符串转Date
  String format(Date date);   Date转String    

模拟用户注册:

private static void userRegister() {
​
        Scanner input = new Scanner(System.in);
        System.out.println("录入name:");
        String name = input.nextLine();
        System.out.println("录入birthday:");
        String birthday = input.nextLine();//2020-01-01
​
​
        UserInfo userInfo = new UserInfo();
        userInfo.setName(name);
        userInfo.setBirthday(DateUtil.strConvertToDate(birthday, false));
        userInfo.setCreateTime(new Date());
​
        System.out.println("注册成功");
        System.out.println("用户详细信息:" + userInfo.toString());
    }

 

public class DateUtil {


    private static final String PATTERN = "yyyy-MM-dd";//false
    private static final String PATTERN1 = "yyyy-MM-dd HH:mm:ss";//true

    private DateUtil() {
    }


    //String转Date
    public static Date strConvertToDate(String dateStr, boolean flag) {

        if (dateStr == null || dateStr.isEmpty()) {
            throw new NumberFormatException(dateStr + "不符合数据格式");
        }

        String result;
        if (flag) {
            result = PATTERN1;
        } else {
            result = PATTERN;
        }
        DateFormat dateFormat = new SimpleDateFormat(result);
        try {
            return dateFormat.parse(dateStr);
        } catch (ParseException e) {
            e.printStackTrace();
        }
        return null;

    }

    //Date转String
    public static String dateConvertToStr(Date date, boolean flag) {

        Objects.requireNonNull(date);
        String result;
        if (flag) {
            result = PATTERN1;
        } else {
            result = PATTERN;
        }
        DateFormat dateFormat = new SimpleDateFormat(result);
        return dateFormat.format(date);

    }
}

 

 

2. NumberFormat

public class DecimalFormatDemo {
    public static void main(String[] args) {
        Double number = 2342353411.1236666;
        Double number2 = 0.1276666;
        //NumberFormat decimalFormat = new DecimalFormat(".####");保留几位小数，一个#一位
        //NumberFormat decimalFormat = new DecimalFormat(",###.####");整数三个用，分割
        //百分数
        NumberFormat decimalFormat = new DecimalFormat(".##%");
        System.out.println(decimalFormat.format(number2));
    }
}

 

 

3. 随机数类Random

public class RandomDemo {
    public static void main(String[] args) {
        //多线程使用 ThreadLocalRandom
        ThreadLocalRandom localRandom = ThreadLocalRandom.current();
​
        for (int i = 0; i < 5; i++) {
            for (int i1 = 0; i1 < 5; i1++) {
                int i2 = localRandom.nextInt(1000, 10000);
                System.out.print(i2+"\t");
            }
            System.out.println();
        }
        System.out.println("-----------------------------");
        //可以不给seed 200
        Random random = new Random(200);
        for (int i = 0; i < 5; i++) {
            //Random random = new Random(200);放在里面5轮结果相同，放在外面都不相同
            for (int i1 = 0; i1 < 5; i1++) {
                int num = random.nextInt(9000) + 1000;
                System.out.print(num+"\t");
            }
            System.out.println();
        }
    }
}

 

4. MD5

md5不可逆，信息摘要算法的一种 MessageDegest

package javasm;
​
import java.math.BigInteger;
import java.nio.charset.Charset;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Objects;
​
public class Md5Util {
    private static char[] ARRAY = {'0','1','2','3','4','5','6','7','8','9','a','b','c','d','e','f',};
​
    private static  final String ENCODING = "UTF-8";
    private static  final String SALT = "JINITAIMEI_KUNKUN++";
    private Md5Util() {
    }
​
    public static void main(String[] args) {
        System.out.println(md5Encode("1234"));
    }
​
    public static String md5Encode(String sourceStr){
        Objects.requireNonNull(sourceStr);
        StringBuilder builder = new StringBuilder();
        try {
            //1.创建信息摘要对象
            MessageDigest messageDigest = MessageDigest.getInstance("MD5");
            //2.更新信息摘要对象，将需要加密的内容放入算法中
            sourceStr = SALT+sourceStr;//加固的的盐值salt(自定义)
            messageDigest.update(sourceStr.getBytes(Charset.forName(ENCODING)));
            //3.加密
            byte[] encodeArray = messageDigest.digest();
            //------------
            //jdk提供的
​
            BigInteger bigInteger = new BigInteger(1,encodeArray);
            System.out.println("bigPass:"+bigInteger.toString(16));
            //--------------
            for (byte by : encodeArray) {
                builder.append(byteHex(by));
            }
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        }
        return builder.toString().toUpperCase();
    }
​
    private static String byteHex(byte by) {
        int num = by;
        if(num<0){
            num+=256;
        }
        int highIndex = num / 16;
        int lowIndex = num % 16;
        return  ARRAY[highIndex]+""+ARRAY[lowIndex];
    }
}

 

 

5. Base64

Base64: 加密(编码)/解密(解码)。可逆 A-Za-z0-9 组成的字符串

public class PassDemo {
    private static final String ENCODING = "UTF-8";
​
    public static void main(String[] args) {
        System.out.println(reg("1234"));//MTIzNA==
        System.out.println(login("1234"));
    }
​
    //两种比较：1.获得注册时候加密后的数据在解密进行比较
    //2.在登陆时获得登陆数据加密在和注册后加密的数据比较
    private static boolean login(String sourcePass) {
        Objects.requireNonNull(sourcePass);
        //Base64   1.获得解码器
        Base64.Decoder decoder = Base64.getDecoder();
        //2.解码
        byte[] decode = decoder.decode("MTIzNA==");
        return sourcePass.equals(new String(decode, Charset.forName(ENCODING)));
    }
​
    private static String reg(String sourceStr) {
        //Base64   1.获得编码器
        Objects.requireNonNull(sourceStr);
        Base64.Encoder encoder = Base64.getEncoder();
        //2.编码
        byte[] bytes = sourceStr.getBytes(Charset.forName(ENCODING));
​
        return encoder.encodeToString(bytes);
    }
​
}