日常编码小技巧

Java基础：

List转Map集合：

/**
 * 将List转为Map
 *
 * @param list         原数据
 * @param keyExtractor Key的抽取规则
 * @param <K>          Key
 * @param <V>          Value
 * @return
 */
public static <K, V> Map<K, V> listToMap(List<V> list, Function<V, K> keyExtractor) {
    /*等于空就直接返回空的map*/
    if (list == null || list.isEmpty()) {
        return new HashMap<>();
    }
    Map<K, V> map = new HashMap<>(list.size());
    for (V element : list) {
        /*设置map的K为list的值*/
        K key = keyExtractor.apply(element);
        if (key == null) {
            continue;
        }
        /*设置map的V为list的值*/
        map.put(key, element);
    }
    return map;
}

使用：

1 public static void main(String[] args) {
2     // 1.创建List集合
3     List<? extends Serializable> list = new ArrayList<>(Arrays.asList(1, 2, 42, "23"));
4     // 2.调用方法将list集合转map集合
5     Map<? extends Serializable, ? extends Serializable> map = listToMap(list, Function.identity());
6     // 3.遍历map集合
7     Set<? extends Map.Entry<? extends Serializable, ? extends Serializable>> entries = map.entrySet();
8     entries.forEach(System.out::println);
9 }

输出：

封装好的日期时间类 

package com.mixky.mobile.policy.util;

import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.Locale;

import com.mixky.toolkit.DateUtil;

public class DateFormatUtil {
    
     public static SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    /**
     * 格式化结束日期，并加一天
     * @param endtime
     * @return
     */
    public static String formatEndDate(String endtime){
        Date endDate=DateUtil.parseDate(endtime, "yyyy-MM-dd");
        Calendar c = Calendar.getInstance();  
        c.setTime(endDate);
        c.add(Calendar.DAY_OF_MONTH, 1);// 今天+1天  
        String endDateStr=DateUtil.format(c.getTime(), "yyyy-MM-dd");
        return endDateStr;
    }
    
    /**
     * 格式化结束日期 不做任何处理
     * @param endtime
     * @return
     */
    public static String formatEndDateNow(String endtime){
        Date endDate=DateUtil.parseDate(endtime, "yyyy-MM-dd");
        Calendar c = Calendar.getInstance();  
        c.setTime(endDate);
        //c.add(Calendar.DAY_OF_MONTH, 1);// 今天+1天  
        String endDateStr=DateUtil.format(c.getTime(), "yyyy-MM-dd");
        return endDateStr;
    }
    
    /**
     * 日期加/减**天
     * @param date
     * @param day
     * @return
     */
    public static String formateDateHandleDay(String date, int day){
        Date endDate=DateUtil.parseDate(date, "yyyy-MM-dd");
        Calendar c = Calendar.getInstance();  
        c.setTime(endDate);
        c.add(Calendar.DAY_OF_MONTH, day);
        String endDateStr=DateUtil.format(c.getTime(), "yyyy-MM-dd");
        return endDateStr;
    }
    
    /**
     * 日期加/减**月
     * @param date
     * @param month
     * @return
     */
    public static String formateDateHandleMonth(String date, int month, String formate){
        Date endDate=DateUtil.parseDate(date, formate);
        Calendar c = Calendar.getInstance();  
        c.setTime(endDate);
        c.add(Calendar.MONTH, month);
        String endDateStr=DateUtil.format(c.getTime(), formate);
        return endDateStr;
    }
    
    /**
     * 日期加/减**年
     * @param date
     * @param year
     * @return
     */
    public static String formateDateHandleYear(String date, int year){
        Date endDate=DateUtil.parseDate(date, "yyyy");
        Calendar c = Calendar.getInstance();  
        c.setTime(endDate);
        c.add(Calendar.YEAR, year);
        String endDateStr=DateUtil.format(c.getTime(), "yyyy");
        return endDateStr;
    }
    
     
    /**
     * 获取当前月的第一天
     * @return
     */
    public static String formateDateFirstDay(){
        Calendar cale =  Calendar.getInstance();
        String firstday;  
        //获取前月的第一天  
        cale = Calendar.getInstance();  
        cale.add(Calendar.MONTH, 0);  
        cale.set(Calendar.DAY_OF_MONTH, 1); 
        
        //将小时至0
        cale.set(Calendar.HOUR_OF_DAY, 0);
        //将分钟至0
        cale.set(Calendar.MINUTE, 0);
        //将秒至0
        cale.set(Calendar.SECOND,0);
        //将毫秒至0
        cale.set(Calendar.MILLISECOND, 0);  
        
        firstday = sdf.format(cale.getTime());
        return firstday;
    }
    
    /**
     * 获取当前月的最后一天
     * @return
     */
    public static String formateDateLastDay(){
        Calendar cale =  Calendar.getInstance();
        String lastday;  
        //获取前月的最后一天  
        cale = Calendar.getInstance();  
        cale.add(Calendar.MONTH, 1);  
        cale.set(Calendar.DAY_OF_MONTH, 0); 
       
        //将小时至23
        cale.set(Calendar.HOUR_OF_DAY, 23);
        //将分钟至59
        cale.set(Calendar.MINUTE, 59);
        //将秒至59
        cale.set(Calendar.SECOND,59);
        //将毫秒至59
        cale.set(Calendar.MILLISECOND, 59);
        lastday = sdf.format(cale.getTime());
        return lastday;
    }
    
    //获取当前月的天数
    public static int getDayOfMonth(){
       Calendar aCalendar = Calendar.getInstance(Locale.CHINA);
       int day=aCalendar.getActualMaximum(Calendar.DATE);
       return day;
    }
    
    //获取当天凌晨0点0分0秒Date
    public Date getZeroOfDay(){
        Calendar calendar = Calendar.getInstance();
        calendar.set(calendar.get(Calendar.YEAR), calendar.get(Calendar.MONTH), calendar.get(Calendar.DAY_OF_MONTH),
                    0, 0, 0);
        Date beginOfDate = calendar.getTime();
        return beginOfDate;
    }
    
    //获取当天23点59分59秒Date
    public static Date getLastOfDay(){
        Calendar calendar = Calendar.getInstance();
        calendar.set(calendar.get(Calendar.YEAR), calendar.get(Calendar.MONTH), calendar.get(Calendar.DAY_OF_MONTH),
                    23, 59, 59);
        Date endOfDate  = calendar.getTime();
        return endOfDate ;
    }
    
 
    /**
     * 获取当前时间的前一天同一时间
     * 
     */
    private String getBeforeDay() {        
        Calendar calendar = Calendar.getInstance();
        int dd2 = calendar.get(Calendar.DATE);
        calendar.set(Calendar.DATE, dd2 - 1);
        calendar.set(calendar.get(Calendar.YEAR), calendar.get(Calendar.MONTH), calendar.get(Calendar.DAY_OF_MONTH),
                23, 59, 59);
        String beforeDay = sdf.format(calendar.getTime());
        return beforeDay;
    }

    /**
     * 获取当前时间的后一天同一时间
     * 
     */
    private String getAfterDay() {
        Calendar calendar = Calendar.getInstance();
        int dd2 = calendar.get(Calendar.DATE);
        calendar.set(Calendar.DATE, dd2 + 1);
        String afterDay = sdf.format(calendar.getTime());
        return afterDay;
    }
 
    /**
     * 获取当前时间的前一天0点0分0秒
     * 
     */
    public String getZeroOfBeforeDay() {        
        Calendar calendar = Calendar.getInstance();
        int dd2 = calendar.get(Calendar.DATE);
        calendar.set(Calendar.DATE, dd2 - 1);
        calendar.set(calendar.get(Calendar.YEAR), calendar.get(Calendar.MONTH), calendar.get(Calendar.DAY_OF_MONTH),
                0, 0, 0);
        String beforeDay = sdf.format(calendar.getTime());
        return beforeDay;
    }
 
    /**
     * 获取当前时间的前一天23点59分59秒
     * 
     */
    public String getLastOfBeforeDay() {        
        Calendar calendar = Calendar.getInstance();
        int dd2 = calendar.get(Calendar.DATE);
        calendar.set(Calendar.DATE, dd2 - 1);
        calendar.set(calendar.get(Calendar.YEAR), calendar.get(Calendar.MONTH), calendar.get(Calendar.DAY_OF_MONTH),
                23, 59, 59);
        String beforeDay = sdf.format(calendar.getTime());
        return beforeDay;
    }
    
    /**
     * 获取当前时间后一天0点0分0秒
     * 
     */
    private String getZeroOfAfterDay() {
        Calendar calendar = Calendar.getInstance();
        int dd2 = calendar.get(Calendar.DATE);
        calendar.set(Calendar.DATE, dd2 + 1);
        calendar.set(calendar.get(Calendar.YEAR), calendar.get(Calendar.MONTH), calendar.get(Calendar.DAY_OF_MONTH),
                0, 0, 0);
        String afterDay = sdf.format(calendar.getTime());
        return afterDay;
    }
    
    /**
     * 获取当前时间后一天23点59分59秒
     * 
     */
    private String getLastOfAfterDay() {
        Calendar calendar = Calendar.getInstance();
        int dd2 = calendar.get(Calendar.DATE);
        calendar.set(Calendar.DATE, dd2 + 1);
        calendar.set(calendar.get(Calendar.YEAR), calendar.get(Calendar.MONTH), calendar.get(Calendar.DAY_OF_MONTH),
                23, 59, 59);
        String afterDay = sdf.format(calendar.getTime());
        return afterDay;
    }
    
    /**
     * 获取当前月的第count天0分0秒0分
     * @return
     */
    public String getZeroOfDays(int count){
        Calendar cale =  Calendar.getInstance();
        //获取前月的第一天  
        cale = Calendar.getInstance();  
        cale.add(Calendar.MONTH, 0);  
        cale.set(Calendar.DAY_OF_MONTH, 1); 
        
        int dd2 = cale.get(Calendar.DATE);
        cale.set(Calendar.DATE, dd2 + count);
        cale.set(cale.get(Calendar.YEAR), cale.get(Calendar.MONTH), cale.get(Calendar.DAY_OF_MONTH),
                0, 0, 0);
        String day = sdf.format(cale.getTime());
        return day;
    }
    
    /**
     * 获取当前月的第count天23分59秒59分
     * @return
     */
    public String getLastOfDays(int count){
        Calendar cale =  Calendar.getInstance(); 
        //获取前月的第一天  
        cale = Calendar.getInstance();  
        cale.add(Calendar.MONTH, 0);  
        cale.set(Calendar.DAY_OF_MONTH, 1); 
        
        int dd2 = cale.get(Calendar.DATE);
        cale.set(Calendar.DATE, dd2 + count);
        cale.set(cale.get(Calendar.YEAR), cale.get(Calendar.MONTH), cale.get(Calendar.DAY_OF_MONTH),
                23, 59, 59);
        String day = sdf.format(cale.getTime());
        return day;
    }
    
    /**
     * 获取当前月的第count天
     * @return
     */
    public static Date getDays(int count){
        Calendar cale =  Calendar.getInstance(); 
        //获取前月的第一天  
        cale = Calendar.getInstance();  
        cale.add(Calendar.MONTH, 0);  
        cale.set(Calendar.DAY_OF_MONTH, 1); 
        
        int dd2 = cale.get(Calendar.DATE);
        cale.set(Calendar.DATE, dd2 + count);
        Date date = cale.getTime();
        return date;
    }
    
    
    /**
     * 获取当前时间的前一月同一时间
     * 
     */
    public static String getBeforeMonth(Date date) {        
        Calendar calendar = Calendar.getInstance();
         //过去一月
        calendar.setTime(date);
        calendar.add(Calendar.MONTH, -1);
        Date m = calendar.getTime();
        String mon = sdf.format(m);
        return mon;
    }
    
    /**
     * 获取上个月的第一天
     * @return
     */
    public static String getBeforeMonthFirstDay(){
        Calendar cale =  Calendar.getInstance();
        String firstday;  
        //获取上个月的第一天  
        cale = Calendar.getInstance();  
        cale.add(Calendar.MONTH, -1);  
        cale.set(Calendar.DAY_OF_MONTH, 1); 
        
        //将小时至0
        cale.set(Calendar.HOUR_OF_DAY, 0);
        //将分钟至0
        cale.set(Calendar.MINUTE, 0);
        //将秒至0
        cale.set(Calendar.SECOND,0);
        //将毫秒至0
        cale.set(Calendar.MILLISECOND, 0);  
        
        firstday = sdf.format(cale.getTime());
        return firstday;
    }
    
    /**
     * 获取下个月的最后一天
     * @return
     */
    public static String getBeforeMonthLastDay(){
        Calendar cale =  Calendar.getInstance();
        String lastday;  
        //获取下个月的最后一天  
        cale = Calendar.getInstance();  
        cale.add(Calendar.MONTH, 0);  
        cale.set(Calendar.DAY_OF_MONTH, 0); 
       
        //将小时至23
        cale.set(Calendar.HOUR_OF_DAY, 23);
        //将分钟至59
        cale.set(Calendar.MINUTE, 59);
        //将秒至59
        cale.set(Calendar.SECOND,59);
        //将毫秒至59
        cale.set(Calendar.MILLISECOND, 59);
        lastday = sdf.format(cale.getTime());
        return lastday;
    }
  
    
}

 正确停止一个线程：

终止一个线程可以调用线程的stop方法，但是stop这个方法会强行终止，没有保存的数据将会丢失，实际开发中一般会采用boolean标记的方式进行终止：

public class FileDemo {
    static boolean flag = false;

    public static void setFlag(boolean flag) {
        FileDemo.flag = flag;
    }

    public static void main(String[] args) throws InterruptedException {
        final Thread t1 = new Thread(new Runnable() {
            @Override
            public void run() {
                for (int i = 0; i < 10; i++) {
                    if (flag) {
                        return;
                    }
                    System.out.println(Thread.currentThread().getName() + "==》" + i);
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        }, "t1");
        t1.start();
        
        Thread.sleep(5000);
        /*5S后终止线程*/
        setFlag(true);
    }
}

正则匹配IP的合法性

/**
 * 判断IP地址的合法性，这里采用了正则表达式的方法来判断
 * return true，合法
 */
public static boolean ipCheck(String text) {
    if (text != null && !text.isEmpty()) {
        // 定义正则表达式
        String regex = "^(1\d{2}|2[0-4]\d|25[0-5]|[1-9]\d|[1-9])\." +
                "(1\d{2}|2[0-4]\d|25[0-5]|[1-9]\d|\d)\." +
                "(1\d{2}|2[0-4]\d|25[0-5]|[1-9]\d|\d)\." +
                "(1\d{2}|2[0-4]\d|25[0-5]|[1-9]\d|\d)$";
        // 判断ip地址是否与正则表达式匹配
        if (text.matches(regex)) {
            // 返回判断信息
            return true;
        } else {
            // 返回判断信息
            return false;
        }
    }
    return false;
}

　　

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原文地址：https://www.cnblogs.com/zhangzhixi/p/14849998.html