Java8新特性一点通 | 回顾字符转日期&JoinArray使用

素颜马尾好姑娘i 2022-05-17 05:24 128阅读 0赞

*   *  StringToDate日期转换
     *  Join Array使用

## **StringToDate日期转换** ##

*  Convert string to date in ISO8601 format
    
     *  利用`LocalDate.parse(CharSequence text)` 直接以ISO8601方式格式化

String originalDate = "2018-08-07";
            LocalDate localDate = LocalDate.parse(originalDate);
            System.out.println("Date:"+localDate);
    
    Output:
    
    Date:2018-08-07

*  Convert string to date in custom formats  
    
    
     *  利用`DateTimeFormatter.ofPattern(String pattern)`和`LocalDate.parse(CharSequence text, DateTimeFormatter formatter)`结合对日期以指定格式格式化

String originalDate1 = "2018-08-07 10:47:00";
            DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd hh:mm:ss");
            LocalDate localDate1 = LocalDate.parse(originalDate1,formatter);
            System.out.println("custom date:"+localDate1);
    
    Output:
    
    custom date:2018-08-07

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## **Join Array使用** ##

对现有数组添加字符串组成新的字符串的几个方法：  
\- `String.join(CharSequence delimiter, CharSequence… elements)` 场景：可以对现有数组添加分隔符组成新的字符串

String joinedString = String.join(",", "hello", "world", "!");
            System.out.println("示例1:" + joinedString);
    
    Output:
    
    示例1:hello,world,!

*  `String.join(CharSequence delimiter, Iterable elements)` 场景：可以对现有列表添加分隔符组成新的字符串

List<String> strList = Arrays.asList("hello", "world", "!");
            String joinedString1 = String.join(",", strList);
            System.out.println("示例2:" + joinedString1);
    Output:
    
    示例2:hello,world,!

*  `StringJoiner(CharSequence delimiter)` 场景：添加分隔符

StringJoiner stringJoiner1 = new StringJoiner(",");
            stringJoiner1.add("hello").add("world").add("!");
            System.out.println("示例3:" + stringJoiner1.toString());
    
    Output:
    
    示例3:hello,world,!

*  `StringJoiner(CharSequence delimiter, CharSequence prefix, CharSequence suffix)` 场景:添加分隔符以及前后缀

StringJoiner stringJoiner2 = new StringJoiner(",", "[", "]");
            stringJoiner2.add("hello").add("world").add("!");
            System.out.println("示例4:" + stringJoiner2.toString());
    
    Output:
    
    示例4:[hello,world,!]

*  `Collectors.joining` 场景:在lambda表达式里面用，针对添加分隔符和前后缀的场景

List<String> strList1 = Arrays.asList("hello", "world", "!");
            String joinedString3 = strList1.stream().collect(Collectors.joining(",","[","]"));
            System.out.println("示例5:"+joinedString3);
    
    Output:
    
    示例5:[hello,world,!]

*  `StringUtils.join()` 场景：跟以上用法差不多，使用工具类去把数据和列表组成单独的字符串

String[] strArray = {
       "hello", "world", "!"};
            String joinedString4 = StringUtils.join(strArray, ",");
            System.out.println("示例6:" + joinedString4);
    
    Output:
    
    示例6:hello,world,!