Java8新特性一点通 | 回顾字符转日期&JoinArray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,!