java8 对于字符串的连接很方便，使用lamda 可以对于字符串的连接更加简洁和方便

1.Api

• joining

  public static Collector<CharSequence,?,String> joining()

  返回一个 Collector ，将输入元素连接到一个 String ，按照顺序。

  结果

  一个 Collector ，将输入元素连接到一个 String中，按照顺序

• joining

  public static Collector<CharSequence,?,String> joining(CharSequence delimiter)

  返回一个 Collector ，以遇到的顺序连接由指定的分隔符分隔的输入元素。

  参数

  delimiter - 要在每个元素之间使用的分隔符

  结果

  A Collector ，它以相遇顺序连接由指定的分隔符分隔的CharSequence元素

• joining

  public static Collector<CharSequence,?,String> joining(CharSequence delimiter,
                                                         CharSequence prefix,
                                                         CharSequence suffix)

  返回一个 Collector ，以按照顺序将指定的 Collector分隔的输入元素与指定的前缀和后缀相连接。

  参数

  delimiter - 要在每个元素之间使用的分隔符

  prefix - 在连接结果开始时使用的字符序列

  suffix - 连接结果末尾要使用的字符序列

  结果

  一个 Collector ，它以相遇的顺序连接由指定的分隔符分隔的CharSequence元素

2. 实例    

public class Joining {

    public static String ArrayJoin(String[] arr){
        return Arrays.stream(arr).collect(Collectors.joining("','","'","'"));
    }

    public static String ListJoin(List<String> list){
        return list.stream().collect(Collectors.joining(","));
    }

    public static String CharJoin(List<CharSequence> charList){
        return charList.stream().collect(Collectors.joining());
    }
}

public class LamdaJoining {

    @Test
    public void testArrayJoining(){
        String[]  helloWorld = new String[]{"H","e","l","l","o"," ","W","o","r","l","d","!"};
        System.out.println(Joining.ArrayJoin(helloWorld));
    }

    @Test
    public void testListJoining(){
        List<String> helloWorld = Arrays.asList("H","e","l","l","o"," ","W","o","r","l","d","!");
        System.out.println(Joining.ListJoin(helloWorld));
    }

    @Test
    public void testCharSequenceJoining(){
        List<CharSequence> helloWorld = Arrays.asList("H","e","l","l","o"," ","W","o","r","l","d","!");
        System.out.println(Joining.CharJoin(helloWorld));
    }
}

          output:

'H','e','l','l','o',' ','W','o','r','l','d','!'

H,e,l,l,o, ,W,o,r,l,d,!

Hello World!