jdk8 stringjoin

stringjoin可以帮助避免用stringbuilder那样去拼字符串，

public StringJoiner(CharSequence delimiter,
                        CharSequence prefix,
                        CharSequence suffix) {
        Objects.requireNonNull(prefix, "The prefix must not be null");
        Objects.requireNonNull(delimiter, "The delimiter must not be null");
        Objects.requireNonNull(suffix, "The suffix must not be null");
        // make defensive copies of arguments
        this.prefix = prefix.toString();
        this.delimiter = delimiter.toString();
        this.suffix = suffix.toString();
        this.emptyValue = this.prefix + this.suffix;
    }

可以指定分隔符，也可以指定前后缀。

比如map转string

    private  String formatMap(Map<Integer, Long> map, String delimiter, String prefix, String suffix) {

        StringJoiner result = new StringJoiner(delimiter, prefix, suffix);
        for (Entry<Integer,Long> entry : map.entrySet()) {
            result.add("{\"key\":"+entry.getKey()+",\"value\":\""+entry.getValue()+"\"}");
        }
        return result.toString();
    }

使用：

 String s =formatMap(paramsMap,",","[","]");
就可以拼成：中括号开头结尾，中间元素是逗号分隔的。字符串。便于json解析。