guava源码阅读之Joiner

建议：简单看下appendTo即可 

Joiner 主要用来将字符串或者字符串数组、列表之类的东西，拼接成一个以指定符号分隔各个元素的字符串，比如把 [a, b, c] 拼接成 “a b c”。

举个栗子：

String str1[] = {"a", "b", "c", "d"};
String str2[] = {"a", "b", "c", "d", null};
String temp = Joiner.on(",").join(str1);
LOGGER.info(temp);

temp = Joiner.on(',').skipNulls().join(str2);
LOGGER.info(temp);

temp = Joiner.on(',').useForNull("空").join(str2);
LOGGER.info(temp);

关于appendTo(A appendable, Iterator<?> parts)

public <A extends Appendable> A appendTo(A appendable, Iterator<?> parts) throws IOException {
    Preconditions.checkNotNull(appendable);
    if (parts.hasNext()) {
        appendable.append(this.toString(parts.next()));

        while(parts.hasNext()) {
            appendable.append(this.separator);
            appendable.append(this.toString(parts.next()));
        }
    }

    return appendable;
}

关于传入的类型，贴个图就明白了