由SQL where 1=1想到的字符串处理方法

字符串拆成集合简单,集合再合成字符串就有点麻烦.
对于Javascript,一个join方法就可以解决问题,可惜Java的集合没有提供join的方法.

不过强大的Java的三方库提供了类似的功能,例如

//Commons Lang:
org.apache.commons.lang.StringUtils.join(list, conjunction);

//Spring:
org.springframework.util.StringUtils.
    collectionToDelimitedString(list, conjunction);

//Commons Lang:

org.apache.commons.lang.StringUtils.join(list, conjunction);

//Spring:

org.springframework.util.StringUtils.

collectionToDelimitedString(list, conjunction);

当然也可以自己写一个实现,常见的写法为

public static String join(Collection c, String delim) {
	if (c == null || c.size()==0) {
		return "";
	}
	StringBuilder sb = new StringBuilder();
	Iterator it = c.iterator();
	int i = 0;
	while (it.hasNext()) {
		if (i++ > 0) {
			sb.append(delim);
		}
		sb.append(it.next());
	}
	return sb.toString();
}

public static String join(Collection c, String delim) {

if (c == null || c.size()==0) {

return "";

}

StringBuilder sb = new StringBuilder();

Iterator it = c.iterator();

int i = 0;

while (it.hasNext()) {

if (i++ > 0) {

sb.append(delim);

}

sb.append(it.next());

}

return sb.toString();

}

总觉得循环中的if很别扭，很想把它干掉,于是有了稍稍优雅的写法:

public static String join(String delimiter, Iterable<? extends Object> objs) {
	if (objs == null || !objs.hasNext()) {
		return "";
	}
	Iterator<? extends Object> iter = objs.iterator();
	StringBuilder buffer = new StringBuilder();
	buffer.append(iter.next());
	while (iter.hasNext()) {
		buffer.append(delimiter).append(iter.next());
	}
	return buffer.toString();
}

public static String join(String delimiter, Iterable<? extends Object> objs) {

if (objs == null || !objs.hasNext()) {

return "";

}

Iterator<? extends Object> iter = objs.iterator();

StringBuilder buffer = new StringBuilder();

buffer.append(iter.next());

while (iter.hasNext()) {

buffer.append(delimiter).append(iter.next());

}

return buffer.toString();

}

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