public static String substringBetween(String str, String tag) {
		return substringBetween(str, tag, tag);
	}
<p>
Gets the String that is nested in between two instances of the same String.
</p>

<p>
A <code>null</code> input String returns <code>null</code>. A <code>null</code> tag
returns <code>null</code>.
</p>

<pre>
StringUtils.substringBetween(null, *)            = null
StringUtils.substringBetween("", "")             = ""
StringUtils.substringBetween("", "tag")          = null
StringUtils.substringBetween("tagabctag", null)  = null
StringUtils.substringBetween("tagabctag", "")    = ""
StringUtils.substringBetween("tagabctag", "tag") = "abc"
</pre>
@param str the String containing the substring, may be null
@param tag the String before and after the substring, may be null
@return the substring, <code>null</code> if no match
@since 2.0
spring-cloud-alibaba-starters/spring-alibaba-nacos-config/src/main/java/com/alibaba/cloud/nacos/utils/StringUtils.java