如何相互转换逗号分隔的字符串和list

String str = "a,b,c";  
List<String> result = Arrays.asList(str.split(","));

String str = "a, b, c";  
List<String> result = Splitter.on(",").trimResults().splitToList(str);

String str = "a,b,c";  
List<String> result = Arrays.asList(StringUtils.split(str,","));

String str = "a,b,c";  
List<String> str = Arrays.asList(StringUtils.commaDelimitedListToStringArray(str));

public String listToString(List list, char separator) {  
	StringBuilder sb = new StringBuilder();  
	for (int i = 0; i < list.size(); i++) {  
  		if (i == list.size() - 1) {  
  			sb.append(list.get(i));  
  		} else {  
  			sb.append(list.get(i));  
  			sb.append(separator);  
  		}  
	}  
	return sb.toString();  
} 
public String listToString(List list, char separator) {  
	StringBuilder sb = new StringBuilder();  
	for (int i = 0; i < list.size(); i++) {  
  		sb.append(list.get(i)).append(separator);  
	}  
	return sb.toString().substring(0,sb.toString().length()-1);  
}

List<String> list = new ArrayList<String>();  
list.add("a");  
list.add("b");  
list.add("c");  
String str = Joiner.on(",").join(list);

List<String> list = new ArrayList<String>();  
list.add("a");  
list.add("b");  
list.add("c");  
String str = StringUtils.join(list.toArray(), ",");

List<String> list = new ArrayList<String>();  
list.add("a");  
list.add("b");  
list.add("c");  
String str = StringUtils.collectionToDelimitedString(list, ",");