Guava 的 API 对字符串去空格，去空值，list去空值null

 String a = ",abcd,,efg,l";System.out.println(Splitter.on(",").trimResults().omitEmptyStrings().splitToList(a));// 依次 join 多个字符串，Joiner 是 Guava 提供的 APIJoiner joiner = Joiner.on(",").skipNulls();String result = joiner.join("hello",null,"china");System.out.println(  "依次 join 多个字符串:{}"+result  );List<String> list = Lists.newArrayList(new String[]{"hello","china",null});System.out.println("自动删除 list 中空值:{}" + joiner.join(list));