背景

代码中的到处散乱着如下的代码

开发到处拷贝粘贴导致，事实上某些情况下开发还需要处理最后一个分隔符

解决方案

StringBuilder

Sonar给出的方案

The method seems to be building a String using concatenation in a loop. In each iteration, the String is converted to a StringBuffer/StringBuilder, appended to, and converted back to a String. This can lead to a cost quadratic in the number of iterations, as the growing string is recopied in each iteration.

Better performance can be obtained by using a StringBuffer (or StringBuilder in Java 1.5) explicitly.

For example:

// This is bad  String s = "";  for (int i = 0; i < field.length; ++i) {    s = s + field[i];  }    // This is better  StringBuffer buf = new StringBuffer();  for (int i = 0; i < field.length; ++i) {    buf.append(field[i]);  }  String s = buf.toString();

对于栈上私有对象来说应当考虑StringBuilder更好

Joiner

当然我们更好的方法是使用Guava 的Joiner

比如

   List<String> list = Lists.transform(tbRoleOrgList, new Function<TbRoleOrg, String>() {           @Nullable           @Override           public String apply(@Nullable TbRoleOrg input) {               return input == null ? null : input.getOrgId();           }       });       Joiner joiner = Joiner.on(",").skipNulls(); return joiner.join(list);

joiner 提供了比较多的api

当然还有MapJoiner也是很常用的工具类

Joiner.MapJoiner mapJoiner = Joiner.on("&").withKeyValueSeparator("="); return  mapJoiner.join(errorMap);

十分方便【更重要的是Joiner和MapJoiner是线程安全的~】

某些拼接URL的场景十分合用！