Google Guava提供了Joiner类专门用来连接String。

譬如说有个String数组,里面有"a","b","c",我们可以通过使用StringBuilder来创建String "a,b,c"。

Joiner提供了这一类的功能。

譬如:


1. Joiner joiner = Joiner.on(";");  
2. assertEquals("a;b;c", joiner.join(new String[}{"a","b","c"}));

当然Joiner.join还提供了参数为Iterable的overload形式。也就是说你可以传各种List和Set。

如果被连接String里面要过滤null,可以这样:


1. Joiner joiner = Joiner.on(";").skipNulls();  
2. assertEquals("a;c", joiner.join(new String[]{"a",null,"c"}));


或者对null进行替换操作:


1. Joiner joiner = Joiner.on(";").useForNull("!");  
2. assertEquals("a;!;c", joiner.join(new String[]{"a",null,"c"}));

Joiner还提供了appendTo函数,对传入的StringBuilder作处理:


1. Joiner joiner = Joiner.on(";");  
2. StringBuilder ab = new StringBuilder("start: ");  
3. assertEquals("start: a;b;c", joiner.appendTo(ab, new String[]{"a","b","c"}).toString());

除此之外,相关的MapJoiner类也利用Joiner提供了Map的join功能:


1. Map<Integer, String> map = new HashMap<Integer, String>();  
2. map.put(1, "a");  
3. map.put(2, "b");  
4. MapJoiner joiner = Joiner.on(";").withKeyValueSeparator("->");  
5. assertEquals("1->a;2->b", joiner.join(map));

 

 

static final来用没问题。但是这样的话,正如javadoc所举的例子:

第1行的Joiner对象就是第3行的对象,第2行的skipNulls()其实是返回一个Joiner的一个匿名子类,而对之前的joiner对象没有影响,所以第3行的Joiner对象根本没有skip null的功能。

// Bad! Do not do this!  Joiner joiner = Joiner.on(',');  joiner.skipNulls(); // does nothing!  return joiner.join("wrong", null, "wrong");