Guava 工具类之joiner的使用

　　joiner主要用于对字符串的连接，也可用于对map中key value的连接

public class JoinerTest {

    private static final List<String> list1 = Arrays.asList
                ("google","guava","java","scala","kafka");

    private static final List<String> list2 = Arrays.asList
            ("google","guava","java",null,"scala","kafka");

    public static void main(String[] args) throws IOException {

        //1.用指定的字符连接
        String join = Joiner.on("#").join(list1);
        System.out.println("用 # 号连接的字符串是："+join);

        //2.跳过连接中的null值
        String joinNull = Joiner.on("#").skipNulls().join(list2);
        System.out.println("用 # 号连接的字符串,跳过中间的null值："+joinNull);

        //3.有null值存在时用指定值代替
        String joinUseForNull = Joiner.on("#").useForNull("DEFAULT").join(list2);
        System.out.println("用指定值代替集合中的null值："+joinUseForNull);

        //4.把集合变成一个stringBuilder 或者stringBuffer
        StringBuilder builder = Joiner.on("#").useForNull("DEFAULT").appendTo(new StringBuilder(), list2);
        StringBuffer buffer = Joiner.on("#").useForNull("DEFAULT").appendTo(new StringBuffer(), list2);
        System.out.println("拼接成的 builder是："+builder);
        System.out.println("拼接成的buffer是："+buffer);

        //5.对于map中key value的分隔
        Map<String, String> map = new HashMap<String, String>();
        map.put("hello", "java");
        map.put("scala", "guava");
        String joinMap = Joiner.on("#").withKeyValueSeparator("=").join(map);
        System.out.println("key value 的分隔符："+joinMap);

    }
}
//打印结果

用 # 号连接的字符串,跳过中间的null值：google#guava#java#scala#kafka
用指定值代替集合中的null值:google#guava#java#DEFAULT#scala#kafka
拼接成的 builder是：google#guava#java#DEFAULT#scala#kafka
拼接成的buffer是：google#guava#java#DEFAULT#scala#kafka
key value 的分隔符：scala=guava#hello=java