1.去除字符串中的空格
① trim() 用法：str.trim()
② java.util.StringTokenizer 用法：
String s = "hello world";
StringTokenizer str = new StringTokenizer(s," ");
StringBuffer sb = new StringBuffer();
while (str.hasMoreTokens()){
sb.append(str.nextToken());
}
System.out.print(sb.toString());
③replaceAll() 用法 str.replaceAll(" ","");
常见日期格式化转换符
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