这有用吗？

poemText = poemText.trim().replaceAll("\n ", "\n")

因为句子之间有空格，所以首先trim（）去掉字符串的开头和结尾，然后用 \n

你可以用 ^\h+ 要匹配字符串开头的一个或多个水平空格字符，请使用 (?m) 启用多行。
在替换中使用空字符串。

val poemText = """
Blow the candles real hard,
 Coz now you have aged,
Don't pretend so much my dear,
 Don't behave so sage,
 Happy birthday to you,
 Have a nice day,
Make the most of your day!"""

    println(
        """(?m)^\h+"""
        .toRegex()
        .replace(poemText, "")
    )

输出

Blow the candles real hard,
Coz now you have aged,
Don't pretend so much my dear,
Don't behave so sage,
Happy birthday to you,
Have a nice day,
Make the most of your day!

查看kotlin演示

您可以这样使用replace with regex：

poemText = poemText.replace("""^\s*|\s*$""".toRegex(), "")
                   .replace("""\s*(\r|\n|\r\n)\s*""".toRegex(), "\n")

代码示例
第一个替换将删除文本开头和结尾的所有空格，第二个替换将删除每行结尾和开头的空格。

我想你可以把java变成kotlin

String text = "Blow the candles real hard,\n " +
            "    Coz now you have aged,\n " +
            "    Don't pretend so much my dear,\n " +
            "    Don't behave so sage,\n " +
            "    Happy birthday to you,\n " +
            "    Have a nice day,\n " +
            "    Make the most of your day!";

    String[] lines = null;
    lines = text.split("\n");

    String newText = "";
    for(int i = 0 ; i<lines.length ; i++){
        newText = (newText + lines[i]).trim()+"\n";
    }

    Log.e("newText",newText);