import org.apache.commons.lang3.StringUtils;

    String multiline = StringUtils.join(new String[] {
        "It was the best of times, it was the worst of times ", 
        "it was the age of wisdom, it was the age of foolishness",
        "it was the epoch of belief, it was the epoch of incredulity",
        "it was the season of Light, it was the season of Darkness",
        "it was the spring of hope, it was the winter of despair",
        "we had everything before us, we had nothing before us",
        }, "\n");

使用Properties.loadFromXML (InputStream)。不需要外部库。

比起混乱的代码(因为可维护性和设计是您所关心的)，最好不要使用长字符串。 从读取xml属性开始:

 InputStream fileIS = YourClass.class.getResourceAsStream("MultiLine.xml");
 Properties prop = new Properies();
 prop.loadFromXML(fileIS);

然后，您可以使用您的多行字符串在一个更可维护的方式…

static final String UNIQUE_MEANINGFUL_KEY = "Super Duper UNIQUE Key";
prop.getProperty(UNIQUE_MEANINGFUL_KEY) // "\n    MEGA\n   LONG\n..."

MultiLine.xml`位于同一个文件夹YourClass:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd">

<properties>
    <entry key="Super Duper UNIQUE Key">
       MEGA
       LONG
       MULTILINE
    </entry>
</properties>

注:你可以使用<![CDATA[”…"]]>为类似xml的字符串。

JEP 378: Text Blocks涵盖了此功能，并且包含在JDK 15中。它最初出现在JDK 13中的JEP 355: Text Blocks(预览)和JDK 14中的JEP 368: Text Blocks(第二预览)，可以在这些版本中通过——enable-preview javac选项启用。

语法允许这样写:

String s = """
           text
           text
           text
           """;

在此之前，在JDK 12中，JEP 326: Raw String Literals旨在实现类似的功能，但最终被撤回:

请注意:这原本是JDK 12中的预览语言功能，但它已被撤回，并没有出现在JDK 12中。它在JDK 13中被文本块(JEP 355)所取代。

当使用一长串的+时，只会创建一个StringBuilder，除非在编译时确定String，在这种情况下不使用StringBuilder !

StringBuilder唯一更高效的情况是使用多个语句构造String。

String a = "a\n";
String b = "b\n";
String c = "c\n";
String d = "d\n";

String abcd = a + b + c + d;
System.out.println(abcd);

String abcd2 = "a\n" +
        "b\n" +
        "c\n" +
        "d\n";
System.out.println(abcd2);

注意:只创建了一个StringBuilder。

  Code:
   0:   ldc     #2; //String a\n
   2:   astore_1
   3:   ldc     #3; //String b\n
   5:   astore_2
   6:   ldc     #4; //String c\n
   8:   astore_3
   9:   ldc     #5; //String d\n
   11:  astore  4
   13:  new     #6; //class java/lang/StringBuilder
   16:  dup
   17:  invokespecial   #7; //Method java/lang/StringBuilder."<init>":()V
   20:  aload_1
   21:  invokevirtual   #8; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
   24:  aload_2
   25:  invokevirtual   #8; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
   28:  aload_3
   29:  invokevirtual   #8; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
   32:  aload   4
   34:  invokevirtual   #8; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
   37:  invokevirtual   #9; //Method java/lang/StringBuilder.toString:()Ljava/lang/String;
   40:  astore  5
   42:  getstatic       #10; //Field java/lang/System.out:Ljava/io/PrintStream;
   45:  aload   5
   47:  invokevirtual   #11; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
   50:  ldc     #12; //String a\nb\nc\nd\n
   52:  astore  6
   54:  getstatic       #10; //Field java/lang/System.out:Ljava/io/PrintStream;
   57:  aload   6
   59:  invokevirtual   #11; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
   62:  return

为了进一步澄清我的问题，我根本不关心性能。我关心的是可维护性和设计问题。

尽你所能让它清晰简单。

Java 13预览:

Text Blocks Come to Java. Java 13 delivers long-awaited multiline string by Mala Gupta With text blocks, Java 13 is making it easier for you to work with multiline string literals. You no longer need to escape the special characters in string literals or use concatenation operators for values that span multiple lines. Text block is defined using three double quotes (""") as the opening and closing delimiters. The opening delimiter can be followed by zero or more white spaces and a line terminator.

例子:

 String s1 = """
 text
 text
 text
 """;

这看起来可能有点疯狂，但由于这里文档是单行声明的语法糖，并转义了换行符，因此可以为Java文件编写预处理程序，在预处理期间将这里文档更改为单行。

这需要在编译阶段(对于ant/maven构建)之前为预处理文件编写适当的插件，并为IDE编写插件。

从意识形态的观点来看，它与f.g.没有什么不同。“泛型”，这也是一种预处理的语法加糖铸造。

然而，这是一个大量的工作，所以我会在你的地方只使用.properties文件。