我至少看到了一种应该避免使用外部文件处理长字符串的情况:如果这些长字符串是单元测试文件中的预期值，因为我认为测试应该始终以一种不依赖任何外部资源的方式编写。

注意:这个答案适用于Java 14及以上版本。

Java 15引入了文本块(多行文字)。详情请看这个答案。

听起来像是要做一个多行文字，这在Java中是不存在的。

你最好的选择是用+ d组合的字符串。人们提到的一些其他选项(StringBuilder, String。format, String.join)只有当你从一个字符串数组开始时才更可取。

考虑一下:

String s = "It was the best of times, it was the worst of times,\n"
         + "it was the age of wisdom, it was the age of foolishness,\n"
         + "it was the epoch of belief, it was the epoch of incredulity,\n"
         + "it was the season of Light, it was the season of Darkness,\n"
         + "it was the spring of hope, it was the winter of despair,\n"
         + "we had everything before us, we had nothing before us";

与StringBuilder:

String s = new StringBuilder()
           .append("It was the best of times, it was the worst of times,\n")
           .append("it was the age of wisdom, it was the age of foolishness,\n")
           .append("it was the epoch of belief, it was the epoch of incredulity,\n")
           .append("it was the season of Light, it was the season of Darkness,\n")
           .append("it was the spring of hope, it was the winter of despair,\n")
           .append("we had everything before us, we had nothing before us")
           .toString();

与String.format ():

String s = String.format("%s\n%s\n%s\n%s\n%s\n%s"
         , "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"
);

相对于Java8 String.join():

String s = String.join("\n"
         , "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"
);

如果您想在特定的系统中使用换行符，您要么需要使用system . lineseparator()，要么可以在String.format中使用%n。

另一种选择是将资源放在文本文件中，只读取该文件的内容。对于非常大的字符串，这将是可取的，以避免不必要地膨胀您的类文件。

我至少看到了一种应该避免使用外部文件处理长字符串的情况:如果这些长字符串是单元测试文件中的预期值，因为我认为测试应该始终以一种不依赖任何外部资源的方式编写。

在Eclipse中，如果你打开选项“在粘贴到字符串文字时转义文本”(在Preferences > Java > Editor > Typing中)并在引号中粘贴一个多行字符串，它将自动为你的所有行添加“和\n”+。

String str = "paste your text here";

参见Java Stringfier。如果需要，将文本转换为StringBuilder java块转义。

这个问题有两个答案:

In you want to stick to pure Java, with Java 14 being released in March 2020, you can leverage the JEP 368 - Text Blocks, in Second Preview mode. Actually the feature is in preview mode in other releases (at least 13 has it). I created and example set here. While this feature is useful, it can be easily abused. Remember that Java requires compilation - having large character arrays in your code can be an easy way to shoot yourself in the leg (if you want a quick change, you will need recompilation - that toolset might not be available to the guy operating your application).

根据我的经验，建议在配置文件中保留大字符串(通常是应用程序操作员可以/应该在运行时更改的字符串)。

总结:负责地使用文本块:)。