来自Perl,我肯定错过了在源代码中创建多行字符串的“here-document”方法:

$string = <<"EOF"  # create a three-line string
text
text
text
EOF

在Java中,当我从头开始连接多行字符串时,我必须在每一行上使用繁琐的引号和加号。

有什么更好的选择吗?在属性文件中定义我的字符串?

编辑:有两个答案说StringBuilder.append()比加号更可取。谁能详细解释一下他们为什么这么想?在我看来,这一点也不可取。我正在寻找一种方法来解决多行字符串不是一级语言结构这一事实,这意味着我绝对不想用方法调用取代一级语言结构(字符串连接与加号)。

编辑: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。


当前回答

另一种方法是将长字符串存储在外部文件中,然后将文件读入字符串。

其他回答


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。

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";

我所知道的唯一方法是用加号连接多行

在属性文件中定义我的字符串?

属性文件中不允许多行字符串。您可以在属性文件中使用\n,但我认为这在您的情况下不是一个很好的解决方案。

我有时使用一个并行groovy类来充当一个字符串包

这里的java类

public class Test {
    public static void main(String[] args) {
        System.out.println(TestStrings.json1);
        // consume .. parse json
    }
}

以及TestStrings.groovy中令人垂涎的多行字符串

class TestStrings {
    public static String json1 = """
    {
        "name": "Fakeer's Json",
        "age":100,
        "messages":["msg 1","msg 2","msg 3"]
    }""";
}

当然,这只适用于静态字符串。如果我必须在文本中插入变量,我会将整个文件更改为groovy。只要保持强类型实践,它就可以实现。