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

我还没有看到的另一个答案是java.io.PrintWriter。

StringWriter stringWriter = new StringWriter();
PrintWriter writer = new PrintWriter(stringWriter);
writer.println("It was the best of times, it was the worst of times");
writer.println("it was the age of wisdom, it was the age of foolishness,");
writer.println("it was the epoch of belief, it was the epoch of incredulity,");
writer.println("it was the season of Light, it was the season of Darkness,");
writer.println("it was the spring of hope, it was the winter of despair,");
writer.println("we had everything before us, we had nothing before us");
String string = stringWriter.toString();

此外,java.io.BufferedWriter有一个newLine()方法的事实也未被提及。

其他回答

一个非常高效且与平台无关的解决方案是使用系统属性的行分隔符和StringBuilder类来构建字符串:

String separator = System.getProperty("line.separator");
String[] lines = {"Line 1", "Line 2" /*, ... */};

StringBuilder builder = new StringBuilder(lines[0]);
for (int i = 1; i < lines.length(); i++) {
    builder.append(separator).append(lines[i]);
}
String multiLine = builder.toString();

当我读到多行语法确实是为jdk7计划的(在java存在了多少年之后?)时,我有点恼火。有趣的是,甚至还没有readAll()函数用于读取文件的完整内容(仅从jdk7读取,啊啊),因此下面的代码读取单行。

/*
  MakeMultiline v1.0 (2010) - Free to use and copy.

  Small gadget to turn text blobs into one java string literal
  (doing the split in lines, adding \n at each end and enclosing
  in double quotes). Does escape quotes encountered in the text blob.

  Useful for working around missing multiline string syntax in java
  prior jdk7. Use with:

     java MakeMultiline "    "
  or
     java MakeMultiline "    " mytextfile.txt
*/

import java.io.*;

class MakeMultiline {
  public static void main(String[] args) {
    try {
      // args[0]: indent
      // args[1]: filename to read (optional; stdin if not given)
      // Beware the nmb of newlines at the end when using stdin!

      String indent = (args.length > 0 ? args[0] : "");
      FileReader fr = null; BufferedReader br;
      if (args.length > 1)
        { fr =  new FileReader(args[1]); br = new BufferedReader(fr); }
      else
        { br = new BufferedReader(new InputStreamReader(System.in)); }
      String s; String res = "";
      while((s = br.readLine()) != null) {
        if (res.length() > 0) res += " +\n";
        res += indent + "\"" + s.replace("\"", "\\\"") + "\\n\"";
      }
      br.close(); if (fr != null) fr.close();
      System.out.println(res + ";");
    }
    catch(Exception e) {
      System.out.println("Exception: " + e);
    }
  }
}

这对我来说是最快的解决办法。(2010-01-27)

看到所有的答案,我认为没有人提到比在java的新版本,你可以这样做:

String s = """
    This
    is 
    a
    multiline
    string
    """;
System.out.println(s);

这是它打印的内容:

This
is
a
multiline
string
    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");

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。