Java 是否支持多行字符串？

Question

Coming from Perl, I sure am missing the "here-document" means of creating a multi-line string in source code:

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

In Java, I have to have cumbersome quotes and plus signs on every line as I concatenate my multiline string from scratch.

What are some better alternatives? Define my string in a properties file?

Edit : Two answers say StringBuilder.append() is preferable to the plus notation. Could anyone elaborate as to why they think so? It doesn't look more preferable to me at all. I'm looking for a way around the fact that multiline strings are not a first-class language construct, which means I definitely don't want to replace a first-class language construct (string concatenation with plus) with method calls.

Edit : To clarify my question further, I'm not concerned about performance at all. I'm concerned about maintainability and design issues.

Answer 1

It sounds like you want to do a multiline literal, which does not exist in Java.

Your best alternative is going to be strings that are just + 'd together. Some other options people have mentioned (StringBuilder, String.format, String.join) would only be preferable if you started with an array of strings.

Consider this:

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";

Versus 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();

Versus 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"
);

Versus 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"
);

If you want the newline for your particular system, you either need to use System.lineSeparator() , or you can use %n in String.format .

Another option is to put the resource in a text file, and just read the contents of that file. This would be preferable for very large strings to avoid unnecessarily bloating your class files.

Answer 2

在 Eclipse 中，如果您打开选项“粘贴到字符串文字时转义文本”（在 Preferences > Java > Editor > Typing 中）并粘贴多行字符串，它会在引号中自动添加"和\\n" +你的台词。

String str = "paste your text here";

Answer 3

Stephen Colebourne has created a proposal for adding multi-line strings in Java 7.

Also, Groovy already has support formulti-line strings .

Answer 4

This is an old thread, but a new quite elegant solution (with only 4 maybe 3 little drawbacks) is to use a custom annotation.

Check : http://www.adrianwalker.org/2011/12/java-multiline-string.html

A project inspired from that work is hosted on GitHub:

https://github.com/benelog/multiline

Example of Java code:

import org.adrianwalker.multilinestring.Multiline;
...
public final class MultilineStringUsage {

  /**
  <html>
    <head/>
    <body>
      <p>
        Hello<br/>
        Multiline<br/>
        World<br/>
      </p>
    </body>
  </html>
  */
  @Multiline
  private static String html;

  public static void main(final String[] args) {
    System.out.println(html);
  }
}

The drawbacks are

1. that you have to activate the corresponding (provided) annotation processor.
2. that String variable can not be defined as local variable Check Raw String Literals project where you can define variables as local variables
3. that String cannot contains other variables as in Visual Basic .Net with XML literal ( <%= variable %> ) :-)
4. that String literal is delimited by JavaDoc comment (/**)

And you probably have to configure Eclipse/Intellij-Idea to not reformat automatically your Javadoc comments.

One may find this weird (Javadoc comments are not designed to embed anything other than comments), but as this lack of multiline string in Java is really annoying in the end, I find this to be the least worst solution.

Answer 5

另一种选择可能是将长字符串存储在外部文件中并将文件读入字符串。

Answer 6

This is something that you should never use without thinking about what it's doing. But for one-off scripts I've used this with great success:

Example:

    System.out.println(S(/*
This is a CRAZY " ' ' " multiline string with all sorts of strange 
   characters!
*/));

Code:

// From: http://blog.efftinge.de/2008/10/multi-line-string-literals-in-java.html
// Takes a comment (/**/) and turns everything inside the comment to a string that is returned from S()
public static String S() {
    StackTraceElement element = new RuntimeException().getStackTrace()[1];
    String name = element.getClassName().replace('.', '/') + ".java";
    StringBuilder sb = new StringBuilder();
    String line = null;
    InputStream in = classLoader.getResourceAsStream(name);
    String s = convertStreamToString(in, element.getLineNumber());
    return s.substring(s.indexOf("/*")+2, s.indexOf("*/"));
}

// From http://www.kodejava.org/examples/266.html
private static String convertStreamToString(InputStream is, int lineNum) {
    /*
     * To convert the InputStream to String we use the BufferedReader.readLine()
     * method. We iterate until the BufferedReader return null which means
     * there's no more data to read. Each line will appended to a StringBuilder
     * and returned as String.
     */
    BufferedReader reader = new BufferedReader(new InputStreamReader(is));
    StringBuilder sb = new StringBuilder();

    String line = null; int i = 1;
    try {
        while ((line = reader.readLine()) != null) {
            if (i++ >= lineNum) {
                sb.append(line + "\n");
            }
        }
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        try {
            is.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    return sb.toString();
}

Answer 7

String.join

Java 8 added a new static method to java.lang.String which offers a slightly better alternative:

String.join( CharSequence delimiter , CharSequence... elements )

Using it:

String s = String.join(
    System.getProperty("line.separator"),
    "First line.",
    "Second line.",
    "The rest.",
    "And the last!"
);

Answer 8

JEP 378: Text Blocks covers this functionality and is included in JDK 15. It first appeared as JEP 355: Text Blocks (Preview) in JDK 13 and JEP 368: Text Blocks (Second Preview) in JDK 14 and can be enabled in these versions with the ––enable–preview javac option.

The syntax allows to write something like:

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

Previous to this JEP, in JDK 12, JEP 326: Raw String Literals aimed to implement a similar feature, but it was eventually withdrawn:

Please note: This was intended to be a preview language feature in JDK 12, but it was withdrawn and did not appear in JDK 12. It was superseded by Text Blocks ( JEP 355 ) in JDK 13.

Answer 9

Java 13 and beyond

Multiline Strings are now supported in Java via Text Blocks . In Java 13 and 14, this feature requires you to set the ––enable–preview option when building and running your project. In Java 15 and later, this option is no longer required as Text Blocks have become a standard feature. Check out the official Programmer's Guide to Text Blocks for more details.

Now, prior to Java 13, this is how you'd write a query:

List<Tuple> posts = entityManager
.createNativeQuery(
    "SELECT *\n" +
    "FROM (\n" +
    "    SELECT *,\n" +
    "           dense_rank() OVER (\n" +
    "               ORDER BY \"p.created_on\", \"p.id\"\n" +
    "           ) rank\n" +
    "    FROM (\n" +
    "        SELECT p.id AS \"p.id\",\n" +
    "               p.created_on AS \"p.created_on\",\n" +
    "               p.title AS \"p.title\",\n" +
    "               pc.id as \"pc.id\",\n" +
    "               pc.created_on AS \"pc.created_on\",\n" +
    "               pc.review AS \"pc.review\",\n" +
    "               pc.post_id AS \"pc.post_id\"\n" +
    "        FROM post p\n" +
    "        LEFT JOIN post_comment pc ON p.id = pc.post_id\n" +
    "        WHERE p.title LIKE :titlePattern\n" +
    "        ORDER BY p.created_on\n" +
    "    ) p_pc\n" +
    ") p_pc_r\n" +
    "WHERE p_pc_r.rank <= :rank\n",
    Tuple.class)
.setParameter("titlePattern", "High-Performance Java Persistence %")
.setParameter("rank", 5)
.getResultList();

Thanks to Java 13 Text Blocks, you can rewrite this query as follows:

List<Tuple> posts = entityManager
.createNativeQuery("""
    SELECT *
    FROM (
        SELECT *,
               dense_rank() OVER (
                   ORDER BY "p.created_on", "p.id"
               ) rank
        FROM (
            SELECT p.id AS "p.id",
                   p.created_on AS "p.created_on",
                   p.title AS "p.title",
                   pc.id as "pc.id",
                   pc.created_on AS "pc.created_on",
                   pc.review AS "pc.review",
                   pc.post_id AS "pc.post_id"
            FROM post p
            LEFT JOIN post_comment pc ON p.id = pc.post_id
            WHERE p.title LIKE :titlePattern
            ORDER BY p.created_on
        ) p_pc
    ) p_pc_r
    WHERE p_pc_r.rank <= :rank
    """,
    Tuple.class)
.setParameter("titlePattern", "High-Performance Java Persistence %")
.setParameter("rank", 5)
.getResultList();

Much more readable, right?

IDE support

IntelliJ IDEA provides support for transforming legacy String concatenation blocks to the new multiline String format:

JSON, HTML, XML

The multiline String is especially useful when writing JSON, HTML, or XML.

Consider this example using String concatenation to build a JSON string literal:

entityManager.persist(
    new Book()
    .setId(1L)
    .setIsbn("978-9730228236")
    .setProperties(
        "{" +
        "   \"title\": \"High-Performance Java Persistence\"," +
        "   \"author\": \"Vlad Mihalcea\"," +
        "   \"publisher\": \"Amazon\"," +
        "   \"price\": 44.99," +
        "   \"reviews\": [" +
        "       {" +
        "           \"reviewer\": \"Cristiano\", " +
        "           \"review\": \"Excellent book to understand Java Persistence\", " +
        "           \"date\": \"2017-11-14\", " +
        "           \"rating\": 5" +
        "       }," +
        "       {" +
        "           \"reviewer\": \"T.W\", " +
        "           \"review\": \"The best JPA ORM book out there\", " +
        "           \"date\": \"2019-01-27\", " +
        "           \"rating\": 5" +
        "       }," +
        "       {" +
        "           \"reviewer\": \"Shaikh\", " +
        "           \"review\": \"The most informative book\", " +
        "           \"date\": \"2016-12-24\", " +
        "           \"rating\": 4" +
        "       }" +
        "   ]" +
        "}"
    )
);

You can barely read the JSON due to the escaping characters and the abundance of double quotes and plus signs.

With Java Text Blocks, the JSON object can be written like this:

entityManager.persist(
    new Book()
    .setId(1L)
    .setIsbn("978-9730228236")
    .setProperties("""
        {
           "title": "High-Performance Java Persistence",
           "author": "Vlad Mihalcea",
           "publisher": "Amazon",
           "price": 44.99,
           "reviews": [
               {
                   "reviewer": "Cristiano",
                   "review": "Excellent book to understand Java Persistence",
                   "date": "2017-11-14",
                   "rating": 5
               },
               {
                   "reviewer": "T.W",
                   "review": "The best JPA ORM book out there",
                   "date": "2019-01-27",
                   "rating": 5
               },
               {
                   "reviewer": "Shaikh",
                   "review": "The most informative book",
                   "date": "2016-12-24",
                   "rating": 4
               }
           ]
        }
        """
    )
);

Ever since I used C# in 2004, I've been wanting to have this feature in Java, and now we finally have it.

Answer 10

If you define your strings in a properties file it'll look much worse. IIRC, it'll look like:

string:text\u000atext\u000atext\u000a

Generally it's a reasonable idea to not embed large strings in to source. You might want to load them as resources, perhaps in XML or a readable text format. The text files can be either read at runtime or compiled into Java source. If you end up placing them in the source, I suggest putting the + at the front and omitting unnecessary new lines:

final String text = ""
    +"text "
    +"text "
    +"text"
;

If you do have new lines, you might want some of join or formatting method:

final String text = join("\r\n"
    ,"text"
    ,"text"
    ,"text"
);

Answer 11

In the IntelliJ IDE you just need to type:

""

Then position your cursor inside the quotation marks and paste your string. The IDE will expand it into multiple concatenated lines.

Answer 12

Pluses are converted to StringBuilder.append, except when both strings are constants so the compiler can combine them at compile time. At least, that's how it is in Sun's compiler, and I would suspect most if not all other compilers would do the same.

So:

String a="Hello";
String b="Goodbye";
String c=a+b;

normally generates exactly the same code as:

String a="Hello";
String b="Goodbye":
StringBuilder temp=new StringBuilder();
temp.append(a).append(b);
String c=temp.toString();

On the other hand:

String c="Hello"+"Goodbye";

is the same as:

String c="HelloGoodbye";

That is, there's no penalty in breaking your string literals across multiple lines with plus signs for readability.

Answer 13

Sadly, Java does not have multi-line string literals. You either have to concatenate string literals (using + or StringBuilder being the two most common approaches to this) or read the string in from a separate file.

For large multi-line string literals I'd be inclined to use a separate file and read it in using getResourceAsStream() (a method of the Class class). This makes it easy to find the file as you don't have to worry about the current directory versus where your code was installed. It also makes packaging easier, because you can actually store the file in your jar file.

Suppose you're in a class called Foo. Just do something like this:

Reader r = new InputStreamReader(Foo.class.getResourceAsStream("filename"), "UTF-8");
String s = Utils.readAll(r);

The one other annoyance is that Java doesn't have a standard "read all of the text from this Reader into a String" method. It's pretty easy to write though:

public static String readAll(Reader input) {
    StringBuilder sb = new StringBuilder();
    char[] buffer = new char[4096];
    int charsRead;
    while ((charsRead = input.read(buffer)) >= 0) {
        sb.append(buffer, 0, charsRead);
    }
    input.close();
    return sb.toString();
}

Answer 14

String newline = System.getProperty ("line.separator");
string1 + newline + string2 + newline + string3

But, the best alternative is to use String.format

String multilineString = String.format("%s\n%s\n%s\n",line1,line2,line3);

Answer 15

You may use scala-code, which is compatible to java, and allows multiline-Strings enclosed with """:

package foobar
object SWrap {
  def bar = """John said: "This is
  a test
  a bloody test,
  my dear." and closed the door.""" 
}

(note the quotes inside the string) and from java:

String s2 = foobar.SWrap.bar ();

Whether this is more comfortable ...?

Another approach, if you often handle long text, which should be placed in your sourcecode, might be a script, which takes the text from an external file, and wrappes it as a multiline-java-String like this:

sed '1s/^/String s = \"/;2,$s/^/\t+ "/;2,$s/$/"/' file > file.java

so that you may cut-and-paste it easily into your source.

Answer 16

Since Java does not (yet) native support multi-line strings, the only way for now is to hack around it using one of the aforementioned techniques. I built the following Python script using some of the tricks mentioned above:

import sys
import string
import os

print 'new String('
for line in sys.stdin:
    one = string.replace(line, '"', '\\"').rstrip(os.linesep)
    print '  + "' + one + ' "'
print ')'

Put that in a file named javastringify.py and your string in a file mystring.txt and run it as follows:

cat mystring.txt | python javastringify.py

You can then copy the output and paste it into your editor.

Modify this as needed to handle any special cases but this works for my needs. Hope this helps!

Answer 17

You can concatenate your appends in a separate method like:

public static String multilineString(String... lines){
   StringBuilder sb = new StringBuilder();
   for(String s : lines){
     sb.append(s);
     sb.append ('\n');
   }
   return sb.toString();
}

Either way, prefer StringBuilder to the plus notation.

Answer 18

    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");

Answer 19

Actually, the following is the cleanest implementation I have seen so far. It uses an annotation to convert a comment into a string variable...

/**
  <html>
    <head/>
    <body>
      <p>
        Hello<br/>
        Multiline<br/>
        World<br/>
      </p>
    </body>
  </html>
  */
  @Multiline
  private static String html;

So, the end result is that the variable html contains the multiline string. No quotes, no pluses, no commas, just pure string.

This solution is available at the following URL... http://www.adrianwalker.org/2011/12/java-multiline-string.html

Hope that helps!

Answer 20

See Java Stringfier . Turns your text into a StringBuilder java block escaping if needed.

Answer 21

An alternative I haven't seen as answer yet is the 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();

Also the fact that java.io.BufferedWriter has a newLine() method is unmentioned.

Answer 22

If you like google's guava as much as I do, it can give a fairly clean representation and a nice, easy way to not hardcode your newline characters too:

String out = Joiner.on(newline).join(ImmutableList.of(
    "line1",
    "line2",
    "line3"));

Answer 23

Use Properties.loadFromXML(InputStream) . There's no need for external libs.

Better than a messy code (since maintainability and design are your concern), it is preferable not to use long strings.

Start by reading xml properties:

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

then you can use your multiline string in a more maintainable way...

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

MultiLine.xml` gets located in the same folder 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>

PS.: You can use <![CDATA[" ... "]]> for xml-like string.

Answer 24

With JDK/12 early access build # 12 , one can now use multiline strings in Java as follows :

String multiLine = `First line
    Second line with indentation
Third line
and so on...`; // the formatting as desired
System.out.println(multiLine);

and this results in the following output:

 First line Second line with indentation Third line and so on...

Edit: Postponed to java 13

Answer 25

Java 13 preview:

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.

Example:

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

Answer 26

One good option.

import static some.Util.*;

    public class Java {

        public static void main(String[] args) {

            String sql = $(
              "Select * from java",
              "join some on ",
              "group by"        
            );

            System.out.println(sql);
        }

    }


    public class Util {

        public static String $(String ...sql){
            return String.join(System.getProperty("line.separator"),sql);
        }

    }

Answer 27

A quite efficient and platform independent solution would be using the system property for line separators and the StringBuilder class to build strings:

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();

Answer 28

I suggest using a utility as suggested by ThomasP, and then link that into your build process. An external file is still present to contain the text, but the file is not read at runtime. The workflow is then:

1. Build a 'textfile to java code' utility & check into version control
2. On each build, run the utility against the resource file to create a revised java source
3. The Java source contains a header like class TextBlock {... followed by a static string which is auto-generated from the resource file
4. Build the generated java file with the rest of your code

Answer 29

I know this is an old question, however for intersted developers Multi line literals gonna be in #Java12

http://mail.openjdk.java.net/pipermail/amber-dev/2018-July/003254.html

Answer 30

Define my string in a properties file?

Multiline strings aren't allowed in properties files. You can use \\n in properties files, but I don't think that is much of a solution in your case.

Answer 31

Late model JAVA has optimizations for + with constant strings, employs a StringBuffer behind the scenes, so you do not want to clutter your code with it.

It points to a JAVA oversight, that it does not resemble ANSI C in the automatic concatenation of double quoted strings with only white space between them, eg:

const char usage = "\n"
"Usage: xxxx <options>\n"
"\n"
"Removes your options as designated by the required parameter <options>,\n"
"which must be one of the following strings:\n"
"  love\n"
"  sex\n"
"  drugs\n"
"  rockandroll\n"
"\n" ;

I would love to have a multi-line character array constant where embedded linefeeds are honored, so I can present the block without any clutter, eg:

String Query = "
SELECT
    some_column,
    another column
  FROM
      one_table a
    JOIN
      another_table b
    ON    a.id = b.id
      AND a.role_code = b.role_code
  WHERE a.dept = 'sales'
    AND b.sales_quote > 1000
  Order BY 1, 2
" ;

To get this, one needs to beat on the JAVA gods.

Answer 32

One small trick. Using this I inject javascritp in a dynamically created HTML page

StringBuilder builder = new StringBuilder();

public String getString()
{
    return builder.toString();
}
private DropdownContent _(String a)
{
    builder.append(a);
    return this;
}

public String funct_showhide()
{
   return
    _("function slidedown_showHide(boxId)").
    _("{").
    _("if(!slidedown_direction[boxId])slidedown_direction[boxId] = 1;").
    _("if(!slideDownInitHeight[boxId])slideDownInitHeight[boxId] = 0;").
    _("if(slideDownInitHeight[boxId]==0)slidedown_direction[boxId]=slidedownSpeed; ").
    _("else slidedown_direction[boxId] = slidedownSpeed*-1;").
    _("slidedownContentBox = document.getElementById(boxId);").
    _("var subDivs = slidedownContentBox.getElementsByTagName('DIV');").
    _("for(var no=0;no<subDivs.length;no++){").
    _(" if(subDivs[no].className=='dhtmlgoodies_content')slidedownContent = subDivs[no];").
    _("}").
    _("contentHeight = slidedownContent.offsetHeight;").
    _("slidedownContentBox.style.visibility='visible';").
    _("slidedownActive = true;").
    _("slidedown_showHide_start(slidedownContentBox,slidedownContent);").
    _("}").getString();

}

Answer 33

Java15 现在像 Python 一样支持三引号字符串。

Answer 34

When a long series of + are used, only one StringBuilder is created, unless the String is determined at compile time in which case no StringBuilder is used!

The only time StringBuilder is more efficient is when multiple statements are used to construct the 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);

Note: Only one StringBuilder is created.

  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

To clarify my question further, I'm not concerned about performance at all. I'm concerned about maintainability and design issues.

Make it as clear and simple as you can.

Answer 35

It may seem a little crazy, but since heredocs are syntactic sugar over one-line declarations with linebreaks escaped, one could write pre-processor for Java files that would change heredocs into single-liners during preprocessing.

It would require writing proper plugins for preprocessing files before compilation phase (for ant/maven build) and a plugin to IDE.

From an ideological point of view, it differs nothing from fg "generics", that is also a kind of pre-processed syntactic sugar over casting.

It's, however, a lot of work, so I would at your place just use .properties files.

Answer 36

I sometimes use a parallel groovy class just to act as a bag of strings

The java class here

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

And the coveted multiline strings here in TestStrings.groovy

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

Of course this is for static strings only. If I have to insert variables in the text I will just change the entire file to groovy. Just maintain strong-typing practices and it can be pulled off.

Answer 37

我至少看到一种情况，应该避免对长字符串使用外部文件：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不使用的方式编写依赖任何外部资源。

Answer 38

Using this library

https://github.com/alessio-santacroce/multiline-string-literals

it is possible to write things like this

System.out.println(newString(/*
      Wow, we finally have
      multiline strings in
      Java! HOOO!
*/));

Very nice and easy, but works only for unit tests

Answer 39

Two answers to this question:

1. 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 .
2. 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).

In my experience, it is advisable to keep large strings (and generally strings that could/should be altered at runtime by app operators) in configuration files.

Summary: use text blocks responsibly :).

Answer 40

我知道的唯一方法是用加号连接多行

Answer 41

A simple option is to edit your java-code with an editor like SciTE ( http://www.scintilla.org/SciTEDownload.html ), which allows you to WRAP the text so that long strings are easily viewed and edited. If you need escape characters you just put them in. By flipping the wrap-option off you can check that your string indeed is still just a long single-line string. But of course, the compiler will tell you too if it isn't.

Whether Eclipse or NetBeans support text-wrapping in an editor I don't know, because they have so many options. But if not, that would be a good thing to add.

Answer 42

I got a bit annoyed with reading that multiline syntax is indeed been planned for jdk7 (after about how many decades of java existence?). Funnily, there is not even yet a readAll() function for reading the complete contents of a file (from jdk7 only, huhh), so the code below reads single lines.

/*
  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);
    }
  }
}

This was the quickest solution for me. (2010-01-27)

Answer 43

It's not entirely clear from the question if author is interested in working with some sort of formatted large strings that need to have some dynamic values, but if that's the case a templating engine like StringTemplate ( http://www.stringtemplate.org/ ) might be very useful.

A simple sample of the code that uses StringTemplate is below. The actual template ("Hello, < name >") could be loaded from an external plain text file. All indentation in the template will be preserved, and no escaping is necessary.

import org.stringtemplate.v4.*;
 
public class Hello {
    public static void main(String[] args) {
        ST hello = new ST("Hello, <name>");
        hello.add("name", "World");
        System.out.println(hello.render());
    }
}

PS It's always a good idea to remove large chunks of text from source code for readability and localization purposes.

Answer 44

You can use Kotlin multiple line string support..

Just Create a Kotlin class, and use it there,

You can call kotlin class as java synxtax

//Kotlin

    fun jsIncreaseOrDecreaseWebFonts(webView : YHYWebView, sliderValue : Int, intFontSize : Int){
            var initialData = """
                  bla bla
                """

}

//From Java

 KotlinFunctions t = new KotlinFunctions();
 t.jsIncreaseOrDecreaseWebFonts(webView,progresValue,incOrDec);