Java multi-line string, text blocks
This article will show you a few ways to declare and use a multi-line string in Java.
String + String + StringStringBuilderString.formatStringWriterString.join(Java 8)Files.lines(Java 8)(""")Java 13 and Java 14 text blocks (preview feature)
Review an HTML and a JSON string, and we will use the above methods to declare the following multi-line string in Java.
<html>
<body>
<p>Hello, World</p>
</body>
</html>
{
"name":"mkyong",
"age":38
}
1. String + String + String
The simplest solution, add a multi-line string with +.
String html = "<html>\n"
+ " <body>\n"
+ " <p>Hello, World</p>\n"
+ " </body>\n"
+ "</html>";
String json = "{\n"
+ " \"name\":\"mkyong\",\n"
+ " \"age\":38\n"
+ "}";
2. String Builder
This method is a commonly used pattern.
String html = new StringBuilder()
.append("<html>\n")
.append(" <body>\n")
.append(" <p>Hello, World</p>\n")
.append(" </body>\n")
.append("</html>")
.toString();
String json = new StringBuilder()
.append("{\n")
.append(" \"name\":\"mkyong\",\n")
.append(" \"age\":38\n")
.append("}").toString();
3. String Format
It works, but not recommend, it is too hard to count the number of %s.
String html = String.format("%s\n%s\n%s\n%s\n%s"
, "<html>"
, " <body>"
, " <p>Hello, World</p>"
, " </body>"
, "</html>");
String json = String.format("%s\n%s\n%s\n%s"
, "{"
, " \"name\":\"mkyong\","
, " \"age\":38"
, "}");
4. String Writer
A bit weird, but it works.
// no need close this
StringWriter sw = new StringWriter();
PrintWriter pw = new PrintWriter(sw);
pw.println("<html>");
pw.println(" <body>");
pw.println(" <p>Hello, World</p>");
pw.println(" </body>");
pw.println("</html>");
String html = sw.toString();
StringWriter sw2 = new StringWriter();
PrintWriter pw2 = new PrintWriter(sw2);
pw2.println("{");
pw2.println(" \"name\":\"mkyong\",");
pw2.println(" \"age\":38");
pw2.println("}");
String json = sw2.toString();
5. Java 8 String.join
Java 8, joins multi-lines string with a new line.
String html = String.join("\n"
, "<html>"
, " <body>"
, " <p>Hello, World</p>"
, " </body>"
, "</html>");
String json = String.join("\n"
, "{"
, " \"name\":\"mkyong\","
, " \"age\":38"
, "}");
6. Files.lines
It is common to put a multi-line string into a file. This example uses Files.lines to load a file from a classpath resources folder, and convert it into a Stream<String> for processing.
<html>
<body>
<p>Hello, World</p>
</body>
</html>
package com.mkyong.java13.jep355;
import java.io.IOException;
import java.net.URISyntaxException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class MultiLineString6 {
public static void main(String[] args) throws IOException, URISyntaxException {
Stream<String> lines = Files.lines(
Paths.get(ClassLoader.getSystemResource("test.html").toURI())
);
System.out.println(lines.collect(Collectors.joining("\n")));
}
}
Output
<html>
<body>
<p>Hello, World</p>
</body>
</html>
7. Text Blocks (Preview in Java 13, 14)
7.1 Now, we can use three double-quote characters (""") to declare multi-line string in Java. This text block is the recommended solution, simple and beautiful, hope it will become a standard feature soon.
P.S This text blocks is a preview feature in Java 13 and Java 14, it might change again in a future release.
String html = """
<html>
<body>
<p>Hello, World</p>
</body>
</html>
""";
String json = """
{
"name":"mkyong",
"age":38
}
""";
This text blocks:
"""
line 1
line 2
line 3
"""
is equivalent to this:
"line 1\nline 2\nline 3\n"
7.2 This text block supports escape sequences.
String html = """
<html>
\t<body>
\t\t<p>Hello, World</p>
\t</body>
</html>
""";
7.3 The quote characters (") can be used inside a text block; see this multi-lines JSON formatted string.
String json = """
{
"name":"mkyong",
"age":38
}
""";
7.4 Concatenation of text blocks, below is a valid syntax.
String html = "<html>\n" +
"""
<body>
<p>Hello, World</p>
</body>
"""+
"</html>";
7.5 In Java 13, three methods added to support text blocks.
String::stripIndent(): Strip away incidental white space from the text block content.String::translateEscapes(): Translate escape sequences.String::formatted(Object... args): For value substitution in the text block.
The String::formatted example for value substitution in a text block.
String json = """
{
"name":"%s",
"age":%d,
"address":"%s"
}
""";
System.out.println(json.formatted("mkyong", 38, "abc"));
We can get the same result with the standard String::replace or String.format like this:
// String.format
String json = """
{
"name":"%s",
"age":%d,
"address":"%s"
}
""";
System.out.println(String.format(json, "mkyong", 38, "abc"));
// String::replace
String json2 = """
{
"name":"$name",
"age":$age,
"address":"$address"
}
""";
System.out.println(json2
.replace("$name", "mkyong")
.replace("$age", "38")
.replace("$address", "abc"));
Do we need a new API String::formatted(Object... args) for value substitution?
7.6 In Java 14, two methods added to support text blocks.
\<end-of-line>suppresses the line termination.\sis translated into a single space.
String html = """
<html>
<body>\
<p>Hello, '\s' World</p>\
</body>
</html>
""";
Output
<html>
<body> <p>Hello, ' ' World</p> </body>
</html>
7.7 Java 15 (not released yet), to be continued.
Download Source Code
$ git clone https://github.com/mkyong/core-java
$ cd java-13
$ cd java-14
References
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