1. Overview
In this article, we’ll learn about breaking YAML strings over multiple lines.
In order to parse and test our YAML files, we’ll make use of the SnakeYAML library.
2. Multi-Line Strings
Before we begin, let’s create a method to simply read a YAML key from a file into a String:
String parseYamlKey(String fileName, String key) {
InputStream inputStream = this.getClass()
.getClassLoader()
.getResourceAsStream(fileName);
Map<String, String> parsed = yaml.load(inputStream);
return parsed.get(key);
}
In the next subsections, we’ll look over a few strategies for splitting strings over multiple lines.
We’ll also learn how YAML handles leading and ending line breaks represented by empty lines at the beginning and end of a block.
3. Literal Style
The literal operator is represented by the pipe (“|”) symbol. It keeps our line breaks but reduces empty lines at the end of the string down to a single line break.
Let’s take a look at the YAML file literal.yaml:
key: |
Line1
Line2
Line3
We can see that our line breaks are preserved:
String key = parseYamlKey("literal.yaml", "key");
assertEquals("Line1\nLine2\nLine3", key);
Next, let’s take a look at literal2.yaml, which has some leading and ending line breaks:
key: |
Line1
Line2
Line3
...
We can see that every line break is present except for ending line breaks, which are reduced to one:
String key = parseYamlKey("literal2.yaml", "key");
assertEquals("\n\nLine1\n\nLine2\n\nLine3\n", key);
Next, we’ll talk about block chomping and how it gives us more control over starting and ending line breaks.
We can change the default behavior by using two chomping methods: keep and strip.
3.1. Keep
Keep is represented by “+” as we can see in literal_keep.yaml:
key: |+
Line1
Line2
Line3
...
By overriding the default behavior, we can see that every ending empty line is kept:
String key = parseYamlKey("literal_keep.yaml", "key");
assertEquals("Line1\nLine2\nLine3\n\n", key);
3.2. Strip
The strip is represented by “-” as we can see in literal_strip.yaml:
key: |-
Line1
Line2
Line3
...
As we might’ve expected, this results in removing every ending empty line:
String key = parseYamlKey("literal_strip.yaml", "key");
assertEquals("Line1\nLine2\nLine3", key);
4. Folded Style
The folded operator is represented by “>” as we can see in folded.yaml:
key: >
Line1
Line2
Line3
By default, line breaks are replaced by space characters for consecutive non-empty lines:
String key = parseYamlKey("folded.yaml", "key");
assertEquals("Line1 Line2 Line3", key);
Let’s look at a similar file, folded2.yaml, which has a few ending empty lines:
key: >
Line1
Line2
Line3
...
We can see that empty lines are preserved, but ending line breaks are also reduced to one:
String key = parseYamlKey("folded2.yaml", "key");
assertEquals("Line1 Line2\n\nLine3\n", key);
We should keep in mind that block chomping affects the folding style in the same way it affects the literal style.
5. Quoting
Let’s have a quick look at splitting strings with the help of double and single quotes.
5.1. Double Quotes
With double quotes, we can easily create multi-line strings by using “\n“:
key: "Line1\nLine2\nLine3"
String key = parseYamlKey("plain_double_quotes.yaml", "key");
assertEquals("Line1\nLine2\nLine3", key);
5.2. Single Quotes
On the other hand, single-quoting treats “\n” as part of the string, so the only way to insert a line break is by using an empty line:
key: 'Line1\nLine2
Line3'
String key = parseYamlKey("plain_single_quotes.yaml", "key");
assertEquals("Line1\\nLine2\nLine3", key);
6. Conclusion
In this quick tutorial, we’ve looked over multiple ways of breaking YAML strings over multiple lines through quick and practical examples.
As always, the code is available over on GitHub.