{"id":59780,"date":"2020-08-18T15:09:14","date_gmt":"2020-08-18T15:09:14","guid":{"rendered":"https:\/\/www.baeldung.com\/?p=85813"},"modified":"2020-08-18T15:09:14","modified_gmt":"2020-08-18T15:09:14","slug":"how-to-define-a-map-in-yaml-for-a-pojo","status":"publish","type":"post","link":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/2020\/08\/18\/how-to-define-a-map-in-yaml-for-a-pojo\/","title":{"rendered":"How to Define a Map in YAML for a POJO?"},"content":{"rendered":"

<\/p>\n

1. Overview<\/h2>\n
<\/div>\n

In this tutorial, we’ll walk through how we can use properties defined in a YAML file to configure values for a Map<\/em> in our POJO classes.<\/p>\n

2. POJO and YAML<\/h2>\n
<\/div>\n

POJO classes are Plain Old Java Objects<\/a>. YAML is a human-readable structured data format that uses indentation to indicate nesting.<\/p>\n

2.1. Simple Map<\/em> Example<\/h3>\n
<\/div>\n

Let’s imagine that we are running an online store, and we are creating a service that translates clothing sizes. At first, we are only selling clothes in the UK. We want to know what UK size the label “S”, “M”, “L” and so on refers to. We create our POJO configuration class:<\/p>\n

@ConfigurationProperties(prefix = \"t-shirt-size\")\r\npublic class TshirtSizeConfig {\r\n    private Map<String, Integer> simpleMapping;\r\n    public TshirtSizeConfig(Map<String, Integer> simpleMapping) {\r\n        this.simpleMapping = simpleMapping;\r\n    }\r\n    \r\n    \/\/getters and setters..\r\n}\r\n<\/code><\/pre>\n
Notice the @ConfigurationProperties<\/em><\/a> with the prefix<\/em> value. We’ll define our mapping under that same root value in our YAML file, as we can see in the next section.<\/p>\n
We also need to remember to enable configuration properties with the following annotation on our Application.class<\/em>:<\/p>\n
@EnableConfigurationProperties(TshirtSizeConfig.class)\r\npublic class DemoApplication {\r\n    public static void main(String[] args) {\r\n        SpringApplication.run(DemoApplication.class, args);\r\n    }\r\n}<\/code><\/pre>\n
2.2. YAML Configuration<\/h3>\n
<\/div>\n
Now we add t-shirt-size<\/code> to our YAML configuration.<\/p>\n
We can use the following structure in our application.yml<\/em> file:<\/p>\n
t-shirt-size:\r\n  simple-mapping:\r\n    XS: 6\r\n    S:  8\r\n    M:  10\r\n    L:  12\r\n    XL: 14<\/code><\/pre>\n
Notice the indentation and the spaces. YAML uses indentation to indicate nesting. The recommended syntax is two spaces for each nested level.<\/p>\n
Notice how we’re using simple-mapping<\/code> with the dash, but our property name in our class is called simpleMapping<\/code>.\u00a0 YAML properties with dashes will automatically translate to the camel-case equivalent in code.<\/p>\n
2.3. More Complex Map<\/em> Example<\/h3>\n
<\/div>\n
After our successful UK shops, we now need to consider translating sizes to other countries’ measurements. For example, we now want to know what size is the label “S” in France and the US. We need to add another layer of data to our configuration.<\/p>\n
We can alter our application.yml<\/em> with a more complex mapping:<\/p>\n
t-shirt-size:\r\n  complex-mapping:\r\n    XS:\r\n      uk: 6\r\n      fr: 34\r\n      us: 2\r\n    S:\r\n      uk: 8\r\n      fr: 36\r\n      us: 4\r\n    M:\r\n      uk: 10\r\n      fr: 38\r\n      us: 6\r\n    L:\r\n      uk: 12\r\n      fr: 40\r\n      us: 8\r\n    XL:\r\n      uk: 14\r\n      fr: 42\r\n      us: 10\r\n<\/code><\/pre>\n
The corresponding field in our POJO will be a map of maps:<\/p>\n
private Map<String, Map<String, Integer>> complexMapping;<\/code><\/pre>\n
3. Conclusion<\/h2>\n
<\/div>\n
In this article, we saw how we could define simple and more complex nested maps in a YAML configuration file for a simple POJO.<\/p>\n
The code for\u00a0this article is available\u00a0over on GitHub<\/a><\/p>\n
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<\/p>","protected":false},"excerpt":{"rendered":"
We’ll walk through how we can use properties defined in a YAML file to configure values for a Map in our POJO classes.<\/p>\n
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