Spring Boot configuration file injection

In Spring Boot, the configuration file is application.yml or application.properties.

Yml grammar

The syntax of a YML configuration file is as follows:

• key:[space] value
• Case sensitivity
• Spaces (Tab) control hierarchies

Value can be a simple data type (number, string) or a complex data type (array, object, collection, Map, etc.).

Note: For strings, the default is no double or single quotes.

Configuration file injection

Assume that the configuration file contains the following contents:

coder:
  name: smartpig  // Simple data
  lang: [Java,Kotlin] //List
  softwares: {cut: pr,image: ps} //Map
  pet:  / / object
    name: bigdog
    type: dog
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• Use @value to get the Value in the configuration file

In the controller, use @value (” ${} “) to get the Value in the configuration file, as follows to get the Value of name in the coder

@Controller
public class Hello {
    @Value("${coder.name}")
    private String name;

    @RequestMapping("/hello")
    @ResponseBody
    public String hello(a){
        return "hello "+ name; }}Copy the code

• The configuration file is mapped using @ConfigurationProperties(perfix=””) and @Compent

  Write Pet class, write Coder class

@Component
@ConfigurationProperties(prefix = "coder")
public class Coder {
    private String name;
    private List<String> lang; / / array
    private Map<String,String> softwares; //Map
    private Pet pet; / / object
    / / omit getter/setter/toString
}
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The test is then performed in the test class

@SpringBootTest
class DemoSpringbootApplicationTests {
    @Autowired
    Coder coder;
    
    @Test
    void contextLoads(a) { System.out.println(coder.toString()); }}Copy the code

Enter the value in the configuration file

Using a plug-in makes writing the corresponding configuration in YML prompt

<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-configuration-processor</artifactId>
</dependency>
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Do the mapping in the Properties configuration file

If you use a properties configuration file, everything is the same as in YML except for the writing format.

coder.name=smartpig
coder.lang=Java,Kotlin
coder.softwares.cut=pr
coder.softwares.image=ps
coder.pet.name=bigdog
coder.pet.type=dog
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@value and @ConfigurationProperties

• EL expression

  Modify the configuration file as follows

  coder:
    name: ${smartpig} // Change to the EL expression
    lang: [Java,Kotlin]
    softwares: {cut: pr,image: ps}
    pet:
      name: bigdog
      type: dog
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  ConfigurationProperties: Could not resolve ‘smartPig’ in value “${smartPig}”; If you use @value, you don’t get an error

• check

  Added a check to the Coder class to verify that coder.name is not an empty string

  @Component
  @Validated
  @ConfigurationProperties(prefix = "coder")
  public class Coder {
      @NotEmpty
      private String name;
  }
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  Change the configuration file to

  coder:
    name:  / / to empty
    lang: [Java,Kotlin]
    softwares: {cut: pr,image: ps}
    pet:
      name: bigdog
      type: dog
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  Error: @configurationProperties

  Property: coder. Name Value: Origin: class Path Resource [Application. Yml]:2:8 Reason: Cannot be emptyCopy the code

  Using @value does not validate

• The complex type

  Using @value to inject coder. Name is fine, if using @value to inject complex types such as List

  @Component
  //@ConfigurationProperties(prefix = "coder")
  public class Coder {
      private String name;
      @Value("${coder.lang}")  // Use complex type injection lang
      private List<String> lang;
      private Map<String,String> softwares;
      private Pet pet;
  }
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  Could not resolve ‘coder. Lang ‘in value “${coder. Lang}”

conclusion

Today I’ve shared how configuration file data can be injected into variables or classes; You can use @Value for small amounts of data, but you can use @ConfigurationProperties for complex data.

Thanks for watching.