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preface

In real development, we often need to assign values to static properties from either yML or properties files. Instead of using the @Value annotation alone, here are a few ways to inject properties.

We usually use it in the following way:

@Value("${channl.ali.appId}")
String appId;
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Set method injection

Annotate the @value annotation to the set method

@Component
public class StaticValue {

    public static String APP_ID;
    public static String APP_USER;

    @Value("${channl.ali.appId}")
    public void setAppId(String appId) {
        APP_ID = appId;
    }

    @Value("${channl.ali.appUser}")
    public void setAppUser(String appUser) { APP_USER = appUser; }}Copy the code

Note: This class needs to be managed by Spring, and the setXx method name can be arbitrary

use

Use classes directly where they are needed. The attribute name

	@Test
	void contextLoads(a) {
		System.out.println(StaticValue.APP_ID);
		System.out.println(StaticValue.APP_USER);
	}
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@PostConstruct

The PostConstruct annotation is an annotation provided by Java. Methods annotated with the @postConstruct annotation will be called automatically after the constructor and dependency injection have completed. As a small example, the specific source code will be analyzed in a later source code article. If you are interested, you can take a look at other source analysis: Spring source code reading directory

use

    @Value("${channl.ali.appId}")
    private String appId;

    @Value("${channl.ali.appUser}")
    private String appUser;

    //@Autowired
    private Environment environment;

   public StaticValue(a) {
        System.out.println("Constructor execution =" + environment);
    }

    @Autowired
    private void setq(Environment environment){
        System.out.println("Dependency injection method execution =" + environment);
        this.environment = environment;
    }

	@PostConstruct
    public void init(a){
        System.out.println("PostConstruct annotation init method execution.");
        APP_ID = environment.getProperty("channl.ali.appId");
        APP_USER = environment.getProperty("channl.ali.appUser");
        //APP_ID = appId;
        //APP_USER = appUser;} at project startup you should see the control print the following statement: constructor execution =nullDependency injection method performs = StandardServletEnvironment {activeProfiles = [], defaultProfiles = [default], propertySources=[ConfigurationPropertySourcesPropertySource {name='configurationProperties'}, StubPropertySource {name='servletConfigInitParams'}, ServletContextPropertySource {name='servletContextInitParams'}, PropertiesPropertySource {name='systemProperties'}, OriginAwareSystemEnvironmentPropertySource {name='systemEnvironment'}, RandomValuePropertySource {name='random'}, OriginTrackedMapPropertySource {name='Config resource 'classpath:/application.yml' via location 'optional:classpath:/' '}]} PostConstruct annotation init method is executedCopy the code

Note: Both Environment and @value are acceptable. So constructor > @AutoWired (dependency injection) > @postConstruct (annotated method)

Implement the InitializingBean interface

Implement the InitializingBean interface and rewrite its afterPropertiesSet method. Get the value of the configuration file using @Value, and then assign the value to the static property in the afterPropertiesSet method. The InitializingBean interface will also be analyzed in a later source code article. If you are interested, you can take a look at other source analysis: Spring source code reading directory

use

    @Value("${channl.ali.appId}")
    private String appId;

    @Value("${channl.ali.appUser}")
    private String appUser;

    //@Autowired
    private Environment environment;

  @Override
    public void afterPropertiesSet(a) throws Exception {
        System.out.println("AfterPropertiesSet initialization method execution");
// //APP_ID = environment.getProperty("channl.ali.appId");
// // APP_USER = environment.getProperty("channl.ali.appUser");
        APP_ID = appId;
        APP_USER = appUser;
    }

    @PostConstruct
    public void init(a){
        System.out.println("PostConstruct annotation init method execution.");
        //APP_ID = environment.getProperty("channl.ali.appId");
        //APP_USER = environment.getProperty("channl.ali.appUser");
        //APP_ID = appId;
        //APP_USER = appUser;} at project startup you should see the control print the following statement: constructor execution =nullDependency injection method performs = StandardServletEnvironment {activeProfiles = [], defaultProfiles = [default], propertySources=[ConfigurationPropertySourcesPropertySource {name='configurationProperties'}, StubPropertySource {name='servletConfigInitParams'}, ServletContextPropertySource {name='servletContextInitParams'}, PropertiesPropertySource {name='systemProperties'}, OriginAwareSystemEnvironmentPropertySource {name='systemEnvironment'}, RandomValuePropertySource {name='random'}, OriginTrackedMapPropertySource {name='Config resource 'classpath:/application.yml' via location 'optional:classpath:/' '}]} PostConstruct annotation init method executes afterPropertiesSet initialization method executionCopy the code

Note: Both Environment and @value are acceptable.

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