Troubleshooting pits using @ Value of ${× × × values from properties files

@ Value (${× × ×)) takes value from properties file

Premises:

Your entity class has been added to the IOC container (with annotations such as @ Compenet)

Error reporting code:

@Value("${driver}")
private String driver;
@Value("${url}")
private String url;
@Value("${username}")
private String userName;
@Value("${password}")
private String password;

properties file

driver=com.mysql.cj.jdbc.Driver
url=jdbc:mysql://localhost:3306/abc?serverTimezone=UTC&useUnicode=true&characterEncoding=utf8&useSSL=false
username=root
password=admin

At this time, you can't get the value in properties file by writing @ Value annotation like this

You must prefix the properties file attributes (arbitrary)

Such as:

jdbc.driver=com.mysql.cj.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/abc?serverTimezone=UTC&useUnicode=true&characterEncoding=utf8&useSSL=false
jdbc.username=root
jdbc.password=admin

The corresponding class should also be modified

@Value("${jdbc.driver}")
private String driver;
@Value("${jdbc.url}")
private String url;
@Value("${jdbc.username}")
private String userName;
@Value("${jdbc.password}")
private String password;

So you can get it normally

Additional:

1. Static variables cannot be injected

2. The default properties file for Springboot is application. properties

Spring @ Value ("${}") null value processing

Scenario:

The Test class has one property email configured in application. properties

@Value("${email}")
private String email;

If email is not configured in the configuration, when the application starts, it will report that this attribute exception cannot be found, resulting in startup failure.

Solution 1:

Add @ Component and @ Lazy to the Test class at the same time

Solution 2:

The @ ConditionalOnProperty annotation is provided in springboot

Set injection conditions

@ConditionalOnProperty(name = "flag", havingValue = "true")

bean is instantiated only if the flag property in the configuration file application. properties is true