Spring - Read Property Value from Properties File in Static Field of Class

How to assign a value from application.properties to a static variable?

Think about your problem for a second. You don't have to keep any properties from application.properties in static fields. The "workaround" suggested by Patrick is very dirty:

• you have no idea when this static field is modified
• you don't know which thread modifies it's value
• any thread at any time can change value of this static field and you are screwed
• initializing private static field that way has no sense to me

Keep in mind that when you have bean controlled by @Service annotation you delegate its creation to Spring container. Spring controls this bean lifecycle by creating only one bean that is shared across the whole application (of course you can change this behavior, but I refer to a default one here). In this case any static field has no sense - Spring makes sure that there is only one instance of UserService. And you get the error you have described, because static fields initialization happens many processor-cycles before Spring containers starts up. Here you can find more about when static fields are initialized.

Suggestion

It would be much better to do something like this:

@Service
public class UserService {
    private final String svnUrl;

    @Autowired
    public UserService(@Value("${SVN_URL}") String svnUrl) {
        this.svnUrl = svnUrl;
    }
}

This approach is better for a few reasons:

• constructor injection describes directly what values are needed to initialize the object
• final field means that this value wont be changed after it gets initialized in a constructor call (you are thread safe)

Using @ConfigurationProperties

There is also another way to load multiple properties to a single class. It requires using prefix for all values you want to load to your configuration class. Consider following example:

@ConfigurationProperties(prefix = "test")
public class TestProperties {

    private String svnUrl;

    private int somePort;

    // ... getters and setters
}

Spring will handle TestProperties class initialization (it will create a testProperties bean) and you can inject this object to any other bean initialized by Spring container. And here is what exemplary application.properties file look like:

test.svnUrl=https://svn.localhost.com/repo/
test.somePort=8080

Baeldung created a great post on this subject on his blog, I recommend reading it for more information.

Alternative solution

If you need somehow to use values in static context it's better to define some public class with public static final fields inside - those values will be instantiated when classloader loads this class and they wont be modified during application lifetime. The only problem is that you won't be able to load these values from Spring's application.properties file, you will have to maintain them directly in the code (or you could implement some class that loads values for these constants from properties file, but this sounds so verbose to the problem you are trying to solve).

spring - read property value from properties file in static field of class

In you Utility class you can have a setter method to set the properties and then you can use MethdInvokingFactoryBean.

class Utility{
    static String username;
    static String password;
    public static setUserNameAndPassword(String username, String password){
        Utility.username = username;
        Utility.password = password;
    }
    //other stuff
}

<bean
    class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
    <property name="locations">
        <list>
            <value>classpath*:/myservice_detaults.properties</value>
            <value>classpath*:/log4j.properties</value>
        </list>
    </property>
</bean>

<bean class="org.springframework.beans.factory.config.MethodInvokingFactoryBean">
    <property name="staticMethod" value="foo.bar.Utility.setUserNameAndPassword"/>
    <property name="arguments">
        <list>
            <value>${username}</value>
            <value>${password}</value>
        </list>
   </property>
</bean>

JAVA Spring Boot : How to access application.properties values in normal class

There's no "magic" way to inject values from a property file into a class that isn't a bean. You can define a static java.util.Properties field in the class, load values from the file manually when the class is loading and then work with this field:

public final class AppUtils {
    private static final Properties properties;

    static {
        properties = new Properties();

        try {
            ClassLoader classLoader = AppUtils.class.getClassLoader();
            InputStream applicationPropertiesStream = classLoader.getResourceAsStream("application.properties");
            applicationProperties.load(applicationPropertiesStream);
        } catch (Exception e) {
            // process the exception
        }
    }
}

How to inject property value using @Value into static fields

The only way is to use setter for this value

@Value("${value}")
public void setOutputPath(String outputPath) {
    AClass.outputPath = outputPath;
} 

However you should avoid doing this. Spring is not designed for static injections. Thus you should use another way to set this field at start of your application, e.g. constructor.
Anyway @Value annotation uses springs PropertyPlaceholder which is still resolved after static fields are initialized. Thus you won't have any advantages for this construction

How to read a property on a static field in a spring-boot application?

You can achieve this using the class Environment from the package org.springframework.core.env.

Example :

@SpringBootApplication
public class Example {

    // autowire the Environment
    @Autowired
    private Environment environment;

    private static String fatalCode; 

    public void someMethod(String errorNumber) {
      fatalCode = environment.getProperty("app.directory.errorcode." + errorNumber);
    }

    public static void main(String[] args) {
        SpringApplication.run(Example.class, args);
    }

}

I hope this may help you.

Thanks :)

How to inject a property from properties file to a non-managed class in Spring?

You might do one of the following:

1. Make the class a "normal" Java class where the regex is passed in via constructor or method parameter by the Spring managed class who uses it.
2. Give the class a static field "regex" (with a default value perhaps) that gets set by a Spring bean via a setter on startup (@PostConstruct).
3. Give the class a static field "regex" (with a default value perhaps) that gets set using a static block in your class reading from the properties file (if it is available on the classpath!).
4. Make the class a "normal" Singleton (with default values perhaps) that gets initialized on Spring startup (https://www.baeldung.com/running-setup-logic-on-startup-in-spring)

Why I fail to use properties from application.properties file in Spring Boot?

Alternatively, you can do the following, the setter method will handle for the injection:

@Component
public class PostDao
{
    public static String DATABASE_URL;


    @Value("${url}")
    public void setUrlStatic(String name){
        PostDao.DATABASE_URL = name;
    }

    // And others..
}

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