How to get OS environment variable from Spring Boot?

Question

I am novice to java and spring framework. My questions is how to inject OS(ubuntu) environment variable to spring boot bean. What I tried:

@Configuration @EnableWebMvc public class CorsConfig implements WebMvcConfigurer { @Value("${COMPONENT_PARAM_CORS}") private String COMPONENT_PARAM_CORS; @Override public void addCorsMappings(CorsRegistry registry) { registry.addMapping("/"+COMPONENT_PARAM_CORS); } }

export COMPONENT_PARAM_CORS=**

printenv

says me that its present, but when I try to mvn clean install: error occured

java.lang.IllegalStateException: Failed to load ApplicationContext Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'corsConfig': Injection of autowired dependencies failed; nested exception is java.lang.IllegalArgumentException: Could not resolve placeholder 'COMPONENT_PARAM_CORS' in value "${COMPONENT_PARAM_CORS}" Caused by: java.lang.IllegalArgumentException: Could not resolve placeholder 'COMPONENT_PARAM_CORS' in value "${COMPONENT_PARAM_CORS}"

and then my unit test also droped (I am trying to search this error, but all topics is old and uses params from application.properties, but I need to use env var not application.properties)

Bohdan Levchenko · Accepted Answer · 2018-07-11 10:07:26Z

You can use System.getenv(<environment name>) method to retrieve an environment variable value. Like:

registry.addMapping("/" + System.getenv("COMPONENT_PARAM_CORS"));

or with default value:

registry.addMapping("/" + System.getenv().getOrDefault("COMPONENT_PARAM_CORS", "DEFAULT_VALUE"))

More information here https://docs.oracle.com/javase/tutorial/essential/environment/env.html

If you really want to inject variable value you can modify your code to something like:

@Value("#{systemEnvironment['COMPONENT_PARAM_CORS'] ?: 'DEFAULT_VALUE'}") private String COMPONENT_PARAM_CORS;

I know about System.getenv(), but it work when app is compiled, but I need to receive params when I run application, or @value also precompiled?
Both System.getenv() and SPEL expression within @Value will be executed at runtime, not compile time, so both options should work for you.
For default value you can use argumentless System.getenv() call which gives you a Map<String, String>. Then call getOrDefault(key, defaultValue) method (java 1.8+). And for SPEL option just use elvis operator: ?:. I have adjusted my answer to show this.

agrim khanna · Accepted Answer · 2018-07-10 10:51:12Z

You should use System.getenv(), for example:

import java.util.Map; public class EnvMap { public static void main (String[] args) { Map<String, String> env = System.getenv(); for (String envName : env.keySet()) { System.out.format("%s=%s%n", envName, env.get(envName)); } } }

Please refer to This documentation and this question.

faceoff · Accepted Answer · 2018-07-13 12:21:53Z

@Configuration @EnableWebMvc public class CorsConfig implements WebMvcConfigurer { @Value("#{systemEnvironment['COMPONENT_PARAM_CORS']?:'**'}") private String COMPONENT_PARAM_CORS; @Override public void addCorsMappings(CorsRegistry registry) { registry.addMapping("/"+COMPONENT_PARAM_CORS); } }

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