Java 在 SpringBoot 中读取环境变量
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Read environment variable in SpringBoot
提问by Micha? Szewczyk
What is the best way to read environment variablesin SpringBoot?
In Java I did it using:
在SpringBoot 中读取环境变量的最佳方法是什么？
在Java中，我使用：
String foo = System.getenv("bar");
Is it possible to do it using @Valueannotation?
是否可以使用@Value注释来做到这一点？
采纳答案by g00glen00b
Quoting the documentation:
引用文档：
Spring Boot allows you to externalize your configuration so you can work with the same application code in different environments. You can use properties files, YAML files, environment variablesand command-line arguments to externalize configuration. Property values can be injected directly into your beans using the
@Valueannotation, accessed via Spring'sEnvironmentabstraction or bound to structured objects via@ConfigurationProperties.
Spring Boot 允许您将配置外部化，以便您可以在不同环境中使用相同的应用程序代码。您可以使用属性文件、YAML 文件、环境变量和命令行参数来外部化配置。属性值可以使用
@Valueannotation直接注入到您的 bean 中，通过 Spring 的Environment抽象访问或通过 .bin绑定到结构化对象@ConfigurationProperties。
So, since Spring boot allows you to use environment variables for configuration, and since Spring boot also allows you to use @Valueto read a property from the configuration, the answer is yes.
因此，由于 Spring boot 允许您使用环境变量进行配置，并且 Spring boot 还允许您使用@Value从配置中读取属性，因此答案是肯定的。
This can be tested easily, the following will give the same result:
这可以很容易地测试，以下将给出相同的结果：
@Component
public class TestRunner implements CommandLineRunner {
@Value("${bar}")
private String bar;
private final Logger logger = LoggerFactory.getLogger(getClass());
@Override
public void run(String... strings) throws Exception {
logger.info("Foo from @Value: {}", bar);
logger.info("Foo from System.getenv(): {}", System.getenv("bar")); // Same output as line above
}
}
回答by Rlarroque
You can do it with the @Value annotation:
您可以使用 @Value 注释来做到这一点：
@Value("${bar}")
private String myVariable;
You can also use colon to give a default value if not found:
如果未找到，您还可以使用冒号给出默认值：
@Value("${bar:default_value}")
private String myVariable;
回答by nobar
Here are three "placeholder" syntaxes that work for accessing a system environment variable named MY_SECRET:
以下是用于访问名为 的系统环境变量的三种“占位符”语法MY_SECRET：
@Value("${MY_SECRET:aDefaultValue}")
private String s1;
@Value("#{environment.MY_SECRET}")
private String s2;
@Value("${myApp.mySecretIndirect:aDefaultValue}") // via application property
private String s3;
In the third case, the placeholder references an application property that has been initialized from the system environment in a properties file:
在第三种情况下，占位符引用了一个应用程序属性，该属性已从属性文件中的系统环境初始化：
myApp.mySecretIndirect=${MY_SECRET:aDefaultValue}
For @Valueto work, it must be used inside a live @Component(or similar). There are extra gochas if you want this to work during unit testing -- see my answer to Why is my Spring @Autowired field null?
为了@Value工作，它必须在 live @Component（或类似的）中使用。如果您希望它在单元测试期间工作，还有额外的 gochas - 请参阅我对为什么我的 Spring @Autowired 字段为空的回答？
回答by Saikat
Alternatively, you can use the org.springframework.core.env.Environmentinterface to access environment variables:
或者，您可以使用该org.springframework.core.env.Environment接口访问环境变量：
@Autowired
private Environment env;
...
System.out.println(env.getProperty("bar"));
