开发中经常涉及调用各种资源的情况,包含普通文件、网址、配置文件、系统环境变量等,我们可以使用Spring的表达式语言实现资源的注入,Spring主要在@Value注解中使用表达式。
一:添加依赖。增加commons-io可简化文件相关操作。将文件可转化为字符串
<dependency> <groupId>commons-io</groupId> <artifactId>commons-io</artifactId> <version>2.3</version> </dependency>
项目结构已经资源情况如下图:
二:直接注入普通字符串如下类:
import org.springframework.beans.factory.annotation.Value; import org.springframework.stereotype.Service; @Service public class DemoService { @Value("其他类的属性") //注入普通字符串 private String another; public String getAnother() { return another; } public void setAnother(String another) { this.another = another; } }
三:配置类(操作各种资源)
import org.apache.commons.io.IOUtils; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.beans.factory.annotation.Value; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.ComponentScan; import org.springframework.context.annotation.Configuration; import org.springframework.context.annotation.PropertySource; import org.springframework.context.support.PropertySourcesPlaceholderConfigurer; import org.springframework.core.env.Environment; import org.springframework.core.io.Resource; @Configuration @ComponentScan("com.flysun.el") @PropertySource(value="classpath:com/flysun/el/test.properties")//7:注入配置文件需要@PropertySource注解指定文件位置,若还使用@Value //注入文件中的内容,还要配置一个PropertySourcesPlaceholderConfigurer的bean.注意此时@Value("${book.name}")使用的是$而不是#。 //注入的properties还可以从Environment中获得 public class ElConfig { @Value("I Love You!") //1注入普通字符串 private String normal; @Value("#{systemProperties['os.name']}") //2注入操作系统属性 private String osName; @Value("#{ T(java.lang.Math).random() * 100.0 }") //3注入表达式结果 private double randomNumber; @Value("#{demoService.another}") //4注入其他bean的属性 private String fromAnother; @Value("classpath:com/flysun/el/test.txt") //5注入文件资源 private Resource testFile; @Value("http://www.baidu.com") //6注入网址资源 private Resource testUrl; @Value("${book.name}") //7读取配置文件中的属性 private String bookName; @Autowired private Environment environment; //7 @Bean //7 public static PropertySourcesPlaceholderConfigurer propertyConfigure() { return new PropertySourcesPlaceholderConfigurer(); } public void outputResource() { try { System.out.println(normal); System.out.println(osName); System.out.println(randomNumber); System.out.println(fromAnother); System.out.println(IOUtils.toString(testFile.getInputStream())); System.out.println(IOUtils.toString(testUrl.getInputStream())); System.out.println(bookName); System.out.println(environment.getProperty("book.author")); System.out.println(demoService.getAnother()); } catch (Exception e) { e.printStackTrace(); } } }
四:运行
import org.springframework.context.annotation.AnnotationConfigApplicationContext; public class Main { public static void main(String[] args) { AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(ElConfig.class); ElConfig resourceService = context.getBean(ElConfig.class); resourceService.outputResource(); context.close(); } }也可以参考这个:https://www.cnblogs.com/sxdcgaq8080/p/7659074.html。在SpringBoot中还时常用