springboot 注入 / 静态注入

1. 参数配置：application.properties

sc.crm.upDirPath=

2. 注入：

spring boot 的任意组件都能使用，这里声明了一个简单组件 @Component,该注解通常用来定义一些需要配置的常量或者用于注入的工具类，而不用手动去 new 了

@Componentpublic class CrmProperties {    @Value("${sc.crm.upDirPath}")    private String uploadPath;    public String getUploadPath() {        return uploadPath;    }    public void setUploadPath(String uploadPath) {        this.uploadPath = uploadPath;    }}

3. 使用：直接注入

@Servicepublic class CustomerServiceImpl implements CustomerService {    @Autowired    private CrmProperties crmProperties;    //也可以定义为属性/字段直接使用    @Value("${sc.crm.upDirPath}")    private String uploadPath;    }

4. 静态注入：

4.1. 实现 spring 的一个获取上下文的工具类

import org.springframework.beans.BeansException;import org.springframework.context.ApplicationContext;import org.springframework.context.ApplicationContextAware;import org.springframework.stereotype.Component;/** * Spring工具类,获取Spring上下文对象等 */@Componentpublic class SpringContextUtil implements ApplicationContextAware {    private static ApplicationContext applicationContext = null;    @Override    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {        if(SpringContextUtil.applicationContext == null){            SpringContextUtil.applicationContext  = applicationContext;        }    }    public static ApplicationContext getApplicationContext() {        return applicationContext;    }    public static Object getBean(String name){        return getApplicationContext().getBean(name);    }    public static 
    
      T getBean(Class
     
       clazz){        return getApplicationContext().getBean(clazz);    }    public static 
      
        T getBean(String name,Class
       
         clazz){        return getApplicationContext().getBean(name, clazz);    }}
       
      
     
    

4.2. 静态注入：

public final class UpDownLoadUtil {    private static String uploadPath ;    //通过静态代码块，给变量赋值    static{        CrmProperties crmProperties = SpringContextUtil.getBean(CrmProperties.class);        uploadPath = crmProperties.getUploadPath();    }        //将构造方法私有化,所有静态工具只能通过静态调用    private UpDownLoadUtil(){        throw new AssertionError();    }        public static void testUtil(){        systom.out.println(uploadPath);    }    }

到这里，就可以在静态方法中正常使用该配置常量了

=============== 分割线 ===============

==注意：典型错误示例,这样写虽然不会报错，但是根据类的加载机制，这里不能正确的获取到想要的参数，最后输出只有null，切记==

//错误的使用方法@Value("${sc.gp.url.db}")private static String url_DB;@PostMapping("/rest1")public static void test1() {    String s = url_DB;    System.out.println(s);}