springboot如何读取配置文件到静态工具类

import javax.annotation.PostConstruct; 
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.core.env.Environment;
import org.springframework.stereotype.Component; 
/**
 * 
 * @Description: 配置常量类——根据不同的spring-profile加载不同的配置
 * @author: eric.zhang
 * @date: 2018年7月20日 上午10:59:24
 */
@Component
public class ConfigConstant {
  @Autowired
  private Environment env;  
  public static String url;
  public static String param;  
 
  @PostConstruct
  public void readConfig() {
    url = env.getProperty("config.url");
    param = env.getProperty("config.param");
  }
}

import java.io.UnsupportedEncodingException;
import java.lang.reflect.Field; 
import javax.annotation.PostConstruct; 
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.core.env.Environment;
import org.springframework.stereotype.Component; 
/**
 * 
 * @Description: 配置常量类——根据不同的spring-profile加载不同的配置,变量名要与配置文件里写的名一致
 * @author: eric.zhang
 * @date: 2018年7月20日 上午10:59:24
 */
@Component
public class ConfigConstant {
  @Autowired
  private Environment env;  
  public static String url;
  public static String name;  
  
  @PostConstruct
  public void readConfig() throws Exception {
    String prefix = "config.";
    Field[] fields = ConfigConstant.class.getFields();
    for(Field field : fields ){
      field.set(null, getProperty(prefix + field.getName()));
    }
  }
  
  private String getProperty(String key) throws UnsupportedEncodingException {
    return new String(env.getProperty(key).getBytes("ISO-8859-1"), "UTF-8");
  }
}

import java.io.InputStreamReader;
import java.lang.reflect.Field;
import java.util.Properties; 
/**
 * 
 * @Description: 配置常量类——根据不同的spring-profile加载不同的配置
 *               变量名把配置文件的key中的"."替换成"_"命名
 * @author: eric.zhang
 * @date: 2018年7月20日 上午10:59:24
 */
public class ConfigConstant { 
  public static String CONFIG_URL;
  public static String CONFIG_NAME;
 
  static {
    try {
      Properties props = new Properties();
      props.load(new InputStreamReader(
          ConfigConstant.class.getClassLoader().getResourceAsStream("application.properties"),
          "UTF-8"));
      String profile = props.getProperty("spring.profiles.active");
      String envFile = "application-" + profile + ".properties";
      Properties envProps = new Properties();
      envProps.load(new InputStreamReader(
          ConfigConstant.class.getClassLoader().getResourceAsStream(envFile), "UTF-8"));
      Field[] fields = ConfigConstant.class.getFields();
      for (Field field : fields) {
        field.set(null, envProps.getProperty(field.getName().replace("_", ".").toLowerCase()));
      }
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
}

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
 
    <groupId>com.csrcb</groupId>
    <artifactId>spring_static</artifactId>
    <version>1.0-SNAPSHOT</version>
 
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.6.RELEASE</version>
    </parent>
 
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
        </dependency>
    </dependencies> 
</project>

/**
 * @Classname TestConfig
 * @Description 加载配置文件的配置类
 * @Date 2020/6/16 16:28
 * @Created by gangye
 */
@Configuration
@Data
public class TestConfig {
    @Value("${ftp.username}")
    private String username;
 
    @Value("${ftp.passwd}")
    private String passwd;
 
    @PostConstruct
    public void init(){
        ClientUtil.setConfigInfo(this);
    }
}

/**
 * @Classname ClientUtil
 * @Description 工具类，将配置文件的数据通过config引入到静态变量中
 * @Date 2020/6/16 16:29
 * @Created by gangye
 */
@Slf4j
public class ClientUtil { 
    private static String USERNAME;
    private static String PASSWD; 
    public static void setConfigInfo(TestConfig testConfig) {
        ClientUtil.USERNAME = testConfig.getUsername();
        ClientUtil.PASSWD = testConfig.getPasswd();
    }
 
    public static String getValue(){
        log.info("获得配置文件的username的值:{}",USERNAME);
        return USERNAME;
    }
}

/**
 * @Classname controller
 * @Date 2020/6/16 16:35
 * @Created by gangye
 */
@RestController
@RequestMapping(value = "/test")
public class TestController {
 
    @GetMapping("/getvalue")
    public String getValue(){
        return ClientUtil.getValue();
    }
}

/**
 * @Classname AppStart
 * @Description 启动类
 * @Date 2020/6/16 16:26
 * @Created by gangye
 */
@SpringBootApplication
public class AppStart {
    public static void main(String[] args) {
        SpringApplication.run(AppStart.class,args);
    }
}

-Dspring.profiles.active=sit

    /**
     * Caused by: java.lang.IllegalArgumentException: Could not resolve placeholder ‘name' in value “${name}”
     * @Description 为了防止启动时配置类的@Value注解找不到配置文件中的值，一个配置文件找不到继续找
     * @Date 2020年6月17日14:40:08
     * @return
     */
    @Bean
    public static PropertySourcesPlaceholderConfigurer placeholderConfigurer(){
        PropertySourcesPlaceholderConfigurer c = new PropertySourcesPlaceholderConfigurer();
        c.setIgnoreUnresolvablePlaceholders(true);
        return c;
    }