在调用工具类时，若工具类中含有@Autowired注解，这此工具类对象必须同样使用@Autowired注解，否则工具类中的Spring注入的对象都为空值,这里的HadoopTest就是这样

比如MyConfig类是

配置层

@Component

@ConfigurationProperties(prefix = "project")

public class MyConfig {

    private String version;

    private String name;

    public String getVersion() {

        return version;

    }

    public void setVersion(String version) {

        this.version = version;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

}

HadoopTest类引用了MyConfig

public class HadoopTest {

    @Autowired

    MyConfig myConfig; //这里用了注入，所以controller层的test类中  HadoopTest hadoopTest=new HadoopTest();是无效的

    public void getName() {

        System.out.println(myConfig.getName());

    }

}

Controller中

@RestController

public class test {

    HadoopTest hadoopTest=new HadoopTest();

    @GetMapping("hello")

    public void hello() {

        hadoopTest.getName();

    }

}

这样在System.out.println(myConfig.getName());中是找不到myconfig的，我们应该改成

配置层

@Component

@ConfigurationProperties(prefix = "project")

public class MyConfig {

    private String version;

    private String name;

    public String getVersion() {

        return version;

    }

    public void setVersion(String version) {

        this.version = version;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

}

HadoopTest类引用了MyConfig

@Component

public class HadoopTest {

    @Autowired

    MyConfig myConfig;

    public void getName() {

        System.out.println(myConfig.getName());

    }

}

Controller类中

@RestController

public class test {

   @Autowired

    HadoopTest hadoopTest;

    @GetMapping("hello")

    public void hello() {

        hadoopTest.getName();

    }

}

或者是

配置层

@Compoment

@ConfigurationProperties(prefix = "project")

public class MyConfig {

    private String version;

    private String name;

    public String getVersion() {

        return version;

    }

    public void setVersion(String version) {

        this.version = version;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

}

HadoopTest类引用了MyConfig

public class HadoopTest {

    MyConfig myConfig=new Myconfig;

    public void getName() {

        System.out.println(myConfig.getName());

    }

}

Controller类中

@RestController

public class test {

    HadoopTest hadoopTest=new HadoopTest();

    @GetMapping("hello")

    public void hello() {

        hadoopTest.getName();

    }

}

也就是一条逻辑线上，HadoopTest注入了MyConfig,那么在test中必须也是注入而不是new,原因以后在补充。

补充：1.在第三种情况中，虽然MyConfig被注释了，但是只要不去注入它就没关系。