spring注入bean的3种方式

1.属性注入（DI依赖注入）**

public class SysCollectionExtServiceTest extends AbstractSimpleTest {

    @Autowired
    private SysCollectionExtService sysCollectionExtService;

    @Test
    public void testTuck() {
       
    }
}

优点：简单整洁

缺点：循环依赖注入问题

2.Setter方法注入*

public class SysCollectionExtServiceTest extends AbstractSimpleTest {

    private SysCollectionExtService sysCollectionExtService;
    @Autowired
    public void setSysCollectionExtService(SysCollectionExtService 			      sysCollectionExtService) {
        this.sysCollectionExtService = sysCollectionExtService;
    }

    @Test
    public void testTuck() {
       
    }
}

优点：依赖注入的话，使用的时候会报错

缺点：不简洁，注入太多，显得当前类过于臃肿

提醒：一个类过于太多注入操作，违背了 单一职责原则

3.构造器注入***

public class SysCollectionExtServiceTest extends AbstractSimpleTest {
    
    private SysCollectionExtService sysCollectionExtService;

    @Autowired
    public SysCollectionExtServiceTest(SysCollectionExtService sysCollectionExtService) {
        this.sysCollectionExtService = sysCollectionExtService;
    }

    @Test
    public void testTuck() {
        
    }
}

优点：服务启动，如果存在循环依赖，会报错

缺点：不整洁，注入麻烦

但是4.x以后版本推荐此类注入方式