Spring中在静态方法中调用@Autowired注入的实例对象

我就是我 2022-10-17 00:51 105阅读 0赞

## Spring加载类对象的时机？ ##

*  spring启动时资源的加载顺序：类的属性->静态方法–>无参构造–>注入@Autowired修饰的依赖–>执行@postConstruct修饰的init()方法。

## Spring中在静态方法中调用@Autowired注入的实例对象 ##

*  了解完spring加载资源的顺序后，可知如下编码是不能顺利使用的，虽然能编译过，但在执行的时候会报空指针异常

@Component
    public class Application { 
     	@Autowired
        private static BookDao bookDao;
        
        public static void main(String[] args) { 
            ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
            for (int i = 10; i < 20; i++) { 
                Book book = new Book();
                book.setName("java编程思想" + i);
                book.setNumber(i);
                book.setDetail("java书籍" + i);
                bookDao.addBook(book);
            }
        }
    }

## 那么问题来了如何实现在静态方法中使用@Autowired注入的实例对象呢？ ##

### 方式一： ###

@Component
    public class Application { 
        // 方式1: 使用set方法
       private static BookDao bookDao;
        @Autowired
        public void setBookDao(BookDao bookDao) { 
            Application.bookDao = bookDao;
        }
        public static void main(String[] args) { 
            ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
            for (int i = 10; i < 20; i++) { 
                Book book = new Book();
                book.setName("java编程思想" + i);
                book.setNumber(i);
                book.setDetail("java书籍" + i);
                bookDao.addBook(book);
            }
        }
    }

### 方式二： ###

@Component
    public class Application { 
        //方式2:使用构造方法
        private static BookDao bookDao;
        @Autowired
        public Application(BookDao bookDao) { 
            Application.bookDao = bookDao;
        }
        public static void main(String[] args) { 
            ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
            for (int i = 10; i < 100; i++) { 
                Book book = new Book();
                book.setName("java编程思想" + i);
                book.setNumber(i);
                book.setDetail("java书籍" + i);
                bookDao.addBook(book);
            }
        }
    }

### 方式3： ###

@Component
    public class Application { 
        //方式3:使用@PostConståruct注解(意义不是很大,主要了解下@PostConstruct注解)
        private static BookDao bookDao;
        @Autowired
        private BookDao bookDao1;
    
        @PostConstruct //该注解在构造方法之后会被执行
        private void beforeInit() { 
            this.bookDao = bookDao1;
        }
        public static void main(String[] args) { 
            ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
            for (int i = 10; i < 100; i++) { 
                Book book = new Book();
                book.setName("java编程思想" + i);
                book.setNumber(i);
                book.setDetail("java书籍" + i);
                bookDao.addBook(book);
            }
        }
    }