Spring IoC与DI（依赖注入）

Spring Ioc

所谓控制反转，即将传统的需要代码进行的操作，交由Spring容器来做。下面以添加book为例进行比较一下：
BookService.java

public interface BookService {
    void addBook();
}

BookServiceImpl .java

public class BookServiceImpl implements BookService {
    @Override
    public void addBook() {
        System.out.println("add book by ioc");
    }

}

Spring 配置文件

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="
            http://www.springframework.org/schema/beans
            http://www.springframework.org/schema/beans/spring-beans.xsd">

<!-- bean definitions here -->
<bean id="bookService" class="[包名].bookServiceImpl"></bean>
</beans>

测试：

public class TestIoc {

    @Test
    public void demo01(){
        //传统方法
        BookService bookService= new bookServiceImpl();
        bookService.addBook();
    }

    @Test
    public void demo02(){
        //从spring容器获得
        //1 获得容器
        ApplicationContext applicationContext =
                                new ClassPathXmlApplicationContext("com/spring/ioc/beans.xml");

        //2获得内容 --不需要自己new，都是从spring容器获得
        BookService bookService= (BookService ) applicationContext.getBean("bookService");
        bookService.addBook();
    }

}

DI(Dependency Injection)

has a：有一个，成员变量，依赖。
class B {
private A a; //B类依赖A类
}
依赖：一个对象需要使用另一个对象
注入：通过setter方法进行另一个对象实例设置。
举例如下：

public interface BookDao {
    void save();
}

public class BookDaoImpl implements BookDao{
    @Override
    public void save(){
        System.out.println("DI -> add a book");
    }
}

public interface BookService {
    void addBook();
}

public class BookServiceImpl implements BookService {
    private BookDao bookDao;

    public void setBookDao(BookDao bookDao){
        this.bookDao=bookDao;
    }

    @Override
    public void addBook() {
        this.bookDao.save();
    }

}

public class TestDI {

    @Test
    public void demo01(){
        String xmlPath = "com/*/spring/ioc2/beans.xml";
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext(xmlPath);
        BookService bookService = (BookService) applicationContext.getBean("bookService");
        bookService.addBook();
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="
            http://www.springframework.org/schema/beans
            http://www.springframework.org/schema/beans/spring-beans.xsd">

<!--
    模拟spring执行过程
        创建service实例：BookService bookService = new BookServiceImpl() IoC  <bean>
        创建dao实例：BookDao bookDao = new BookDaoImpl()         IoC
        将dao设置给service：bookService.setBookDao(bookDao);     DI   <property>

        <property> 用于进行属性注入
            name： bean的属性名，通过setter方法获得
            ref ：另一个bean的id值的引用
     -->

<bean id="bookService" class="[包名].BookServiceImpl">
    <property name="bookDao" ref="bookDao"></property>
</bean>

<bean id="bookDao" class="[包名].BookDaoImpl"></bean>
</beans>

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