Spring：DI依赖注入的方式

Spring为我们提供了两种注入方式，分别是:

setter注入
- 简单类型
- 引用类型
构造器注入
- 简单类型
- 引用类型

setter注入

在bean中定义引用类型属性，并提供可访问的set方法
配置中使用property标签ref属性注入引用类型对象

(1)项目中添加BookDao、BookDaoImpl、UserDao、UserDaoImpl、BookService和BookServiceImpl类

public interface BookDao {public void save();
}// 有基本类型变量 setter方法
public class BookDaoImpl implements BookDao {private String databaseName;private int connectionNum;public void setConnectionNum(int connectionNum) {this.connectionNum = connectionNum;}public void setDatabaseName(String databaseName) {this.databaseName = databaseName;}public void save() {System.out.println("book dao save ..."+databaseName+","+connectionNum);}
}
public interface UserDao {public void save();
}
public class UserDaoImpl implements UserDao {public void save() {System.out.println("user dao save ...");}
}public interface BookService {public void save();
}// 有引用类型setter方法
public class BookServiceImpl implements BookService{private BookDao bookDao;private UserDao userDao;public void setUserDao(UserDao userDao) {this.userDao = userDao;}public void setBookDao(BookDao bookDao) {this.bookDao = bookDao;}public void save() {System.out.println("book service save ...");bookDao.save();userDao.save();}
}

(2)resources下提供spring的配置文件
在applicationContext.xml配置文件中使用property标签注入

<?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 id="bookDao" class="com.itheima.dao.impl.BookDaoImpl"><property name="databaseName" value="mysql"/><property name="connectionNum" value="10"/></bean><bean id="userDao" class="com.itheima.dao.impl.UserDaoImpl"/><bean id="bookService" class="com.itheima.service.impl.BookServiceImpl"><property name="bookDao" ref="bookDao"/><property name="userDao" ref="userDao"/></bean>
</beans>

说明:

对于引用数据类型使用的是<property name="" ref=""/>
对于简单数据类型使用的是<property name="" value=""/>
value:后面跟的是简单数据类型，对于参数类型，Spring在注入的时候会自动转换

（3）编写AppForDISet运行类，加载Spring的IOC容器，并从中获取对应的bean对象

public class AppForDISet {public static void main( String[] args ) {ApplicationContext ctx = new ClassPathXmlApplicationContext("applicationContext.xml");BookService bookService = (BookService) ctx.getBean("bookService");bookService.save();}
}

运行结果：
在这里插入图片描述

构造器注入

构造器注入也就是构造方法注入
(1)项目中添加BookDao、BookDaoImpl、UserDao、UserDaoImpl、BookService和BookServiceImpl类

public interface BookDao {public void save();
}
// 添加多个简单属性并提供构造方法
public class BookDaoImpl implements BookDao {private String databaseName;private int connectionNum;public BookDaoImpl(String databaseName, int connectionNum) {this.databaseName = databaseName;this.connectionNum = connectionNum;}public void save() {System.out.println("book dao save ..."+databaseName+","+connectionNum);}
}
public interface UserDao {public void save();
}
public class UserDaoImpl implements UserDao {public void save() {System.out.println("user dao save ...");}
}public interface BookService {public void save();
}// 在BookServiceImpl声明userDao并提供多个参数的构造函数
public class BookServiceImpl implements BookService{private BookDao bookDao;private UserDao userDao;public BookServiceImpl(BookDao bookDao,UserDao userDao) {this.bookDao = bookDao;this.userDao = userDao;}public void save() {System.out.println("book service save ...");bookDao.save();userDao.save();}
}

(2)resources下提供spring的配置文件

<?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 id="bookDao" class="com.itheima.dao.impl.BookDaoImpl"><constructor-arg name="databaseName" value="mysql"/><constructor-arg name="connectionNum" value="666"/></bean><bean id="userDao" class="com.itheima.dao.impl.UserDaoImpl"/><bean id="bookService" class="com.itheima.service.impl.BookServiceImpl"><constructor-arg name="bookDao" ref="bookDao"/><constructor-arg name="userDao" ref="userDao"/></bean>
</beans>

(3)编写AppForDIConstructor运行类，加载Spring的IOC容器，并从中获取对应的bean对象

public class AppForDIConstructor {public static void main( String[] args ) {ApplicationContext ctx = new ClassPathXmlApplicationContext("applicationContext.xml");BookService bookService = (BookService) ctx.getBean("bookService");bookService.save();}
}