一、setter注入
- 依赖注入,是IOC的一个方面,是个通常的概念,它有多种解释。这概念是说你不用创建对象,而只需要描述它如何被创建。你不在代码里直接组装你的组件和服务,但是要在配置文件里描述哪些组件需要哪些服务,之后一个容器(IOC容器)负责把他们组装起来。
1.1简单类型
- 配置中使用
property
标签ref
属性注入引用类型对象
<?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.practice.dao.impl.BookDaoImpl1"/> <bean id="userDao" class="com.practice.dao.impl.UserDaoImpl"/> <bean id="bookService" class="com.practice.service.impl.BookServiceImpl"> <property name="bookDao" ref="bookDao"/> <property name="userDao" ref="userDao"/> </bean> </beans>
- 在bean中定义引用类型属性并提供可访问的
set
方法
package com.practice.service.impl; import com.practice.dao.BookDao; import com.practice.dao.UserDao; import com.practice.dao.impl.BookDaoImpl1; import com.practice.service.BookService; /** * @Author YJ * @Date 2023/7/25 11:28 * Description: */ public class BookServiceImpl implements BookService{ private BookDao bookDao; private UserDao userDao; public void setBookDao(BookDaoImpl1 bookDao) { this.bookDao=bookDao; } public void setUserDao(UserDao userDao) { this.userDao = userDao; } public void save() { System.out.println("bookService save..."); bookDao.save(); userDao.save(); } }
package com.practice; import com.practice.dao.BookDao; import com.practice.service.BookService; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; /** * @Author YJ * @Date 2023/7/26 11:32 * Description: */ public class AppForDiSet { public static void main(String[] args) { //获取IoC容器 ApplicationContext act = new ClassPathXmlApplicationContext("applicationContext.xml"); BookService bookService = (BookService) act.getBean("bookService"); bookService.save(); } }
1.2引用类型(基本数据类型与String)
- 配置中使用
property
标签value
属性注入简单数据类型
<?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.practice.dao.impl.BookDaoImpl1"> <property name="databaseName" value="mysql"/> <property name="connectionNum" value="5"/> </bean> <bean id="userDao" class="com.practice.dao.impl.UserDaoImpl"/> <bean id="bookService" class="com.practice.service.impl.BookServiceImpl"> <property name="bookDao" ref="bookDao"/> <property name="userDao" ref="userDao"/> </bean> </beans>
- 在bean中定义引用类型属性并提供可访问的
set
方法
package com.practice.dao.impl; import com.practice.dao.BookDao; /** * @Author YJ * @Date 2023/7/26 11:24 * Description: */ public class BookDaoImpl1 implements BookDao { private int connectionNum; private String databaseName; public void setConnectionNum(int connectionNum) { this.connectionNum = connectionNum; } public void setDatabaseName(String databaseName) { this.databaseName = databaseName; } public void save() { System.out.println("bookDao save~" + databaseName + "," + connectionNum); } }
package com.practice; import com.practice.dao.BookDao; import com.practice.service.BookService; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; /** * @Author YJ * @Date 2023/7/26 11:40 * Description: */ public class AppForDiSet { public static void main(String[] args) { //获取IoC容器 ApplicationContext act = new ClassPathXmlApplicationContext("applicationContext.xml"); BookService bookService = (BookService) act.getBean("bookService"); bookService.save(); } }
二、构造器注入
1.1简单类型
<?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.practice.dao.impl.BookDaoImpl1"/> <bean id="userDao" class="com.practice.dao.impl.UserDaoImpl"/> <bean id="bookService" class="com.practice.service.impl.BookServiceImpl"> <constructor-arg name="bookDao" ref="bookDao"/> <constructor-arg name="userDao" ref="userDao"/> </bean> </beans>
package com.practice.service.impl; import com.practice.dao.BookDao; import com.practice.dao.UserDao; import com.practice.dao.impl.BookDaoImpl1; import com.practice.service.BookService; /** * @Author YJ * @Date 2023/7/25 11:28 * Description: */ public class BookServiceImpl implements BookService{ private BookDao bookDao; private UserDao userDao; /** * 构造方法 * @param bookDao * @param userDao */ public BookServiceImpl(BookDao bookDao, UserDao userDao) { this.bookDao = bookDao; this.userDao = userDao; } public void save() { System.out.println("bookService save..."); bookDao.save(); userDao.save(); } }
public class AppForDiSet { public static void main(String[] args) { //获取IoC容器 ApplicationContext act = new ClassPathXmlApplicationContext("applicationContext.xml"); BookService bookService = (BookService) act.getBean("bookService"); bookService.save(); } }
1.2引用类型(基本数据类型与String)
<?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.practice.dao.impl.BookDaoImpl1"> <constructor-arg name="databaseName" value="mysql"/> <constructor-arg name="connectionNum" value="56"/> </bean> <bean id="userDao" class="com.practice.dao.impl.UserDaoImpl"/> <bean id="bookService" class="com.practice.service.impl.BookServiceImpl"> <constructor-arg name="bookDao" ref="bookDao"/> <constructor-arg name="userDao" ref="userDao"/> </bean> </beans>
package com.practice.dao.impl; import com.practice.dao.BookDao; /** * @Author YJ * @Date 2023/7/25 11:24 * Description: */ public class BookDaoImpl1 implements BookDao { private int connectionNum; private String databaseName; /** * 构造方法 * @param connectionNum * @param databaseName */ public BookDaoImpl1(int connectionNum, String databaseName) { this.connectionNum = connectionNum; this.databaseName = databaseName; } public void save() { System.out.println("bookDao save~" + databaseName + ", " + connectionNum); } }
public class AppForDiSet { public static void main(String[] args) { //获取IoC容器 ApplicationContext act = new ClassPathXmlApplicationContext("applicationContext.xml"); BookService bookService = (BookService) act.getBean("bookService"); bookService.save(); } }
<!--解决形参名称问题,与形参不耦合了--> <bean id="bookDao" class="com.practice.dao.impl.BookDaoImpl1"> <constructor-arg type="java.lang.String" value="mysql"/> <constructor-arg type="int" value="56"/> </bean> <bean id="userDao" class="com.practice.dao.impl.UserDaoImpl"/> <bean id="bookService" class="com.practice.service.impl.BookServiceImpl"> <constructor-arg name="bookDao" ref="bookDao"/> <constructor-arg name="userDao" ref="userDao"/> </bean>
<!--解决参数类型重复问题,使用位置解决参数匹配--> <bean id="bookDao" class="com.practice.dao.impl.BookDaoImpl1"> <constructor-arg index="1" value="mysql"/> <constructor-arg index="0" value="516"/> </bean> <bean id="userDao" class="com.practice.dao.impl.UserDaoImpl"/> <bean id="bookService" class="com.practice.service.impl.BookServiceImpl"> <constructor-arg name="bookDao" ref="bookDao"/> <constructor-arg name="userDao" ref="userDao"/> </bean>
三、依赖注入方式选择
- 1.强制依赖使用构造器进行,使用setter注入有概率不进行注入导致null对象出现
- 2.可选择依赖使用setter注入进行,灵活性强
- 3.Spring框架倡导使用构造器,第三方框架内部大多数采用构造器注入的形式进行数据初始化,相对严谨
- 4.如果有必要可以两者同时使用,使用构造器注入完成强制依赖的注入,使用setter注入完成可选依赖的注入
- 5.实际开发过程中还要根据实际情况分析,如果受控对象没有提供setter方法就必须使用构造器注入
- 6.自己开发的模块推荐使用setter注入
四、自动装配
- IoC容器根据bean所依赖的资源在容器中自动查找并注入到bean的过程称为自动装配
- 方式:
- 按类型
- 按名称
- 按构造方法
- 不启用自动装配
<bean id="bookDao" class="com.practice.dao.impl.BookDaoImpl2"/> <bean id="bookService" class="com.practice.service.impl.BookServiceImpl1" autowire="byType"/>
public class BookDaoImpl2 implements BookDao { public void save() { System.out.println("bookDao save~" ); } }
public class BookServiceImpl1 implements BookService { private BookDao bookDao; public void save() { System.out.println("bookService save..."); bookDao.save(); } public void setBookDao(BookDaoImpl2 bookDao) { this.bookDao = bookDao; } }
public class AppForDiSet { public static void main(String[] args) { //获取IoC容器 ApplicationContext act = new ClassPathXmlApplicationContext("applicationContext.xml"); BookService bookService = (BookService) act.getBean("bookService"); bookService.save(); } }
<bean id="bookDao" class="com.practice.dao.impl.BookDaoImpl2"/> <bean id="bookService" class="com.practice.service.impl.BookServiceImpl1" autowire="byName"/>
public class BookServiceImpl1 implements BookService { private BookDao bookDao; public void save() { System.out.println("bookService save..."); bookDao.save(); } public void setBookDao(BookDaoImpl2 bookDao) { this.bookDao = bookDao; } }
依赖自动装配特征
- 自动装配用于引用类型依赖注入,不能对简单类型进行操作
- 使用按类型装配时必须保证容器中相同类型的bean值唯一,推荐使用
- 使用按名称装配时必须保证容器中具有指定名称的bean,因变量名与配置耦合,不推荐使用
- 自动装配优先级低于setter注入与构造器注入,同时出现时自动装配失效
总结
通过这篇文章我们掌握了几个比较方便的注入方式,这在之后的注解开发会经常用到,欢迎各位点赞+关注!!!