spring依赖注入的方式有4种
- 构造方法注入
- 属性注入
- 工厂注入
- 注解注入
下面通过一个实例统一讲解:
User.java
package com.bjsxt.model; public class User {
private String username;
private String password;
public User(){}
public User(String username, String password) {
super();
this.username = username;
this.password = password;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
@Override
public String toString() {
return "User [username=" + username + ", password=" + password + "]";
}
}
UserDAO.java
package com.bjsxt.dao;
import com.bjsxt.model.User; public interface UserDAO {
public void save(User user);
}
UserDAO实现类UserDAOImpl
package com.bjsxt.dao.impl; import com.bjsxt.dao.UserDAO;
import com.bjsxt.model.User; public class UserDAOImpl implements UserDAO { public void save(User user) {
//Hibernate
//JDBC
//XML
//NetWork
System.out.println("user saved!");
} }
工厂类
第一个:UserFactory
package com.bjsxt.factory; import com.bjsxt.model.User; public class UserFactory {
public User CreatUser () {
User user=new User();
user.setUsername("周1");
user.setPassword("oumyye");
return user;
}
}
第二个:UserFactory2
package com.bjsxt.factory; import com.bjsxt.model.User; public class UserFactory2 {
public static User CreatUser () {
User user=new User();
user.setUsername("偶my耶1");
user.setPassword("oumyye");
return user;
}
}
控制层:UserService
package com.bjsxt.service;
import com.bjsxt.dao.UserDAO;
import com.bjsxt.model.User; public class UserService { private UserDAO userDAO; public void init() {
System.out.println("###########init");
} public void save(User user) {
userDAO.save(user);
}
public UserDAO getUserDAO() {
return userDAO;
}
public void setUserDAO(UserDAO userDAO) {
this.userDAO = userDAO;
} public UserService(UserDAO userDAO) {
super();
this.userDAO = userDAO;
} public void destroy() {
System.out.println("destroy");
}
}
配置文件:bean.xml
<?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-2.5.xsd">
<!-- 构造方法注入 -->
<bean id="user" class="com.bjsxt.model.User" >
<constructor-arg index="0" type="String" value="zhou"></constructor-arg>
<constructor-arg index="1" type="String" value="password"></constructor-arg>
</bean> <!-- 属性注入 -->
<bean id="user1" class="com.bjsxt.model.User" >
<property name="username" value="zhang"></property>
<property name="password" value="oumyye"></property>
</bean>
<!-- 工厂注入 -->
<bean id= "userFactory" class="com.bjsxt.factory.UserFactory" > </bean>
<bean id="user2" factory-bean="userFactory" factory-method="CreatUser"></bean> <!-- 静态工厂注入 -->
<bean id= "user3" class="com.bjsxt.factory.UserFactory2" factory-method="CreatUser"> </bean> <bean id="u" class="com.bjsxt.dao.impl.UserDAOImpl"></bean> <bean id="userService" class="com.bjsxt.service.UserService" init-method="init" destroy-method="destroy" scope="prototype"> <!-- <property name="userDAO" ref="u" /> --> <!-- 构造方法注入 -->
<constructor-arg>
<ref bean="u"/>
</constructor-arg>
</bean> </beans>
测试类:
package com.bjsxt.service; import static org.junit.Assert.*; import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext; import com.bjsxt.model.User; public class UserServiceTest { @Test
public void test() {
ApplicationContext applicationContext=new ClassPathXmlApplicationContext("beans.xml");
UserService userService=(UserService) applicationContext.getBean("userService");
//构造方法注入
User user=(User) applicationContext.getBean("user");
//属性注入
User user1=(User) applicationContext.getBean("user1");
//工厂注入
User user2=(User) applicationContext.getBean("user2");
//工厂注入
User user3=(User) applicationContext.getBean("user3"); System.out.println(user);
System.out.println(user1);
System.out.println(user2);
System.out.println(user3);
userService.save(user);
userService.destroy();
} }
结果:
###########init
User [username=zhou, password=password]
User [username=zhang, password=oumyye]
User [username=周1, password=oumyye]
User [username=偶my耶1, password=oumyye]
user saved!
destroy
注解方式在后面详细介绍
依赖注入—自动装配
Spring中提供了自动装配依赖对象的机制,但是在实际应用中并不推荐使用自动装配,因为自动装配会产生未知情况,开发人员无法预见最终的装配结果。
自动装配是在配置文件中实现的,如下:
<bean id="***" class="***" autowire="byType">
只需要配置一个autowire属性即可完成自动装配,不用再配置文件中写<property>,但是在类中还是要生成依赖对象的setter方法。
Autowire的属性值有如下几个:
· byType 按类型装配 可以根据属性类型,在容器中寻找该类型匹配的bean,如有多个,则会抛出异常,如果没有找到,则属性值为null;
· byName 按名称装配 可以根据属性的名称在容器中查询与该属性名称相同的bean,如果没有找到,则属性值为null;
· constructor 与byType方式相似,不同之处在与它应用于构造器参数,如果在容器中没有找到与构造器参数类型一致的bean,那么将抛出异常;
· autodetect 通过bean类的自省机制(introspection)来决定是使用constructor还是byType的方式进行自动装配。如果发现默认的构造器,那么将使用byType的方式。