bean依赖注入三种方式

bean依赖注入的三种方式如下：

1、构造方法注入
2、set方法注入
3、P命名空间注入

此处演示的项目结构如下：

方法一： 构造方法注入

UserDaoImpl.java

public class UserDaoImpl implements IUserDao {
    @Override
    public void save() {
        System.out.println("save方法执行成功...");
    }
}

UserServiceImpl.java

public class UserServiceImpl implements IUserService {

    private IUserDao userDao;

    public UserServiceImpl(IUserDao userDao) {
        this.userDao = userDao;
    }

    @Override
    public void save() {
        userDao.save();
    }
}

applicationContext.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.xsd"
       xmlns:p="http://www.springframework.org/schema/p">

    <!--构造方法注入-->
    <bean id="userDao" class="com.hy.dao.impl.UserDaoImpl" />
    <bean id="userService" class="com.hy.service.impl.UserServiceImpl">
    　　<constructor-arg name="userDao" ref="userDao" />
    </bean>

</beans>

TestDependencyInjection.java

public class TestDependencyInjection {

    /**
     * 方式一、构造方法注入
     */
    @Test
    public void test1(){
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");
        IUserService userService = (IUserService) applicationContext.getBean("userService");
        userService.save();
    }
}

输出结果

UserDao.java和TestDependencyInjection.java代码一致，下面的方法二和方法三省略此处

方法二、set方法注入

UserServiceImpl.java

public class UserServiceImpl implements IUserService {

    private IUserDao userDao;

    public void setUserDao(IUserDao userDao) {
        this.userDao = userDao;
    }

    @Override
    public void save() {
        userDao.save();
    }
}

applicationContext.xml

<bean id="userDao" class="com.hy.dao.impl.UserDaoImpl" />
<bean id="userService" class="com.hy.service.impl.UserServiceImpl">
　　<property name="userDao" ref="userDao" />
</bean>

其中property标签中的name属性值为UserServiceImplz类中的userDao字段

方法三：P命名空间注入(原理也是set方法注入)

applicationContext.xml首先引入P命名空间

xmlns:p="http://www.springframework.org/schema/p"

UserServiceImpl.java

public class UserServiceImpl implements IUserService {

    private IUserDao userDao;

    public void setUserDao(IUserDao userDao) {
        this.userDao = userDao;
    }

    @Override
    public void save() {
        userDao.save();
    }
}

applicationContext.xml

<bean id="userDao" class="com.hy.dao.impl.UserDaoImpl" />
<bean id="userService" class="com.hy.service.impl.UserServiceImpl" p:userDao="userDao" p:userDao-ref="userDao" />

详细代码地址如下：https://gitee.com/duy123456/dependency-injection