Spring的依赖注入(DI)

1.DI

概述：DI（Dependency Injection）依赖注入，在Spring创建对象的同时，为其属性赋值，称之为依赖注入。

1.1构造函数注入

顾名思义，就是使用类中的构造函数，给成员变量赋值。注意，赋值的操作不是我们自己做的，而是通过配置的方式，让spring框架来为我们注入。具体代码如下：

1.1.1service

package com.by.service;

import com.by.dao.UserDao;
import com.by.dao.UserDaoImpl;

public class UserServiceImpl implements UserService{
    private UserDao userDao;
   private String msg;

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

    public void setMsg(String msg) {
        this.msg = msg;
    }

    public UserServiceImpl(UserDao userDao, String msg) {
        this.userDao = userDao;
        this.msg = msg;
    }

    @Override
    public void adduser() {
        System.out.println(userDao+"============"+msg);
           userDao.adduser();
    }
}

1.1.2applicationContext.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">

    <!--
		2、把对象交给spring来创建
       		id：给对象在容器中提供一个唯一标识。用于获取对象
		   	class：指定类的全限定类名。用于反射创建对象。默认情况下调用无参构造函数
	-->
    <bean id="userDao" class="com.by.dao.UserDaoImpl"></bean>
    <bean id="userService" class="com.by.service.UserServiceImpl">
<!--    <bean id="userService" class="com.by.service.UserServiceImpl" scope="prototype"-->
<!--          init-method="init" destroy-method="destroy" autowire="byType">-->
        <!--    构造器注入

               要求：类中需要提供一个对应参数列表的构造函数。
               标签：constructor-arg
                       ==给谁赋值:==
				           index:指定参数在构造函数参数列表的索引位置
				           name:指定参数在构造函数中的名称
				       ==赋什么值:==
				           value:它能赋的值是基本数据类型和String类型
				           ref:它能赋的值是其他bean类型，也就是说，必须得是在配置文件中配置过的bean

-->
        <constructor-arg name="userDao" ref="userDao"></constructor-arg>
        <constructor-arg index="1" value="我真帅"></constructor-arg>
  </bean>



</beans>

?1.1.3测试

package com.by.web;

import com.by.dao.UserDao;
import com.by.service.UserService;
import org.springframework.beans.factory.xml.XmlBeanFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.core.io.ClassPathResource;
import org.springframework.core.io.ContextResource;

public class Client {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
  /**
         * 测试di
         */
        UserService userService = context.getBean("userService", UserService.class);
        userService.adduser();
   }
}

1.1.4结果

1.2set方法注入?

顾名思义，就是在类中提供需要注入成员的set方法。具体代码如下： ?

?1.2.1service

package com.by.service;

import com.by.dao.UserDao;
import com.by.dao.UserDaoImpl;

public class UserServiceImpl implements UserService{
    private UserDao userDao;
   private String msg;

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

    public void setMsg(String msg) {
        this.msg = msg;
    }

    public UserServiceImpl(UserDao userDao, String msg) {
        this.userDao = userDao;
        this.msg = msg;
    }

    @Override
    public void adduser() {
        System.out.println(userDao+"============"+msg);
           userDao.adduser();
    }
}

1.2.2applicationContext.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">

    <!--
		2、把对象交给spring来创建
       		id：给对象在容器中提供一个唯一标识。用于获取对象
		   	class：指定类的全限定类名。用于反射创建对象。默认情况下调用无参构造函数
	-->
    <bean id="userDao" class="com.by.dao.UserDaoImpl"></bean>
    <bean id="userService" class="com.by.service.UserServiceImpl">
<!--           set注入
                      ==给谁赋值:==
				           name:找的是类中set方法后面的部分
				       ==赋什么值:==
				           value:它能赋的值是基本数据类型和String类型
				           ref:它能赋的值是其他bean类型，也就是说，必须得是在配置文件中配置过的bean
    -->
        <property name="userDao" ref="userDao"></property>
        <property name="msg" value="我今年发大财"></property>

    </bean>



</beans>

??1.2.3测试

package com.by.web;

import com.by.dao.UserDao;
import com.by.service.UserService;
import org.springframework.beans.factory.xml.XmlBeanFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.core.io.ClassPathResource;
import org.springframework.core.io.ContextResource;

public class Client {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
  /**
         * 测试di
         */
        UserService userService = context.getBean("userService", UserService.class);
        userService.adduser();
   }
}

1.2.4结果

?

1.3自动注入

?不用在配置中 指定为哪个属性赋值，由spring自动根据某个 "原则" ，在工厂中查找一个bean并为属性注入值。具体代码如下：

1.3.1service

package com.by.service;

import com.by.dao.UserDao;
import com.by.dao.UserDaoImpl;

public class UserServiceImpl implements UserService{
    private UserDao userDao;
   private String msg;

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

    public void setMsg(String msg) {
        this.msg = msg;
    }

    public UserServiceImpl(UserDao userDao, String msg) {
        this.userDao = userDao;
        this.msg = msg;
    }

    @Override
    public void adduser() {
        System.out.println(userDao+"============"+msg);
           userDao.adduser();
    }
}

1.3.2applicationContext.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">

    <!--
		2、把对象交给spring来创建
       		id：给对象在容器中提供一个唯一标识。用于获取对象
		   	class：指定类的全限定类名。用于反射创建对象。默认情况下调用无参构造函数
	-->
    <bean id="userDao" class="com.by.dao.UserDaoImpl"></bean>
    <bean id="userService" class="com.by.service.UserServiceImpl" autowire="byType">
   </bean>



</beans>

?1.3.3测试

package com.by.web;

import com.by.dao.UserDao;
import com.by.service.UserService;
import org.springframework.beans.factory.xml.XmlBeanFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.core.io.ClassPathResource;
import org.springframework.core.io.ContextResource;

public class Client {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
  /**
         * 测试di
         */
        UserService userService = context.getBean("userService", UserService.class);
        userService.adduser();
   }
}

1.3.4结果

?1.4注入集合类型的属性

顾名思义，就是给类中的集合成员传值，它用的也是set方法注入的方式，只不过变量的数据类型都是集合。我们这里介绍注入数组，List,Set,Map。具体代码如下：

1.4.1service

package com.zhy.pojo;

import java.util.*;

public class Student {
    private String name;
    private Address address;
    private String[] books;
    private List<String> hobbys;
    private Map<String,String> card;
    private Set<String> games;
    private String wife;
    private Properties info;

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", address=" + address.toString() +
                ", books=" + Arrays.toString(books) +
                ", hobbys=" + hobbys +
                ", card=" + card +
                ", games=" + games +
                ", wife='" + wife + '\'' +
                ", info=" + info +
                '}';
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Address getAddress() {
        return address;
    }

    public void setAddress(Address address) {
        this.address = address;
    }

    public String[] getBooks() {
        return books;
    }

    public void setBooks(String[] books) {
        this.books = books;
    }

    public List<String> getHobbys() {
        return hobbys;
    }

    public void setHobbys(List<String> hobbys) {
        this.hobbys = hobbys;
    }

    public Map<String, String> getCard() {
        return card;
    }

    public void setCard(Map<String, String> card) {
        this.card = card;
    }

    public Set<String> getGames() {
        return games;
    }

    public void setGames(Set<String> games) {
        this.games = games;
    }

    public String getWife() {
        return wife;
    }

    public void setWife(String wife) {
        this.wife = wife;
    }

    public Properties getInfo() {
        return info;
    }

    public void setInfo(Properties info) {
        this.info = info;
    }
}

1.4.2applicationContext.xml

<?xml version="1.0" encoding="UTF-8"?>
<!--1、注意：要导入schema约束-->
<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="address" class="com.zhy.pojo.Address">
        <property name="address" value="驻马店"></property>
     </bean>
    <bean id="student" class="com.zhy.pojo.Student">
<!--        第一种！普通注入，value-->
        <property name="name" value="赵玉真"></property>
<!--        第二种Bean注入-->
        <property name="address" ref="address"></property>
        <property name="books">
            <array>
                <value>西游记</value>
                <value>水浒传</value>
                <value>红楼梦</value>
                <value>三国演义</value>
            </array>
        </property>
        <property name="hobbys">
            <list>
                <value>听歌</value>
                <value>看电影</value>
                <value>敲代码</value>
            </list>
        </property>
        <property name="card">
            <map>
                <entry key="身份证" value="111111222222333333"></entry>
                <entry key="银行卡" value="444444444444777777"></entry>
            </map>
        </property>
        <property name="games">
            <set>
                <value>LOL</value>
                <value>COC</value>
                <value>BoB</value>
            </set>
        </property>
        <property name="wife">
            <null></null>
        </property>
        <property name="info">
            <props>
                <prop key="sex">男</prop>
                <prop key="ID">20231228</prop>
                <prop key="username">root</prop>
                <prop key="password">123456</prop>
                <prop key="role">懂事早</prop>
            </props>
        </property>
     </bean>
</beans>

?1.4.3测试

import com.zhy.pojo.Student;
import com.zhy.pojo.User;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MyTest {
    public static void main(String[] args) {
      ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
        Student student = (Student) context.getBean("student");
        System.out.println(student.toString());
        /**
         * Student{name='赵玉真', address=Address{address='驻马店'},
         * books=[西游记, 水浒传, 红楼梦, 三国演义],
         * hobbys=[听歌, 看电影, 敲代码],
         * card={身份证=111111222222333333, 银行卡=444444444444777777},
         * games=[LOL, COC, BoB],
         * wife='null',
         * info={ID=20231228, password=123456, sex=男, username=root, role=懂事早}}
         */
    }
}

?1.4.4结果