Spring的依赖注入(DI)-编程知识

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;}@Overridepublic 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/beanshttp://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;}@Overridepublic 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/beanshttp://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;}@Overridepublic 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/beanshttp://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;@Overridepublic 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/beanshttp://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}}*/}
}