Spring 控制反转(IoC)

tech2023-01-19 107

Spring笔记二：

控制反转(IoC)：

1、什么是IoC？

IoC，Inversion of Control（控制反转）。

是一种设计思想，在Java开发中，将你设计好的对象交给容器控制，而不是显示地用代码进行对象的创建。

把创建和查找依赖对象的控制权交给 IoC 容器，由 IoC 容器进行注入、组合对象。这样对象与对象之间是松耦合、便于测试、功能可复用（减少对象的创建和内存消耗），使得程序的整个体系结构可维护性、灵活性、扩展性变高。

使用 IoC 的好处：

资源集中管理，实现资源的可配置和易管理降低了资源的依赖程度，即松耦合便于测试功能可复用（减少对象的创建和内存消耗）使得程序的整个体系结构可维护性、灵活性、扩展性变高

DI（Dependency Injection）依赖注入，是 IoC 容器装配、注入对象的一种方式。通过依赖注入机制，简单的配置即可注入需要的资源，完成自身的业务逻辑，不需要关心资源的出处和具体实现。

spring 提供了三种主要的方式来配置 IoC 容器中的 bean 1.基于 XML 文件配置 2.基于注解配置 3.基于注解 + java 代码显式配置

=DI不是IoC=

2、demo(xml文件配置)：

实体类：

package com.itcast.pojo; public class Hello { private String str; public Hello() { } public Hello(String str) { this.str = str; } public String getStr() { return str; } public void setStr(String str) { this.str = str; } @Override public String toString() { return "Hello{" + "str='" + str + '\'' + '}'; } }

使用spring配置文件beans.xml 将实体类属性注入值 bean相当于new 对比： Hello hello = new Hello(); id:变量名、 class 类型、 <property 属性注入，name字段名 value/ref 注入的值或引用

测试：

import com.itcast.pojo.Hello; import org.junit.Test; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public class MyTest { @Test public void HelloIoc(){ ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("beans.xml"); Hello hello = context.getBean("hello", Hello.class); System.out.println(hello.toString()); } }

【也可以使用构造器注入（不好用）】

3、*.xml配置

①别名：alias / name

测试：

ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("beans.xml"); Hello h1 = context.getBean("abcxyz", Hello.class); System.out.println(h1.toString());

② import：可以将多个配置文件导入到一个配置文件中

4、DI（依赖注入）

①构造器注入(不好用) ②set方式依赖注入依赖：bean对象的创建依赖于容器注入：bean对象的属性，由容器来注入准备：实体类： Student

package com.itcast.pojo; import java.util.*; public class Student { private String name; private Address address; private String[] books; private List<String> hobbies; private Map<String, String> card; private Set<String> games; private String wife; private Properties info; public Student() { } public Student(String name, Address address, String[] books, List<String> hobbies, Map<String, String> card, Set<String> games, String wife, Properties info) { this.name = name; this.address = address; this.books = books; this.hobbies = hobbies; this.card = card; this.games = games; this.wife = wife; this.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> getHobbies() { return hobbies; } public void setHobbies(List<String> hobbies) { this.hobbies = hobbies; } 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; } @Override public String toString() { return "Student{" + "name='" + name + '\'' + ", address=" + address + ", books=" + Arrays.toString(books) + ", hobbies=" + hobbies + ", card=" + card + ", games=" + games + ", wife='" + wife + '\'' + ", info=" + info + '}'; } }

Address

package com.itcast.pojo; public class Address { private String address; public String getAddress() { return address; } public void setAddress(String address) { this.address = address; } @Override public String toString() { return "Address{" + "address='" + address + '\'' + '}'; } }

beans.xml注入

<?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 https://www.springframework.org/schema/beans/spring-beans.xsd"> <bean name="address" class="com.itcast.pojo.Address"> <property name="address" value="quanzhou"/> </bean> <bean name="student" class="com.itcast.pojo.Student">  <property name="name" value="Lutra"/>  <property name="address" ref="address"/>  <property name="books"> <array> <value>Java</value> <value>MySQL</value> <value>Vue</value> </array> </property>  <property name="hobbies"> <list> <value>唱</value> <value>跳</value> <value>Rap</value> </list> </property>  <property name="card"> <map> <entry key="ID" value="123321"/> </map> </property>  <property name="games"> <set> <value>WZRY</value> <value>LOL</value> </set> </property>  <property name="info"> <props> <prop key="姓名">kkk</prop> <prop key="sex">male</prop> <prop key="age">28</prop> </props> </property>  <property name="wife"> <null/> </property> </bean> </beans>

测试：

import com.itcast.pojo.Student; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public class MyTest { public static void main(String[] args) { ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml"); Student s = context.getBean("student", Student.class); System.out.println(s.toString()); } }

结果：

Student{name='Lutra', address=Address{address='quanzhou'}, books=[Java, MySQL, Vue], hobbies=[唱, 跳, Rap], card={ID=123321}, games=[WZRY, LOL], wife='null', info={姓名=kkk, sex=male, age=28}}

③其它方式 p命名方式 / c命名方式 p命名方式（set方式）： *.xml导入约束：

xmlns:p="http://www.springframework.org/schema/p" <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p" xsi:schemaLocation="http://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans.xsd"> <bean id="myDataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close" p:driverClassName="com.mysql.jdbc.Driver" p:url="jdbc:mysql://localhost:3306/mydb" p:username="root" p:password="misterkaoli"/> </beans>

c命名方式（构造器方式）： *.xml导入约束：

xmlns:c="http://www.springframework.org/schema/c" <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:c="http://www.springframework.org/schema/c" xsi:schemaLocation="http://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans.xsd"> <bean id="beanTwo" class="x.y.ThingTwo"/> <bean id="beanThree" class="x.y.ThingThree"/>  <bean id="beanOne" class="x.y.ThingOne"> <constructor-arg name="thingTwo" ref="beanTwo"/> <constructor-arg name="thingThree" ref="beanThree"/> <constructor-arg name="email" value="something@somewhere.com"/> </bean>  <bean id="beanOne" class="x.y.ThingOne" c:thingTwo-ref="beanTwo" c:thingThree-ref="beanThree" c:email="something@somewhere.com"/> </beans>

5、Bean的作用域

①singleton（默认） (Default) Scopes a single bean definition to a single object instance for each Spring IoC container.

②Prototype Scopes a single bean definition to any number of object instances.

③Request, Session, Application, and WebSocket Scopes

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