Spring 控制反转(IoC)

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

<?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 id="hello" class="com.itcast.pojo.Hello">
        <property name="str" value="Hello Spring IoC"/>
    </bean>
</beans>

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

    <alias name="hello" alias="abcxyz"/>
    <bean id="hello" class="com.itcast.pojo.Hello">
        <property name="str" value="Hello Spring IoC"/>
    </bean>

<!--    <alias name="hello" alias="abcxyz"/>-->
    <bean id="hello" class="com.itcast.pojo.Hello" name="abcxyz">
        <property name="str" value="Hello Spring IoC"/>
    </bean>

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">
<!--        普通值注入 value-->
        <property name="name" value="Lutra"/>
<!--        bean注入 ref-->
        <property name="address" ref="address"/>
<!--        数组array-->
        <property name="books">
            <array>
                <value>Java</value>
                <value>MySQL</value>
                <value>Vue</value>
            </array>
        </property>
<!--        list-->
        <property name="hobbies">
            <list>
                <value>唱</value>
                <value>跳</value>
                <value>Rap</value>
            </list>
        </property>
<!--        Map-->
        <property name="card">
            <map>
                <entry key="ID" value="123321"/>
            </map>
        </property>
<!--        Set-->
        <property name="games">
            <set>
                <value>WZRY</value>
                <value>LOL</value>
            </set>
        </property>
<!--        Properties-->
        <property name="info">
            <props>
                <prop key="姓名">kkk</prop>
                <prop key="sex">male</prop>
                <prop key="age">28</prop>
            </props>
        </property>
<!--        null-->
        <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"/>

    <!-- traditional declaration with optional argument names -->
    <bean id="beanOne" class="x.y.ThingOne">
        <constructor-arg name="thingTwo" ref="beanTwo"/>
        <constructor-arg name="thingThree" ref="beanThree"/>
        <constructor-arg name="email" value="[e-mail]"/>
    </bean>

    <!-- c-namespace declaration with argument names -->
    <bean id="beanOne" class="x.y.ThingOne" c:thingTwo-ref="beanTwo"
        c:thingThree-ref="beanThree" c:email="[e-mail]"/>
</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.

<bean id="accountService" class="com.something.DefaultAccountService"/>

<!-- the following is equivalent, though redundant (singleton scope is the default) -->
<bean id="accountService" class="com.something.DefaultAccountService" scope="singleton"/>

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

<bean id="accountService" class="com.something.DefaultAccountService" scope="prototype"/>

③Request, Session, Application, and WebSocket Scopes