[Java知识库]Spring学习-DI依赖注入

Spring学习-DI依赖注入

构造器注入

见本专栏中 Spring学习-第一个Spring程序&IoC创建对象的方式

Set方式注入【重点】

• 依赖注入：set注入
  • 依赖：bean对象的创建依赖于容器
  • 注入：bean对象的所有属性，由容器来注入

【环境搭建】

1. 复杂类型

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 + '\'' +
                '}';
    }
}

2. 真实测试对象

package com.lyh.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;

    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;
    }

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

3. beans.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
        https://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="student" class="com.lyh.pojo.Student">
        <!--第一种：普通值注入，value-->
        <property name="name" value="admin" />

    </bean>
</beans>

4. 测试

public class MyTest {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
        Student student = (Student) context.getBean("student");
        System.out.println(student.getName());
    }
}

5. 完善注册信息

<?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="address" class="com.lyh.pojo.Address" >
        <property name="address" value="山东" />
    </bean>
    <bean id="student" class="com.lyh.pojo.Student">
        <!--第一种：普通值注入，value-->
        <property name="name" value="admin" />
        <!--第二种，Bean注入，ref-->
        <property name="address" ref="address" />

        <!--数组注入，ref-->
        <property name="books">
            <array>
                <value>数据结构</value>
                <value>计算机组成原理</value>
                <value>操作系统</value>
                <value>计算机网络</value>
            </array>
        </property>

        <!--List-->
        <property name="hobbys">
            <list>
                <value>综艺</value>
                <value>代码</value>
                <value>游戏</value>
                <value>电视剧</value>
            </list>
        </property>

        <!--Map-->
        <property name="card">
            <map>
                <entry key="身份证" value="370829200104029999" />
                <entry key="银行卡" value="31611642134431341643" />
            </map>
        </property>

        <!--Set-->
        <property name="games">
            <set>
                <value>王者荣耀</value>
                <value>香肠派对</value>
                <value>百变大侦探</value>
            </set>
        </property>

        <!--null-->
        <property name="wife">
            <null />
        </property>

        <!--Properties-->
        <property name="info">
            <props>
                <prop key="学号">2018XXXXXX</prop>
                <prop key="性别">女</prop>
                <prop key="姓名">lyh</prop>
            </props>
        </property>
    </bean>
</beans>

拓展方式注入

可以使用p命名空间和c命名空间注入

<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"
       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">

    <!--p命名空间注入，set注入，可以直接注入属性的值：property-->
    <bean id="user" class="com.lyh.pojo.User" p:name="admin" p:age="18" />

    <!--c命名空间注入，通过构造器注入：construct-args-->
    <bean id="user" class="com.lyh.pojo.User" c:age="18" c:name="admin"/>
    
</beans>

注意点：P命名和c命名空间不能直接使用，需要在需要使用的spring配置文件中导入xml配置
xmlns:p="http://www.springframework.org/schema/p"
xmlns:c="http://www.springframework.org/schema/c"

bean的作用域

1. 单例模式（Spring默认机制）

<bean id="user" class="com.lyh.pojo.User" c:age="18" c:name="admin" scope="singleton"/>

2. 原型模式：每次从容器中get的时候，都会产生一个新对象

<bean id="user" class="com.lyh.pojo.User" c:age="18" c:name="admin" scope="prototype"/>

3. 其余的request、session、application这些只能在web开发中使用到！