Spring中IOC创建对象的几种注入方式，你知道有哪些?-蒲公英云

IOC简单来说就是对象由Spring创建，管理和装配

IOC在创建对象的可用依赖注入方式有多种，分别是构造器注入，set方式注入和其他方式注入，下面分别演示一下这三种方式怎么用

构造器注入

无参构造器：spring默认是用无参构造器创建对象，如：

public class Hello {
    private String name;
    public void show() {
        System.out.println("hello"+name);
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}

在Bean中直接指明属性名和值就可以

<bean id="hello" class="com.ys.pojo.Hello">
    <property name="name" value="spring"/>
</bean>

有参构造器，如:

public class Teacher {
    private String name;
    private int phone;
//    有参构造函数
    public Teacher(String name, int phone) {
        this.name = name;
        this.phone = phone;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getPhone() {
        return phone;
    }
    public void setPhone(int phone) {
        this.phone = phone;
    }
}

对应的Bean:（有参构造器其有三种方式注入：下标指明赋值，指明类型赋值，指明参数名赋值）

<!--    有参构造下标赋值-->
    <bean id="teacher1" class="com.ys.pojo.Teacher">
        <constructor-arg index="0" value="李老师" />
        <constructor-arg index="1" value="333"/>
    </bean>
    <!--类型赋值法（不推荐这个）-->
    <bean id="teacher2" class="com.ys.pojo.Teacher">
        <constructor-arg type="java.lang.String" value="王老师"/>
        <constructor-arg type="int" value="34"/>
    </bean>
    <!--直接通过参数名设置-->
    <bean id="teacher3" class="com.ys.pojo.Teacher">
        <constructor-arg name="name" value="谢老师"/>
        <constructor-arg name="phone" value="5454545"/>
    </bean>

Set方式注入

set方式是依赖注入，依赖是指bean对象的创建依赖容器，注入是指bean对象中的所有属性，有容器来注入，如：

实体类Address

public class Address {
    private String name;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    @Override
    public String toString() {
        return "Address{" +
                "name='" + name + '\'' +
                '}';
    }
}
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 +
                ", 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;
    }
}

对应的bean

<bean id="address" class="com.ys.pojo.Address">
        <property name="name" value="辽宁"/>
    </bean>
    <bean id="student1" class="com.ys.pojo.Student">
        <!--普通值注入，直接属性名+属性值-->
        <property name="name" value="小红"/>
        <!--Bean注入,ref+对应Bean的id-->
        <property name="address" ref="address"/>
        <!--数组注入-->
        <property name="books">
            <array>
                <value>设计模式</value>
                <value>Java</value>
                <value>编程思想</value>
            </array>
        </property>
        <!--List注入-->
        <property name="hobbys">
            <list>
                <value>旅游</value>
                <value>学习</value>
            </list>
        </property>
        <!--Map注入-->
        <property name="card">
            <map>
                <entry key="QQ号" value="6666666"/>
                <entry key="手机号" value="8888888888"/>
            </map>
        </property>
        <!--Set注入-->
        <property name="games">
            <set>
                <value>飞车</value>
                <value>使命召唤</value>
            </set>
        </property>
        <!--NULL注入-->
        <property name="wife">
            <null/>
        </property>
        <!--Properties注入-->
        <property name="info">
            <props>
                <prop key="学号">121212</prop>
                <prop key="姓名">小明</prop>
            </props>
        </property>
    </bean>

测试：

@Test
    public void Test1() {
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
        Student student = context.getBean("student1", Student.class);
        System.out.println(student);
    }

测试结果：

其他方式注入

p命名注入：前提类里是无参构造，如:

public class User {
    private int id;
    private String name;
    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}

在bean中要引入约束

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:p="http://www.springframework.org/schema/p"
       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="user1" class="com.ys.pojo.User" p:id="111111" p:name="小李"/>
</beans>

注意:p 命名空间不如标准 XML 格式灵活。例如，声明属性引用的格式与以结尾的属性冲突Ref，而标准 XML 格式则不然。我们建议您仔细选择您的方法并将其传达给您的团队成员，以避免生成同时使用所有三种方法的 XML 文档。p 命名空间不如标准 XML 格式灵活。例如，声明属性引用的格式与以结尾的属性冲突Ref，而标准 XML 格式则不然。我们建议您仔细选择您的方法并将其传达给您的团队成员，以避免生成同时使用所有三种方法的 XML 文档。

============================

C命名注入：前提是类有有参构造器，如

public class User {
    private int id;
    private String name;
    public User(int id, String name) {
        this.id = id;
        this.name = name;
    }
    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}

在bean中引入约束

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:c="http://www.springframework.org/schema/c"
       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="user1" class="com.ys.pojo.User" c:id="333" c:name="阿猫"/>
</beans>