Spring中IOC创建对象的几种注入方式，你知道有哪些?

港控/mmm° 2021-09-09 05:12 469阅读 0赞

> **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

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）

<bean id="teacher1" class="com.ys.pojo.Teacher">
            <constructor-arg index="0" value="李老师" />
            <constructor-arg index="1" value="333"/>
        </bean>
    
        
        <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>
    
        
        <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

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：

![20210727135210662.png][]

--------------------

### 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

![20210727144522971.png][]

<?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

![20210727145144331.png][]

<?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>

注意:由于 XML 语法的原因，索引符号要求存在前导，`_`因为 XML 属性名称不能以数字开头（即使某些 IDE 允许）

\---------------------------

以上是在学spring中的一些总结，有不对的地方欢迎指正！！！

觉得不错三连支持一下哦，O(∩\_∩)O哈哈~

[20210727135210662.png]: /images/20210813/a6589f8a5ed341a28c1c85bb5930c863.png
[20210727144522971.png]: /images/20210813/d7d1fd3f4e5b4fde9e45b1b4b452507d.png
[20210727145144331.png]: /images/20210813/405a53b21f3e4c11a522a4a451f806e7.png