Spring 实现对象实例化的几种方式

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本文深入解析Spring框架中的依赖注入技术，包括构造器注入、setter注入、p-namespace和c-namespace的使用方法及实例，帮助读者理解不同注入方式的特点与适用场景。

构造器注入

<?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">

    <!-- 无参数构造方法 默认-->
    <bean id="userService" class="guhong.test1.UserService"/>

    <!-- 有参构造：下标赋值 -->
    <bean id="userService2" class="guhong.test1.UserService2">
        <constructor-arg index="0" value="小西瓜"/>
        <constructor-arg index="1" value="23"/>
    </bean>

    <!-- 有参构造：类型赋值 参数类型必须各不相同 不推荐-->
    <bean id="userService3" class="guhong.test1.UserService3">
        <constructor-arg type="java.lang.String" value="刷该"/>
        <constructor-arg type="int" value="33"/>
    </bean>

    <!-- 有参构造：名称赋值 -->
    <bean id="userService4" class="guhong.test1.UserService4">
        <constructor-arg name="age" value="444"/>
        <constructor-arg name="name" value="name"/>
    </bean>

</beans>

setter注入

    public class Student {
    
        private String name;
        private Address address;
        private String[] books;
        private List<String> hobbys;
        private Map<String, String> cards;
        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> getCards() {
            return cards;
        }
    
        public void setCards(Map<String, String> cards) {
            this.cards = cards;
        }
    
        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 +
                    ", cards=" + cards +
                    ", games=" + games +
                    ", wife='" + wife + '\'' +
                    ", info=" + info +
                    '}';
        }
    }

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="demo.guhong.test04.Student">
    <!-- 普通值注入 value -->
    <property name="name" value="guhong"/>
    <!-- bean注入 ref -->
    <property name="address" ref="address"/>

    <!-- 数组 -->
    <property name="books">
        <array>
            <value>西游记</value>
            <value>水浒传</value>
            <value>红楼梦</value>
            <value>三国演义</value>
        </array>
    </property>

    <!-- 列表 -->
    <property name="hobbys">
        <list>
            <value>篮球</value>
            <value>足球</value>
            <value>羽毛球</value>
            <value>乒乓球</value>
        </list>
    </property>

    <!-- map -->
    <property name="cards">
        <map>
            <entry key="公交卡" value="122343" />
            <entry key="学生卡" value="1dweesdsf22343" />
            <entry key="老人卡" value="43fdgdereg" />
        </map>
    </property>

    <!-- set -->
    <property name="games">
        <set>
            <value>CF</value>
            <value>LOL</value>
            <value>cs1.5</value>
        </set>
    </property>

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

    <property name="info">
        <props>
            <prop key="学号">12323232</prop>
            <prop key="年龄">16</prop>
            <prop key="性别">male</prop>
            <prop key="姓名">guhong</prop>
            <prop key="userName">guhong</prop>
            <prop key="password">232323</prop>
        </props>
    </property>

</bean>

    <bean id="address" class="demo.guhong.test04.Address">
        <property name="address" value="亚特兰蒂斯"/>
    </bean>

</beans>

p-namespace:

主要是加入： xmlns:p="http://www.springframework.org/schema/p"

如果在XML中加入上述URL，显示红色的话，请看这里

可以直接注入属性的值,使用的的无参数的构造方式

public class User {

    private String name;
    private int age;

    public User(){
        System.out.println("User 无参构造");
    }

    public User(String name, int age) {
        System.out.println("User 有参数构造");
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<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
      http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">

    <bean id="user" class="demo.guhong.test04.User" p:name="sdd" p:age="12" />

</beans>

c-namespace

加入：xmlns:c="http://www.springframework.org/schema/c"

使用的有参数的构造方法

public class Car {

    private String name;

    private double price;

    public Car(){
        System.out.println("Car 无参构造");
    }

    public Car(String name, double price) {
        System.out.println(" Car 有参数构造");
        this.name = name;
        this.price = price;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }


    @Override
    public String toString() {
        return "Car{" +
                "name='" + name + '\'' +
                ", price=" + price +
                '}';
    }
}

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"
       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">

    <!-- c命名空间注入,通过构造器注入，construct args -->
    <bean id="car" class="demo.guhong.test04.Car" c:name="sdsd" c:price="12"/>

</beans>

p-namespace 和c-namesapce的结果测试

我在 User 和Car中都显示增加了无参构造和有参构造

public User(){
    System.out.println("User 无参构造");
}

public User(String name, int age) {
    System.out.println("User 有参数构造");
    this.name = name;
    this.age = age;
}

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

public Car(){
    System.out.println("Car 无参构造");
}

public Car(String name, double price) {
    System.out.println(" Car 有参数构造");
    this.name = name;
    this.price = price;
}

测试结果如下：

User 无参构造
 Car 有参数构造
User{name='sdd', age=12}
Car{name='sdsd', price=12.0}

Process finished with exit code 0

参考：狂神说