目录

• Bean的作用域
• 默认配置
• scope = “singleton”
• scope = “prototype”
• Bean的自动装配
• 通过name自动装配
• 通过type自动装配

Bean的作用域

Spring中bean的作用域共有singleton、prototype、request、session、application、websocket六种

其中后四种都是用在Web应用程序中的，主要介绍前两种singleton(单例)和prototype(原型)

Bean的作用域范围为singleton时，所有实例共享一个对象。

Spring的默认配置为scope = “singleton”，以下两种配置的效果是一样的：

默认配置

<?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"
       xmlns:c="http://www.springframework.org/schema/c"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
    <!--Spring默认配置为scope = "singleton"-->
    <bean id = "user" class="indi.stitch.pojo.User" />
</beans>

scope = “singleton”

<?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"
       xmlns:c="http://www.springframework.org/schema/c"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
    <!--Spring默认配置为scope = "singleton"-->
    <bean id = "user" class="indi.stitch.pojo.User" scope = "singleton" />
</beans>

测试类及输出结果：

import indi.stitch.pojo.User;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class MyTest {
    
    @Test
    public void test2() {
        ApplicationContext context = new ClassPathXmlApplicationContext("namespace.xml");
        User user = context.getBean("user", User.class);
        User user2 = context.getBean("user", User.class);
        System.out.println(user == user2);
    }
}

scope = “prototype”

<?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"
       xmlns:c="http://www.springframework.org/schema/c"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
    <!--Spring默认配置为scope = "singleton"-->
    <bean id = "user" class="indi.stitch.pojo.User" scope = "prototype" />
</beans>

测试类及输出结果：

import indi.stitch.pojo.User;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class MyTest {
    @Test
    public void test2() {
        ApplicationContext context = new ClassPathXmlApplicationContext("namespace.xml");
        User user = context.getBean("user", User.class);
        User user2 = context.getBean("user", User.class);
        System.out.println(user == user2);
    }
}

Bean的自动装配

Spring中Bean的自动装配基于autowired标签实现

首先创建实体类People、Cat、Dog，People和Cat、Dog是组合关系，People中定义了依赖于Cat、Dog的属性

People实体类

package indi.stitch.pojo;
public class People {
    private Cat cat;
    private Dog dog;
    public Cat getCat() {
        return cat;
    }
    public void setCat(Cat cat) {
        this.cat = cat;
    }
    public Dog getDog() {
        return dog;
    }
    public void setDog(Dog dog) {
        this.dog = dog;
    }
    @Override
    public String toString() {
        return "People{" +
                "cat=" + cat +
                ", dog=" + dog +
                '}';
    }
}

Cat实体类

package indi.stitch.pojo;
public class Cat {
    public void shout() {
        System.out.println("miao~");
    }
}

Dog实体类

package indi.stitch.pojo;
public class Dog {
    public void shout() {
        System.out.println("wang~");
    }
}

通过name自动装配

<?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 http://www.springframework.org/schema/beans/spring-beans.xsd">
    <bean id = "cat" class="indi.stitch.pojo.Cat" />
    <bean id = "dog" class="indi.stitch.pojo.Dog" />
    <!--在Spring上下文中通过检索name完成自动装配，检索依据为bean中属性的set方法除set部分外的后缀-->
    <bean id = "people" class="indi.stitch.pojo.People" autowire="byName"/>
</beans>

测试类及输出结果：

import indi.stitch.pojo.People;
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");
        People people = context.getBean("people", People.class);
        people.getCat().shout();
        people.getDog().shout();
    }
}

输出结果

通过type自动装配

<?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 http://www.springframework.org/schema/beans/spring-beans.xsd">
    <bean id = "cat" class="indi.stitch.pojo.Cat" />
    <bean id = "dog" class="indi.stitch.pojo.Dog" />
    <!--在Spring上下文中通过对属性对应类型进行检索完成自动装配，Spring配置中不能存在被依赖的相同类型的多个bean,被依赖的bean在Spring中配置时可以省略id属性-->
    <bean id = "people" class="indi.stitch.pojo.People" autowire="byType"/>
</beans>

测试类和结果和上面相同

import indi.stitch.pojo.People;
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");
        People people = context.getBean("people", People.class);
        people.getCat().shout();
        people.getDog().shout();
    }
}

输出结果

以上为个人经验，希望能给大家一个参考，也希望大家多多支持自由互联。

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