Spring中Bean的作用域和自動裝配方式

更新時間：2021年09月28日 09:21:37 作者：想飛的魚Stitch

這篇文章主要介紹了Spring中Bean的作用域和自動裝配方式，具有很好的參考價值，希望對大家有所幫助。如有錯誤或未考慮完全的地方，望不吝賜教

Bean的作用域

Spring中bean的作用域共有singleton、prototype、request、session、application、websocket六種

其中后四種都是用在Web應(yīng)用程序中的，主要介紹前兩種singleton(單例)和prototype(原型)

Bean的作用域范圍為singleton時，所有實例共享一個對象。

Spring的默認配置為scope = “singleton”，以下兩種配置的效果是一樣的：

默認配置

<?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默認配置為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默認配置為scope = "singleton"-->
    <bean id = "user" class="indi.stitch.pojo.User" scope = "singleton" />
</beans>

測試類及輸出結(jié)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);
    }
}

在這里插入圖片描述

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默認配置為scope = "singleton"-->
    <bean id = "user" class="indi.stitch.pojo.User" scope = "prototype" />
</beans>

測試類及輸出結(jié)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);
    }
}

在這里插入圖片描述

Bean的自動裝配

Spring中Bean的自動裝配基于autowired標(biāo)簽實現(xiàn)

首先創(chuàng)建實體類People、Cat、Dog，People和Cat、Dog是組合關(guān)系，People中定義了依賴于Cat、Dog的屬性

People實體類

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實體類

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

Dog實體類

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

通過name自動裝配

<?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上下文中通過檢索name完成自動裝配，檢索依據(jù)為bean中屬性的set方法除set部分外的后綴-->
    <bean id = "people" class="indi.stitch.pojo.People" autowire="byName"/>
</beans>

測試類及輸出結(jié)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();
    }
}

輸出結(jié)果

在這里插入圖片描述

通過type自動裝配

<?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上下文中通過對屬性對應(yīng)類型進行檢索完成自動裝配，Spring配置中不能存在被依賴的相同類型的多個bean,被依賴的bean在Spring中配置時可以省略id屬性-->
    <bean id = "people" class="indi.stitch.pojo.People" autowire="byType"/>
</beans>

測試類和結(jié)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();
    }
}

輸出結(jié)果

在這里插入圖片描述