一篇文章教帶你了解Java Spring之自動(dòng)裝配

更新時(shí)間：2021年09月18日 09:24:18 作者：可愛(ài)多一點(diǎn)@

今天小編就為大家分享一篇關(guān)于Spring中的自動(dòng)裝配，小編覺(jué)得內(nèi)容挺不錯(cuò)的，現(xiàn)在分享給大家，具有很好的參考價(jià)值，需要的朋友一起跟隨小編來(lái)看看吧

在Spring中有三種裝配的方式：

在xml中顯示的配置
在java中顯示配置
隱式的自動(dòng)裝配bean

1.Bean的自動(dòng)裝配

自動(dòng)裝配是Spring滿足bean依賴的一種方式，Spring會(huì)在上下文中自動(dòng)尋找，并自動(dòng)給bean裝配屬性。

1.1 autowire="byName" 實(shí)現(xiàn)自動(dòng)裝配

byname會(huì)自動(dòng)在容器上下文中查找，和自己對(duì)象set方法后面的值對(duì)應(yīng)的bean id。

需要保證所有bean的id唯一，并且這個(gè)bean需要和自動(dòng)注入的屬性的set方法的值一致。

People.java

package org.example;
public class People {
    private Cat cat;
    private Dog dog;
    private String name;
    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;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    @Override
    public String toString() {
        return "People{" +
                "cat=" + cat +
                ", dog=" + dog +
                ", name='" + name + '\'' +
                '}';
    }
}

cat.java

package org.example;
public class Cat {
    public void shut(){
        System.out.println("喵喵喵……");
    }
}

Dog.java

package org.example;
public class Dog {
    public void shut(){
        System.out.println("汪汪汪……");
    }
}

applicationContext.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 http://www.springframework.org/schema/beans/spring-beans.xsd">
    <bean id="cat" class="org.example.Cat"></bean>
    <bean id="dog" class="org.example.Dog"></bean>
    <bean id="people" class="org.example.People" autowire="byName">
        <property name="name" value="小狂神"></property>
    </bean>
</beans>

測(cè)試類

package org.example;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class App {
    public static void main( String[] args ) {
        //獲取ApplicationContext對(duì)象
        ApplicationContext application=new ClassPathXmlApplicationContext("ApplicationContext.xml");
        //通過(guò)ApplicationContext獲得TestHello對(duì)象
        //getBean（）方法中的參數(shù)即為配置文件中Bean的id的值
        People people=(People) application.getBean("people");
        people.getCat().shut();
        people.getDog().shut();
    }
}

1.2 autowire="byType" 實(shí)現(xiàn)自動(dòng)裝配

byType:會(huì)自動(dòng)在容器上下文中查找，和自己對(duì)象屬性類型相同的bean。

需要保證所有bean的class唯一，并且這個(gè)bean需要和自動(dòng)注入的屬性的類型一致。

<?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="org.example.Cat"></bean>
    <bean id="dog" class="org.example.Dog"></bean>
    <bean id="people" class="org.example.People" autowire="byType">
        <property name="name" value="小狂神"></property>
    </bean>
</beans>

2.注解實(shí)現(xiàn)自動(dòng)裝配

JDK1.5支持的注解，Spring2.5就支持注解了。

2.1 配置注解

只需在applicationContext.xml文件中加入

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:util="http://www.springframework.org/schema/util"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/util https://www.springframework.org/schema/util/spring-util.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">
<!--開(kāi)啟注解的支持-->
    <context:component-scan base-package="org.example"/>
</beans>

2.2 @Autowired注解

直接在屬性上使用即可，也可以在set方式上使用。使用@Autowired 可以不用編寫(xiě)set方法了，前提是你這個(gè)自動(dòng)裝配的屬性在IOC（Spring）容器中存在，且符合byname。

People.java

package org.example;
import org.springframework.beans.factory.annotation.Autowired;
public class People {
    @Autowired
    private Cat cat;
    @Autowired
    private Dog dog;
    private String name;
    public Cat getCat() {
        return cat;
    }
//set方法可以省略
    public void setCat(Cat cat) {
        this.cat = cat;
    }
    public Dog getDog() {
        return dog;
    }
    public void setDog(Dog dog) {
        this.dog = dog;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    @Override
    public String toString() {
        return "People{" +
                "cat=" + cat +
                ", dog=" + dog +
                ", name='" + name + '\'' +
                '}';
    }
}

applicationContext.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:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">
    <bean id="cat" class="org.example.Cat"></bean>
    <bean id="dog" class="org.example.Dog"></bean>
    <bean id="people" class="org.example.People" ></bean>
    <context:component-scan base-package="org.example"/>
</beans>

2.3 @Resource注解

People.java

package org.example;
import org.springframework.beans.factory.annotation.Autowired;
import javax.annotation.Resource;
public class People {
//如果沒(méi)有（name="cat"）那么就會(huì)找不到
    @Resource(name = "cat2")
    private Cat cat;
    @Resource
    private Dog dog;
    private String name;
    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;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    @Override
    public String toString() {
        return "People{" +
                "cat=" + cat +
                ", dog=" + dog +
                ", name='" + name + '\'' +
                '}';
    }
}

applicationContext.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:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">
    <bean id="cat1" class="org.example.Cat"></bean>
    <bean id="cat2" class="org.example.Cat"></bean>
    <bean id="dog" class="org.example.Dog"></bean>
    <bean id="people" class="org.example.People" ></bean>
    <context:component-scan base-package="org.example"/>
</beans>

2.4小結(jié)

@Autowired和@Resource的區(qū)別：

都是用來(lái)自動(dòng)裝配的，都可以放在屬性字段上
@Autowired通過(guò)byType的方式實(shí)現(xiàn)，而且必須要求這個(gè)對(duì)象存在
@Resource默認(rèn)通過(guò)byname的方式實(shí)現(xiàn)，如果找不到名字，則通過(guò)byType實(shí)現(xiàn)。如果兩個(gè)都找不到的情況就會(huì)報(bào)錯(cuò)。
執(zhí)行順序不同：@Autowired通過(guò)byType;@Resource默認(rèn)通過(guò)byname的方式實(shí)現(xiàn)。