一篇文章教带你了解Java Spring之自动装配
目录
- 在Spring中有三种装配的方式:
- 1.Bean的自动装配
- 1.1 autowire="byName" 实现自动装配
- 1.2 autowire="byType" 实现自动装配
- 2.注解实现自动装配
- 2.1 配置注解
- 2.2 @Autowired注解
- 2.3 @Resource注解
- 2.4小结
- 3.介绍一个idea中做笔记的小技巧
- 总结
在Spring中有三种装配的方式:
- 在xml中显示的配置
- 在java中显示配置
- 隐式的自动装配bean
1.Bean的自动装配
自动装配是Spring满足bean依赖的一种方式,Spring会在上下文中自动寻找,并自动给bean装配属性。
1.1 autowire="byName" 实现自动装配
byname会自动在容器上下文中查找,和自己对象set方法后面的值对应的bean id。
需要保证所有bean的id唯一,并且这个bean需要和自动注入的属性的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>
测试类
package org.example; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public class App { public static void main( String[] args ) { //获取ApplicationContext对象 ApplicationContext application=new ClassPathXmlApplicationContext("ApplicationContext.xml"); //通过ApplicationContext获得TestHello对象 //getBean()方法中的参数即为配置文件中Bean的id的值 People people=(People) application.getBean("people"); people.getCat().shut(); people.getDog().shut(); } }
1.2 autowire="byType" 实现自动装配
byType:会自动在容器上下文中查找,和自己对象属性类型相同的bean。
需要保证所有bean的class唯一,并且这个bean需要和自动注入的属性的类型一致。
<?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.注解实现自动装配
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"> <!--开启注解的支持--> <context:component-scan base-package="org.example"/> </beans>
2.2 @Autowired注解
直接在属性上使用即可,也可以在set方式上使用。使用@Autowired 可以不用编写set方法了,前提是你这个自动装配的属性在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 { //如果没有(name="cat")那么就会找不到 @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小结
@Autowired和@Resource的区别:
- 都是用来自动装配的,都可以放在属性字段上
- @Autowired通过byType的方式实现,而且必须要求这个对象存在
- @Resource默认通过byname的方式实现,如果找不到名字,则通过byType实现。如果两个都找不到的情况就会报错。
- 执行顺序不同:@Autowired通过byType;@Resource默认通过byname的方式实现。
3.介绍一个idea中做笔记的小技巧
总结
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