一：對象，JavaBean，SpringBean的區(qū)別
1.什么是JavaBean
javaBean要求所有屬性為私有,該類必須有一個(gè)公共無參構(gòu)造函數(shù),private屬性必須提供公共的Getter setter給外部訪問
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/** * @author yzh * @date 2021/4/29 8:42 **/public class User { //javaBean要求所有屬性為私有,該類必須有一個(gè)公共無參構(gòu)造函數(shù),private屬性必須提供公共的Getter setter給外部訪問 private String name; public String getName() { return name; } public void setName(String name) { this.name = name; }} |
2.什么是SpringBean
SpringBean是受Spring管理的對象,所有能受Spring管理的對象都可以是SpringBean
3.SpringBean和JAVABean的區(qū)別
- 用處不同：傳統(tǒng)javabean更多地作為值傳遞參數(shù)，而spring中的bean用處幾乎無處不在，任何組件都可以被稱為bean
- 寫法不同：傳統(tǒng)javabean作為值對象，要求每個(gè)屬性都提供getter和setter方法；但spring中的bean只需為接受設(shè)值注入的屬性提供setter方法
生命周期不同：傳統(tǒng)javabean作為值對象傳遞，不接受任何容器管理其生命周期；spring中的bean有spring管理其生命周期行為
二：如何定義一個(gè)SpringBean
準(zhǔn)備工作:引入Spring依賴包
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<!-- https://mvnrepository.com/artifact/org.springframework/spring-context --><dependency> <groupId>org.springframework</groupId> <artifactId>spring-context</artifactId> <version>5.2.14.RELEASE</version></dependency> |
1.通過ClassPathXmlApplicationContext
通過ClassPathXmlApplicationContext需要指定configLocation,所有我們現(xiàn)在resources目錄下新建一個(gè)Spring.xml文件
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<?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-3.2.xsd"> <!-- 使用設(shè)值注入方式裝配實(shí)例 --> <bean id="user1" class="org.example.bean.User"> <property name="name" value="zhangsan" /> </bean> <!-- 使用構(gòu)造方法裝配實(shí)例 --> <!--使用構(gòu)造方法裝配需要在相應(yīng)類提供構(gòu)造函數(shù)--> <bean id="user2" class="org.example.bean.User"> <constructor-arg index="0" value="lisi" /> </bean></beans> |
同時(shí)相應(yīng)對象重寫toString方法,便于更好觀察user1和user2
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package org.example.bean;/** * @author yzh * @date 2021/4/29 8:42 **/public class User { //javaBean要求所有屬性為私有,該類必須有一個(gè)公共無參構(gòu)造函數(shù),private屬性必須提供公共的Getter setter給外部訪問 private String name; public String getName() { return name; } public void setName(String name) { this.name = name; } public User(String name) { this.name = name; } public User() { } @Override public String toString() { return "User{" + "name='" + name + '\'' + '}'; }} |
運(yùn)行測試類
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package org.example.bean;import org.springframework.context.support.ClassPathXmlApplicationContext;/** * @author yzh * @date 2021/4/29 8:45 **/public class Main { public static void main(String[] args) { ClassPathXmlApplicationContext classPathXmlApplicationContext = new ClassPathXmlApplicationContext(); classPathXmlApplicationContext.setConfigLocation("Spring.xml"); classPathXmlApplicationContext.refresh(); User user1 = classPathXmlApplicationContext.getBean("user1",User.class); System.out.println(user1); User user2 = classPathXmlApplicationContext.getBean("user2", User.class); System.out.println(user2); }} |
運(yùn)行結(jié)果如下
User{name='zhangsan'}
User{name='lisi'}
2.通過AnnotationConfigApplicationContext底層
也是通過BeanDefinition實(shí)現(xiàn)
*@Bean@Component@Service@Controller都可以;一般@Service用于Service層,@Controller用于Controller層,此處以@Bean為例
新建一個(gè)Config類,并給User打上@Bean標(biāo)簽
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package org.example.bean;import org.springframework.context.annotation.Bean;/** * @author yzh * @date 2021/4/29 9:20 **/public class Config { @Bean public User user(){ return new User(); }} |
通過AnnotationConfigApplicationContext獲取bean,并打印bean對象
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package org.example.bean;import org.springframework.context.annotation.AnnotationConfigApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext;/** * @author yzh * @date 2021/4/29 8:45 **/public class Main { public static void main(String[] args) { AnnotationConfigApplicationContext annotationConfigApplicationContext = new AnnotationConfigApplicationContext(); annotationConfigApplicationContext.register(Config.class); annotationConfigApplicationContext.refresh(); User user = annotationConfigApplicationContext.getBean("user",User.class); System.out.println(user); }} |
運(yùn)行結(jié)果
User{name='null'}
3.通過BeanDefinition
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package org.example.bean;import org.springframework.beans.factory.support.AbstractBeanDefinition;import org.springframework.beans.factory.support.BeanDefinitionBuilder;import org.springframework.context.annotation.AnnotationConfigApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext;/** * @author yzh * @date 2021/4/29 8:45 **/public class Main { public static void main(String[] args) { AnnotationConfigApplicationContext annotationConfigApplicationContext = new AnnotationConfigApplicationContext(); AbstractBeanDefinition beanDefinition = BeanDefinitionBuilder.genericBeanDefinition().getBeanDefinition(); //定義一個(gè)Bean beanDefinition.setBeanClass(User.class); //把生成的Bean注冊到容器中 annotationConfigApplicationContext.refresh(); annotationConfigApplicationContext.registerBeanDefinition("userTest",beanDefinition); User userTest = annotationConfigApplicationContext.getBean("userTest", User.class); System.out.println(userTest); }} |
運(yùn)行結(jié)果
User{name='null'}
4.通過FactoryBean
4.1通過FactoryBean與注解方式
首先新建一個(gè)Person類
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package org.example.bean;import org.springframework.stereotype.Component;/** * @author yzh * @date 2021/4/29 10:00 **/public class Person {} |
然后新建一個(gè)PersonFactoryBean類,并實(shí)現(xiàn)FactoryBean接口,重寫其方法,為其打上@component注解, 此處和在Person類上打注解是同一效果
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package org.example.bean;import org.springframework.beans.factory.FactoryBean;import org.springframework.stereotype.Component;/** * @author yzh * @date 2021/4/29 10:01 **/@Component("person")public class PersonFactoryBean implements FactoryBean { @Override public Object getObject() throws Exception { return new Person(); } @Override public Class<?> getObjectType() { return Person.class; }} |
其次添加一個(gè)Config類打上@ComponentScan("org.example.bean"),目的是為了掃描包下的注解
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package org.example.bean;import org.springframework.context.annotation.ComponentScan;/** * @author yzh * @date 2021/4/29 9:20 **/@ComponentScan("org.example.bean")public class Config {} |
最后通過AnnotationConfigApplicationContext獲取Bean
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package org.example.bean;import org.springframework.beans.factory.support.AbstractBeanDefinition;import org.springframework.beans.factory.support.BeanDefinitionBuilder;import org.springframework.context.annotation.AnnotationConfigApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext;/** * @author yzh * @date 2021/4/29 8:45 **/public class Main { public static void main(String[] args) { //Config類為包掃描配置類 AnnotationConfigApplicationContext annotationConfigApplicationContext = new AnnotationConfigApplicationContext(Config.class); Person person = annotationConfigApplicationContext.getBean("person", Person.class); System.out.println(person); }} |
運(yùn)行結(jié)果
org.example.bean.Person@28ac3dc3
4.2通過Factory和BeanDefinition
1.同4.1一樣新建一個(gè)Person類
2.同4.1一樣新建一個(gè)PersonFactoryBean類,實(shí)現(xiàn)FactoryBean接口,但是不打注解
3.通過BeanDefinition獲取對象
此處和注解生成的差別在于通過BeanDefinition注冊的會生成兩個(gè)Bean對象,一個(gè)是person對應(yīng)的類型是Person,另一個(gè)是&person對應(yīng)的類型是PersonFactoryBean,通過下面代碼的getBean方法可以看出來!!
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package org.example.bean;import org.springframework.beans.factory.support.AbstractBeanDefinition;import org.springframework.beans.factory.support.BeanDefinitionBuilder;import org.springframework.context.annotation.AnnotationConfigApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext;/** * @author yzh * @date 2021/4/29 8:45 **/public class Main { public static void main(String[] args) { AnnotationConfigApplicationContext annotationConfigApplicationContext = new AnnotationConfigApplicationContext(Config.class); AbstractBeanDefinition beanDefinition = BeanDefinitionBuilder.genericBeanDefinition().getBeanDefinition(); ////定義一個(gè)Bean beanDefinition.setBeanClass(PersonFactoryBean.class); //把生成的Bean注冊到容器中 //annotationConfigApplicationContext.refresh(); //此處會生成2個(gè)Bean對象 第一個(gè)對象為&person對應(yīng)的類型的PersonFactoryBean 第二個(gè)對象為person對應(yīng)的類型為Person; annotationConfigApplicationContext.registerBeanDefinition("person",beanDefinition); PersonFactoryBean personFactoryBean = annotationConfigApplicationContext.getBean("&person", PersonFactoryBean.class); System.out.println(personFactoryBean); Person person = annotationConfigApplicationContext.getBean("person", Person.class); System.out.println(person); }} |
運(yùn)行結(jié)果如下
org.example.bean.PersonFactoryBean@3aeaafa6
org.example.bean.Person@76a3e297
注
FactoryBean接口提供三個(gè)方法,但是我們重寫了兩個(gè)方法,這是因?yàn)榱硗庖粋€(gè)方法是默認(rèn)實(shí)現(xiàn)了的
FactoryBean接口方法如下:
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package org.springframework.beans.factory;import org.springframework.lang.Nullable;public interface FactoryBean<T> { String OBJECT_TYPE_ATTRIBUTE = "factoryBeanObjectType"; @Nullable T getObject() throws Exception; @Nullable Class<?> getObjectType(); //默認(rèn)實(shí)現(xiàn)方法,是否是單例 default boolean isSingleton() { return true; }} |
5.通過Supplier
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package org.example.bean;import org.springframework.beans.factory.support.AbstractBeanDefinition;import org.springframework.beans.factory.support.BeanDefinitionBuilder;import org.springframework.context.annotation.AnnotationConfigApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext;import java.util.function.Supplier;/** * @author yzh * @date 2021/4/29 8:45 **/public class Main { public static void main(String[] args) { AnnotationConfigApplicationContext annotationConfigApplicationContext = new AnnotationConfigApplicationContext(); annotationConfigApplicationContext.refresh(); annotationConfigApplicationContext.registerBean(User.class, new Supplier<User>() { @Override public User get() { User user = new User(); user.setName("123"); return user; } }); User user = annotationConfigApplicationContext.getBean("user", User.class); System.out.println(user); }} |
bean的注入方式本文只是提供了多種api，很多情況下底層其實(shí)用的都是一樣的東西，只是提供了不同的使用方式，具體可以通過源碼查看。
以上為個(gè)人經(jīng)驗(yàn)，希望能給大家一個(gè)參考，也希望大家多多支持服務(wù)器之家。
原文鏈接：https://www.jianshu.com/p/2e6e07e59599
