一：对象，JavaBean，SpringBean的区别
1.什么是JavaBean
javaBean要求所有属性为私有,该类必须有一个公共无参构造函数,private属性必须提供公共的Getter setter给外部访问
public class User {
//javaBean要求所有属性为私有,该类必须有一个公共无参构造函数,private属性必须提供公共的Getter setter给外部访问
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管理的对象,所有能受Spring管理的对象都可以是SpringBean
3.SpringBean和JAVABean的区别
- 用处不同：传统javabean更多地作为值传递参数，而spring中的bean用处几乎无处不在，任何组件都可以被称为bean
- 写法不同：传统javabean作为值对象，要求每个属性都提供getter和setter方法；但spring中的bean只需为接受设值注入的属性提供setter方法
生命周期不同：传统javabean作为值对象传递，不接受任何容器管理其生命周期；spring中的bean有spring管理其生命周期行为
二：如何定义一个SpringBean
准备工作:引入Spring依赖包
<!-- 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.通过ClassPathXmlApplicationContext
通过ClassPathXmlApplicationContext需要指定configLocation,所有我们现在resources目录下新建一个Spring.xml文件
<?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">
<!-- 使用设值注入方式装配实例 -->
<bean id="user1" class="org.example.bean.User">
<property name="name" value="zhangsan" />
</bean>
<!-- 使用构造方法装配实例 -->
<!--使用构造方法装配需要在相应类提供构造函数-->
<bean id="user2" class="org.example.bean.User">
<constructor-arg index="0" value="lisi" />
</bean>
</beans>
同时相应对象重写toString方法,便于更好观察user1和user2
package org.example.bean;
public class User {
//javaBean要求所有属性为私有,该类必须有一个公共无参构造函数,private属性必须提供公共的Getter setter给外部访问
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 + '\'' +
'}';
}
}
运行测试类
package org.example.bean;
import org.springframework.context.support.ClassPathXmlApplicationContext;
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);
}
}
运行结果如下
User{name='zhangsan'}
User{name='lisi'}
2.通过AnnotationConfigApplicationContext底层
也是通过BeanDefinition实现
*@Bean@Component@Service@Controller都可以;一般@Service用于Service层,@Controller用于Controller层,此处以@Bean为例
新建一个Config类,并给User打上@Bean标签
package org.example.bean;
import org.springframework.context.annotation.Bean;
public class Config {
@Bean
public User user(){
return new User();
}
}
通过AnnotationConfigApplicationContext获取bean,并打印bean对象
package org.example.bean;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
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);
}
}
运行结果
User{name='null'}
3.通过BeanDefinition
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;
public class Main {
public static void main(String[] args) {
AnnotationConfigApplicationContext annotationConfigApplicationContext = new AnnotationConfigApplicationContext();
AbstractBeanDefinition beanDefinition = BeanDefinitionBuilder.genericBeanDefinition().getBeanDefinition();
//定义一个Bean
beanDefinition.setBeanClass(User.class);
//把生成的Bean注册到容器中
annotationConfigApplicationContext.refresh();
annotationConfigApplicationContext.registerBeanDefinition("userTest",beanDefinition);
User userTest = annotationConfigApplicationContext.getBean("userTest", User.class);
System.out.println(userTest);
}
}
运行结果
User{name='null'}
4.通过FactoryBean
4.1通过FactoryBean与注解方式
首先新建一个Person类
package org.example.bean;
import org.springframework.stereotype.Component;
public class Person {
}
然后新建一个PersonFactoryBean类,并实现FactoryBean接口,重写其方法,为其打上@component注解, 此处和在Person类上打注解是同一效果
package org.example.bean;
import org.springframework.beans.factory.FactoryBean;
import org.springframework.stereotype.Component;
@Component("person")
public class PersonFactoryBean implements FactoryBean {
@Override
public Object getObject() throws Exception {
return new Person();
}
@Override
public Class<?> getObjectType() {
return Person.class;
}
}
其次添加一个Config类打上@ComponentScan("org.example.bean"),目的是为了扫描包下的注解
package org.example.bean;
import org.springframework.context.annotation.ComponentScan;
@ComponentScan("org.example.bean")
public class Config {
}
最后通过AnnotationConfigApplicationContext获取Bean
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;
public class Main {
public static void main(String[] args) {
//Config类为包扫描配置类
AnnotationConfigApplicationContext annotationConfigApplicationContext = new AnnotationConfigApplicationContext(Config.class);
Person person = annotationConfigApplicationContext.getBean("person", Person.class);
System.out.println(person);
}
}
运行结果
org.example.bean.Person@28ac3dc3
4.2通过Factory和BeanDefinition
1.同4.1一样新建一个Person类
2.同4.1一样新建一个PersonFactoryBean类,实现FactoryBean接口,但是不打注解
3.通过BeanDefinition获取对象
此处和注解生成的差别在于通过BeanDefinition注册的会生成两个Bean对象,一个是person对应的类型是Person,另一个是&person对应的类型是PersonFactoryBean,通过下面代码的getBean方法可以看出来!!
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;
public class Main {
public static void main(String[] args) {
AnnotationConfigApplicationContext annotationConfigApplicationContext = new AnnotationConfigApplicationContext(Config.class);
AbstractBeanDefinition beanDefinition = BeanDefinitionBuilder.genericBeanDefinition().getBeanDefinition();
////定义一个Bean
beanDefinition.setBeanClass(PersonFactoryBean.class);
//把生成的Bean注册到容器中
//annotationConfigApplicationContext.refresh();
//此处会生成2个Bean对象 第一个对象为&person对应的类型的PersonFactoryBean 第二个对象为person对应的类型为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);
}
}
运行结果如下
org.example.bean.PersonFactoryBean@3aeaafa6
org.example.bean.Person@76a3e297
注
FactoryBean接口提供三个方法,但是我们重写了两个方法,这是因为另外一个方法是默认实现了的
FactoryBean接口方法如下:
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();
//默认实现方法,是否是单例
default boolean isSingleton() {
return true;
}
}
5.通过Supplier
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;
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种api，很多情况下底层其实用的都是一样的东西，只是提供了不同的使用方式，具体可以通过源码查看。
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编程网。
