spring创建bean的三种方式

1、使用构造器创建bean

1.1、使用无参构造器创建

package com.ly.spring;
public class Person {
    private String name;
    public void say(String name) {
        System.out.println("你好，我叫"+name);
    }
}

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="person" class="com.ly.spring.Person">bean>
beans>

 

1.2、使用有参构造器创建

package com.ly.spring;
public class Person {
    private String name;
    public Person(String name) {
        this.name = name;
    }
    public void say() {
        System.out.println("我的名字叫"+this.name);
    }
}

 

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="person" class="com.ly.spring.Person">
    
    <constructor-arg name="name" value="有参构造">constructor-arg>
bean>
beans>

2、使用静态工厂方法创建bean

Person:

package com.ly.spring;
public class Person {
    private String name;
    public Person(String name) {
        this.name = name;
    }
    public void say() {
        System.out.println("我的名字叫"+this.name);
    }
}

 

Chinese:

package com.ly.spring;
public class Chinese implements Person {
    private String name;
    public void setName(String name) {
        this.name = name;
    }
    @Override
    public void say() {
        System.out.println("我的名字叫"+this.name);
    }
}

 

American:

package com.ly.spring;
public class American implements Person {
    private String name;
    public void setName(String name) {
        this.name = name;
    }
    @Override
    public void say() {
        System.out.println("我的名字叫"+this.name);
    }
}

 

工厂类PersonFactory:

package com.ly.spring;
public class PersonFactory {
    public static Person getPerson(String name) {
        if("Chinese".equals(name)) {
            return new Chinese();
        }else if("American".equals(name)) {
            return new American();
        }
        return null;
    }
}

配置文件：

xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd">
    
    <bean id="chinese" class="com.ly.spring.PersonFactory"  factory-method="getPerson">
        
        <constructor-arg name="name" value="Chinese">constructor-arg>
        
        <property name="name" value="中国人">property>
    bean>
    <bean id="american" class="com.ly.spring.PersonFactory" factory-method="getPerson">
        <constructor-arg name="name" value="American">constructor-arg>
        <property name="name" value="美国人">property>
    bean>
beans>

 

测试类：

package com.ly.spring.test;
import com.ly.spring.Person;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class MainTest {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("bean.xml");
        Person p1 = context.getBean("chinese", Person.class);//获取到的其实是Chinese类
        p1.say();//执行时会调用Chinese类的方法
        Person p2 = context.getBean("american",Person.class);//获取到的其实是American类
        p2.say();//执行时会调用American类的方法
    }
}

3、使用实例工厂方法创建bean

修改后的工厂类PersonFactory:

package com.ly.spring;
public class PersonFactory {
    //这里不再是静态方法
    public Person getPerson(String name) {
        if("Chinese".equals(name)) {
            return new Chinese();
        }else if("American".equals(name)) {
            return new American();
        }
        return null;
    }
}

 

修改后的配置文件：

xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd">
    
    <bean id="personFactory" class="com.ly.spring.PersonFactory">bean>
    
    <bean id="chinese" factory-bean="personFactory" factory-method="getPerson">
        
        <constructor-arg name="name" value="Chinese">constructor-arg>
        
        <property name="name" value="中国人">property>
    bean>
    <bean id="american" factory-bean="personFactory" factory-method="getPerson">
        <constructor-arg name="name" value="American">constructor-arg>
        <property name="name" value="美国人">property>
    bean>
beans>

4、扩展：利用工厂bean的知识注入Date类型的属性

Person:

package com.ly.spring;
import java.util.Date;
public class Person {
    private Date birthday;
    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }
    public void showBirthday() {
        System.out.println("我的生日是："+this.birthday);
    }
}

 

配置文件：

xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd">
    
    <bean id="simpleDateFormat" class="java.text.SimpleDateFormat">
        <constructor-arg name="pattern" value="yyyy-MM-dd HH:mm:ss">constructor-arg>
    bean>
    <bean id="date" factory-bean="simpleDateFormat" factory-method="parse">
        <constructor-arg name="source" value="2020-02-19 13:17:30">constructor-arg>
    bean>
    <bean id="person" class="com.ly.spring.Person">
        
        <property name="birthday" ref="date">property>
    bean>
beans>

 

测试类：

package com.ly.spring.test;
import com.ly.spring.Person;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class MainTest {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("bean.xml");
        Person person = context.getBean("person",Person.class);
        person.showBirthday();
    }
}