spring建立bean的三種方式

時間 2020-02-27

原文原文鏈接

一、使用構造器建立bean

1.一、使用無參構造器建立

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">
    <!--若沒有無參構造器會報錯-->
    <bean id="person" class="com.ly.spring.Person"></bean>
</beans>

1.二、使用有參構造器建立

package com.ly.spring;
public class Person {
    private String name;
    public Person(String name) {
        this.name = name;
    }
    public void say() {
        System.out.println("個人名字叫"+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">
    <!--指定構造器對應參數名對應的值-->
    <constructor-arg name="name" value="有參構造"></constructor-arg>
</bean>
</beans>

二、使用靜態工廠方法建立bean

Person:java

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

Chinese:spring

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("個人名字叫"+this.name);
    }
}

American:ide

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("個人名字叫"+this.name);
    }
}

工廠類PersonFactory:測試

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：this

<?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">
    <!--
    class指定工廠類類路徑
    factory-method指定工廠類的靜態方法
    -->
    <bean id="chinese" class="com.ly.spring.PersonFactory"  factory-method="getPerson">
        <!--給工廠的靜態方法注入參數-->
        <constructor-arg name="name" value="Chinese"></constructor-arg>
        <!--經過set方法給Chinese類的name屬性注入值-->
        <property name="name" value="中國人"></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="美國人"></property>
    </bean>
</beans>

測試類：spa

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);//獲取到的實際上是Chinese類
        p1.say();//執行時會調用Chinese類的方法
        Person p2 = context.getBean("american",Person.class);//獲取到的實際上是American類
        p2.say();//執行時會調用American類的方法
    }
}

三、使用實例工廠方法建立bean

修改後的工廠類PersonFactory:code

package com.ly.spring;
public class PersonFactory {
    //這裏再也不是靜態方法
    public Person getPerson(String name) {
        if("Chinese".equals(name)) {
            return new Chinese();
        }else if("American".equals(name)) {
            return new American();
        }
        return null;
    }
}

修改後的配置文件：orm

<?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">
    <!--配置工廠bean-->
    <bean id="personFactory" class="com.ly.spring.PersonFactory"></bean>
    <!--
    factory-bean指定配置的工廠bean
    factory-method指定工廠類的實例方法
    -->
    <bean id="chinese" factory-bean="personFactory" factory-method="getPerson">
        <!--給工廠的實例方法注入參數-->
        <constructor-arg name="name" value="Chinese"></constructor-arg>
        <!--經過set方法給Chinese類的name屬性注入值-->
        <property name="name" value="中國人"></property>
    </bean>
    <bean id="american" factory-bean="personFactory" factory-method="getPerson">
        <constructor-arg name="name" value="American"></constructor-arg>
        <property name="name" value="美國人"></property>
    </bean>
</beans>

四、擴展：利用工廠bean的知識注入Date類型的屬性

Person:xml

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("個人生日是："+this.birthday);
    }
}

配置文件：blog

<?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">
    <!--SimpleDateFormat可看做日期的工廠bean-->
    <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">
        <!--使用Person類的set方法注入屬性值-->
        <property name="birthday" ref="date"></property>
    </bean>
</beans>

測試類：

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();
    }
}