Spring第三章：创建对象的三种方式

Spring 创建对象的三种方式

　　1. 通过构造方法创建

　　　　1.1 无参构造创建:默认情况.

　　　　1.2 有参构造创建:需要明确配置

　　　　　　1.2.1 需要在类中提供有参构造方法

　　　　　　

package com.bjsxt.pojo;

public class People {
    private int id;
    private String name;

    /**
     *注意这里一旦使用了有参的构造器之后就必须生成这个
     * 无参的构造器不然spring会报错No matching constructor found in class 'People'
     */
    public People() {

    }


    public People(int id, String name) {
        this.id = id;
        this.name = name;
    }

    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    @Override
    public String toString() {
        return "People [id=" + id + ", name=" + name + "]";
    }
}

　　　　　　1.2.2 在 applicationContext.xml 中设置调用哪个构造方法创建对象

　　　　　　

<?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">

    <!-- 使用无参构造器注入对象-->
    <bean id="peo" class="com.bjsxt.pojo.People" />

    <!--使用有参构造器注入对象 需要set方法和有参构造器支持-->
    <bean id="peo2" class="com.bjsxt.pojo.People">
        <constructor-arg index="0" value="1"></constructor-arg>
        <constructor-arg index="1" value="zhangsan"></constructor-arg>
    </bean>

</beans>

　　　　　　　　1.2.2.1 如果设定的条件匹配多个构造方法执行最后的构造方法

　　　　　　　　1.2.2.2 index : 参数的索引,从 0 开始

　　　　　　　　1.2.2.3 name: 参数名

　　　　　　　　1.2.2.4 type:类型(区分开关键字和封装类 int 和 Integer)

　　　　1.2.3测试类

package com.bjsxt.test;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.bjsxt.pojo.People;
import com.bjsxt.pojo.PeopleFactory;

public class Test {
    public static void main(String[] args) {

        ApplicationContext ac = new ClassPathXmlApplicationContext("applicationContext.xml");

        People peo = ac.getBean("peo",People.class);
        System.out.println(peo);

        People peo2 = ac.getBean("peo2",People.class);
        System.out.println(peo2);

    }
}

　　　　1.2.4运行结果

二月 27, 2019 10:59:41 下午 org.springframework.context.support.ClassPathXmlApplicationContext prepareRefresh
信息: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@179d3b25: startup date [Wed Feb 27 22:59:41 CST 2019]; root of context hierarchy
二月 27, 2019 10:59:41 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [applicationContext.xml]
People [id=0, name=null]
People [id=1, name=zhangsan]

　　2. 实例工厂

　　　　2.1 工厂设计模式:帮助创建类对象.一个工厂可以生产多个对象.

　　　　2.2 实例工厂:需要先创建工厂,才能生产对象

 

　　　　2.3 实现步骤:

　　　　　　2.3.1 必须要有一个实例工厂

　　　　　　

package com.bjsxt.pojo;

public class People {
    private int id;
    private String name;

    /**
     *注意这里一旦使用了有参的构造器之后就必须生成这个
     * 无参的构造器不然spring会报错No matching constructor found in class 'People'
     */
    public People() {

    }


    public People(int id, String name) {
        this.id = id;
        this.name = name;
    }

    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    @Override
    public String toString() {
        return "People [id=" + id + ", name=" + name + "]";
    }
}

package com.bjsxt.pojo;

public class PeopleFactory {

    /**
     * 注意这里千万不能定义为stataic的
     * @return
     */
    public  People newInstance(){
        return new People(1,"测试");
    }
}

　　　　　　2.3.2 在 applicationContext.xml 中配置工厂对象和需要创建的对象

　　

<?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">

    <!--&lt;!&ndash; 使用无参构造器注入对象&ndash;&gt;
    <bean id="peo" class="com.bjsxt.pojo.People" />

    &lt;!&ndash;使用有参构造器注入对象 需要set方法和有参构造器支持&ndash;&gt;
    <bean id="peo2" class="com.bjsxt.pojo.People">
        <constructor-arg index="0" value="1"></constructor-arg>
        <constructor-arg index="1" value="zhangsan"></constructor-arg>
    </bean>-->

    <bean id="factory"  class="com.bjsxt.pojo.PeopleFactory"></bean>

    <bean id="peo3" factory-bean="factory" factory-method="newInstance"></bean>

</beans>

　　　　　　2.3.3 测试类

package com.bjsxt.test;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.bjsxt.pojo.People;
import com.bjsxt.pojo.PeopleFactory;

public class Test {
    public static void main(String[] args) {

        ApplicationContext ac = new ClassPathXmlApplicationContext("applicationContext.xml");

//        People peo = ac.getBean("peo",People.class);
//        System.out.println(peo);
//
//        People peo2 = ac.getBean("peo2",People.class);
//        System.out.println(peo2);

        People peo = ac.getBean("peo3",People.class);
        System.out.println(peo);

    }
}

　　　　　　2.3.4 测试结果　　

二月 27, 2019 11:12:24 下午 org.springframework.context.support.ClassPathXmlApplicationContext prepareRefresh
信息: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@179d3b25: startup date [Wed Feb 27 23:12:24 CST 2019]; root of context hierarchy
二月 27, 2019 11:12:24 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [applicationContext.xml]
People [id=1, name=测试]

　　3. 静态工厂

　　　　3.1 不需要创建工厂,快速创建对象.

　　　　3.2 实现步骤

　　　　　　3.2.1 编写一个静态工厂(在方法上添加 static)

　　　　　　　　

package com.bjsxt.pojo;

public class PeopleFactory1 {

    /**
     * 注意这里静态工厂需要定义为statis的
     * @return
     */
    public  static People newInstance(){
        return new People(1,"测试");
    }
}

package com.bjsxt.pojo;

public class People {
    private int id;
    private String name;

    /**
     *注意这里一旦使用了有参的构造器之后就必须生成这个
     * 无参的构造器不然spring会报错No matching constructor found in class 'People'
     */
    public People() {

    }


    public People(int id, String name) {
        this.id = id;
        this.name = name;
    }

    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    @Override
    public String toString() {
        return "People [id=" + id + ", name=" + name + "]";
    }
}

　　　　　　3.2.2 在 applicationContext.xml 中

　　　　

<?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">

    <!--&lt;!&ndash; 使用无参构造器注入对象&ndash;&gt;
    <bean id="peo" class="com.bjsxt.pojo.People" />

    &lt;!&ndash;使用有参构造器注入对象 需要set方法和有参构造器支持&ndash;&gt;
    <bean id="peo2" class="com.bjsxt.pojo.People">
        <constructor-arg index="0" value="1"></constructor-arg>
        <constructor-arg index="1" value="zhangsan"></constructor-arg>
    </bean>-->

    <!--<bean id="factory"  class="com.bjsxt.pojo.PeopleFactory"></bean>-->

    <!--<bean id="peo3" factory-bean="factory" factory-method="newInstance"></bean>-->

    <!--静态工厂注入-->
    <bean id="peo4" class="com.bjsxt.pojo.PeopleFactory1" factory-method="newInstance" />

</beans>

　　　　　　3.2.3 测试类

package com.bjsxt.test;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.bjsxt.pojo.People;
import com.bjsxt.pojo.PeopleFactory;

public class Test {
    public static void main(String[] args) {

        ApplicationContext ac = new ClassPathXmlApplicationContext("applicationContext.xml");

//        People peo = ac.getBean("peo",People.class);
//        System.out.println(peo);
//
//        People peo2 = ac.getBean("peo2",People.class);
//        System.out.println(peo2);

//        People peo3 = ac.getBean("peo3",People.class);
//        System.out.println(peo3);

        People peo4 = ac.getBean("peo4",People.class);
        System.out.println(peo4);

    }
}

　　　　　　3.2.4运行结果

二月 27, 2019 11:16:54 下午 org.springframework.context.support.ClassPathXmlApplicationContext prepareRefresh
信息: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@179d3b25: startup date [Wed Feb 27 23:16:54 CST 2019]; root of context hierarchy
二月 27, 2019 11:16:55 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [applicationContext.xml]
People [id=1, name=测试]