spring bean 基于xml的4中初始化方法

本例主要介绍基于xml文件配置的4中初始化方法
1、使用property配置Bean
2、使用P标签简化配置Bean
3、使用构造函数初始化Bean
4、使用基础来初始化Bean

applicationContext.xml

<?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"
    xmlns:util="http://www.springframework.org/schema/util"
    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.3.xsd
    http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-4.3.xsd">

    <!-- 1. 使用property初始化Bean属性 -->
    <bean id="user1" class="cn.com.infcn.bean.User">
        <property name="userName" value="lisi" />
        <property name="age">
            <value>20</value>
        </property>

        <property name="cars">
            <!-- 使用 list 元素来装配集合属性 -->
            <list>
                <ref bean="audiCar" />
                <ref bean="bmwCar" />
            </list>
        </property>
    </bean>
    
    <!-- 使用util标签：声明集合类型的 bean -->
    <util:list id="cars">
        <ref bean="audiCar" />
        <ref bean="bmwCar" />
    </util:list>

    <!-- 2. 使用P标签简化bean配置 -->
    <bean id="user2" class="cn.com.infcn.bean.User" p:userName="zhangsan"
        p:age="1" p:cars-ref="cars"></bean>


    <!-- 3. 使用构造函数进行初始化bean -->
    <bean id="user3" class="cn.com.infcn.bean.User">
        <constructor-arg>
            <value>wangwu</value>
        </constructor-arg>
        <constructor-arg value="5"></constructor-arg>
    </bean>
    
    <!-- 4. bean 的配置能够继承吗 ? 使用 parent 来完成继承 --> 
    <bean id="user4" parent="user3" p:cars-ref="cars"></bean>

    
    <bean id="audiCar" class="cn.com.infcn.bean.Car" p:brand="audi"></bean>
    <bean id="bmwCar" class="cn.com.infcn.bean.Car" p:brand="bmw"></bean>
</beans>

Car.java

package cn.com.infcn.bean;

/**
 * @author jijs
 */
public class Car {
    private String brand;
    public String getBrand() {
        return brand;
    }
    public void setBrand(String brand) {
        this.brand = brand;
    }
    @Override
    public String toString() {
        return brand;
    }
}

User.java

package cn.com.infcn.bean;
import java.util.List;

/**
 * @author jijs
 */
public class User {
    private String userName;
    private int age;
    private List<Car> cars;

    public User() {
    }
    public User(String userName, int age) {
        this.userName = userName;
        this.age = age;
    }
    public String getUserName() {
        return userName;
    }
    public void setUserName(String userName) {
        this.userName = userName;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public List<Car> getCars() {
        return cars;
    }
    public void setCars(List<Car> cars) {
        this.cars = cars;
    }
    @Override
    public String toString() {
        return "User [userName=" + userName + ", age=" + age + ", cars=" + cars
                + "]";
    }
}

BeanInstantiation.java

package cn.com.infcn.springdemo;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import cn.com.infcn.bean.User;

/**
 * @author jijs
 */
public class BeanInstantiation {
    public static void main(String[] args) {
        ApplicationContext ac = new ClassPathXmlApplicationContext("applicationContext.xml");
        // 1、使用property配置Bean
        printUser(ac, "user1");
        // 2、使用P标签简化配置Bean
        printUser(ac, "user2");
        // 3、使用使用构造初始化Bean
        printUser(ac, "user3");
        // 4、使用基础来初始化Bean
        printUser(ac, "user4");
    }

    private static void printUser(ApplicationContext ac, String beanName) {
        User user = User.class.cast(ac.getBean(beanName));
        System.out.println(user);
    }
}

输出结果

User [userName=lisi, age=20, cars=[audi, bmw]]
User [userName=zhangsan, age=1, cars=[audi, bmw]]
User [userName=wangwu, age=5, cars=null]
User [userName=wangwu, age=5, cars=[audi, bmw]]

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