Spring框架学习笔记——配置bean

Posted 2020-08-21 灼眼的健

1、属性注入

（1）根据setter方法属性注入，这里使用的是property标签。需要bean属性提供对应的setter方法，比如笔记（1）里的 HelloWorld使用的就是这种方法。

<!-- 根据setter方法属性注入 -->
<bean id="helloworld" class="com.broadtext.beans.Helloworld">
    <property name="name" value="Helloworld"></property>
</bean>

（2）根据构造器属性注入，这里使用的是constructor-arg标签。可以不提供setter方法，但是要提供对应的构造器，如果缺少构造器或者构造器里缺少属性就会报错。可以指定参数的位置(index)和类型(type)以区分参数。特殊字符可以使用<![CDATA[<Shanghai>]]>

<!-- 根据构造器属性注入，可以指定参数的位置和类型以区分参数 -->
<bean id="car" class="com.broadtext.beans.Car">
    <constructor-arg index="0" value="Audi"></constructor-arg>
    <constructor-arg value="Shanghai"></constructor-arg>
    <constructor-arg type="double" value="300000"></constructor-arg>
</bean>

<bean id="car2" class="com.broadtext.beans.Car">
    <constructor-arg value="BMW"></constructor-arg>
    <constructor-arg>
        <value><![CDATA[<Shanghai>]]></value>
    </constructor-arg>
    <constructor-arg type="int" value="240"></constructor-arg>
</bean>

2、通过ref属性建立bean之间的关系，这里在创建person bean的时候会将配置好的car2作为属性注入到person bean里，如果ref指向一个不存在的bean会报undefine错误。

<!-- ref属性建立bean之间的关系 -->
<bean id="person" class="com.broadtext.beans.Person">
    <property name="name" value="Tom"></property>
    <property name="age" value="24"></property>
    <property name="car" ref="car2"></property>
</bean>

3、配置内部bean

<!-- 内部bean不能被外部使用 -->
<bean id="person1" class="com.broadtext.beans.Person">
    <property name="name" value="Tom"></property>
    <property name="age" value="24"></property>
    <property name="car">
        <bean class="com.broadtext.beans.Car">
            <constructor-arg value="Ford"></constructor-arg>
            <constructor-arg value="Shanghai"></constructor-arg>
            <constructor-arg type="double" value="300000"></constructor-arg>
        </bean>
    </property>
</bean>

4、null值的注入

<!-- 测试null值和构造注入 -->
<bean id="person2" class="com.broadtext.beans.Person">
    <constructor-arg value="Jreey"></constructor-arg>
    <constructor-arg value="24"></constructor-arg>
    <constructor-arg><null></null></constructor-arg>
</bean>

5、为级联属性注入

<!-- 级联属性赋值 -->
<bean id="person3" class="com.broadtext.beans.Person">
    <constructor-arg value="Jreey"></constructor-arg>
    <constructor-arg value="24"></constructor-arg>
    <!-- 要先初始化才可以为级联属性赋值，否则会报null错误 -->
    <constructor-arg ref="car"></constructor-arg>
    <property name="car.maxSpeed" value="250"></property>
</bean>

6、Car.java、Person.java、Main.java

Car.java

package com.broadtext.beans;

public class Car {
    private String brand;
    private String corp;
    private double price;
    private int maxSpeed;

    public Car(String brand, String corp, double price) {
        super();
        this.brand = brand;
        this.corp = corp;
        this.price = price;
    }

    public Car(String brand, String corp, int maxSpeed) {
        super();
        this.brand = brand;
        this.corp = corp;
        this.maxSpeed = maxSpeed;
    }

    @Override
    public String toString() {
        return "Car [brand=" + brand + ", corp=" + corp + ", price=" + price + ", maxSpeed=" + maxSpeed + "]";
    }

    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }

    public String getCorp() {
        return corp;
    }

    public void setCorp(String corp) {
        this.corp = corp;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int maxSpeed) {
        this.maxSpeed = maxSpeed;
    }

}

Person.java

package com.broadtext.beans;

public class Person {
    private String name;
    private int age;
    private Car car;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public Car getCar() {
        return car;
    }

    public void setCar(Car car) {
        this.car = car;
    }

    @Override
    public String toString() {
        return "Person [name=" + name + ", age=" + age + ", car=" + car + "]";
    }

    public Person() {
    }

    public Person(String name, int age, Car car) {
        super();
        this.name = name;
        this.age = age;
        this.car = car;
    }

}

Main.java

package com.broadtext.beans;

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

public class Main {

    public static void main(String[] args) {

        //ApplicationContext IOC容器
        //ClassPathXmlApplicationContext IOC容器的实现类
        //走完这一步就会创建出XML里面配的bean
        ApplicationContext ctx = new ClassPathXmlApplicationContext("applicationContext.xml");

        //根据配置bean的id获取
        Helloworld helloworld = (Helloworld) ctx.getBean("helloworld");
        System.out.println(helloworld.getName());
        //根据配置bean的类型获取
        helloworld = ctx.getBean(Helloworld.class);
        System.out.println(helloworld.getName());

        //构造器属性注入
        Car car = (Car) ctx.getBean("car");
        System.out.println(car.toString());
        car = (Car) ctx.getBean("car2");
        System.out.println(car.toString());

        //ref
        Person person = (Person) ctx.getBean("person");
        System.out.println(person.toString());
        //内部bean
        person = (Person) ctx.getBean("person1");
        System.out.println(person.toString());
        person = (Person) ctx.getBean("person2");
        System.out.println(person.toString());
        person = (Person) ctx.getBean("person3");
        System.out.println(person.toString());

    }

}