Spring入门第十课

Posted 2020-09-19 alittlecomputer

Spring表达式语言：SpEL

Spring表达式语言（简称SpEL）是一个支持运行时查询和操作对象图的强大的表达式语言。

语法类似于EL：SpEL使用#{...}作为定界符，所有在大括号中的字符都将被认为是SpEL

SpEL为bean的属性进行动态复制提供了便利。

通过SpEL可以实现：

-通过bean的id对bean进行引用

-调用方法以及引用对象中的属性

-计算表达式的值

-正则表达式的匹配

下面看如何使用

package logan.spring.study.spel;

public class Car {
    
    private String brand;
    private int price;
    
    private double tyrePerimeter;
    
    public String getBrand() {
        return brand;
    }
    public void setBrand(String brand) {
        this.brand = brand;
    }
    public int getPrice() {
        return price;
    }
    public void setPrice(int price) {
        this.price = price;
    }
    public double getTyrePerimeter() {
        return tyrePerimeter;
    }
    public void setTyrePerimeter(double tyrePerimeter) {
        this.tyrePerimeter = tyrePerimeter;
    }
    @Override
    public String toString() {
        return "Car [brand=" + brand + ", price=" + price + ", tyrePerimeter=" + tyrePerimeter + "]";
    }
}

package logan.spring.study.spel;

public class Address {
    
    private String city;
    
    private String street;

    public String getCity() {
        return city;
    }

    public void setCity(String city) {
        this.city = city;
    }

    public String getStreet() {
        return street;
    }

    public void setStreet(String street) {
        this.street = street;
    }

    @Override
    public String toString() {
        return "Address [city=" + city + ", street=" + street + "]";
    }
    
    

}

package logan.spring.study.spel;

public class Person {
    
    private String name;
    
    
    
    private Car car;
    
    //引用 address bean 的city属性
    private String city;
    //根据car的price确定info:car的price >=300000位金领，否则为白领
    private String info;

    public String getName() {
        return name;
    }

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

    public Car getCar() {
        return car;
    }

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

    public String getCity() {
        return city;
    }

    public void setCity(String city) {
        this.city = city;
    }

    public String getInfo() {
        return info;
    }

    public void setInfo(String info) {
        this.info = info;
    }

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

    
}

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="address" class="logan.spring.study.spel.Address">
        <!-- 使用spel为属性赋一个字面值 -->
        <property name="city" value="#{‘BeiJing‘}"></property>
        <property name="street" value="WuDaoKou"></property>
    </bean>
    
    <bean id="car" class="logan.spring.study.spel.Car">
        <property name="brand" value="Audi"></property>
        <property name="price" value="500000"></property>
        <!-- 使用SPEL使用类的静态属性 -->
        <property name="tyrePerimeter" value="#{T(java.lang.Math).PI * 80}"></property>
    </bean>
    
    <bean id="person" class="logan.spring.study.spel.Person">
        <property name="car" value="#{car}"></property>
        <property name="city" value="#{address.city}"></property>
        <property name="info" value="#{car.price > 30 ? ‘金领‘:‘白领‘}"></property>
        <property name="name" value="Tom"></property>
    </bean>


</beans>

package logan.spring.study.spel;

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

public class Main {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        
        ApplicationContext ctx = new ClassPathXmlApplicationContext("beans-spel.xml");
        Address address = (Address) ctx.getBean("address");
        System.out.println(address);
        
        Car car = (Car) ctx.getBean("car");
        
        System.out.println(car);
        
        Person person = (Person) ctx.getBean("person");
        System.out.println(person);

    }

}

下面是输出结果

五月 21, 2017 10:01:50 上午 org.springframework.context.support.ClassPathXmlApplicationContext prepareRefresh
信息: Refreshing org[email protected]7aec35a: startup date [Sun May 21 10:01:50 CST 2017]; root of context hierarchy
五月 21, 2017 10:01:50 上午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [beans-spel.xml]
Address [city=BeiJing, street=WuDaoKou]
Car [brand=Audi, price=500000, tyrePerimeter=251.32741228718345]
Person [name=Tom, car=Car [brand=Audi, price=500000, tyrePerimeter=251.32741228718345], city=BeiJing, info=金领]