spring学习笔记（8）——SpEL

阳光穿透心脏的1/2处 2022-08-08 06:13 168阅读 0赞

# 什么是SpEL #

spel就是spring的表达式语言，看下图（该图来自尚硅谷）  
![这里写图片描述][20150507110634922]

> SpEL很重要的一个功能就是能够实现 **动态赋值**

# 最简单的用法 #

![这里写图片描述][20150507110813717]

> 以上的用法其实没有什么意义，并不能体现出SpEL的强大

# SpEL使用 #

先写三个实体类

package com.zj.spel;
    
    public class Address { 
    
        private String province;
        private String city;
    
        public String getProvince() {
            return province;
        }
        public void setProvince(String province) {
            this.province = province;
        }
        public String getCity() {
            return city;
        }
        public void setCity(String city) {
            this.city = city;
        }
        @Override
        public String toString() {
            return "Address [province=" + province + ", city=" + city + "]";
        }
    
    }

package com.zj.spel;
    
    public class Car { 
    
        private String brand;
        private double price;
        private double tyrePerimeter;//轮胎周长
    
        public String getBrand() {
            return brand;
        }
        public void setBrand(String brand) {
            this.brand = brand;
        }
        public double getPrice() {
            return price;
        }
        public void setPrice(double 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 com.zj.spel;
    
    public class Person { 
    
        private String name;
        private Car car;
        //引用Address的city属性
        private String city;
        //根据car的价格：价格>300000，有钱人；价格<300000：普通人
        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 + "]";
        }
    
    }

配置文件中使用spel

<?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:context="http://www.springframework.org/schema/context" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.0.xsd">
    
        
        <bean id="address" class="com.zj.spel.Address">
            <property name="province" value="#{'福建'}"></property>
            <property name="city" value="#{'福州'}"></property>
        </bean>
        
        <bean id="car" class="com.zj.spel.Car">
            <property name="brand" value="bmw"></property>
            <property name="price" value="350000"></property>
            
            <property name="tyrePerimeter" value="#{T(java.lang.Math).PI * 80}"></property>
        </bean>
    
        <bean id="person" class="com.zj.spel.Person">
            <property name="name" value="tom"></property>
            
            <property name="car" value="#{car}"></property>
            
            <property name="city" value="#{address.city}"></property>
            
            <property name="info" value="#{car.price > 300000 ? '有钱人' : '普通人'}"></property>
        </bean>
    
    </beans>

写一个测试方法

public static void main(String[] args) {
    
            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);
    
        }

结果  
![这里写图片描述][20150507113226407]

# 用法总结 #

截图来自尚硅谷  
![这里写图片描述][20150507113133535]

![这里写图片描述][20150507113402020]

![这里写图片描述][20150507113232472]

![这里写图片描述][20150507113510644]

[20150507110634922]: /images/20220805/14d89a02190f44b698da6486f020b3a6.png
[20150507110813717]: /images/20220805/4832125ce2624801a4adb3b532f1a9ca.png
[20150507113226407]: /images/20220805/4dc1e772cdcb4fd093a6f62177e40f50.png
[20150507113133535]: /images/20220805/a1ac15c6f9f04b93a4b344eb9f00792d.png
[20150507113402020]: /images/20220805/de166025498e417a9dfbd8d1027f48d0.png
[20150507113232472]: /images/20220805/7b2ef9de2fa9486c87513ad3d2914ceb.png
[20150507113510644]: /images/20220805/86d32237b91f4c85bf2ae2209ebed531.png