07 SpEL

SpEL:Spring表达式语言,是一个支持运行时查询和操作对象图的强大表达式语言

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被认为是SpEL

SpEL为Bean的属性进行动态赋值提供了便利

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

SpEL字面量(意义不大):

• 整数:<property name = "count" value="#{5}"/>
• 小数:<property name = "frequency" value="#{89.7}"/>
• 科学计数法:<property name = "capacity" value="#{1e4}"/>
• String可以使用单引号或者双引号作为字符串的定界符号:<property name = "name" value="#{'Chuck'}"/>或者:<property name = "name" value='#{"Chuck"}'/>
• Boolean:<property name="enabled" value="#{false}"/>

引用Bean、属性和方法

• 引用其他对象
• 引用其他对象的属性
• 调用其他方法,还可以链式操作

支持的运算符号

• 算数运算符:+,-,*,/,%,^
• 加号可拼接字符串
• 比较运算符:<,>,==,<=,>=,lt,gt,eg,le,ge
• 逻辑运算符:and,or,not
• if-else运算符:?:(tenmary),?:(Elvis)
• if-else的变体
• 正则表达式:matches
• 调用静态方法或静态属性:通过T()调用一个类的静态方法,他将返回一个Class Object,然后再调用相应的方法或属性

Address.java

package spel;/*
 * @Author Sheng WenZeng
 * @Date 2019/8/11 8:46
 * @Version 1.0
 */

/**
 * @author Sheng Wenzeng
 * @ClassName Address
 * @Description TODO
 * @Date 2019/8/11 8:46
 * @Version 1.0
 */
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 + '\'' +
                '}';
    }
}

Car.java

package spel;/*
 * @Author Sheng WenZeng
 * @Date 2019/8/11 8:44
 * @Version 1.0
 */

/**
 * @author Sheng Wenzeng
 * @ClassName Car
 * @Description TODO
 * @Date 2019/8/11 8:44
 * @Version 1.0
 */
public class Car {
    private double price;
    private String brand;
    private int typePerimeter;

    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 int getTypePerimeter() {
        return typePerimeter;
    }

    public void setTypePerimeter(int typePerimeter) {
        this.typePerimeter = typePerimeter;
    }

    @Override
    public String toString() {
        return "Car{" +
                "brand='" + brand + '\'' +
                ", price=" + price +
                ", typePerimeter=" + typePerimeter +
                '}';
    }
}

Person.java

package spel;/*
 * @Author Sheng WenZeng
 * @Date 2019/8/11 8:44
 * @Version 1.0
 */

/**
 * @author Sheng Wenzeng
 * @ClassName Person
 * @Description TODO
 * @Date 2019/8/11 8:44
 * @Version 1.0
 */
public class Person {
    private String name;
    private Car car;
    private String city;
    private String info;

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

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

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

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

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

Main.java

package spel;/*
 * @Author Sheng WenZeng
 * @Date 2019/8/11 8:49
 * @Version 1.0
 */

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

/**
 * @author Sheng Wenzeng
 * @ClassName Main
 * @Description TODO
 * @Date 2019/8/11 8:49
 * @Version 1.0
 */
public class Main {
    public static void main(String[] args) {
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("spel/spel.xml");
        Car car = (Car) applicationContext.getBean("car_1");
        System.out.println(car);

        Address address = (Address) applicationContext.getBean("address");
        System.out.println(address);

        Person person = (Person) applicationContext.getBean("person");
        System.out.println(person);
    }
}

spel.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"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
    <!--使用spel表达式引用类中的静态方法-->
    <bean id="car_1" class="spel.Car" p:brand="Audi" p:price="300000" p:typePerimeter="#{T(Math).PI*80}"/>
    <bean id="address" class="spel.Address" p:city="HeFei" p:street="ShuangDun"/>
    <!--引用其他Bean中的属性:address.city;  使用if-else语句:car_1.price>10000? '金领':'白领'-->
    <bean id="person" class="spel.Person" p:car="#{car_1}" p:city="#{address.city}" p:name="Sheng"
          p:info="#{car_1.price>10000? '金领':'白领'}"/>
</beans>

运行结果:

Car{brand='Audi', price=300000.0, typePerimeter=251}
Address{city='HeFei', street='ShuangDun'}
Person{name='Sheng', car=Car{brand='Audi', price=300000.0, typePerimeter=251}, city='HeFei', info='金领'}

注意:引用其他Bean的属性时,需要被引用的Bean的类中有getter方法或者要引用的属性是public的