•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,所有在大框号中的字符都将被认为是 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
字面量的表示
–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'}"/>
<property name='name' value='#{"Chuck"}'/>
–Boolean
<property name="enabled" value="#{false}"/>
引用其他对象
通过value属性和SpEL配置Bean之间的应用关系
<!--通过value属性和SpEL配置Bean之间的应用关系,相当于ref属性 -->
<property name="prefix" value="#{prefixGenerator}"></property>
引用其他对象的属性
<!--通过value属性和SpEL配置suffix属性值为另一个Bean的suffix属性值-->
<property name="suffix" value="#{sequenceGenerator2.suffix}"/>
调用其他方法,还可以链式操作
<!--通过value属性和SpEL配置suffix属性值为另一个Bean的方法的返回值-->
<property name="suffix" value="#{sequenceGenerator2.toString()}"/>
方法的连接
<!--方法的连接-->
<property name="suffix"
value="#{seqenceGenerator2.toString().toUpperCase()}"/>
SpEL支持的运算符号
•算数运算符:+, -, *, /, %, ^:
•加号还可以用作字符串连接:
•比较运算符: <, >, ==, <=, >=, lt, gt, eq, le, ge
•逻辑运算符号: and, or, not, |
•if-else 运算符:?: (ternary), ?: (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,它将返回一个 Class Object,然后再调用相应的方法或属性:
举个例子
新建一个包,名为com.yorkmass.spring.beans.spel
新建3个类:Address、Car、Person类,一个主类Main
Address类:
package com.yorkmass.spring.beans.spel;
public class Address {
private String street;
private String city;
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类:
package com.yorkmass.spring.beans.spel;
public class Car {
private String brand;
private double price;
private double tyrePerimeter;//轮胎的周长
public double getTyrePerimeter() {
return tyrePerimeter;
}
public void setTyrePerimeter(double tyrePerimeter) {
this.tyrePerimeter = tyrePerimeter;
}
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;
}
@Override
public String toString() {
return "Car [brand=" + brand + ", price=" + price + ", tyrePerimeter=" + tyrePerimeter + "]";
}
public Car(){
System.out.println("Car's constructor");
}
}
Person类:
package com.yorkmass.spring.beans.spel;
public class Person {
private String name;
private Car car;
private String city;
//引用address bean 的city属性
private String info;
//根据car的price确定info:car的price>=300000:金领
//否则为:白领
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 + "]";
}
}
新建xml配置文件,命名为:beans-spel.xml
bean-spel.xml代码:
<?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="com.yorkmass.spring.beans.spel.Address">
<property name="city" value="beijing"></property>
<property name="street" value="wudaokou"></property>
</bean>
<bean id="car" class="com.yorkmass.spring.beans.spel.Car">
<property name="brand" value="audi"></property>
<property name="price" value="500000"></property>
<!-- 使用SpEL引用类的静态属性 -->
<property name="tyrePerimeter" value="#{T(java.lang.Math).PI*80}"></property>
</bean>
<bean id="person" class="com.yorkmass.spring.beans.spel.Person">
<!-- 使用SpEL来引用其他的bean -->
<property name="car" value="#{car}"></property>
<!-- 使用SpEL来引用其他的bean的属性 -->
<property name="city" value="#{address.city}"></property>
<!-- 在SpEL使用运算符 ,动态赋值,根据收入情况确定info是金领白领-->
<property name="info" value="#{car.price>300000?'金领':'白领'}"></property>
<property name="name" value="#{'Tom'}"></property>
</bean>
</beans>
Main类:
package com.yorkmass.spring.beans.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);
}
}
程序输出结果:
一月 16, 2019 4:41:22 下午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
信息: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@176fe71: startup date [Wed Jan 16 16:41:22 CST 2019]; root of context hierarchy
一月 16, 2019 4:41:22 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [beans-spel.xml]
Car's constructor
Address [city=beijing, street=wudaokou]
Car [brand=audi, price=500000.0, tyrePerimeter=251.32741228718345]
Person [name=Tom, car=Car [brand=audi, price=500000.0, tyrePerimeter=251.32741228718345], city=beijing, info=金领]