Spring SpEL表达式语言

Spring SpEL表达式语言

一、说在前面

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：

（1）通过 bean 的 id 对 bean 进行引用；

（2）调用方法以及引用对象中的属性；

（3）计算表达式的值；

（4）正则表达式的匹配。

二、举例说明

1、Address、Car和Person类

Address类：

package com.at.beans.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 + "]";
}

}

Car类

package com.at.beans.spel;

public class Car {

private String brand;
private double price;
//轮胎周长
private double ltzhouchang;
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 getLtzhouchang() {
return ltzhouchang;
}
public void setLtzhouchang(double ltzhouchang) {
this.ltzhouchang = ltzhouchang;
}
@Override
public String toString() {
return "Car [brand=" + brand + ", price=" + price + ", ltzhouchang="
+ ltzhouchang + "]";
}
}

Person类

package com.at.beans.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属性来确定info：car的price>400000为金领，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 + "]";
}
}

2、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="com.at.beans.spel.Address">
<!-- 使用SpEL为属性赋一个字面值 -->
<property name="city" value="#{'BeiJing'}"></property>

<property name="street" value="huoying"></property>
</bean>

<bean id="car" class="com.at.beans.spel.Car">
<property name="brand" value="Audi"></property>
<property name="price" value="300000"></property>

<!-- 使用SpEL引用类的静态属性 -->
<property name="ltzhouchang" value="#{T(java.lang.Math).PI * 50}"></property>
</bean>

<bean id="person" class="com.at.beans.spel.Person">
<!-- 使用SpEL来应用其他的bean -->
<property name="car" value="#{car}"></property>

<!-- 使用SpEL来应用其他的bean的属性 -->
<property name="city" value="#{address.city}"></property>

<!-- 使用SpEL中使用运算符 -->
<property name="info" value="#{car.price > 400000 ? '金领':'白领'}"></property>

<property name="name" value="luoyepiaoxue2014"></property>
</bean>
</beans>

3、测试函数

package com.at.beans.spel;

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

public class TestSpel {

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);
}
}

4、测试结果

五月 24, 2017 9:40:45 下午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
信息: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@427a39ea: startup date [Wed May 24 21:40:45 CST 2017]; root of context hierarchy
五月 24, 2017 9:40:45 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [beans-spel.xml]
Address [city=BeiJing, street=huoying]
Car [brand=Audi, price=300000.0, ltzhouchang=157.07963267948966]
Person [name=luoyepiaoxue2014, car=Car [brand=Audi, price=300000.0, ltzhouchang=157.07963267948966], city=BeiJing, info=白领]

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