Spring入门学习（SpEL表达式） 第八节

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Spring表达式语言

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
动态赋值提供了便利

1. 创建要使用的三个类：

   package com.fafa.spring.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 + "]";
   	}
   }
   

   package com.fafa.spring.beans.spel;
   
   public class Car {
   
   	private String brand;
   	private double price;
   	
   	// 轮胎的周长
   	private double 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;
   	}
   	
   	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 + "]";
   	}
   	
   	public Car(){
   		System.out.println("Car's constructor....");
   	}
   }
   

   package com.fafa.spring.beans.spel;
   
   public class Person {
   
   	private String name;
   
   	// 引用address bean的city属性
   	private String city;
   	
   	// 根据car的price确定info：car的price>=300000：金领，否则白领
   	private String info;
   
   	private Car car;
   
   	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 + ", city="
   				+ city + ", info=" + info + ", car=" + car + "]";
   	}
   }
   

2. 创建beans-spel.xml配置文件
   常用的字面量：整数,小数，科学计数法，String，Boolean

   <bean id="address" class="com.fafa.spring.beans.spel.Address">
   	<!-- 使用Spel为属性赋值一个字面值 -->
   	<property name="city" value="#{'BeiJing'}"></property>
   	<property name="street" value="WuDaoKou"></property>
   </bean>
   
   <bean id="car" class="com.fafa.spring.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="tyrePerimeter" value="#{T(java.lang.Math).PI * 80}"></property>
   </bean>
   
   <bean id="person" class="com.fafa.spring.beans.spel.Person">
   	<!-- 使用SpEL来引用其它的bean -->
   	<property name="car" value="#{car}"></property>
   	<!-- 使用SpEL来引用其它bean的属性 -->
   	<property name="city" value="#{address.city}"></property>
   	<!-- 在SpEL中使用运算符 -->
   	<property name="info" value="#{car.price > 300000 ? '金领' : '白领'}"></property>
   	<property name="name" value="Tom"></property>
   </bean>
   

   测试方法获取bean：

   @Test
   public void testSpel(){
   	ApplicationContext ctx = new ClassPathXmlApplicationContext("classpath*: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);
   }
   

   测试结果：

   Address [city=BeiJing, street=WuDaoKou]
   Car [brand=Audi, price=300000.0, tyrePerimeter=251.32741228718345]
   Person [name=Tom, city=BeiJing, info=白领, car=Car [brand=Audi, price=300000.0, tyrePerimeter=251.32741228718345]]