从头认识Spring-1.14 SpEl表达式（3）-SpEl表达式的两个坑：Bean的顺序与Bean的toString方法

这一章节我们来说一下SpEl表达式的坑，以及补充一下SpEl表达式操作类的方法与常量。

1.domain

厨师类：（新增一个朋友属性）

package com.raylee.my_new_spring.my_new_spring.ch01.topic_1_16;

public class Chief {

	private String name = "";

	private Oven oven;

	private Chief friend;

	public Chief getFriend() {
		return friend;
	}

	public void setFriend(Chief friend) {
		this.friend = friend;
	}

	public String getName() {
		return name;
	}

	public Oven getOven() {
		return oven;
	}

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

	public void setOven(Oven oven) {
		this.oven = oven;
	}

	public void userOven() {
		System.out.println(name + " use " + oven);
	}

}

package com.raylee.my_new_spring.my_new_spring.ch01.topic_1_16;

public class Oven {
	private String name = "";

	private double size = 0;

	public double getSize() {
		return size;
	}

	public void setSize(double size) {
		this.size = size;
	}

	@Override
	public String toString() {
		return name;
	}

	public String getName() {
		return name;
	}

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

}

package com.raylee.my_new_spring.my_new_spring.ch01.topic_1_16;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = {
		"/com/raylee/my_new_spring/my_new_spring/ch01/topic_1_16/ApplicationContext-test.xml" })
public class ChiefTest {

	@Autowired
	private ApplicationContext applicationContext;

	@Test
	public void testChief() {
		Chief jack = (Chief) applicationContext.getBean("jack");
		jack.userOven();
		Chief mike = (Chief) applicationContext.getBean("mike");
		mike.userOven();
		Chief rose = (Chief) applicationContext.getBean("rose");
		rose.userOven();
	}
}

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:context="http://www.springframework.org/schema/context" xmlns:p="http://www.springframework.org/schema/p"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:tx="http://www.springframework.org/schema/tx"
	xmlns:aop="http://www.springframework.org/schema/aop"
	xsi:schemaLocation="
        http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
		http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsd
		http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.1.xsd
		http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-3.1.xsd
		http://www.springframework.org/schema/data/jpa http://www.springframework.org/schema/data/jpa/spring-jpa-1.0.xsd
		http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd">

	<bean id="smallOven"
		class="com.raylee.my_new_spring.my_new_spring.ch01.topic_1_16.Oven"
		p:name="smallOven" p:size="#{T(java.lang.Math).PI}" />

	<bean id="mike"
		class="com.raylee.my_new_spring.my_new_spring.ch01.topic_1_16.Chief"
		p:name="mike">
		<property name="oven" ref="#{jack.oven}" />
		<property name="friend" ref="jack" />
	</bean>

	<bean id="jack"
		class="com.raylee.my_new_spring.my_new_spring.ch01.topic_1_16.Chief"
		p:name="jack">
		<property name="oven" ref="smallOven" />
		<property name="friend" ref="mike" />
	</bean>

	<bean id="rose"
		class="com.raylee.my_new_spring.my_new_spring.ch01.topic_1_16.Chief"
		p:name="rose">
		<property name="oven" ref="#{jack.getFriend().getOven()}" />
		<property name="friend" ref="jack" />
	</bean>
</beans>

（1）我们使用#{T(class).xxx}来控制类的方法与常量

（2）在执行的过程中一定要注意Bean前后属性，当上面的mike与jack互换位置的时候，就会抛异常，上面的是正确的

（3）在执行的过程中必须注意toString的问题，就像上面的#{jack.oven}和#{jack.getFriend().getOven()}其实就是先调用oven的toString方法，得到相应的名称，然后再放到配置文件去（我返回的名字跟id一致），然后再读取这个返回值的Bean在不在，如果不重写toString或者toString返回的字符串跟你Bean里面的id不匹配，直接抛异常

总结：这一章节通过一个例子来说明SpEl表达式的坑。

目录：http://blog.csdn.net/raylee2007/article/details/50611627 

我的github：https://github.com/raylee2015/my_new_spring

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