概要
本篇讲述了Spring Expression Language —— 即Spring3中功能丰富强大的表达式语言，简称SpEL。SpEL是类似于OGNL和JSF EL的表达式语言，能够在运行时构建复杂表达式，存取对象属性、对象方法调用等。所有的SpEL都支持XML和Annotation两种方式，格式：#{ SpEL expression }
一、第一个Spring EL例子—— HelloWorld Demo
这个例子将展示如何利用SpEL注入String、Integer、Bean到属性中。
1.Spring El的依赖包
首先在Maven的pom.xml中加入依赖包，这样会自动下载SpEL的依赖。
文件：pom.xml
<dependencies>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
<version>3.2.4.RELEASE</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
<version>3.2.4.RELEASE</version>
</dependency>
</dependencies>
2.Spring Bean
接下来写两个简单的Bean，稍后会用SpEL注入value到属性中。
Item.java如下：
package com.lei.demo.el;
public class Item {
private String name;
private int total;
//getter and setter...
}
Customer.java如下：
package com.lei.demo.el;
public class Customer {
private Item item;
private String itemName;
@Override
public String toString() {
return "itemName=" +this.itemName+" "+"Item.total="+this.item.getTotal();
}
//getter and setter...
}
3. Spring EL——XML
SpEL格式为#{ SpEL expression }，xml配置见下。
文件：Spring-EL.xml
<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-3.0.xsd">
<bean id="itemBean" class="com.lei.demo.el.Item">
<property name="name" value="itemA" />
<property name="total" value="10" />
</bean>
<bean id="customerBean" class="com.lei.demo.el.Customer">
<property name="item" value="#{itemBean}" />
<property name="itemName" value="#{itemBean.name}" />
</bean>
</beans>
注解：
1. #{itemBean}——将itemBean注入到customerBean的item属性中。
2. #{itemBean.name}——将itemBean 的name属性，注入到customerBean的属性itemName中。
4.Spring EL——Annotation
SpEL的Annotation版本。
注意：要在Annotation中使用SpEL，必须要通过annotation注册组件。如果你在xml中注册了bean和在java class中定义了@Value，@Value在运行时将失败。
Item.java如下：
package com.lei.demo.el;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;
@Component("itemBean")
public class Item {
@Value("itemA")//直接注入String
private String name;
@Value("10")//直接注入integer
private int total;
//getter and setter...
}
Customer.java如下：
package com.lei.demo.el;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;
@Component("customerBean")
public class Customer {
@Value("#{itemBean}")
private Item item;
@Value("#{itemBean.name}")
private String itemName;
//getter and setter...
}
Xml中配置组件自动扫描
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.0.xsd">
<context:component-scan base-package="com.lei.demo.el" />
</beans>
在Annotation模式中，用@Value定义EL。在这种情况下，直接注入一个String和integer值到itemBean中，然后注入itemBean到customerBean中。
5. 输出结果
App.java如下：
package com.lei.demo.el;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class App {
public static void main(String[] args) {
ApplicationContext context = new ClassPathXmlApplicationContext("Spring-EL.xml");
Customer obj = (Customer) context.getBean("customerBean");
System.out.println(obj);
}
}
输出结果如下：itemName=itemA item.total=10
二、Spring EL Method Invocation——SpEL 方法调用
SpEL允许开发者用El运行方法函数，并且允许将方法返回值注入到属性中。
1.Spring EL Method Invocation之Annotation
此段落演示用@Value注释，完成SpEL方法调用。
Customer.java如下：
package com.lei.demo.el;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;
@Component("customerBean")
public class Customer {
@Value("#{'lei'.toUpperCase()}")
private String name;
@Value("#{priceBean.getSpecialPrice()}")
private double amount;
//getter and setter...省略
@Override
public String toString() {
return "Customer [name=" + name + ", amount=" + amount + "]";
}
}
Price.java如下：
package com.lei.demo.el;
import org.springframework.stereotype.Component;
@Component("priceBean")
public class Price {
public double getSpecialPrice() {
return new Double(99.99);
}
}
输出结果：Customer[name=LEI,amount=99.99]
上例中，以下语句调用toUpperCase()方法
@Value("#{'lei'.toUpperCase()}")
private String name;
上例中，以下语句调用priceBean中的getSpecialPrice()方法
@Value("#{priceBean.getSpecialPrice()}")
private double amount;
2. Spring EL Method Invocation之XML
在XMl中配置如下，效果相同
<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-3.0.xsd">
<bean id="customerBean" class="com.leidemo.el.Customer">
<property name="name" value="#{'lei'.toUpperCase()}" />
<property name="amount" value="#{priceBean.getSpecialPrice()}" />
</bean>
<bean id="priceBean" class="com.lei.demo.el.Price" />
</beans>
三、Spring EL Operators——SpEL 操作符
Spring EL 支持大多数的数学操作符、逻辑操作符、关系操作符。
1.关系操作符
包括：等于 (==, eq)，不等于 (!=, ne)，小于 (<, lt),，小于等于(<= , le)，大于(>, gt)，大于等于 (>=, ge)
2.逻辑操作符
包括：and，or，and not(!)
3.数学操作符
包括：加 (+)，减 (-)，乘 (*)，除 (/)，取模 (%)，幂指数 (^)。
1. Spring EL Operators之Annotation
Numer.java如下
package com.lei.demo.el;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;
@Component("numberBean")
public class Number {
@Value("999")
private int no;
public int getNo() {
return no;
}
public void setNo(int no) {
this.no = no;
}
}
Customer.java如下
package com.lei.demo.el;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;
@Component("customerBean")
public class Customer {
//Relational operators
@Value("#{1 == 1}") //true
private boolean testEqual;
@Value("#{1 != 1}") //false
private boolean testNotEqual;
@Value("#{1 < 1}") //false
private boolean testLessThan;
@Value("#{1 <= 1}") //true
private boolean testLessThanOrEqual;
@Value("#{1 > 1}") //false
private boolean testGreaterThan;
@Value("#{1 >= 1}") //true
private boolean testGreaterThanOrEqual;
//Logical operators , numberBean.no == 999
@Value("#{numberBean.no == 999 and numberBean.no < 900}") //false
private boolean testAnd;
@Value("#{numberBean.no == 999 or numberBean.no < 900}") //true
private boolean testOr;
@Value("#{!(numberBean.no == 999)}") //false
private boolean testNot;
//Mathematical operators
@Value("#{1 + 1}") //2.0
private double testAdd;
@Value("#{'1' + '@' + '1'}") //1@1
private String testAddString;
@Value("#{1 - 1}") //0.0
private double testSubtraction;
@Value("#{1 * 1}") //1.0
private double testMultiplication;
@Value("#{10 / 2}") //5.0
private double testDivision;
@Value("#{10 % 10}") //0.0
private double testModulus ;
@Value("#{2 ^ 2}") //4.0
private double testExponentialPower;
@Override
public String toString() {
return "Customer [testEqual=" + testEqual + ", testNotEqual="
+ testNotEqual + ", testLessThan=" + testLessThan
+ ", testLessThanOrEqual=" + testLessThanOrEqual
+ ", testGreaterThan=" + testGreaterThan
+ ", testGreaterThanOrEqual=" + testGreaterThanOrEqual
+ ", testAnd=" + testAnd + ", testOr=" + testOr + ", testNot="
+ testNot + ", testAdd=" + testAdd + ", testAddString="
+ testAddString + ", testSubtraction=" + testSubtraction
+ ", testMultiplication=" + testMultiplication
+ ", testDivision=" + testDivision + ", testModulus="
+ testModulus + ", testExponentialPower="
+ testExponentialPower + "]";
}
}
运行如下代码：
Customer obj = (Customer) context.getBean("customerBean");
System.out.println(obj);
结果如下：
Customer [
testEqual=true,
testNotEqual=false,
testLessThan=false,
testLessThanOrEqual=true,
testGreaterThan=false,
testGreaterThanOrEqual=true,
testAnd=false,
testOr=true,
testNot=false,
testAdd=2.0,
testAddString=1@1,
testSubtraction=0.0,
testMultiplication=1.0,
testDivision=5.0,
testModulus=0.0,
testExponentialPower=4.0
]
2. Spring EL Operators之XML
以下是等同的xml配置。
注意，类似小于号“<”，或者小于等于“<=”，在xml中是不直接支持的，必须用等同的文本表示方法表示，
例如，“<”用“lt”替换；“<=”用“le”替换，等等。
<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-3.0.xsd">
<bean id="customerBean" class="com.lei.demo.el.Customer">
<property name="testEqual" value="#{1 == 1}" />
<property name="testNotEqual" value="#{1 != 1}" />
<property name="testLessThan" value="#{1 lt 1}" />
<property name="testLessThanOrEqual" value="#{1 le 1}" />
<property name="testGreaterThan" value="#{1 > 1}" />
<property name="testGreaterThanOrEqual" value="#{1 >= 1}" />
<property name="testAnd" value="#{numberBean.no == 999 and numberBean.no lt 900}" />
<property name="testOr" value="#{numberBean.no == 999 or numberBean.no lt 900}" />
<property name="testNot" value="#{!(numberBean.no == 999)}" />
<property name="testAdd" value="#{1 + 1}" />
<property name="testAddString" value="#{'1' + '@' + '1'}" />
<property name="testSubtraction" value="#{1 - 1}" />
<property name="testMultiplication" value="#{1 * 1}" />
<property name="testDivision" value="#{10 / 2}" />
<property name="testModulus" value="#{10 % 10}" />
<property name="testExponentialPower" value="#{2 ^ 2}" />
</bean>
<bean id="numberBean" class="com.lei.demo.el.Number">
<property name="no" value="999" />
</bean>
</beans>
四、Spring EL 三目操作符condition?true:false
SpEL支持三目运算符，以此来实现条件语句。
1. Annotation
Item.java如下：
package com.lei.demo.el;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;
@Component("itemBean")
public class Item {
@Value("99")
private int qtyOnHand;
public int getQtyOnHand() {
return qtyOnHand;
}
public void setQtyOnHand(int qtyOnHand) {
this.qtyOnHand = qtyOnHand;
}
}
Customer.java如下：
package com.lei.demo.el;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;
@Component("customerBean")
public class Customer {
@Value("#{itemBean.qtyOnHand < 100 ? true : false}")
private boolean warning;
public boolean isWarning() {
return warning;
}
public void setWarning(boolean warning) {
this.warning = warning;
}
@Override
public String toString() {
return "Customer [warning=" + warning + "]";
}
}
输出：Customer [warning=true]
2. XMl
Xml配置如下，注意：应该用“<；”代替小于号“<”
<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-3.0.xsd">
<bean id="customerBean" class="com.lei.demo.el.Customer">
<property name="warning"
value="#{itemBean.qtyOnHand < 100 ? true : false}" />
</bean>
<bean id="itemBean" class="com.lei.demo.el.Item">
<property name="qtyOnHand" value="99" />
</bean>
</beans>
输出：Customer [warning=true]
五、Spring EL 操作List、Map集合取值
此段演示SpEL怎样从List、Map集合中取值，简单示例如下：
//get map where key = 'MapA'
@Value("#{testBean.map['MapA']}")
private String mapA;
//get first value from list, list is 0-based.
@Value("#{testBean.list[0]}")
private String list;
1. Annotation
首先，创建一个HashMap和ArrayList，并初始化一些值。
Test.java如下：
package com.lei.demo.el;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import org.springframework.stereotype.Component;
@Component("testBean")
public class Test {
private Map<String, String> map;
private List<String> list;
public Test() {
map = new HashMap<String, String>();
map.put("MapA", "This is A");
map.put("MapB", "This is B");
map.put("MapC", "This is C");
list = new ArrayList<String>();
list.add("List0");
list.add("List1");
list.add("List2");
}
public Map<String, String> getMap() {
return map;
}
public void setMap(Map<String, String> map) {
this.map = map;
}
public List<String> getList() {
return list;
}
public void setList(List<String> list) {
this.list = list;
}
}
然后，用SpEL取值，Customer.java如下
package com.lei.demo.el;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;
@Component("customerBean")
public class Customer {
@Value("#{testBean.map['MapA']}")
private String mapA;
@Value("#{testBean.list[0]}")
private String list;
public String getMapA() {
return mapA;
}
public void setMapA(String mapA) {
this.mapA = mapA;
}
public String getList() {
return list;
}
public void setList(String list) {
this.list = list;
}
@Override
public String toString() {
return "Customer [mapA=" + mapA + ", list=" + list + "]";
}
}
调用代码如下：
Customer obj = (Customer) context.getBean("customerBean");
System.out.println(obj);
输出结果：Customer [mapA=This is A, list=List0]
2. XML
Xml配置如下：
<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-3.0.xsd">
<bean id="customerBean" class="com.lei.demo.el.Customer">
<property name="mapA" value="#{testBean.map['MapA']}" />
<property name="list" value="#{testBean.list[0]}" />
</bean>
<bean id="testBean" class="com.lei.demo.el.Test" />
</beans>
作者：逆舟
https://www.cnblogs.com/zy-jiayou/
本博客文章均为作者原创，转载请注明作者和原文链接。
https://www.cnblogs.com/zy-jiayou/
本博客文章均为作者原创，转载请注明作者和原文链接。
