Spring3系列6 - Spring 表达式语言(Spring EL)
Spring3系列6-Spring 表达式语言(Spring EL)
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
二、 Spring EL Method Invocation——SpEL 方法调用
三、 Spring EL Operators——SpEL 操作符
四、 Spring EL 三目操作符condition?true:false
五、 Spring EL 操作List、Map集合取值
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>