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“&lt；”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 &lt; 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>

 

 转载于：http://www.cnblogs.com/leiOOlei/p/3543222.html