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
org.springframework
spring-core
3.2.4.RELEASE
org.springframework
spring-context
3.2.4.RELEASE
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:
packagecom.lei.demo.el;
public classItem {
privateString name;
private inttotal;
//getter and setter...
}
Customer.java如下:
packagecom.lei.demo.el;
public classCustomer {
privateItem item;
privateString itemName;
@Override
publicString 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
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:
packagecom.lei.demo.el;
importorg.springframework.beans.factory.annotation.Value;
importorg.springframework.stereotype.Component;
@Component("itemBean")
public classItem {
@Value("itemA")//直接注入String
privateString name;
@Value("10")//直接注入integer
private inttotal;
//getter and setter...
}
Customer.java如下:
packagecom.lei.demo.el;
importorg.springframework.beans.factory.annotation.Value;
importorg.springframework.stereotype.Component;
@Component("customerBean")
public classCustomer {
@Value("#{itemBean}")
privateItem item;
@Value("#{itemBean.name}")
privateString itemName;
//getter and setter...
}
Xml中配置组件自动扫描
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:
packagecom.lei.demo.el;
importorg.springframework.context.ApplicationContext;
importorg.springframework.context.support.ClassPathXmlApplicationContext;
public classApp {
public static voidmain(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:
packagecom.lei.demo.el;
importorg.springframework.beans.factory.annotation.Value;
importorg.springframework.stereotype.Component;
@Component("customerBean")
public classCustomer {
@Value("#{'lei'.toUpperCase()}")
privateString name;
@Value("#{priceBean.getSpecialPrice()}")
private doubleamount;
//getter and setter...省略
@Override
publicString toString() {
return "Customer [name=" + name + ", amount=" + amount + "]";
}
}
Price.java如下:
packagecom.lei.demo.el;
importorg.springframework.stereotype.Component;
@Component("priceBean")
public classPrice {
public doublegetSpecialPrice() {
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
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 (, 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
packagecom.lei.demo.el;
importorg.springframework.beans.factory.annotation.Value;
importorg.springframework.stereotype.Component;
@Component("numberBean")
public classNumber {
@Value("999")
private intno;
public intgetNo() {
returnno;
}
public void setNo(intno) {
this.no =no;
}
}
Customer.java如下
packagecom.lei.demo.el;
importorg.springframework.beans.factory.annotation.Value;
importorg.springframework.stereotype.Component;
@Component("customerBean")
public classCustomer {
//Relational operators
@Value("#{1 == 1}") //true
private booleantestEqual;
@Value("#{1 != 1}") //false
private booleantestNotEqual;
@Value("#{1 < 1}") //false
private booleantestLessThan;
@Value("#{1 <= 1}") //true
private booleantestLessThanOrEqual;
@Value("#{1 > 1}") //false
private booleantestGreaterThan;
@Value("#{1 >= 1}") //true
private booleantestGreaterThanOrEqual;
//Logical operators , numberBean.no == 999
@Value("#{numberBean.no == 999 and numberBean.no < 900}") //false
private booleantestAnd;
@Value("#{numberBean.no == 999 or numberBean.no < 900}") //true
private booleantestOr;
@Value("#{!(numberBean.no == 999)}") //false
private booleantestNot;
//Mathematical operators
@Value("#{1 + 1}") //2.0
private doubletestAdd;
@Value("#{'1' + '@' + '1'}") //1@1
privateString testAddString;
@Value("#{1 - 1}") //0.0
private doubletestSubtraction;
@Value("#{1 * 1}") //1.0
private doubletestMultiplication;
@Value("#{10 / 2}") //5.0
private doubletestDivision;
@Value("#{10 % 10}") //0.0
private doubletestModulus ;
@Value("#{2 ^ 2}") //4.0
private doubletestExponentialPower;
@Override
publicString 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“
例如,“
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:
packagecom.lei.demo.el;
importorg.springframework.beans.factory.annotation.Value;
importorg.springframework.stereotype.Component;
@Component("itemBean")
public classItem {
@Value("99")
private intqtyOnHand;
public intgetQtyOnHand() {
returnqtyOnHand;
}
public void setQtyOnHand(intqtyOnHand) {
this.qtyOnHand =qtyOnHand;
}
}
Customer.java如下:
packagecom.lei.demo.el;
importorg.springframework.beans.factory.annotation.Value;
importorg.springframework.stereotype.Component;
@Component("customerBean")
public classCustomer {
@Value("#{itemBean.qtyOnHand < 100 ? true : false}")
private booleanwarning;
public booleanisWarning() {
returnwarning;
}
public void setWarning(booleanwarning) {
this.warning =warning;
}
@Override
publicString 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“
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']}")
privateString 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:
packagecom.lei.demo.el;
importjava.util.ArrayList;
importjava.util.HashMap;
importjava.util.List;
importjava.util.Map;
importorg.springframework.stereotype.Component;
@Component("testBean")
public classTest {
private Mapmap;
private Listlist;
publicTest() {
map = new HashMap();
map.put("MapA", "This is A");
map.put("MapB", "This is B");
map.put("MapC", "This is C");
list = new ArrayList();
list.add("List0");
list.add("List1");
list.add("List2");
}
public MapgetMap() {
returnmap;
}
public void setMap(Mapmap) {
this.map =map;
}
public ListgetList() {
returnlist;
}
public void setList(Listlist) {
this.list =list;
}
}
然后,用SpEL取值,Customer.java如下
packagecom.lei.demo.el;
importorg.springframework.beans.factory.annotation.Value;
importorg.springframework.stereotype.Component;
@Component("customerBean")
public classCustomer {
@Value("#{testBean.map['MapA']}")
privateString mapA;
@Value("#{testBean.list[0]}")
privateString list;
publicString getMapA() {
returnmapA;
}
public voidsetMapA(String mapA) {
this.mapA =mapA;
}
publicString getList() {
returnlist;
}
public voidsetList(String list) {
this.list =list;
}
@Override
publicString 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: