Spring3系列6 - Spring 表達式語言(Spring EL)

時間 2019-12-07

原文原文鏈接

Spring3系列6-Spring 表達式語言(Spring EL)

　　本篇講述了Spring Expression Language —— 即Spring3中功能豐富強大的表達式語言，簡稱SpEL。SpEL是相似於OGNL和JSF EL的表達式語言，可以在運行時構建複雜表達式，存取對象屬性、對象方法調用等。全部的SpEL都支持XML和Annotation兩種方式，格式：#{ SpEL expression }java

1、第一個Spring EL例子—— HelloWorld Demo

2、 Spring EL Method Invocation——SpEL 方法調用

3、 Spring EL Operators——SpEL 操做符

4、 Spring EL 三目操做符condition?true:false

5、 Spring EL 操做List、Map集合取值

1、第一個Spring EL例子—— HelloWorld Demo

這個例子將展現如何利用SpEL注入String、Integer、Bean到屬性中。spring

1. Spring El的依賴包express

首先在Maven的pom.xml中加入依賴包，這樣會自動下載SpEL的依賴。ide

文件：pom.xml函數

<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 Beanthis

接下來寫兩個簡單的Bean，稍後會用SpEL注入value到屬性中。spa

Item.java以下：code

package com.lei.demo.el;

public class Item {

    private String name;
    private int total;
    
    //getter and setter...
}

Customer.java以下：component

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——XMLxml

SpEL格式爲#{ SpEL expression }，xml配置見下。

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>

註解：

1. #{itemBean}——將itemBean注入到customerBean的item屬性中。

2. #{itemBean.name}——將itemBean 的name屬性，注入到customerBean的屬性itemName中。

4. Spring EL——Annotation

SpEL的Annotation版本。

注意：要在Annotation中使用SpEL，必需要經過annotation註冊組件。若是你在xml中註冊了bean和在java class中定義了@Value，@Value在運行時將失敗。

Item.java以下：

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以下：

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中配置組件自動掃描

<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定義EL。在這種狀況下，直接注入一個String和integer值到itemBean中，而後注入itemBean到customerBean中。

5. 輸出結果

App.java以下：

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);

    }

}

輸出結果以下：itemName=itemA item.total=10

2、 Spring EL Method Invocation——SpEL 方法調用

SpEL容許開發者用El運行方法函數，而且容許將方法返回值注入到屬性中。

1. Spring EL Method Invocation之Annotation

此段落演示用@Value註釋，完成SpEL方法調用。

Customer.java以下：

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以下：

package com.lei.demo.el;
 
import org.springframework.stereotype.Component;
 
@Component("priceBean")
public class Price {
 
    public double getSpecialPrice() {
        return new Double(99.99);
    }
 
}

輸出結果：Customer[name=LEI,amount=99.99]

上例中，如下語句調用toUpperCase()方法

@Value("#{'lei'.toUpperCase()}")
private String name;

上例中，如下語句調用priceBean中的getSpecialPrice()方法

@Value("#{priceBean.getSpecialPrice()}")
private double amount;

2. Spring EL Method Invocation之XML

在XMl中配置以下，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>

3、 Spring EL Operators——SpEL 操做符

　　Spring EL 支持大多數的數學操做符、邏輯操做符、關係操做符。

　　1.關係操做符

　　包括：等於 (==, eq)，不等於 (!=, ne)，小於 (<, lt),，小於等於(<= , le)，大於(>, gt)，大於等於 (>=, ge)

　　2.邏輯操做符

　　包括：and，or，and not(!)

　　3.數學操做符

　　包括：加 (+)，減 (-)，乘 (*)，除 (/)，取模 (%)，冪指數 (^)。

1. Spring EL Operators之Annotation

Numer.java以下

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以下

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 + "]";
    }
 
}

運行以下代碼：

Customer obj = (Customer) context.getBean("customerBean");
System.out.println(obj);

結果以下：

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

如下是等同的xml配置。

注意，相似小於號「<」，或者小於等於「<=」，在xml中是不直接支持的，必須用等同的文本表示方法表示，

例如，「<」用「lt」替換；「<=」用「le」替換，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>

4、 Spring EL 三目操做符condition?true:false

SpEL支持三目運算符，以此來實現條件語句。

1. Annotation

Item.java以下：

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以下：

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 + "]";
    }
 
}

輸出：Customer [warning=true]

2. XMl

Xml配置以下，注意：應該用「&lt；」代替小於號「<」

<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>

輸出：Customer [warning=true]

5、 Spring EL 操做List、Map集合取值

此段演示SpEL怎樣從List、Map集合中取值，簡單示例以下：

　　//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，建立一個HashMap和ArrayList，並初始化一些值。

Test.java以下：

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;
    }
 
}

而後，用SpEL取值，Customer.java以下

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 + "]";
    }
 
}

調用代碼以下：

Customer obj = (Customer) context.getBean("customerBean");
System.out.println(obj);

輸出結果：Customer [mapA=This is A, list=List0]

2. XML

Xml配置以下：

<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>