springEL

Spring

发布日期: 2021-07-28

为了更加灵活,Spring 还提供了表达式语言Spring EL 。通过Spring EL 可以拥有更为强大的运算规则来更好地装配Bean。

SpringEL表达式

Spring表达式语言（简称SpEL）是一个支持查询和操作运行时对象导航图功能的强大的表达式语言。不直接依赖于Spring,可独立使用。底层实现：接口ExpressionParser负责解析表达式字符串。

XML中使用

相应的实体定义

package com.rrc.entity;

import lombok.Data;

@Data
public class Customer {
    private String name;

    private String telephone;
}

package com.rrc.config;

import com.rrc.entity.Customer;
import lombok.Getter;
import lombok.Setter;

public class ConsumerComponent {
    @Getter
    @Setter
    private Customer customer;

    @Getter
    @Setter
    private String custName;

    @Getter
    @Setter
    private String telephone;
}

XML配置，在resources目录下新建spring-other.xml。

<?xml version="1.0" encoding="UTF-8"?>
<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.xsd">

    <bean id="customer" class="com.rrc.entity.Customer">
        <property name="name" value="张三"/>
        <property name="telephone" value="13666666666"/>
    </bean>

    <bean id="customerDao" class="com.rrc.config.ConsumerComponent">
        <property name="customer" value="#{customer}"></property>
        <property name="custName" value="#{customer.name}"></property>
        <property name="telephone" value="#{customer.telephone}"></property>
    </bean>
</beans>

我们在Application中打印ConsumerComponent类下三个属性的值

package com.rrc;

import com.rrc.config.ConsumerComponent;
import lombok.extern.slf4j.Slf4j;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.ImportResource;

@Slf4j
@SpringBootApplication
@ImportResource(locations = "classpath:spring-other.xml")
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
        ApplicationContext ctx
                = new AnnotationConfigApplicationContext(Application.class);

        ConsumerComponent consumerComponent = ctx.getBean(ConsumerComponent.class);
        log.info("consumerComponent custName {}", consumerComponent.getCustName());
        log.info("consumerComponent telephone {}", consumerComponent.getTelephone());
        log.info("consumerComponent customer {}", consumerComponent.getCustomer());

    }
}

2021-07-29 01:02:09.045 [main] INFO  com.rrc.Application 21 main - consumerComponent custName 张三
2021-07-29 01:02:09.047 [main] INFO  com.rrc.Application 22 main - consumerComponent telephone 13666666666
2021-07-29 01:02:09.047 [main] INFO  com.rrc.Application 23 main - consumerComponent customer Customer(name=张三, telephone=13666666666)

JAVA中使用

我们把在XML中的customerDao的配置从XML移动到JAVA文件中，相应的修改如下。启动项目之后依旧可以打印出相关的信息。

package com.rrc.config;


import com.rrc.entity.Customer;
import lombok.Data;
import lombok.Getter;
import lombok.Setter;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

@Component
@Data
public class ConsumerComponent {
    @Value("#{customer}")
    private Customer customer;

    @Value("#{customer.name}")
    private String custName;

    @Value("#{customer.telephone}")
    private String telephone;
}

EL使用场景

方法：EL可以调用另一个对象的方法或者属性

@Value("#{originBean.getELvalue()}")
private String telephone;



package com.rrc.config;
import org.springframework.stereotype.Component;
@Component
public class OriginBean {

    public String getELvalue() {
        return "EL METHOD";
    }
}

构造：EL可以调用new关键字，实现构造方法调用，实例化出对象来

@Value(“#{new int[]{1,2,3}}”)

@Value(“#{new 包名.类名()}”)

package com.rrc.config;


import com.rrc.entity.School;
import lombok.Data;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

@Component
@Data
public class ConsumerComponent {

    @Value("#{originBean.getELvalue()}")
    private String telephone;

    @Value("#{new int[]{1, 2, 3}}")
    private int[] intArray;

    @Value("#{new com.rrc.entity.School()}")
    private School school;
}