Spring（4）-Spring EL_spring的el-优快云博客

本文链接：https://blog.youkuaiyun.com/weixin_44581342/article/details/108024788

1.简要说明

Spring开发中经常涉及调用各种资源的情况，包含普通文件、网址、配置文件、系统环境
变量等，我们可以使用Spring 的表达式语言实现资源的注入。
Spring主要在注解@Value的参数中使用表达式。
本节演示实现以下几种情况:
(1)注入普通字符:
(2)注入操作系统属性;
(3)注入表达式运算结果;
(4)注入其他Bean的属性;
(5)注入文件内容;
(6)注入网址内容;
(7)注入属性文件。

2.导入相关依赖

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.lglg</groupId>
    <artifactId>spring-demo01</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>5.2.3.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-aop</artifactId>
            <version>5.2.3.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.aspectj</groupId>
            <artifactId>aspectjrt</artifactId>
            <version>1.9.2</version>
        </dependency>
        <dependency>
            <groupId>org.aspectj</groupId>
            <artifactId>aspectjweaver</artifactId>
            <version>1.9.2</version>
        </dependency>
        <dependency>
            <groupId>commons-io</groupId>
            <artifactId>commons-io</artifactId>
            <version>2.5</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.7.0</version>
                <configuration>
                    <source>${java.version}</source>
                    <target>${java.version}</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

3.编写两个测试文件

在这里插入图片描述

4.编写所需要的测试类

package com.lglg.springdemo01;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Service;

/**
 * Date:2020/8/15
 * 演示其他类注入该类的某些属性
 * @author:lg
 */

@Service
public class DemoService {

    @Value("其他类的属性")
    private String another;

    public String getAnother() {
        return another;
    }

    public void setAnother(String another) {
        this.another = another;
    }
}

5.编写各种资源使用el表达式

package com.lglg.config;

import org.apache.commons.io.IOUtils;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.PropertySource;
import org.springframework.context.support.PropertySourcesPlaceholderConfigurer;
import org.springframework.core.env.Environment;
import org.springframework.core.io.Resource;

import java.io.IOException;


/**
 * Date:2020/8/15
 *
 * @author:lg
 */
@Configuration
@ComponentScan("com.lglg")
@PropertySource("classpath:com/lg/el/test.properties")
public class ElConfig {

    @Value("lg i love you")
    private String normal;

    @Value("#{systemProperties['os.name']}")
    private String osName;

    @Value("#{T(java.lang.Math).random()*100.0}")
    private double randomNumber;

    @Value("#{demoService.another}")
    private String another;

    @Value("classpath:com/lg/el/test.txt")
    private Resource testFile;

    @Value("http://www.baidu.com")
    private Resource testUrl;

    @Value("${book.name}")
    private String bookName;

    @Autowired
    private Environment environment;

    @Bean
    public static PropertySourcesPlaceholderConfigurer propertySourcesPlaceholderConfigurer(){
        return new PropertySourcesPlaceholderConfigurer();
    }


    public void outputResource() throws IOException {
        System.out.println(normal);
        System.out.println(osName);
        System.out.println(randomNumber);
        System.out.println(IOUtils.toString(testFile.getInputStream()));

        System.out.println(IOUtils.toString(testUrl.getInputStream()));
        System.out.println(bookName);
        System.out.println(environment.getProperty("book.author"));
    }
}

6. 编写配置类

package com.lglg.config;

import com.lglg.springdemo01.FunctionService;
import com.lglg.springdemo01.UserFunctionService;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.EnableAspectJAutoProxy;

/**
 * Date:2020/8/9
 *
 * @author:lg
 */
@Configuration
@ComponentScan("com.lglg")// 扫面相应的包路径
@EnableAspectJAutoProxy //  注解开启Spring对AspectJ代理的支持
public class LgConfig {

//    @Bean// 通过该注解将该方法上的bean注入到Spring容器中
//    public FunctionService functionService(){
//        return new FunctionService();
//    }
//
//    @Bean
//    public UserFunctionService userFunctionService(){
//        return new UserFunctionService();
//    }
}

7. 编写测试类

package com.lglg.demoTest;

import com.lglg.config.ElConfig;
import com.lglg.config.LgConfig;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

import java.io.IOException;

/**
 * Date:2020/8/15
 *
 * @author:lg
 */
public class Demo04 {
    public static void main(String[] args) throws IOException {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(LgConfig.class);
        ElConfig elConfig = context.getBean(ElConfig.class);
        elConfig.outputResource();
        context.close();
    }
}