Java中Spring EL中如何读取系统环境变量呢?

1.如果el表达式中放入systemEnvironment 时
   则spring会自动读取系统环境变量
2.如果读取systemProperties中的属性
   则使用-D参数启动java,则可以读取所有属性 

Spring配置文件中访问这两个属性：

<?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="program1">
        <property name="logPath" value="#{systemProperties['APP.LOG_PATH']}"/>
    </bean>

    <bean id="program2">
        <property name="logPath" value="#{systemEnvironment['HOME']}"/>
    </bean>

</beans> 


package com.java265.example.spring.el;

public class Program {
    private String logPath;

    public Program() {
    }

    public String getLogPath() {
        return logPath;
    }

    public void setLogPath(String logPath) {
        this.logPath = logPath;
    }
}
最后，让我们创建一个简单的类来执行上面的Spring配置文件并查看代码结果。

package com.java265.example.spring.el;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class SpELEnvironment {
    public static void main(String[] args) {
        ApplicationContext context =
            new ClassPathXmlApplicationContext("spel-environment.xml");

        Program program1 = (Program) context.getBean("program1");
        System.out.println("program.getLogPath() = " + program1.getLogPath());

        Program program2 = (Program) context.getBean("program2");
        System.out.println("program.getLogPath() = " + program2.getLogPath());
    }
}
 
----运行以上代码，将输出以下信息-----

program.getLogPath() = /Users/test/tmp
program.getLogPath() = /Users/test