Sping Environment为Null的原因和解决方法

参考:https://github.com/spring-projects/spring-boot/issues/4711 这个issue提出不到20天给我搜出来了,还是相信google的强大

问题:
在spring的Configuration使用@Bean注册一个BeanFactoryPostProcessor Bean,发现使用@PropertySource,并注入@Resource private Environment env;发现env为null.我调试的大概一个过程,BeanFactoryPostProcessor Bean创建得比较早,创建它之前先创建它的依赖Bean Configuration,而这时发现创建的Configuration的env就是null了.深入的就没去追究了！

解决:
让此Configuration类实现EnvironmentAware接口,这个接口只有一个void setEnvironment(Environment environment);方法.这里的回调能得到Environment,问题解决!

修改前的代码:

package org.exam.config;

import org.exam.service.TestBeanFactoryPostProcessor;

import org.exam.service.UserServiceImpl;

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.core.env.Environment;

import javax.annotation.Resource;

@Configuration

@ComponentScan(basePackages = {"org.exam.service"})

@PropertySource("classpath:config.properties")

public class AppConfigOld {

    @Resource

    private Environment env;

    @Bean

    public UserServiceImpl userService(){

        System.out.println(env);

        return new UserServiceImpl();

    }

    /*

    未加入这个BeanFactoryPostProcessor一切都很正常,一旦加入这个@Bean,env就变为null

    @Bean

    public TestBeanFactoryPostProcessor testBeanFactoryPostProcessor(){

        System.out.println(env);

        return new TestBeanFactoryPostProcessor();

    }

    */

}

修改后的代码:

package org.exam.config;

import org.exam.service.TestBeanFactoryPostProcessor;

import org.exam.service.UserServiceImpl;

import org.springframework.context.EnvironmentAware;

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.core.env.Environment;

@Configuration

@ComponentScan(basePackages = {"org.exam.service"})

@PropertySource("classpath:config.properties")

public class AppConfig implements EnvironmentAware {

    private Environment env;

    @Override

    public void setEnvironment(Environment environment) {

        this.env=environment;

    }

    @Bean

    public UserServiceImpl userService(){

        System.out.println(env);

        return new UserServiceImpl();

    }

    @Bean

    public TestBeanFactoryPostProcessor testBeanFactoryPostProcessor(){

        System.out.println(env);

        return new TestBeanFactoryPostProcessor();

    }

}

值得一提的是:wilkinsona的回答是不建议使用ApplicationContext.虽然可以从ApplicationContext得到Environment,但是这样会在BeanFactoryPostProcessor的创建过程中会引起application context的所有依赖Bean都创建过早,这不是期望的一个结果.