spring 获取bean的几种方式

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本文详细介绍了在Spring框架中获取ApplicationContext的多种方法，包括直接读取XML配置文件、继承Aware类、使用工具类等，适用于不同场景下对Spring上下文的灵活运用。

1.读取xml文件的方式，这种在初学入门的时候比较适用。

　　　　ApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:tt.xml");

　　　　ApplicationContext applicationContext = new FileSystemXmlApplicationContext("classpath:tt.xml");

2.继承spring的Aware类，覆盖方法实现获取上下文，从上下文中获取。

　　　　2.1.继承自抽象类ApplicationObjectSupport
　　　　说明：抽象类ApplicationObjectSupport提供getApplicationContext()方法，可以方便的获取到ApplicationContext。
　　　　Spring初始化时，会通过该抽象类的setApplicationContext(ApplicationContext context)方法将ApplicationContext 对象注入。

　　　　2.2：继承自抽象类WebApplicationObjectSupport
　　　　说明：类似上面方法，调用getWebApplicationContext()获取WebApplicationContext

　　　　2.3：实现接口ApplicationContextAware
　　　　　说明：实现该接口的setApplicationContext(ApplicationContext context)方法，并保存ApplicationContext 对象。
　　　　Spring初始化时，会通过该方法将ApplicationContext对象注入。

3.借助于spring提供的工具类，

　　　　WebApplicationContextUtils.getWebApplicationContext(ServletContext) 需要传入Servletcontext ，

　　　　通常从request中获取req.getSession().getServletContext()。适合于controller或者action中直接获取，但通常会直接@autoWire注入。

package com.controller;

import com.properties.Properties;
import com.service.IMyService;
import com.util.BeanUtil;
import com.util.BeanUtil1;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationListener;
import org.springframework.context.event.ContextRefreshedEvent;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.context.ContextLoader;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.support.WebApplicationContextUtils;
import reactor.core.publisher.Mono;
import sun.misc.Request;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpServletRequest;

/**
 * @author wanjiadong
 * @description
 * @date Create in 10:14 2018/9/4
 */
@RestController
@RequestMapping("/test")
//@EnableAutoConfiguration
public class testController implements ApplicationListener<ContextRefreshedEvent> {

    private ApplicationContext context = null;
    
    @Autowired
    private IMyService myService1;

    @Value("${test.server.name:haha}")
    private String testServerName;

    @Autowired
    private Properties properties;

    @Autowired
    private BeanUtil1 beanUtil1;

    @RequestMapping("/sayHello")
    public String sayHello(HttpServletRequest request) {
//        myService1.sayHello();
//        ContextLoader.getCurrentWebApplicationContext().getBean("properties");
        Properties properties1 = BeanUtil.getBean("properties");
        Properties properties2 = (Properties) context.getBean("properties");
        Properties properties3 = (Properties) WebApplicationContextUtils.getWebApplicationContext(request.getSession().getServletContext()).getBean("properties");
        Properties properties4 = beanUtil1.getBean("properties");
        return properties1.getTestServerName();
    }

    @GetMapping("/getWebFlux")
    public Mono<String> getWebFlux() {
        return Mono.just("getWebFlux");
    }

    @Override
    public void onApplicationEvent(ContextRefreshedEvent contextRefreshedEvent) {
        if(null != contextRefreshedEvent) {
            context = contextRefreshedEvent.getApplicationContext();
        }
    }
}

package com.util;

import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Component;

/**
 * @author wanjiadong
 * @description
 * @date Create in 11:25 2018/12/28
 */
@Component
public class BeanUtil implements ApplicationContextAware {

    private static ApplicationContext context;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.context = applicationContext;
    }

    public static <T> T getBean(String beanName) {
        return (T) context.getBean(beanName);
    }

    public static <T> T getBean(Class<?> var1) {
        return (T) context.getBean(var1);
    }
}

package com.util;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ApplicationObjectSupport;
import org.springframework.stereotype.Component;

/**
 * @author wanjiadong
 * @description
 * @date Create in 11:55 2018/12/28
 */
@Component
public class BeanUtil1 extends ApplicationObjectSupport {

    private ApplicationContext context;

    public <T> T getBean(String beanName) {
        context = getApplicationContext();
        return (T) context.getBean(beanName);
    }
}