Spring Boot下Bean定義方式及調用方式

　　咱們知道若是咱們要在一個類使用spring提供的bean對象，咱們須要把這個類注入到spring容器中，交給spring容器進行管理，可是在實際當中，咱們每每會碰到在一個普通的Java類中，想直接使用spring提供的其餘對象或者說有一些不須要交給spring管理，可是須要用到spring裏的一些對象。若是這是spring框架的獨立應用程序，咱們經過

ApplicationContext ac = new FileSystemXmlApplicationContext("applicationContext.xml");
ac.getBean("beanId"); 

這樣的方式就能夠很輕易的獲取咱們所須要的對象。

可是每每咱們所作的都是Web Application，這時咱們啓動spring容器是經過在web.xml文件中配置，這樣就不適合使用上面的方式在普通類去獲取對象了，由於這樣作就至關於加載了兩次spring容器，而咱們想是否能夠經過在啓動web服務器的時候，就把Application放在某一個類中，咱們經過這個類在獲取，這樣就能夠在普通類獲取spring bean對象了，讓咱們接着往下看

普通類調用Spring bean對象:

能夠參考：http://412887952-qq-com.iteye.com/blog/1479445

這裏有更多這方面的介紹，比較詳細

下面介紹在SpringBoot中是如何使用的

1.在Spring Boot能夠掃描的包下

寫的工具類爲SpringUtil，實現ApplicationContextAware接口，並加入Component註解，讓spring掃描到該bean

springutil:

package me.shijunjie.util;

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

@Component
public class SpringUtil implements ApplicationContextAware {

    private static ApplicationContext applicationContext;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        if(SpringUtil.applicationContext == null) {
            SpringUtil.applicationContext = applicationContext;
        }
        System.out.println("---------------------------------------------------------------------");

        System.out.println("---------------------------------------------------------------------");

        System.out.println("---------------me.shijunjie.util.SpringUtil------------------------------------------------------");

        System.out.println("========ApplicationContext配置成功,在普通類能夠經過調用SpringUtils.getAppContext()獲取applicationContext對象,applicationContext="+SpringUtil.applicationContext+"========");

        System.out.println("---------------------------------------------------------------------");
    }

    //獲取applicationContext
    public static ApplicationContext getApplicationContext() {
        return applicationContext;
    }

    //經過name獲取 Bean.
    public static Object getBean(String name){
        return getApplicationContext().getBean(name);
    }

    //經過class獲取Bean.
    public static <T> T getBean(Class<T> clazz){
        return getApplicationContext().getBean(clazz);
    }

    //經過name,以及Clazz返回指定的Bean
    public static <T> T getBean(String name,Class<T> clazz){
        return getApplicationContext().getBean(name, clazz);
    }

}

爲了測試，咱們再啓動的時候先經過代碼方式給spring容器中注入一個bean，入下所示

package me.shijunjie.config;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import me.shijunjie.entity.Demo2;

@Configuration
public class BeanConfig {
    @Bean(name="testDemo")
    public Demo2 generateDemo() {
        Demo2 demo = new Demo2();
        demo.setId(12345);
        demo.setName("test");
        return demo;
    }
}

而後咱們編寫測試controller，並從剛纔寫的springutil中獲取這個bean

package me.shijunjie.controller;

import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import me.shijunjie.util.SpringUtil;

@RestController
@RequestMapping("/application")
public class TestApplicationController {
    
    @RequestMapping("/test1")
    public Object testSpringUtil1() {
        return SpringUtil.getBean("testDemo");
    }
    
}

測試

啓動web應用，打開瀏覽器輸入http://localhost:8080/application/test1，測試成功

2 不在Spring Boot的掃描包下方式一

這種狀況處理起來也很簡單，先編寫SpringUtil類，一樣須要實現接口：ApplicationContextAware，具體編碼以下：

package me.shijunjie.util;

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

public class SpringUtil2 implements ApplicationContextAware {

    private static ApplicationContext applicationContext;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        if(SpringUtil2.applicationContext == null) {
            SpringUtil2.applicationContext = applicationContext;
        }
        System.out.println("---------------------------------------------------------------------");

        System.out.println("---------------------------------------------------------------------");

        System.out.println("---------------me.shijunjie.util.SpringUtil------------------------------------------------------");

        System.out.println("========ApplicationContext配置成功,在普通類能夠經過調用SpringUtils.getAppContext()獲取applicationContext對象,applicationContext="+SpringUtil2.applicationContext+"========");

        System.out.println("---------------------------------------------------------------------");
    }

    //獲取applicationContext
    public static ApplicationContext getApplicationContext() {
        return applicationContext;
    }

    //經過name獲取 Bean.
    public static Object getBean(String name){
        return getApplicationContext().getBean(name);
    }

    //經過class獲取Bean.
    public static <T> T getBean(Class<T> clazz){
        return getApplicationContext().getBean(clazz);
    }

    //經過name,以及Clazz返回指定的Bean
    public static <T> T getBean(String name,Class<T> clazz){
        return getApplicationContext().getBean(name, clazz);
    }

}

使用@Bean註解，在App.java類中將SpringUtil註解進

package me.shijunjie.controller;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.context.web.SpringBootServletInitializer;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.scheduling.annotation.EnableScheduling;

import me.shijunjie.util.SpringUtil2;

@ComponentScan(basePackages={"me.shijunjie"}) // 掃描該包路徑下的全部spring組件
/*@EnableJpaRepositories("me.shijunjie.dao") // JPA掃描該包路徑下的Repositorie
*//*@EntityScan("me.shijunjie.entity") // 掃描實體類
*/@SpringBootApplication
@EnableScheduling
public class App extends SpringBootServletInitializer{
    @Bean
    public SpringUtil2 getSpringUtil2() {
        return new SpringUtil2();
    }
    
    public static void main(String[] args) {
        SpringApplication.run(App.class, args);
    }
}

測試（使用熱部署的須要重啓服務器）

啓動web應用，打開瀏覽器輸入http://localhost:8080/application/test2，測試成功

除此之外，也能夠在App.java中使用@Import進行導入。

package me.shijunjie.controller;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.context.web.SpringBootServletInitializer;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Import;
import org.springframework.scheduling.annotation.EnableScheduling;

import me.shijunjie.util.SpringUtil2;

@ComponentScan(basePackages={"me.shijunjie"}) // 掃描該包路徑下的全部spring組件
/*@EnableJpaRepositories("me.shijunjie.dao") // JPA掃描該包路徑下的Repositorie
*//*@EntityScan("me.shijunjie.entity") // 掃描實體類
*/@SpringBootApplication
@EnableScheduling
@Import(SpringUtil2.class)
public class App extends SpringBootServletInitializer{
    /*@Bean
    public SpringUtil2 getSpringUtil2() {
        return new SpringUtil2();
    }*/
    
    public static void main(String[] args) {
        SpringApplication.run(App.class, args);
    }
}

跑出結果和上面相同