Spring获取ApplicationContext的几种方法

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SSM框架搭建Web项目

IDEA使用Maven搭建SSM框架Web项目

观前提示：

本文所使用的IDEA版本为ultimate 2019.1，JDK版本为1.8.0_141，Tomcat版本为9.0.12。

本文的例子均在上述链接参考文章搭建的框架。

1.ApplicationContext简介

实用的Bean工厂ApplicationContext。

ApplicationContext的中文意思是“应用前后关系”，它继承自BeanFactory接口，除了包含BeanFactory的所有功能之外，在国际化支持、资源访问（如URL和文件）、事件传播等方面进行了良好的支持，被推荐为Java EE应用之首选，可应用在Java APP与Java Web中。

2.获取方法

2.1 通过Spring提供的工具类WebApplicationContextUtils获取

ApplicationContext ac1 = WebApplicationContextUtils.getRequiredWebApplicationContext(ServletContext);
ApplicationContext ac2 = WebApplicationContextUtils.getWebApplicationContext(ServletContext);

ac1.getBean(Class);
ac2.getBean("beanId");

实例

UserService.java

package com.example.service;

import org.springframework.stereotype.Service;

@Service
public class UserService {
    
    


    public void insertUser() {
    
    
        System.out.println("插入用户成功");
    }

    public boolean updateUser() {
    
    
        System.out.println("更新用户成功");
        return true;
    }
}

拦截器RequestMappingInterceptor.java中的部分测试方法

@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
    
    

    ApplicationContext ac1 = WebApplicationContextUtils.getRequiredWebApplicationContext(request.getServletContext());
    ApplicationContext ac2 = WebApplicationContextUtils.getWebApplicationContext(request.getServletContext());

    UserService u1 = ac1.getBean(UserService.class);
    UserService u2 = ac2.getBean(UserService.class);
    u1.insertUser();
    u2.updateUser();

    return super.preHandle(request, response, handler);
}

测试结果

注：这种方式适合于采用Spring框架的B/S系统，通过ServletContext对象获取ApplicationContext对象，然后在通过它获取需要的类实例。

2.2 初始化时保存ApplicationContext对象

ApplicationContext ac1 = new ClassPathXmlApplicationContext("**/applicationContext.xml");

(Class) ac1.getBean("beanId");
ac1.getBean(Class);

实例

结构如下

applicationContext.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:aop="http://www.springframework.org/schema/aop"
       xmlns:tx="http://www.springframework.org/schema/tx"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.0.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.0.xsd
http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-4.0.xsd
http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-4.0.xsd">

    <!-- 配置自动扫描的包 -->
    <context:component-scan base-package="testApplicationContext"></context:component-scan>
</beans>

TestApplicationContext.java

package testApplicationContext;

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

public class TestApplicationContext{
    
    

    @Test
    public void test() {
    
    
        try {
    
    
            ApplicationContext ac1 = new ClassPathXmlApplicationContext("testApplicationContext/applicationContext.xml");

            UserService u1 = (UserService) ac1.getBean("userService");
            UserService u2 = ac1.getBean(UserService.class);
            u1.insertUser();
            u2.updateUser();
        } catch (Exception e) {
    
    
            e.printStackTrace();
        }
    }
}

运行结果如下

注：这种方式适用于采用Spring框架的独立应用程序，需要程序通过配置文件手工初始化Spring的情况。

2.3 继承自抽象类ApplicationObjectSupport

实例

ApplicationObjectSupportUtil.java

package com.example.util;

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

@Component
public class ApplicationObjectSupportUtil extends ApplicationObjectSupport {
    
    

    private static ApplicationContext applicationContext;

    /**
     * 重写方法，注入applicationContext
     * @param applicationContext
     */
    @Override
    public void initApplicationContext(ApplicationContext applicationContext) {
    
    
        this.applicationContext = applicationContext;
    }

    /**
     * 从静态变量ApplicationContext中取得Bean, 自动转型为所赋值对象的类型.
     */
    public static <T> T getBean(String name) {
    
    
        checkApplicationContext();
        return (T) applicationContext.getBean(name);
    }

    /**
     * 从静态变量ApplicationContext中取得Bean, 自动转型为所赋值对象的类型.
     */
    @SuppressWarnings("unchecked")
    public static <T> T getBean(Class<T> clazz) {
    
    
        checkApplicationContext();
        return (T) applicationContext.getBean(clazz);
    }

    /**
     * 清除applicationContext静态变量.
     */
    public static void cleanApplicationContext() {
    
    
        applicationContext = null;
    }

    private static void checkApplicationContext() {
    
    
        if (applicationContext == null) {
    
    
            throw new IllegalStateException("applicaitonContext未注入,请在applicationContext.xml中定义SpringContextHolder");
        }
    }
}

拦截器RequestMappingInterceptor.java中的部分测试方法

@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
    
    
    UserService userService = ApplicationObjectSupportUtil.getBean(UserService.class);
    userService.insertUser();
    return super.preHandle(request, response, handler);
}

运行结果如下

注：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。

2.4 继承自抽象类WebApplicationObjectSupport

实例

WebApplicationObjectSupportUtils.java

package com.example.util;

import org.springframework.context.ApplicationContext;
import org.springframework.stereotype.Component;
import org.springframework.web.context.support.WebApplicationObjectSupport;

@Component
public class WebApplicationObjectSupportUtils extends WebApplicationObjectSupport {
    
    

    private static ApplicationContext applicationContext;

    /**
     * 重写方法，注入applicationContext
     * @param applicationContext
     */
    @Override
    public void initApplicationContext(ApplicationContext applicationContext) {
    
    
        this.applicationContext = applicationContext;
    }

    /**
     * 从静态变量ApplicationContext中取得Bean, 自动转型为所赋值对象的类型.
     */
    public static <T> T getBean(String name) {
    
    
        checkApplicationContext();
        return (T) applicationContext.getBean(name);
    }

    /**
     * 从静态变量ApplicationContext中取得Bean, 自动转型为所赋值对象的类型.
     */
    @SuppressWarnings("unchecked")
    public static <T> T getBean(Class<T> clazz) {
    
    
        checkApplicationContext();
        return (T) applicationContext.getBean(clazz);
    }

    /**
     * 清除applicationContext静态变量.
     */
    public static void cleanApplicationContext() {
    
    
        applicationContext = null;
    }

    private static void checkApplicationContext() {
    
    
        if (applicationContext == null) {
    
    
            throw new IllegalStateException("applicaitonContext未注入,请在applicationContext.xml中定义SpringContextHolder");
        }
    }
}

拦截器RequestMappingInterceptor.java中的部分测试方法

@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
    
    
    UserService userService = WebApplicationObjectSupportUtils.getBean(UserService.class);
    userService.insertUser();
    return super.preHandle(request, response, handler);
}

运行结果如下

注：类似上面方法，也可以调用getWebApplicationContext()获取WebApplicationContext

2.5 实现接口ApplicationContextAware

实例

SpringContext.java

package com.example.util;

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

@Component
public class SpringContextUtil implements ApplicationContextAware {
    
    

    private static ApplicationContext applicationContext; // Spring应用上下文环境

    /**
     * 实现ApplicationContextAware接口的回调方法，设置上下文环境
     */
    public void setApplicationContext(ApplicationContext applicationContext) {
    
    
        SpringContextUtil.applicationContext = applicationContext;
    }
    /**
     * 获取Spring应用上下文环境
     */
    public static ApplicationContext getApplicationContext() {
    
    
        checkApplicationContext();
        return applicationContext;
    }

    /**
     * 清除applicationContext静态变量.
     */
    public static void cleanApplicationContext() {
    
    
        applicationContext = null;
    }

    /**
     * 获取对象
     */
    @SuppressWarnings("unchecked")
    public static <T> T getBean(String name) {
    
    
        checkApplicationContext();
        return (T) applicationContext.getBean(name);
    }

    /**
     * 获取类型为requiredType的对象
     */
    public static <T> T getBean(Class<T> clz) {
    
    
        checkApplicationContext();
        return applicationContext.getBean(clz);
    }

    /**
     * 如果BeanFactory包含一个与所给名称匹配的bean定义，则返回true
     */
    public static boolean containsBean(String name) {
    
    
        checkApplicationContext();
        return applicationContext.containsBean(name);
    }

    /**
     * 判断以给定名字注册的bean定义是一个singleton还是一个prototype。 如果与给定名字相应的bean定义没有被找到，将会抛出一个异常（NoSuchBeanDefinitionException）
     */
    public static boolean isSingleton(String name) {
    
    
        checkApplicationContext();
        return applicationContext.isSingleton(name);
    }

    /**
     * Class 注册对象的类型
     */
    public static Class<?> getType(String name) {
    
    
        checkApplicationContext();
        return applicationContext.getType(name);
    }

    /**
     * 如果给定的bean名字在bean定义中有别名，则返回这些别名
     */
    public static String[] getAliases(String name) {
    
    
        checkApplicationContext();
        return applicationContext.getAliases(name);
    }

    /**
     * 检查applicaitonContext是否注入
     */
    private static void checkApplicationContext() {
    
    
        if (applicationContext == null) {
    
    
            throw new IllegalStateException("applicaitonContext未注入,请在applicationContext.xml中定义SpringContextHolder");
        }
    }
}

拦截器RequestMappingInterceptor.java中的部分测试方法

@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
    
    
    UserService userService = SpringContext.getBean(UserService.class);
    userService.insertUser();
    return super.preHandle(request, response, handler);
}

运行结果如下

注：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。