springmvc获取上下文ApplicationContext

清疚 2022-06-05 12:54 362阅读 0赞

1、可通过下面工具类获取

package org.mvc.demo.utlis;
    
    import org.springframework.beans.BeansException;
    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上下文
        @Override
        public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
            SpringContextUtil.applicationContext=applicationContext;
        }
        public static ApplicationContext getApplicationContext(){
            return applicationContext;
        }
    
        public static <T> T getBean(String name) throws BeansException{
               return (T)applicationContext.getBean(name);
        }
    }

主要是实现ApplicationContextAware接口

当一个类实现了这个接口（ApplicationContextAware）之后，这个类就可以方便获得ApplicationContext中的所有bean。换句话说，就是这个类可以直接获取spring配置文件中，所有有引用到的bean对象。

另外要注意Spring上下文和SpringMVC上下文的区别。

Spring上下文配置

<context-param>    
            <param-name>contextConfigLocation</param-name>    
            <param-value>classpath:spring-application.xml</param-value>    
        </context-param>  
            
        <listener>    
            <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>    
        </listener>

SpringMVC上下文配置

<servlet>    
            <servlet-name>SpringMVC</servlet-name>    
            <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>    
            <init-param>    
                <param-name>contextConfigLocation</param-name>    
                <param-value>classpath:spring-mvc.xml</param-value>    
            </init-param>    
            <load-on-startup>1</load-on-startup>    
            <async-supported>true</async-supported>    
        </servlet>

**注意：SpringMVC上下文和Spring上下文是分开独立，两者是父子关系。Spring 父------SpringMVC 子。但是SpringMVC上下文是可以取得Spring上下文。反之则不行。**

在tomcat服务启动日志中可以看到，root WebApplicationContext就是Spring的。

再回头来看，我们的SpringContextUtil,它应该放在Spring里面来设置，才有效。放在SpringMVC里面是没法完成自动实例化的。

那么，我们能仿SpringContextUtil建立springMVC的工具类吗？答案是可以。

在做这个之前，我们要先理解springMVC的加载顺序.

<?xml version="1.0" encoding="UTF-8"?>
    <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
             http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
             version="3.1"  metadata-complete="false">
      <context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>
             classpath*:spring-application.xml
        </param-value>
      </context-param>
      <context-param>
        <param-name>log4jRefreshInterval</param-name>
        <param-value>600000</param-value>
      </context-param>
      <context-param>
        <param-name>webAppRootKey</param-name>
        <param-value>webPath</param-value>
      </context-param>
    
      <listener>
        <listener-class>org.springframework.web.util.WebAppRootListener</listener-class>
      </listener>
    
      <listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
      </listener>
    
      <filter>
        <filter-name>encodingFilter</filter-name>
        <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
        <async-supported>true</async-supported>
        <init-param>
          <param-name>encoding</param-name>
          <param-value>UTF-8</param-value>
        </init-param>
      </filter>
    
      <filter-mapping>
        <filter-name>encodingFilter</filter-name>
        <url-pattern>/*</url-pattern>
      </filter-mapping>
    
      <servlet>
        <servlet-name>dispatcher</servlet-name>
        <servlet-class>
          org.springframework.web.servlet.DispatcherServlet
        </servlet-class>
        <init-param>
          <param-name>contextConfigLocation</param-name>
          <param-value>classpath:spring-mvc.xml</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
        <async-supported>true</async-supported>
      </servlet>
      <servlet-mapping>
        <servlet-name>dispatcher</servlet-name>
        <url-pattern>/</url-pattern>
      </servlet-mapping>
    </web-app>

上面贴出的就是web.xml的部分配置，在这里我们首先讲解下web项目启动的加载顺序：

以Tomcat举例，启动Tomcat之后，首先会加载web.xml文件：

a)容器首先读取web.xml中的<context-param>的配置内容和<listener>标签中配置项；

b)紧接着实例化ServletContext对象，并将<context-param>配置的内容转化为键值传递给ServletContext；

c)创建<listener>配置的监听器的类实例，并且启动监听；

d)调用listener的contextInitialized(ServletContextEvent args)方法，ServletContext=  ServletContextEvent.getServletContext();  
此时你可以通过ServletContext获取context-param配置的内容并可以加以修改，此时Tomcat还没完全启动完成。

e)后续加载配置的各类filter；

f)最后加载servlet；

最后的结论是：web.xml中配置项的加载顺序是context-param=>listener=>filter=>servlet,配置项的顺序并不会改变加载顺序，但是同类型的配置项会应该加载顺序，servlet中也可以通过load-on-startup来指定加载顺序。

明白加载顺序之后，我们就可以写一个springMVC上下文的工具类了。

前面说过:这里加载的是spring上下文

<context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>
             classpath*:spring-application.xml
        </param-value>
      </context-param>

这里加载的才是springMVC上下文

<servlet>
        <servlet-name>dispatcher</servlet-name>
        <servlet-class>
          org.springframework.web.servlet.DispatcherServlet
        </servlet-class>
        <init-param>
          <param-name>contextConfigLocation</param-name>
          <param-value>classpath:spring-mvc.xml</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
        <async-supported>true</async-supported>
      </servlet>

这个时候我们看一下spring-mvc.xml这个文件。

<?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:mvc="http://www.springframework.org/schema/mvc"
           xmlns:task="http://www.springframework.org/schema/task"
           xsi:schemaLocation="http://www.springframework.org/schema/beans
            http://www.springframework.org/schema/beans/spring-beans-4.2.xsd
            http://www.springframework.org/schema/context
            http://www.springframework.org/schema/context/spring-context-4.2.xsd
         	http://www.springframework.org/schema/aop
         	http://www.springframework.org/schema/aop/spring-aop-4.2.xsd
    		http://www.springframework.org/schema/mvc
         	http://www.springframework.org/schema/mvc/spring-mvc-4.2.xsd
         	http://www.springframework.org/schema/task
         	http://www.springframework.org/schema/task/spring-task.xsd">
    
        <context:component-scan base-package="com.fwone.controller"></context:component-scan>
        <mvc:default-servlet-handler />
    
        <mvc:annotation-driven>
            <mvc:message-converters register-defaults="false">
                <bean class="com.alibaba.fastjson.support.spring.FastJsonHttpMessageConverter">
                    <property name="supportedMediaTypes">
                        <list>
                            <value>text/html;charset=UTF-8</value>
                            <value>application/json</value>
                        </list>
                    </property>
                    <property name="fastJsonConfig">
                        <bean class="com.alibaba.fastjson.support.config.FastJsonConfig">
                            <property name="serializerFeatures">
                                <list>
                                    <value>QuoteFieldNames</value>
                                    <value>WriteDateUseDateFormat</value>
                                    
                                    <value>DisableCircularReferenceDetect</value>
                                </list>
                            </property>
                        </bean>
                    </property>
                </bean>
            </mvc:message-converters>
        </mvc:annotation-driven>
    
        
        <bean id="viewResolver" class="org.springframework.web.servlet.view.freemarker.FreeMarkerViewResolver">
            <property name="viewClass" value="org.springframework.web.servlet.view.freemarker.FreeMarkerView"/>
            <property name="contentType" value="text/html; charset=utf-8"/>
            <property name="cache" value="true"/>
            <property name="suffix" value=".html"/>
            <property name="prefix" value=""/>
            <property name="requestContextAttribute" value="rc" />
            <property name="order" value="0"/>
    
        </bean>
    
        <bean id="freeMarkerConfigurer" class="org.springframework.web.servlet.view.freemarker.FreeMarkerConfigurer">
            <property name="templateLoaderPath" value="/WEB-INF/page/"/>
        </bean>
    
        
        <bean name="producer" class="com.google.code.kaptcha.impl.DefaultKaptcha" scope="singleton">
            <property name="config">
                <bean class="com.google.code.kaptcha.util.Config">
                    <constructor-arg>
                        <props>
                            <prop key="kaptcha.border">no</prop>
                            <prop key="kaptcha.textproducer.font.color">black</prop>
                            <prop key="kaptcha.textproducer.char.space">5</prop>
                        </props>
                    </constructor-arg>
                </bean>
            </property>
        </bean>
    </beans>

主要看这里

<context:component-scan base-package="com.fwone.controller"></context:component-scan>

我们知道,像Controller都是单独扫描并实例化各个Controller,所以我们要在

com.fwone.controller这个包下写我们的springMVC上下文工具类

到了这里，基本都理解清楚了。直接复制之前的spring上下文工具类

package com.fwone.controller;
    
    import org.springframework.beans.BeansException;
    import org.springframework.context.ApplicationContext;
    import org.springframework.context.ApplicationContextAware;
    import org.springframework.stereotype.Controller;
    
    @Controller
    public class SpringMvcContext implements ApplicationContextAware {
        private static ApplicationContext applicationContext;//springMVC上下文定义
        @Override
        public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
            SpringMvcContext.applicationContext=applicationContext;
        }
        public static ApplicationContext getApplicationContext(){
            return SpringMvcContext.applicationContext;
        }
        public static<T> T getBean(String name)throws BeansException{
            return (T)applicationContext.getBean(name);
        }
    }