解决方案:Spring使用Quartz等无法注入bean,即Xxxservice为null。
为什么注入不成功呢?我们先来了解下Spring和SpringMVC的容器之间的关系吧
两个applicationContext
spring使用mvc时会产生两个context上下文,一个是ContextLoaderListener(spring)产生的,一个是由DispatcherServlet(aringMVC)产生的,它们俩是父子关系。parent WebApplicationContext里的bean可以在child WebApplicationContext里共享,但parent application中的bean取不到child application中的bean。不同的child WebApplicationContext里的bean区不干扰。问题1:
重复构造bean
如果不知道Spring mvc里分有两个WebApplicationContext,在两个context中都定义了相同的bean,由于是放在两个context中加载所以不会报错。但这导致了重复构造bean。问题2
bean无法注入
如果一个bean在child WebApplicationContext里初始化,那么在root WebApplicationContext里的类就没有办法对其进行注入。bean注入不进去的解决方案:
在注入不进去的方法中使用下面的那句话,指定容器即可解决。
SpringBeanAutowiringSupport.processInjectionBasedOnCurrentContext(this);
如果你想彻底了解,不妨我们来分析下:
Spring的上下文:
在web.xml中有下面两个配置
<!-- spring监听器 -->
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
<!-- spring mvc servlet-->
<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:com/fancy/resource/spring-mvc.xml</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
<async-supported>true</async-supported>
</servlet>
<servlet-mapping>
<servlet-name>SpringMVC</servlet-name>
<url-pattern>/</url-pattern>
</servlet-mapping>
其中ContextLoadListener监听器在tomcat容器初始化的时候监听tomcat的servlet上下文,这个上下文给spring的上下文提供了寄生环境,在这个监听器中,spring会初始一个上下文,并将此上下文以key为ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE这个常量,value当然是自己的上下文了。看下面代码就可以看出来:
看看他们的调用顺序:
1.ContextLoaderListener中的
@Override
public void contextInitialized(ServletContextEvent event) {
initWebApplicationContext(event.getServletContext());
}
2.ContextLoad中的
public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {
if (servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE) != null) {
throw new IllegalStateException(
"Cannot initialize context because there is already a root application context present - " +
"check whether you have multiple ContextLoader* definitions in your web.xml!");
}
Log logger = LogFactory.getLog(ContextLoader.class);
servletContext.log("Initializing Spring root WebApplicationContext");
if (logger.isInfoEnabled()) {
logger.info("Root WebApplicationContext: initialization started");
}
long startTime = System.currentTimeMillis();
try {
// Store context in local instance variable, to guarantee that
// it is available on ServletContext shutdown.
if (this.context == null) {
this.context = createWebApplicationContext(servletContext);
}
if (this.context instanceof ConfigurableWebApplicationContext) {
ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context;
if (!cwac.isActive()) {
// The context has not yet been refreshed -> provide services such as
// setting the parent context, setting the application context id, etc
if (cwac.getParent() == null) {
// The context instance was injected without an explicit parent ->
// determine parent for root web application context, if any.
ApplicationContext parent = loadParentContext(servletContext);
cwac.setParent(parent);
}
configureAndRefreshWebApplicationContext(cwac, servletContext);
}
}
servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);
ClassLoader ccl = Thread.currentThread().getContextClassLoader();
if (ccl == ContextLoader.class.getClassLoader()) {
currentContext = this.context;
}
else if (ccl != null) {
currentContextPerThread.put(ccl, this.context);
}
if (logger.isDebugEnabled()) {
logger.debug("Published root WebApplicationContext as ServletContext attribute with name [" +
WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE + "]");
}
if (logger.isInfoEnabled()) {
long elapsedTime = System.currentTimeMillis() - startTime;
logger.info("Root WebApplicationContext: initialization completed in " + elapsedTime + " ms");
}
return this.context;
}
catch (RuntimeException ex) {
logger.error("Context initialization failed", ex);
servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, ex);
throw ex;
}
catch (Error err) {
logger.error("Context initialization failed", err);
//这里很重要
servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, err);
throw err;
}
}
SpringMVC的上下文:
spring的上下文是通过监听器来初始化,SpringMVC的上下文是通过DispatchServelet来加载,因为DispatchServelet会拦截所有我们感兴趣的请求来分发,DispatchServelet初始的时候会创建自己的上下文,并从servlet根上下文中取出我们上面说的spring上下文作为自己上下文的父容器,为什么这么做呢,因为spring中容器存在父子关系,父容器不能访问子容器的资源,而子容器可以访问父容器的资源。这样springMVC的上下文就可以获取父容器的Bean来初始化自己的Bean。
分析DispatchServelet初始化SpringMVC容器的上下文之前需要知道servlet生命周期:
- 调用 init() 方法初始化
- 调用 service() 方法来处理客户端的请求
- 调用 destroy() 方法释放资源,标记自身为可回收
- 被垃圾回收器回收
- 其中在init方法中进行初始化工作,来看看DispatchServelet的继承关系
其中主要的父类:FrameworkServle,HttpServletBean
FrameworkServle主要就是创建上下文,HttpServletBean中
@Override
public final void init() throws ServletException {
if (logger.isDebugEnabled()) {
logger.debug("Initializing servlet '" + getServletName() + "'");
}
// Set bean properties from init parameters.
try {
PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
initBeanWrapper(bw);
bw.setPropertyValues(pvs, true);
}
catch (BeansException ex) {
logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);
throw ex;
}
// Let subclasses do whatever initialization they like.
initServletBean();
if (logger.isDebugEnabled()) {
logger.debug("Servlet '" + getServletName() + "' configured successfully");
}
}
定义了init方法,这个方法中主要调用了initServletBean()方法,这个方法是个抽象方法,是由子类FrameworkServle实现,那么看看FrameworkServle中是如何重写这个方法的:
@Override
protected final void initServletBean() throws ServletException {
getServletContext().log("Initializing Spring FrameworkServlet '" + getServletName() + "'");
if (this.logger.isInfoEnabled()) {
this.logger.info("FrameworkServlet '" + getServletName() + "': initialization started");
}
long startTime = System.currentTimeMillis();
try {
//这里很重要
this.webApplicationContext = initWebApplicationContext();
initFrameworkServlet();
}
catch (ServletException ex) {
this.logger.error("Context initialization failed", ex);
throw ex;
}
catch (RuntimeException ex) {
this.logger.error("Context initialization failed", ex);
throw ex;
}
if (this.logger.isInfoEnabled()) {
long elapsedTime = System.currentTimeMillis() - startTime;
this.logger.info("FrameworkServlet '" + getServletName() + "': initialization completed in " +
elapsedTime + " ms");
}
}
初始化web上下文,这个上下文就是SpringMVC的上下文,那么继续看这个方法的具体实现:
protected WebApplicationContext initWebApplicationContext() {
WebApplicationContext rootContext =
WebApplicationContextUtils.getWebApplicationContext(getServletContext());
WebApplicationContext wac = null;
if (this.webApplicationContext != null) {
// A context instance was injected at construction time -> use it
wac = this.webApplicationContext;
if (wac instanceof ConfigurableWebApplicationContext) {
ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
if (!cwac.isActive()) {
// The context has not yet been refreshed -> provide services such as
// setting the parent context, setting the application context id, etc
if (cwac.getParent() == null) {
// The context instance was injected without an explicit parent -> set
// the root application context (if any; may be null) as the parent
cwac.setParent(rootContext);
}
configureAndRefreshWebApplicationContext(cwac);
}
}
}
if (wac == null) {
// No context instance was injected at construction time -> see if one
// has been registered in the servlet context. If one exists, it is assumed
// that the parent context (if any) has already been set and that the
// user has performed any initialization such as setting the context id
wac = findWebApplicationContext();
}
if (wac == null) {
// No context instance is defined for this servlet -> create a local one
wac = createWebApplicationContext(rootContext);
}
if (!this.refreshEventReceived) {
// Either the context is not a ConfigurableApplicationContext with refresh
// support or the context injected at construction time had already been
// refreshed -> trigger initial onRefresh manually here.
onRefresh(wac);
}
if (this.publishContext) {
// Publish the context as a servlet context attribute.
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
if (this.logger.isDebugEnabled()) {
this.logger.debug("Published WebApplicationContext of servlet '" + getServletName() +
"' as ServletContext attribute with name [" + attrName + "]");
}
}
return wac;
}
其中重要的部分:
if (this.webApplicationContext != null) {
// A context instance was injected at construction time -> use it
wac = this.webApplicationContext;
if (wac instanceof ConfigurableWebApplicationContext) {
ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
if (!cwac.isActive()) {
// The context has not yet been refreshed -> provide services such as
// setting the parent context, setting the application context id, etc
if (cwac.getParent() == null) {
// The context instance was injected without an explicit parent -> set
// the root application context (if any; may be null) as the parent
cwac.setParent(rootContext);
}
configureAndRefreshWebApplicationContext(cwac);
}
}
}
首先从servlet根上下文中获取rootContext,这个上下文就是上面所说的spring上下文,然后将springMVC 上下文中的父容器设置为rootContext,这样父子容器关系就建立起来了。
如果你还是没明白,你可以这样做,把你得定时类,放到controller包下,然后打上@Controller一样的注解,看看看能不能注入,如果能,就在思考下,应该是可以明白的。