我最近下载了 Spring 框架内的 Spring MVC（版本 4.0.2.RELEASE）模块的源代码。我的目的是针对模块的实际源代码而不是实际的源代码运行.jar文件。 （说来话长，仅用于测试目的）。
下载源代码后，我删除了jar我的项目中的文件，编译并部署到服务器。当我点击调度程序 servlet 处理的 URL 之一时，出现了错误：
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter#0': Invocation of init method failed; nested exception is java.lang.Error: Unresolved compilation problems:
The import java.time cannot be resolved
The method toZoneId() is undefined for the type TimeZone
ZoneId cannot be resolved
经过一些研究和深入研究源代码，我意识到错误中提到的类是 JDK/JRE 1.8 的一部分。移除之前.jar文件我的项目在 JDK/JRE 1.7 上运行没有问题。
我的问题是 Spring 如何包含 JDK 1.8 中的类，但仍然能够在 JDK/JRE 1.7 下运行？为什么使用Spring的时候不抛出异常.jar文件，但当我提供源代码时抛出它（并且 jar 文件丢失）？
完整的堆栈跟踪
Mar 26, 2014 7:27:18 AM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Allocate exception for servlet dispatcher
java.lang.Error: Unresolved compilation problems:
The import java.time cannot be resolved
The method toZoneId() is undefined for the type TimeZone
ZoneId cannot be resolved
at org.springframework.web.servlet.mvc.method.annotation.ServletRequestMethodArgumentResolver.<init>(ServletRequestMethodArgumentResolver.java:23)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.getDefaultArgumentResolvers(RequestMappingHandlerAdapter.java:522)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.afterPropertiesSet(RequestMappingHandlerAdapter.java:485)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1612)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1549)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:539)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:475)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:304)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:228)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:300)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:195)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:700)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:760)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:482)
at org.springframework.web.servlet.FrameworkServlet.configureAndRefreshWebApplicationContext(FrameworkServlet.java:658)
at org.springframework.web.servlet.FrameworkServlet.createWebApplicationContext(FrameworkServlet.java:624)
at org.springframework.web.servlet.FrameworkServlet.createWebApplicationContext(FrameworkServlet.java:672)
at org.springframework.web.servlet.FrameworkServlet.initWebApplicationContext(FrameworkServlet.java:543)
at org.springframework.web.servlet.FrameworkServlet.initServletBean(FrameworkServlet.java:484)
at org.springframework.web.servlet.HttpServletBean.init(HttpServletBean.java:136)
at javax.servlet.GenericServlet.init(GenericServlet.java:160)
at org.apache.catalina.core.StandardWrapper.initServlet(StandardWrapper.java:1274)
at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1186)
at org.apache.catalina.core.StandardWrapper.allocate(StandardWrapper.java:858)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:136)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:936)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1004)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:744)
标题问题的答案是：Spring 使用 Java 8 构建，但与 Java 7（和 6）兼容。
ServletRequestMethodArgumentResolver确实进口java.time.ZoneId，但它仅引用嵌套类中的类，除非 Java 8 位于类路径上，否则不会实例化该类。 Spring 源代码中有很多这样的例子（一直如此，例如自从它开始支持 Java 5 以来）。
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