Spring如何使用Java 8类,但它在Java 7上运行？

Question

我最近在Spring Framework中下载了Spring MVC(Version 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.jar文件运行.(长话,仅用于测试目的).

下载源代码后,我jar从项目中删除了文件,编译并部署到服务器.当我点击调度程序servlet处理的其中一个URL时,我遇到了错误:

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

经过一些研究和挖掘源代码后,我意识到错误中提到的类是JDK/JRE 1.8的一部分.在删除.jar文件之前,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,但仍设法在JDK/JRE 1.7下运行？为什么在使用Spring的.jar文件时不会抛出异常,但是当我提供源代码时它被抛出(并且缺少jar文件)？

全栈跟踪

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)

Answer 1

标题问题的答案是:Spring使用Java 8构建,但与Java 7(和6)兼容.

ServletRequestMethodArgumentResolver确实导入java.time.ZoneId,但它只引用嵌套类中的那个类,除非Java 8在类路径上,否则它不会被实例化.在Spring源代码中有很多这样的例子(例如,自从它开始支持Java 5以来一直如此).