javaweb运行报错：has been compiled by a more recent version of the Java Runtime (class file version 55.0)-蒲公英云

javaweb运行报错：has been compiled by a more recent version of the Java Runtime (class file version 55.0)

请求servlet时，网页会报HTTP状态 500 - 内部服务器错误

1.报错信息：

类型异常报告

消息实例化Servlet类[lagou.homework.servlet.LoginServlet]异常

描述服务器遇到一个意外的情况，阻止它完成请求。

例外情况

javax.servlet.ServletException: 实例化Servlet类[example.hello.servlet.LoginServlet]异常
    org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:544)
    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
    org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:690)
    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
    org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:616)
    org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
    org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:831)
    org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1634)
    org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    java.lang.Thread.run(Thread.java:745)
java.lang.UnsupportedClassVersionError: example/hello/servlet/LoginServlet has been compiled by a more recent version of the Java Runtime (class file version 55.0), this version of the Java Runtime only recognizes class file versions up to 52.0 (无法载入的.类 [example.homework.servlet.LoginServlet])
    org.apache.catalina.loader.WebappClassLoaderBase.findClassInternal(WebappClassLoaderBase.java:2411)
    org.apache.catalina.loader.WebappClassLoaderBase.findClass(WebappClassLoaderBase.java:855)
    org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1327)
    org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1180)
    org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:544)
    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
    org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:690)
    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
    org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:616)
    org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
    org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:831)
    org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1634)
    org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    java.lang.Thread.run(Thread.java:745)

2.日志关键内容是：

has been compiled by a more recent version of the Java Runtime (class file version 55.0), this version of the Java Runtime only recognizes class file versions up to 52.0

3.原因：

当前的jre不能对程序进行编译，Tomcat的版本高于JDK的版本导致的，当前运行的jdk是1.8而我用的Tomcat版本是Tomcat 9所以就会出现这个问题。

4.解决方法：

要么降低Tomcat的版本号，要么用更高的版本的JRE。

这里我选择使用高版本的JRE：

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