我们有一个问题，我们无法解释它为什么会发生。也许这里有人可以给我们一些提示，在这种情况下发生了什么。
我们写了一个简单的reproucer来显示问题
package com.example.demo;
import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.builder.SpringApplicationBuilder;
import org.springframework.boot.web.support.SpringBootServletInitializer;
import org.springframework.context.annotation.Bean;
@SpringBootApplication
public class Application extends SpringBootServletInitializer {
@Override
protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
return application.sources(Application.class);
}
public static void main(String[] args) throws Exception {
SpringApplication.run(Application.class, args);
}
@Bean
public CommandLineRunner runner() {
return (args) -> {
final Class<?> refc = Class.forName("com.example.demo.Family$Child");
System.out.println(refc.getClassLoader());
MethodHandle handle1 = MethodHandles.lookup().findStatic(refc, "getFirstChild", MethodType.methodType(refc));
System.out.println("handle1 = " + handle1);
MethodHandle handle2 = MethodHandles.publicLookup().findStatic(refc, "getFirstChild", MethodType.methodType(refc));
System.out.println("handle2 = " + handle2);
};
}
}
class Family {
public enum Child {
TOM, PAUL;
public static Child getFirstChild() {
return TOM;
}
}
}
当我们现在构建一个war文件并将其分解到tomcat时一切都很好，但是当我们使用不同的上下文路径第二次部署它时，它会崩溃并出现以下异常
09-Jun-2017 09:21:54.706 SCHWERWIEGEND [http-nio-8080-exec-5] org.apache.catalina.core.ContainerBase.addChildInternal ContainerBase.addChild: start:
org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[/demo2]]
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:167)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:752)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:728)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:734)
at org.apache.catalina.startup.HostConfig.deployWAR(HostConfig.java:952)
at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java:473)
at org.apache.catalina.startup.HostConfig.check(HostConfig.java:1617)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.apache.tomcat.util.modeler.BaseModelMBean.invoke(BaseModelMBean.java:300)
at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.invoke(DefaultMBeanServerInterceptor.java:819)
at com.sun.jmx.mbeanserver.JmxMBeanServer.invoke(JmxMBeanServer.java:801)
at org.apache.catalina.manager.ManagerServlet.check(ManagerServlet.java:1483)
at org.apache.catalina.manager.HTMLManagerServlet.upload(HTMLManagerServlet.java:279)
at org.apache.catalina.manager.HTMLManagerServlet.doPost(HTMLManagerServlet.java:200)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:661)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.apache.catalina.filters.CsrfPreventionFilter.doFilter(CsrfPreventionFilter.java:136)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.apache.catalina.filters.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:108)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:595)
at org.apache.catalina.valves.RequestFilterValve.process(RequestFilterValve.java:319)
at org.apache.catalina.valves.RemoteAddrValve.invoke(RemoteAddrValve.java:88)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:80)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:624)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342)
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:799)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:861)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1455)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.IllegalStateException: Failed to execute CommandLineRunner
at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:735)
at org.springframework.boot.SpringApplication.callRunners(SpringApplication.java:716)
at org.springframework.boot.SpringApplication.afterRefresh(SpringApplication.java:703)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:304)
at org.springframework.boot.web.support.SpringBootServletInitializer.run(SpringBootServletInitializer.java:151)
at org.springframework.boot.web.support.SpringBootServletInitializer.createRootApplicationContext(SpringBootServletInitializer.java:131)
at org.springframework.boot.web.support.SpringBootServletInitializer.onStartup(SpringBootServletInitializer.java:86)
at org.springframework.web.SpringServletContainerInitializer.onStartup(SpringServletContainerInitializer.java:169)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5196)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
... 48 more
Caused by: java.lang.IllegalAccessException: no such method: com.example.demo.Family$Child.getFirstChild()Child/invokeStatic
at java.lang.invoke.MemberName.makeAccessException(MemberName.java:867)
at java.lang.invoke.MemberName$Factory.resolveOrFail(MemberName.java:1003)
at java.lang.invoke.MethodHandles$Lookup.resolveOrFail(MethodHandles.java:1386)
at java.lang.invoke.MethodHandles$Lookup.findStatic(MethodHandles.java:780)
at com.example.demo.Application.lambda$runner$0(Application.java:32)
at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:732)
... 57 more
Caused by: java.lang.LinkageError: loader constraint violation: when resolving method "com.example.demo.Family$Child.getFirstChild()Lcom/example/demo/Family$Child;" the class loader (instance of <bootloader>) of the current class, java/lang/Object, and the class loader (instance of org/apache/catalina/loader/ParallelWebappClassLoader) for the method's defining class, com/example/demo/Family$Child, have different Class objects for the type com/example/demo/Family$Child used in the signature
at java.lang.invoke.MethodHandleNatives.resolve(Native Method)
at java.lang.invoke.MemberName$Factory.resolve(MemberName.java:975)
at java.lang.invoke.MemberName$Factory.resolveOrFail(MemberName.java:1000)
... 61 more
我们唯一发现的原因是publicLookup()。查看 javadoc 在使用 publicLookup() 时提到了一些问题，我们并不完全理解它。