公司的新项目使用dubbo2.62来搭建，使用rest协议来发布接口，之前测试都正常，突然有一个方法报如下的错误，让我不知所措。
[2018-09-30 11:46:16] ERROR org.jboss.resteasy.resteasy_jaxrs.i18n - RESTEASY002025: Unknown exception while executing GET /services/account/do-register
java.lang.IllegalArgumentException: object is not an instance of declaring class
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.jboss.resteasy.core.ResourceLocatorInvoker.createResource(ResourceLocatorInvoker.java:79)
at org.jboss.resteasy.core.ResourceLocatorInvoker.createResource(ResourceLocatorInvoker.java:58)
at org.jboss.resteasy.core.ResourceLocatorInvoker.invoke(ResourceLocatorInvoker.java:100)
at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:402)
at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:209)
at org.jboss.resteasy.plugins.server.servlet.ServletContainerDispatcher.service(ServletContainerDispatcher.java:221)
at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:56)
at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:51)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
at com.alibaba.dubbo.rpc.protocol.rest.DubboHttpServer$RestHandler.handle(DubboHttpServer.java:89)
at com.alibaba.dubbo.remoting.http.servlet.DispatcherServlet.service(DispatcherServlet.java:61)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:504)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:534)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1081)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:658)
at org.apache.coyote.http11.Http11NioProtocol$Http11ConnectionHandler.process(Http11NioProtocol.java:222)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1566)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1523)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:748)
九月 30, 2018 11:46:16 上午 org.apache.catalina.core.StandardWrapperValve invoke
严重: Servlet.service() for servlet [dispatcher] in context with path [/] threw exception
org.jboss.resteasy.spi.UnhandledException: java.lang.IllegalArgumentException: object is not an instance of declaring class
at org.jboss.resteasy.core.ExceptionHandler.handleException(ExceptionHandler.java:255)
at org.jboss.resteasy.core.SynchronousDispatcher.writeException(SynchronousDispatcher.java:175)
at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:418)
at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:209)
at org.jboss.resteasy.plugins.server.servlet.ServletContainerDispatcher.service(ServletContainerDispatcher.java:221)
at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:56)
at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:51)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
at com.alibaba.dubbo.rpc.protocol.rest.DubboHttpServer$RestHandler.handle(DubboHttpServer.java:89)
at com.alibaba.dubbo.remoting.http.servlet.DispatcherServlet.service(DispatcherServlet.java:61)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:504)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:534)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1081)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:658)
at org.apache.coyote.http11.Http11NioProtocol$Http11ConnectionHandler.process(Http11NioProtocol.java:222)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1566)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1523)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.IllegalArgumentException: object is not an instance of declaring class
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.jboss.resteasy.core.ResourceLocatorInvoker.createResource(ResourceLocatorInvoker.java:79)
at org.jboss.resteasy.core.ResourceLocatorInvoker.createResource(ResourceLocatorInvoker.java:58)
at org.jboss.resteasy.core.ResourceLocatorInvoker.invoke(ResourceLocatorInvoker.java:100)
at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:402)
... 26 more
然后一直国内外网上搜索dubbo rest resteasy "object is not an instance of declaring class" 这些都不能解决，然后就删除方法的参数还是不行，但是同一个类的其他方法可以。最后比较这两个方法才发现，方法前面少写了@GET 或@POST。没想到会报这种错误，按字面理解是就会去想对象没有实例化，接口有多个实现类等其他原因。resteasy也不会给个明确的提示，真坑。
加上@GET ，终于可以调用了，花了大半天的时间。