java.lang.IllegalAccessError with Retrofit 2 at com.google.gson.Gson.newJsonWriter

Question

How to figure out what causes this IllegalAccessError issue? Any help is appreciated.

I already followed some of the fixes/workaround and use Gson 2.8 from maven. Here is the partial Maven configuration:

<dependency>
    <groupId>com.squareup.retrofit2</groupId>
    <artifactId>converter-gson</artifactId>
    <version>2.2.0</version>
    <exclusions>
        <exclusion>
            <groupId>com.google.code.gson</groupId>
            <artifactId>gson</artifactId>
        </exclusion>
    </exclusions>
</dependency>

<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>2.8.0</version>
</dependency>

and full stack trace:

java.lang.IllegalAccessError: tried to access method com.google.gson.Gson.newJsonWriter(Ljava/io/Writer;)Lcom/google/gson/stream/JsonWriter; from class retrofit2.converter.gson.GsonRequestBodyConverter
    at retrofit2.converter.gson.GsonRequestBodyConverter.convert(GsonRequestBodyConverter.java:45)
    at retrofit2.converter.gson.GsonRequestBodyConverter.convert(GsonRequestBodyConverter.java:30)
    at retrofit2.ParameterHandler$Body.apply(ParameterHandler.java:312)
    at retrofit2.ServiceMethod.toRequest(ServiceMethod.java:110)
    at retrofit2.OkHttpCall.createRawCall(OkHttpCall.java:178)
    at retrofit2.OkHttpCall.execute(OkHttpCall.java:162)
    at com.xxxxxx.web.controller.UserController.exchangeAccessToken(UserController.java:2551)
    at com.xxxxxx.web.controller.UserController.plaidtoken(UserController.java:2645)
    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.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:215)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:132)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:745)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:685)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:80)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:919)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:851)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:953)
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:855)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:661)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:829)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:230)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:106)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
    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:478)
    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:341)
    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:745)

Answer 1

According to IllegalAccessError documentation:

Thrown if an application attempts to access or modify a field, or to call a method that it does not have access to.

...this error can only occur at run time if the definition of a class has incompatibly changed.

In your case the exception is throw at runtime which means that at compilation time the classpath was different from the classpath at runtime.

In general case such problem can be solved by analysing transitive dependencies, you can use maven dependency plugin:

mvn dependency:tree

Most likely you'll find transitive dependency in some of your libs with gson version different from the one you declared.

Note: there is hight chance of braking something else if you replace one of transitive dependencies. Be careful with this and make sure you're using compatible libs.

Answer 2

it is solved now. Here is how I did, for anyone else also looking for similar problem:

I used the 'jar -tf filename.jar' to list or dump the content of each package we use, and searched the result for 'gson'.

I was able to identify one of the third party package that includes gson with it. Once this jar file is isolated, the problem went away.

Thanks for reading.