Custom HashMap class get argument type mismatch when using with @RequestParam in Kotlin

Question

I am trying to write a simple route that will handle GET request with some query parameters. To achieve this, I have created my own Customs HashMap class to speed up some process and easily extend some functionality I need as below:

class MMap : HashMap<String, Any>()
{
    fun getString(key: String): String? = get(key) as? String
...
}

And then, in my controller I have everything done as the below code:

   @GetMapping("/user")
    fun find(@RequestParam data: MMap): MMap {
        return data
    }

After that, I have tried to do a get request to this route using GET localhost:8080/user?id=123&username=admin and suddenly in the debug console I got some error:

Method [public com.cc.MMap com.cc.controller.UserController.find(com.cc.MMap)] with argument values:
 [0] [type=java.util.LinkedHashMap] [value={id=123,username=admin}] ] with root cause

java.lang.IllegalArgumentException: argument type mismatch
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na]
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
    at java.base/java.lang.reflect.Method.invoke(Method.java:567) ~[na:na]
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190) ~[spring-web-5.2.0.RC1.jar:5.2.0.RC1]
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138) ~[spring-web-5.2.0.RC1.jar:5.2.0.RC1]
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:105) ~[spring-webmvc-5.2.0.RC1.jar:5.2.0.RC1]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:887) ~[spring-webmvc-5.2.0.RC1.jar:5.2.0.RC1]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:792) ~[spring-webmvc-5.2.0.RC1.jar:5.2.0.RC1]
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.2.0.RC1.jar:5.2.0.RC1]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1039) ~[spring-webmvc-5.2.0.RC1.jar:5.2.0.RC1]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:942) ~[spring-webmvc-5.2.0.RC1.jar:5.2.0.RC1]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1005) ~[spring-webmvc-5.2.0.RC1.jar:5.2.0.RC1]
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:897) ~[spring-webmvc-5.2.0.RC1.jar:5.2.0.RC1]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:634) ~[tomcat-embed-core-9.0.22.jar:9.0.22]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:882) ~[spring-webmvc-5.2.0.RC1.jar:5.2.0.RC1]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) ~[tomcat-embed-core-9.0.22.jar:9.0.22]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.22.jar:9.0.22]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.22.jar:9.0.22]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.22.jar:9.0.22]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.22.jar:9.0.22]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.22.jar:9.0.22]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) ~[spring-web-5.2.0.RC1.jar:5.2.0.RC1]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:118) ~[spring-web-5.2.0.RC1.jar:5.2.0.RC1]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.22.jar:9.0.22]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.22.jar:9.0.22]
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:92) ~[spring-web-5.2.0.RC1.jar:5.2.0.RC1]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:118) ~[spring-web-5.2.0.RC1.jar:5.2.0.RC1]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.22.jar:9.0.22]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.22.jar:9.0.22]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200) ~[spring-web-5.2.0.RC1.jar:5.2.0.RC1]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:118) ~[spring-web-5.2.0.RC1.jar:5.2.0.RC1]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.22.jar:9.0.22]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.22.jar:9.0.22]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) ~[tomcat-embed-core-9.0.22.jar:9.0.22]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) ~[tomcat-embed-core-9.0.22.jar:9.0.22]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:490) ~[tomcat-embed-core-9.0.22.jar:9.0.22]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) ~[tomcat-embed-core-9.0.22.jar:9.0.22]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) ~[tomcat-embed-core-9.0.22.jar:9.0.22]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) ~[tomcat-embed-core-9.0.22.jar:9.0.22]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) ~[tomcat-embed-core-9.0.22.jar:9.0.22]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408) ~[tomcat-embed-core-9.0.22.jar:9.0.22]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) ~[tomcat-embed-core-9.0.22.jar:9.0.22]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:853) ~[tomcat-embed-core-9.0.22.jar:9.0.22]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1587) ~[tomcat-embed-core-9.0.22.jar:9.0.22]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) ~[tomcat-embed-core-9.0.22.jar:9.0.22]
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) ~[na:na]
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) ~[na:na]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) ~[tomcat-embed-core-9.0.22.jar:9.0.22]
    at java.base/java.lang.Thread.run(Thread.java:835) ~[na:na]

I have tried to change from:

1. fun find(@RequestParam data: MMap) to fun find(@RequestParam data: HashMap<String, Object>) and this works quite well but it is not what I really want to use because I have some shortcut in MMap so unless I have no choice otherwise it is not a good option for me.
2. class MMap : HashMap<String, Any>() to class MMap : HashMap<String, Object>() but nothing is working.

So, if anyone can help, please share some idea. Thank you.

Answer 1

You could do something like the following with extension functions and reified type parameters:

inline fun <reified T> Map<String, Any>.get(key: String) = get(key) as? T

You can then call the function on any Map like this:

@GetMapping("/user")
fun find(@RequestParam data: Map<String, Any>): Map<String, Any> {
    val id = data.get<String>("id") // string
    println(id)
    return data
}

Or non-generic extension functions will also work (This is probably the better way to do it because the parameter map will always be of type Map<String, String> and will not automatically convert numbers to integers):

fun Map<String, Any>.getString(key: String) = get(key) as? String
fun Map<String, Any>.getInt(key: String) = getString(key)?.toInt()