Java reflection getDeclaredMethod throws NoSuchMethodException

Question

I have a private method getListSonarMetricsFromRegistry declared in the Class SonarRestApiServiceImpl that I want to call, with Java reflection, but I get the exception:

java.lang.NoSuchMethodException: com.cma.kpibatch.rest.impl.SonarRestApiServiceImpl.getListSonarMetricsFromRegistry(java.util.HashMap)
at java.lang.Class.getDeclaredMethod(Class.java:2130)
at com.test.service.rest.SonarRestApiServiceImplTest.testGetListSonarMetricsFromRegistry(SonarRestApiServiceImplTest.java:81)

I tried to use Java reflection, like below :

    @Test
    public void initTest() throws NoSuchMethodException, SecurityException, IllegalAccessException,
            IllegalArgumentException, InvocationTargetException {
        Map<Long, KpiMetric> tmp = new HashMap<>();
        Method method = sonarRestApi.getClass().getDeclaredMethod("getListSonarMetricsFromRegistry", tmp.getClass());
        method.setAccessible(true);
        List<String> list = (List<String>) method.invoke(sonarRestApi, registry.getKpiMetricMap());
    }

Here is the getListSonarMetricsFromRegistry method declaration:

//This method works correctly, it returns a List of String without error
private List<String> getListSonarMetricsFromRegistry(Map<Long, KpiMetric> map) {
    return //something
}

When I look at the Exception, the trace print my Class with the right package, right name, right method name and right parameters:

com.test.rest.impl.SonarRestApiServiceImpl.getListSonarMetricsFromRegistry(java.util.HashMap) But it say that this method does not exist, which is strange.

The similar questions provided by Stackoverflow did help, but I still have the same Exception.

HashMap is not the same as Map - one is the interface the other the implementation. Your call to getDeclaredMethod uses tmp.getClass which will return HasMap.class and your method takes a Map. You need to call with Map.class. — Boris the Spider
– Boris the Spider, Commented Aug 27, 2019 at 10:02

Jan Thomä · Accepted Answer · 2019-08-27 10:09:39Z

1

I think your problem is that you give a HashMap class instance as an argument to getDeclaredMethod while the method actually accepts Map class instance. Remember, that all generic arguments are stripped out on compilation, so a Map<Whatever,WhateverElse> simply becomes a Map when doing reflection at runtime. So try:

 Method method = sonarRestApi.getClass().getDeclaredMethod("getListSonarMetricsFromRegistry", Map.class);

On a related note, basing tests on reflectively calling private API is probably not a good way to keep tests maintainable in the long run. I'm not sure why you would need to do this trickery, but if you can, try to find a way that works with public API.

edited Aug 27, 2019 at 10:09

answered Aug 27, 2019 at 10:06

Jan Thomä

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1 Comment

Hamza Ince Over a year ago

Indeed that solve the issue, you are also right about what I am doing, being a trick, I'll see if I can find another way of doing, thanks for the help

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