code: @Test public void test_getAdaptiveExtension_defaultAdaptiveKey() throws Exception {
  {
      SimpleExt ext=ExtensionLoader.getExtensionLoader(SimpleExt.class).getAdaptiveExtension();
      Map<String,String> map=new HashMap<String,String>();
      URL url=new URL("p1","1.2.3.4",1010,"path1",map);
      String echo=ext.echo(url,"haha");
      assertEquals("Ext1Impl1-echo",echo);
    }
  {
      SimpleExt ext=ExtensionLoader.getExtensionLoader(SimpleExt.class).getAdaptiveExtension();
      Map<String,String> map=new HashMap<String,String>();
      map.put("simple.ext","impl2");
      URL url=new URL("p1","1.2.3.4",1010,"path1",map);
      String echo=ext.echo(url,"haha");
      assertEquals("Ext1Impl2-echo",echo);
    }
  }
  