Servlet mocking with Mockito

When writing custom servlets, it can be quite useful to unit test them.  In my case, I used a combination of testng and mockito.  The basic idea is simple; mock a HttpServletRequest, and a HttpServletResponse and pass them to the custom servlet.  There is a bit more too it, so here’s an example.

final HttpServletRequest httpServletRequest = mock(HttpServletRequest.class);
when(httpServletRequest.getPathInfo()).thenReturn("/lineup/world.xml");
final HttpServletResponse httpServletResponse = mock(HttpServletResponse.class);
final StubServletOutputStream servletOutputStream = new StubServletOutputStream();
when(httpServletResponse.getOutputStream()).thenReturn(servletOutputStream);
final ServletConfig servletConfig = mock(ServletConfig.class);
when(servletConfig.getInitParameter("defaultPool")).thenReturn("testpool1");

This sets up an HttpServletRequest, an HttpServletResponse, a ServletConfig where i can pass in parameters that the container would have read from web.xml, and a “StubServletOutputStream”, which is just a convenient wrapper around a ByteArrayOutputStream.

My StubServletOutputStream looks like this:

public class StubServletOutputStream extends ServletOutputStream {
 public ByteArrayOutputStream baos = new ByteArrayOutputStream();
   public void write(int i) throws IOException {
    baos.write(i);
 }
}

It’s necessary to init() the servlet, something the container would normally do:

final MyServlet myServlet = new MyServlet();
myServlet.init(servletConfig);

Finally; I invoke my servlet, and check the output:

restCacheServlet.doGet(httpServletRequest, httpServletResponse);
final byte[] data = servletOutputStream.baos.toByteArray();
Assert.assertNotNull(data);
Assert.assertTrue(data.length > 0);