如何在mockito中模拟servlet上下文

Question

我正在为servlet编写测试用例。在测试中，我无法使用mockito将servlet上下文变量传递给servlet。我试过但是在servlet中它给出了空指针异常。下面我提供代码和测试代码：

代码是：

public class httpt_vb_getTableNames extends HttpServlet implements SingleThreadModel {

    int userId;
    String userName;
    String userPassword;

    public void service (HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println( "came to httpt_vb_getTableNames servlet");
        response.setContentType( "text/plain");
        ServletContext sc = getServletContext();
        ServletOutputStream servletOut = response.getOutputStream ();
}

测试代码是：

public class http_vb_getTableNamesServletTest {
@Mock
HttpServletRequest request;
@Mock
HttpServletResponse response;
@Mock
HttpSession session;
@Mock
RequestDispatcher rd;
@Mock
ServletOutputStream  servletOut;
@Mock
ServletContext sc;
@Mock
FilterConfig filterConfig;
public final static String Seperator = new Character((char)1).toString();
public final static String ContentDelimeter = new Character((char)2).toString();

@BeforeClass
public void setUp() throws Exception 
{
    MockitoAnnotations.initMocks(this);
    sc=mock(ServletContext.class);
}

@Test
public void test() throws Exception {
    DataSet ds=new DataSet();

    String buffer=ds.getUserId()+Seperator+ds.getUsername();
    ByteArrayOutputStream bos = new ByteArrayOutputStream ();
    ZipOutputStream out = new ZipOutputStream(bos);
    out.putNextEntry(new ZipEntry("request.txt"));
    out.write(buffer.getBytes("UTF-8"));
    out.closeEntry();
    out.close();
    bos.close();

    String b64String = Base64.encodeBase64String(bos.toByteArray());
    Reader inputString = new StringReader(b64String);
    BufferedReader reqbuffer = new BufferedReader(inputString);
    httpt_vb_getTableNames servlet=new httpt_vb_getTableNames();

    when(request.getReader()).thenReturn(reqbuffer);
    when(request.getServletContext()).thenReturn(sc);
    when(response.getOutputStream()).thenReturn(servletOut);
    when(sc.getRequestDispatcher("/jsp/admin/chooseNeighborhood.jsp")).thenReturn(rd);
    when(sc.getRequestDispatcher("/jsp/admin/joinNeighborhood.jsp")).thenReturn(rd);
    servlet.service(request, response);

    ArgumentCaptor<String> bufferCaptor = ArgumentCaptor.forClass(String.class);
    verify(servletOut).print(bufferCaptor.capture());
    String responseBody = bufferCaptor.getValue();       

    ZipInputStream zipIn = new ZipInputStream(new ByteArrayInputStream(Base64.decodeBase64(responseBody.toString().getBytes())));
    zipIn.getNextEntry();
    StringBuffer sb = new StringBuffer();
    ByteArrayOutputStream out1 = new ByteArrayOutputStream();
    IOUtils.copy(zipIn, out1);
    sb = new StringBuffer();
    sb.append(out1.toString("UTF-8"));

    String[] res=sb.toString().split(Seperator);        
    AssertJUnit.assertEquals("Success",res[0]);
}

}

任何人都可以建议我如何在mocktio中模拟servlet上下文？ 在此先感谢