How to use org.springframework.mock.web

  @Override
  public void flush() throws IOException {
    super.flush();
    setCommitted(true);
  }
}

/**
 * Set a single value for the specified HTTP parameter.
 * <p>If there are already one or more values registered for the given
 * parameter name, they will be replaced.
 */
public void setParameter(String name, String value) {
  setParameter(name, new String[] {value});
}

/**
 * Invalidates this session then unbinds any objects bound to it.
 * @throws IllegalStateException if this method is called on an already invalidated session
 */
@Override
public void invalidate() {
  assertIsValid();
  this.invalid = true;
  clearAttributes();
}

/**
 * Create new MockServletConfig.
 * @param servletContext the ServletContext that the JSP page runs in
 * @param request the current HttpServletRequest
 * @param response the current HttpServletResponse
 * @param servletConfig the ServletConfig (hardly ever accessed from within a tag)
 */
public MockPageContext(@Nullable ServletContext servletContext, @Nullable HttpServletRequest request,
    @Nullable HttpServletResponse response, @Nullable ServletConfig servletConfig) {
  this.servletContext = (servletContext != null ? servletContext : new MockServletContext());
  this.request = (request != null ? request : new MockHttpServletRequest(servletContext));
  this.response = (response != null ? response : new MockHttpServletResponse());
  this.servletConfig = (servletConfig != null ? servletConfig : new MockServletConfig(servletContext));
}

/**
 * Create a new {@link MockHttpServletRequest} based on the supplied
 * {@code ServletContext}.
 * <p>Can be overridden in subclasses.
 */
protected MockHttpServletRequest createServletRequest(ServletContext servletContext) {
  return new MockHttpServletRequest(servletContext);
}

@Override
public RequestPostProcessor beforeMockMvcCreated(ConfigurableMockMvcBuilder<?> builder,
    WebApplicationContext context) {
  return request -> {
    if (this.session != null) {
      request.setSession(this.session);
    }
    return request;
  };
}

  public MockHttpServletRequest postProcessRequest(MockHttpServletRequest request) {
    request.setAttribute(attr, value);
    return request;
  }
}

private void addHeaderValue(String name, Object value) {
  if (setSpecialHeader(name, value)) {
    return;
  }
  doAddHeaderValue(name, value, false);
}

@Override
public void setStatus(int status) {
  if (!this.isCommitted()) {
    this.status = status;
  }
}

/**
 * Invalidate this request, clearing its state.
 */
public void invalidate() {
  close();
  clearAttributes();
}

@Override
public void write(int b) throws IOException {
  super.write(b);
  super.flush();
  setCommittedIfBufferSizeExceeded();
}

@Override
public void setContentLengthLong(long contentLength) {
  this.contentLength = contentLength;
  doAddHeaderValue(HttpHeaders.CONTENT_LENGTH, contentLength, true);
}

  @Override
  public Object evaluate(javax.servlet.jsp.el.VariableResolver variableResolver) throws javax.servlet.jsp.el.ELException {
    return doEvaluate(expression, expectedType, functionMapper);
  }
};

@Override
public void setCharacterEncoding(String characterEncoding) {
  this.characterEncoding = characterEncoding;
  this.charset = true;
  updateContentTypeHeader();
}

public void setSession(HttpSession session) {
  this.session = session;
  if (session instanceof MockHttpSession) {
    MockHttpSession mockSession = ((MockHttpSession) session);
    mockSession.access();
  }
}

@Override
public long getLastAccessedTime() {
  assertIsValid();
  return this.lastAccessedTime;
}

/**
 * The default implementation delegates to {@link #encodeURL},
 * returning the given URL String as-is.
 * <p>Can be overridden in subclasses, appending a session id or the like
 * in a redirect-specific fashion. For general URL encoding rules,
 * override the common {@link #encodeURL} method instead, applying
 * to redirect URLs as well as to general URLs.
 */
@Override
public String encodeRedirectURL(String url) {
  return encodeURL(url);
}

private void setHeaderValue(String name, Object value) {
  if (setSpecialHeader(name, value)) {
    return;
  }
  doAddHeaderValue(name, value, true);
}

@Override
public void setContentLength(int contentLength) {
  this.contentLength = contentLength;
  doAddHeaderValue(HttpHeaders.CONTENT_LENGTH, contentLength, true);
}

@Override
@SuppressWarnings("rawtypes")
public Object evaluate(String expression, Class expectedType, javax.servlet.jsp.el.VariableResolver variableResolver,
    javax.servlet.jsp.el.FunctionMapper functionMapper) throws javax.servlet.jsp.el.ELException {
  return doEvaluate(expression, expectedType, functionMapper);
}