認証フィルターを使い、パラメータの変化によって指定のページに遷移するサーブレットを作りたいのですが…

package union;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class SampleFilter1 implements Filter {
    

    @Override
    public void destroy() {
        
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        
         HttpServletRequest req = (HttpServletRequest) request;
        
        String param = req.getParameter("param");
        
        if (param != "1") {

            ((HttpServletResponse)response).sendRedirect("/html/error.html");
        }
        
        chain.doFilter(request, response);

    }

    @Override
    public void init(FilterConfig config) throws ServletException {
        
    }

}

package union;

import java.io.IOException;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * @author 
 *
 */
public class SampleServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;
    
    @Override
    protected void doGet (HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
        
        response.setContentType("text/html; charset=UTF-8");
            
        String  disp ＝ "/html/sample.html";
        RequestDispatcher dispatch = request.getRequestDispatcher(disp);
        dispatch.forward(request, response);
        
    }

}

<web-app>
  <filter>
  <filter-name>sampleFilter1</filter-name>
  <filter-class>sampleFilter</filter-class>
  </filter>
  <filter-mapping>
  <filter-name>sampleFilter1</filter-name>
  <url-pattern>/sampleServlet</url-pattern>
  </filter-mapping>

 <servlet>
    <servlet-name>sampleServlet1</servlet-name>
    <servlet-class>sampleServlet</servlet-class>
  </servlet>
<servlet-mapping>
    <servlet-name>sampleServlet</servlet-name>
    <url-pattern>/sampleServlet</url-pattern>
  </servlet-mapping>

<!--エラーページ-->
<error-page>
<error-code>404</error-code>
<location>/html/error.html</location>
</error-page>

<error-page>
<error-code>500</error-code>
<location>/html/error.html</location>
</error-page>
</web-app>