编写一个servlet,发送请求参数是username,如果username是zhangsan那么转发到a.html;是lisi重定向到b.html;是wangwu弹框展示很好，到达c.html;是zhaoliu展示按钮到浏览器，按钮上展示zhaoliu;否则展示字符串你好到网页浏览器

好的，以下是代码实现：

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class MyServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String username = request.getParameter("username");
        
        if (username.equals("zhangsan")) {
            request.getRequestDispatcher("/a.html").forward(request, response);
        } else if (username.equals("lisi")) {
            response.sendRedirect("/b.html");
        } else if (username.equals("wangwu")) {
            response.setContentType("text/html;charset=UTF-8");
            response.getWriter().write("<script>alert('很好');</script><a href='/c.html'>跳转到c.html</a>");
        } else if (username.equals("zhaoliu")) {
            response.setContentType("text/html;charset=UTF-8");
            response.getWriter().write("<input type='button' value='" + username + "' onclick='window.location.href=\"/d.html\"'>");
        } else {
            response.setContentType("text/html;charset=UTF-8");
            response.getWriter().write("你好");
        }
    }
    
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }
}

在web.xml中配置servlet：

<servlet>
    <servlet-name>MyServlet</servlet-name>
    <servlet-class>com.example.MyServlet</servlet-class>
</servlet>

<servlet-mapping>
    <servlet-name>MyServlet</servlet-name>
    <url-pattern>/myservlet</url-pattern>
</servlet-mapping>

这样，当访问/myservlet?username=zhangsan时，就会转发到a.html；访问/myservlet?username=lisi时，就会重定向到b.html；访问/myservlet?username=wangwu时，就会弹框展示“很好”，并跳转到c.html；访问/myservlet?username=zhaoliu时，就会展示一个按钮，点击按钮可以跳转到d.html，按钮上展示的是“zhaoliu”；其他情况下，就会展示字符串“你好”到浏览器。