纠正一些关于Servlet的误解

刚才看了几篇对Servlet总结的文章,发现他们都有异曲同工之处,上来就是这样写的:

Servlet三个要素:
      1.必须继承自HttpServlet
      2.必须实现doGet()或者doPost()
      3.必须在web.xml中配置Servlet
      <servlet>
      <servlet-name> </servlet-name>
      <servlet-class> </servlet-class>
      </servlet>

      <servlet-mapping>
      <servlet-name> </servlet-name>
      <url-pattern> </url-pattern>
      </servelt-mapping>

    有谁说了编写一个Servlet必须继承自HttpServlet类,必须实现doGet()或者doPost() ,难道实现Servlet接口就不行了吗?
    其实编写一个Servlet主要有三种方法,一是实现Servlet接口,二是继承抽象类GenericServlet,三是继承HttpServlet类.下面分别用这三种方法去实现Servlet:
    (一)要从实现Servlet接口来编写一个Servlet是比较麻烦的,因为必须实现Servlet接口中的所有方法,Servlet接口主要定义了五个方法,它们分别为:
(1)void init(ServletConfig config) throws ServletException
(2)ServletConfig getServletConfig()
(3)void service(ServletRequest req,ervletResponse res) throws ServletException,IOException
(4)String getServletInfo()
(5)void destroy()
下面用实现Servlet接口的方法编写一个Servlet:

import javax.servlet. * ;
import java.io. * ;
public class TestServlet implements Servlet

{
public void init(ServletConfig config) throws ServletException

{
        System.out.println("init");
        }
    public ServletConfig getServletConfig()

{
        reture null;
        }
    public void service(ServletRequest req,ServletResponse res)
        throws ServletException,IOException

{
            //这里可以实现请求后要做的内容
            PrintWriter out = response.getWriter();
      out.println("Hello World!");

            }
    public String getServletInfo()

{
        return null;
        }
    public void destroy()

{
        System.out.println("destory");
        }
    }

(二)继承抽象类GenericServlet编写一个Serlvet,这个相对比实现Servlet接口要容易一点,GenericServlet类中只有一个抽象方法,即service(ServletRequest req, ServletResponse res),只要实现这个方法就行了,下面看例子:

import javax.servlet. * ;
import java.io.IOException;

public TestGenericServlet extends GenericServlet

{
public abstract void service(ServletRequest req,ServletResponse res)
throws ServletException,IOException

{
     PrintWriter out = response.getWriter();
     out.println("Hello World!");
     }
}

(3)继承HttpServlet类编写Servlet应该是最容易的,而且是最常见的,我们一般要编写Servlet直接继承这个类就行了,重写doGet()或者doPost()方法即可,下面看例子:

import javax.servlet.http. * ;
import javax.servlet. * ;
import java.io. * ;

public TestHttpServlet extends HttpServlet

{
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException

{
  response.setContentType("text/html;charset=gb2312");
  PrintWriter out = response.getWriter();

  out.println("<html>");
  out.println("<head>");
  out.println("<title>HelloWorld</title>");
  out.println("</head>");
  out.println("<body bgcolor=\"white\">");
  out.println("<hr>");
  out.println("HelloWorld");
  out.println("</body></html>");
}

public void doPost(HttpServletRequest request, HttpServletResponse response)
   throws IOException, ServletException

{
doGet(request, response);
}

}

纠正一些关于Servlet的误解

纠正一些关于Servlet的误解

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