面试题练习（9）——简单介绍一下Servlet、Servlet的基本架构

傷城~ 2022-02-18 10:41 215阅读 0赞

**简单介绍一下Servlet：**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxMDQyNTk1_size_16_color_FFFFFF_t_70][]

> ### [Java中servlet的简单介绍][Java_servlet] ###
> 
> ### [servlet简单介绍][servlet] ###
> 
> ### [Servlet简单介绍（一）][Servlet] ###

**Servlet的基本架构：**

> <table> 
>  <tbody> 
>   <tr> 
>    <td colspan="2">HttpServlet类是一个抽象类，可以从该类派生出一个子类来实现一个HttpServlet，接受来自Web站点的请求（该请求来自访问该Web站点的客户浏览器），并将处理后的响应结果发回Web站点（Web站点再将响应结果发送给客户浏览器），在HttpServlet的子类中，必须至少重载下表中的其中一种方法。<br> 方法名&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 用途<br> doGet&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 如果Servlet支持Http GET请求，用于Http GET请求<br> doPost&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;如果Servlet支持Http POST请求，用于Http POST请求<br> doPut&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;如果Servlet支持Http PUT请求，用于Http PUT请求<br> doDelete&nbsp; &nbsp; &nbsp; &nbsp; 如果Servlet支持Http DELETE请求，用于Http DELETE请求<br> init和destroy&nbsp; &nbsp;如果需要管理Servlet生命周期内所持有资源，可以重载这两个方法&nbsp;</td> 
>   </tr> 
>  </tbody> 
> </table>
> 
> 参考资料:通常，不重载service方法，对于上表中的每一种HTTP请求，service方法通过分派它们到相应的Handler线程（doXXX方法）来处理这些标准的HTTP请求。  
> 同样地，通常也不重载doOptions和doTrace方法，service方法通过分派它们到doTrace和doOptions来支持HTTP1.1 TRACE和OPTIONS。  
> Servlet通常运行在多线程的服务器中，因此，所编写的Servlet代码必须能够处理并行请求和对数据资源的同步访问。共享资源包括内存中的数据（例如：实例或类变量）和外部对象（例如：文件、数据库连接或网络连接）。  
>   
> Protected void doGet(HttpServletRequest req,HttpServletResponse resp)throws ServletException,IOException\{\}  
> 从service方法授并处理HTTP GET请求。GET方法允许客户读取来自Web服务器的信息，客户通过传递一个带URL的查询字符串可以告诉服务器它需什么信息。  
> 重载支持GET请求的doGet方法还将自动支持HTTP HEAD请求，HEAD请求也是一个GET请求，它得到的返回响应中只有一个请求头（header）字段，而没有响应信息的内容。  
> 如果重载方法，应该从该请求读数据，在响应中设置整个headers，访问PrintWriter或输出流对象，最后写响应数据。当设置headers时，应确保包含content type和encoding。如果使用PrintWriter对象返回响应，在存取PrintWriter对象之前必须设置content type。  
> Servlet引擎必须在写响应数据之前写headers，因为在写数据之后headers随时都可能被刷新。  
> 如果设置Content-Length头，Servlet可以使用一个持久稳固的连接来将其响应返回给客户机，动态地改善性能。  
> 如果请求的格式不正确，doGet方法将返回一个HTTP BAD\_REQUEST信息。  
> 参数req为一个HttpServletRequest对象，含有客户的Servlet请求；resp是一个HttpServletResponse对象，含有Servlet发送给客户的响应。

简洁版：
    
    package test;
    
    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 ServletName extends HttpServlet {
    
        public void doPost(HttpServletRequest request, HttpServletResponse response)
                throws ServletException, IOException {
    
        }
    
        public void doGet(HttpServletRequest request, HttpServletResponse response)
                throws ServletException, IOException {
    
            }
    }
    
    或者
    
    package com.ht.servlet;
    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 ServletName extends HttpServlet{
    
        private static final long serialVersionUID = 1L;
    
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp)
                throws ServletException, IOException {
            // TODO Auto-generated method stub
            super.doGet(req, resp);
        }
    
        @Override
        protected void doPost(HttpServletRequest req, HttpServletResponse resp)
                throws ServletException, IOException {
            // TODO Auto-generated method stub
            super.doPost(req, resp);
        }
        }

这是新建Servlet默认的代码：
    
    package com.ht.servlet;
    
    import java.io.IOException;
    import java.io.PrintWriter;
    
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    public class test extends HttpServlet {
    
    	/**
    	 * The doGet method of the servlet. <br>
    	 *
    	 * This method is called when a form has its tag value method equals to get.
    	 * 
    	 * @param request the request send by the client to the server
    	 * @param response the response send by the server to the client
    	 * @throws ServletException if an error occurred
    	 * @throws IOException if an error occurred
    	 */
    	public void doGet(HttpServletRequest request, HttpServletResponse response)
    			throws ServletException, IOException {
    
    		response.setContentType("text/html");
    		PrintWriter out = response.getWriter();
    		out
    				.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
    		out.println("<HTML>");
    		out.println("  <HEAD><TITLE>A Servlet</TITLE></HEAD>");
    		out.println("  <BODY>");
    		out.print("    This is ");
    		out.print(this.getClass());
    		out.println(", using the GET method");
    		out.println("  </BODY>");
    		out.println("</HTML>");
    		out.flush();
    		out.close();
    	}
    
    	/**
    	 * The doPost method of the servlet. <br>
    	 *
    	 * This method is called when a form has its tag value method equals to post.
    	 * 
    	 * @param request the request send by the client to the server
    	 * @param response the response send by the server to the client
    	 * @throws ServletException if an error occurred
    	 * @throws IOException if an error occurred
    	 */
    	public void doPost(HttpServletRequest request, HttpServletResponse response)
    			throws ServletException, IOException {
    
    		response.setContentType("text/html");
    		PrintWriter out = response.getWriter();
    		out
    				.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
    		out.println("<HTML>");
    		out.println("  <HEAD><TITLE>A Servlet</TITLE></HEAD>");
    		out.println("  <BODY>");
    		out.print("    This is ");
    		out.print(this.getClass());
    		out.println(", using the POST method");
    		out.println("  </BODY>");
    		out.println("</HTML>");
    		out.flush();
    		out.close();
    	}
    }

> ### [Servlet的基本架构或简单架构][Servlet 1]【主要是第一问的答案】 ###
> 
> ### [基本架构简单讲述，如下图：][Link 1] ###

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxMDQyNTk1_size_16_color_FFFFFF_t_70 1][]

> ### 可以了解下：[面试题练习（13）——（含JAVA或JSP解决方案）主要七种乱码处理、get提交与post提交的区别、doPost,doGet的区别][13_JAVA_JSP_get_post_doPost_doGet]  ###

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[Java_servlet]: http://www.php.cn/java-article-375097.html
[servlet]: https://www.2cto.com/kf/201711/506910.html
[Servlet]: https://blog.csdn.net/zt15732625878/article/details/80877896
[Servlet 1]: https://blog.csdn.net/mr_zhangxiaocao/article/details/73351301
[Link 1]: https://blog.csdn.net/rshp_520/article/details/17240599
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxMDQyNTk1_size_16_color_FFFFFF_t_70 1]: /images/20220218/82d36052a05f4adb94f98f61b5a36f97.png
[13_JAVA_JSP_get_post_doPost_doGet]: https://blog.csdn.net/qq_41042595/article/details/85873308