Servlet技术--开发一个Servlet（二）

小鱼儿 2021-09-23 06:04 357阅读 0赞

MyEclipse下:

步骤：

*  新建一个web project工程[servletTest][]

在MyEclipse中，与项目开发环境对应的运行调试环境的跟目录为     \{Tomcat\_Install\}\\webapps\\ [servletTest][] 那么，该项目的URL位置就是：http://server IP or Domain:port/ [servletTest][]，如下：

![20190825191056927.png][]

*  在项目src目录下创建类包：com.contrlos，在此包中创建Servlet类。MyEclipse会自动将这个Servlet配置好对外的访问路径，而且会自动的继承HttpServlet类。这样我们就可以在doGet和doPost方法中处理客户机的请求了。做法是：
 *  右键单击“com.contrlos”，→new →servlet，在对话窗体中填写类名：FirstServlet，方法选择doGet和doPost，其他选择默认即可

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjcxNzkyOA_size_16_color_FFFFFF_t_70][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjcxNzkyOA_size_16_color_FFFFFF_t_70 1][]

package cn.contrlos;
    
    import java.io.IOException;
    import javax.servlet.ServletException;
    import javax.servlet.annotation.WebServlet;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    /**
     * Servlet implementation class FirstServlet
     */
    @WebServlet("/FirstServlet")
    public class FirstServlet extends HttpServlet {
    	private static final long serialVersionUID = 1L;
           
        /**
         * @see HttpServlet#HttpServlet()
         */
        public FirstServlet() {
            super();
            // TODO Auto-generated constructor stub
        }
    
    	/**
    	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
    	 */
    	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		// TODO Auto-generated method stub
    		response.getWriter().append("Served at: ").append(request.getContextPath());
    	}
    
    	/**
    	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
    	 */
    	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		// TODO Auto-generated method stub
    		doGet(request, response);
    	}
    
    }

然后发现怎么都运行不了，我是在这里弄的，项目右键

![2019082520293915.png][]

后来我在这里搞，other那个：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjcxNzkyOA_size_16_color_FFFFFF_t_70 2][]

感觉图标也是一样。。不知道为什么不同

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjcxNzkyOA_size_16_color_FFFFFF_t_70 3][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjcxNzkyOA_size_16_color_FFFFFF_t_70 4][]

可以/servlet去掉，这样在运行的时候不用加这个路径

package cn.contrlos;
    
    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 SecondServlet 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程序编写好后，需要在Servlet容器中进行配置，才能进行正常访问。 Servlet的配置一般通过配置文件web. xml来实现。web.xml在Web项目的WEB-INF文件夹内（可以ctrl点击那个Servlet的路径，能点进去）

看一下web.xml,自动配置好了

<?xml version="1.0" encoding="UTF-8"?>
    <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
      <display-name>servletTest</display-name>
      
      <servlet>
        <description>This is the description of my J2EE component</description>
        <display-name>This is the display name of my J2EE component</display-name>
        <servlet-name>SecondServlet</servlet-name>
        <servlet-class>cn.contrlos.SecondServlet</servlet-class>
      </servlet>
    
      <servlet-mapping>
        <servlet-name>SecondServlet</servlet-name>
    
        <url-pattern>/servlet/SecondServlet</url-pattern>
      </servlet-mapping>
    </web-app>

输入[http://localhost:8080/servletTest/servlet/SecondServlet][http_localhost_8080_servletTest_servlet_SecondServlet]

![20190825203659876.png][]

javax.servlet.\* 存放与HTTP协议无关的一般性Servlet类；javax.servlet.http.\* 增加了与HTTP协议有关的功能

FirstServlet类继承HttpServlet类。所有Servlet都必须实现javax.servlet.Servlet接口，通常从javax.servlet.GenericServlet或javax.servlet.http.HttpServlet选择其一来实现。如果写的Servlet代码和HTTP协议无关，那么必须继承GenericServlet类；若有关，就必须继承HttpServlet类

**doGet用于对GET请求方法做出响应；doPost用于对Post请求方法做出响应**

可以设定内容类型为HTML网页GBK编码，利用HttpServletResponse接口的setContentType()方法来设定内容类型，显示为HTML网页类型，因此，内容类型设为“text/html”，这是HTML网页的标准MIME类型值

![20190825192715478.png][]

用getWriter()方法返回PrintWriter类型的out对象，它与PrintStream类似，但是它能够对Java的Unicode字符进行编码转换

![20190825192930702.png][]

[servletTest]: http://localhost:8080/servletTest/index.jsp
[20190825191056927.png]: /images/20210923/2933c559ac3044c8b435c35a6965e5ce.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjcxNzkyOA_size_16_color_FFFFFF_t_70]: /images/20210923/6684a015e3274745928414d0553a194e.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjcxNzkyOA_size_16_color_FFFFFF_t_70 1]: /images/20210923/8a5c863731cf4ab3823c7af306c07c62.png
[2019082520293915.png]: /images/20210923/8384be52f8e44fe4bec1bbcdacade952.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjcxNzkyOA_size_16_color_FFFFFF_t_70 2]: /images/20210923/4bbc3a5a9b7d45368653120c0840235d.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjcxNzkyOA_size_16_color_FFFFFF_t_70 3]: /images/20210923/620bb8e5ff23461d8473b74ebed6eb61.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjcxNzkyOA_size_16_color_FFFFFF_t_70 4]: /images/20210923/e27ac5b3e88f48ab861416122a8af7ef.png
[http_localhost_8080_servletTest_servlet_SecondServlet]: http://localhost:8080/servletTest/servlet/SecondServlet
[20190825203659876.png]: /images/20210923/a4405e3c0aa744b988b1c6ccb5724dc3.png
[20190825192715478.png]: /images/20210923/b0e1440cb26848249c470024dd7b99c9.png
[20190825192930702.png]: /images/20210923/bb34e50ffc0144ea9c18f62b7d60256e.png