servlet编程 1 如何开发一个Servlet 2 .Servlet的映射路径 3 servlet缺省路径 4 Sevlet的生命周期(重点) 5 Servlet的自动加载 7 有参的init方法和无参的init方法 8 Servlet的多线程并发问题 9 ServletConfig对象 10 ServletContext对象

  1.1 步骤:

  1)编写java类,继承HttpServlet

  2)重新doGetdoPost方法

  3Servlet程序交给tomcat服务器运行!!

  3.1 servlet程序的class码拷贝到WEB-INF/classes目录

  3.2 web.xml文件中进行配置

<!-- 配置一个servlet -->
  <!-- servlet的配置 -->
  <servlet>
      <!-- servlet的内部名称,自定义。尽量有意义 -->
      <servlet-name>FirstServlet</servlet-name>
      <!-- servlet的类全名: 包名+简单类名 -->
      <servlet-class>gz.itcast.a_servlet.FirstServlet</servlet-class>
  </servlet>
  
  
  <!-- servlet的映射配置 -->
  <servlet-mapping>
      <!-- servlet的内部名称,一定要和上面的内部名称保持一致!! -->
      <servlet-name>FirstServlet</servlet-name>
      <!-- servlet的映射路径(访问servlet的名称) -->
      <url-pattern>/first</url-pattern>
  </servlet-mapping>

tomcat服务器启动时,首先加载webapps中的每个web应用的web.xml配置文件。

http://: http协议

localhost 到本地的hosts文件中查找是否存在该域名对应的IP地址

127.0.0.1

8080    找到tomcat服务器

/day10     tomcatwebapps目录下找 day10的目录

/first    资源名称。

1)在day10web.xml中查找是否有匹配的url-pattern的内容(/first

2)如果找到匹配的url-pattern,则使用当前servlet-name的名称到web.xml文件中查询是否相同名称的servlet配置

3)如果找到,则取出对应的servlet配置信息中的servlet-class内容:

字符串: gz.itcast.a_servlet.FirstServlet

通过反射:

a)构造FirstServlet的对象

b)然后调用FirstServlet里面的方法

2 .Servlet的映射路径

<servlet-mapping>
      <!-- servlet的内部名称,一定要和上面的内部名称保持一致!! -->
      <servlet-name>FirstServlet</servlet-name>
      <!-- servlet的映射路径(访问servlet的名称) -->
      <url-pattern>/first</url-pattern>
  </servlet-mapping>

                      url-pattern                   浏览器输入

精确匹配               /first                 http://localhost:8080/day10/first

          /itcast/demo1          http://localhost:8080/day10/itcast/demo1

模糊匹配             /*                   http://localhost:8080/day10/任意路径

        /itcast/*           http://localhost:8080/day10/itcast/任意路径

        *.后缀名     http://localhost:8080/day10/任意路径.do

        *.do

        *.action

        *.html(伪静态)

注意:

1url-pattern要么以 / 开头,要么以*开头。  例如, itcast是非法路径。

2)不能同时使用两种模糊匹配,例如 /itcast/*.do是非法路径

3)当有输入的URL有多个servlet同时被匹配的情况下:

  3.1 精确匹配优先。(长的最像优先被匹配)

  3.2 以后缀名结尾的模糊url-pattern优先级最低!!!

3 servlet缺省路径

servlet的缺省路径(<url-pattern>/</url-pattern>)是在tomcat服务器内置的一个路径。该路径对应的是一个DefaultServlet(缺省Servlet)。这个缺省的Servlet的作用是用于解析web应用的静态资源文件

问题: URL输入http://localhost:8080/day10/index.html 如何读取文件????

  1)到当前day10应用下的web.xml文件查找是否有匹配的url-pattern

  2)如果没有匹配的url-pattern,则交给tomcat的内置的DefaultServlet处理

  3DefaultServlet程序到day10应用的根目录下查找是存在一个名称为index.html的静态文件。

  4)如果找到该文件,则读取该文件内容,返回给浏览器。

  5)如果找不到该文件,则返回404错误页面。

结论: 先找动态资源,再找静态资源。

4 Sevlet的生命周期(重点)

4.1 引入

  Servlet的生命周期: servlet类对象什么时候创建,什么时候调用什么方法,什么时候销毁。

  以前的对象: new Student(); stu.study();   stu=null;

  Servlet程序的生命周期由tomcat服务器控制的!!!!

4.2 Servlet重要的四个生命周期方法

构造方法: 创建servlet对象的时候调用。默认情况下,第一次访问servlet的时候创建servlet对象 只调用1次。证明servlet对象在tomcat是单实例的。

init方法: 创建完servlet对象的时候调用。只调用1次。

service方法: 每次发出请求时调用。调用n次。

destroy方法: 销毁servlet对象的时候调用。停止服务器或者重新部署web应用时销毁servlet对象。

只调用1次。

4.3 伪代码演示servlet的生命周期

Tomtcat内部代码运行:

  1)通过映射找到到servlet-class的内容,字符串: gz.itcast.a_servlet.FirstServlet

  2)通过反射构造FirstServlet对象

    2.1 得到字节码对象

      Class clazz = class.forName("gz.itcast.a_servlet.FirstServlet");

    2.2 调用无参数的构造方法来构造对象

      Object obj = clazz.newInstance();     ---1.servlet的构造方法被调用

  3)创建ServletConfig对象,通过反射调用init方法

    3.1 得到方法对象

      Method m = clazz.getDeclareMethod("init",ServletConfig.class);

    3.2 调用方法

      m.invoke(obj,config);             --2.servletinit方法被调用

  4)创建requestresponse对象,通过反射调用service方法

    4.1 得到方法对象

    Method m=clazz.getDeclareMethod("service",HttpServletRequest.class,HttpServletResponse.class);

    4.2 调用方法

      m.invoke(obj,request,response);  --3.servletservice方法被调用

  5)当tomcat服务器停止或web应用重新部署,通过反射调用destroy方法

    5.1 得到方法对象

      Method m = clazz.getDeclareMethod("destroy",null);

    5.2 调用方法

      m.invoke(obj,null);            --4.servletdestroy方法被调用

4.4 用时序图来演示servlet的生命周期

代码演示:

package com.http.servletExercise;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;

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

public class servlet extends HttpServlet {
    private ServletConfig path;
    /**
     * Constructor of the object.
     */
    public servlet() {
        System.out.println("创建一个servlet!");
    }
    @Override
    public void init(ServletConfig config) throws ServletException {
        // TODO Auto-generated method stub
        this.path = config;
        super.init(config);
    }
    private void destory() {
        // TODO Auto-generated method stub
        System.out.println("销毁一个servlet");
    }

    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        System.out.println("收到一个请求!");
        super.service(req, resp);
    }
    /**
     * 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
     */
    int count = 0;
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setCharacterEncoding("gb2312");
        synchronized (servlet.class) {
            response.getWriter().write("这是第" + count + "个请求!");
            count++;
//            System.out.println(path.getInitParameter("path") + "MyWeb/temp.txt");/MyWeb/WebRoot/temp.txt
            BufferedReader in = new BufferedReader(new FileReader(path.getInitParameter("path") + "MyWeb/WebRoot/temp.txt"));
            String str;
            while((str = in.readLine()) != null){
                System.out.println(str);
            }
            in.close();
        }
        Enumeration<String> names = this.getServletConfig().getInitParameterNames();
        while(names.hasMoreElements()){
            String name = names.nextElement();
            System.out.println(name + ":" + this.getServletConfig().getInitParameter(name));
        }
        
    }

    /**
     * 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();
    }

}

5 Servlet的自动加载

默认情况下,第一次访问servlet的时候创建servlet对象。如果servlet的构造方法或init方法中执行了比较多的逻辑代码,那么导用户第一次访问sevrlet的时候比较慢。

改变servlet创建对象的时机: 提前到加载web应用的时候!!!

servlet的配置信息中,加上一个<load-on-startup>即可!!

<servlet>
    <servlet-name>LifeDemo</servlet-name>
    <servlet-class>gz.itcast.c_life.LifeDemo</servlet-class>
    <!-- 让servlet对象自动加载 -->
    <load-on-startup>1</load-on-startup>  注意: 整数值越大,创建优先级越低!!
  </servlet>

7 有参的init方法和无参的init方法

8 Servlet的多线程并发问题

  注意: servlet对象在tomcat服务器是单实例多线程的。

  因为servlet是多线程的,所以当多个servlet的线程同时访问了servlet的共享数据,如成员变量,可能会引发线程安全问题。

  解决办法:

    1)把使用到共享数据的代码块进行同步(使用synchronized关键字进行同步)

    2)建议在servlet类中尽量不要使用成员变量。如果确实要使用成员,必须同步。而且尽量缩小同步代码块的范围。(哪里使用到了成员变量,就同步哪里!!),以避免因为同步而导致并发效率降低。

Servlet学习:

     HttpServletRequest  请求对象:获取请求信息

     HttpServletResponse 响应对象: 设置响应对象

     ServletConfig对象    servlet配置对象

     ServletContext对象; servlet的上下文对象

9 ServletConfig对象

  9.1 作用

    ServletConfig对象: 主要是用于加载servlet的初始化参数。在一个web应用可以存在多个ServletConfig对象(一个Servlet对应一个ServletConfig对象)

  9.2 对象创建和得到

    创建时机: 在创建完servlet对象之后,在调用init方法之前创建。

    得到对象: 直接从有参数的init方法中得到!!!

  9.3 servlet的初始化参数配置

  <servlet>
    <servlet-name>ConfigDemo</servlet-name>
    <servlet-class>gz.itcast.f_config.ConfigDemo</servlet-class>
    <!-- 初始参数: 这些参数会在加载web应用的时候,封装到ServletConfig对象中 -->
    <init-param>
        <param-name>path</param-name>
        <param-value>e:/b.txt</param-value>
    </init-param>
  </servlet>

注意: servlet的参数只能由当前的这个sevlet获取!!!!

ServletConfigAPI

  java.lang.String getInitParameter(java.lang.String name)  根据参数名获取参数值

  java.util.Enumeration getInitParameterNames()    获取所有参数

     ServletContext getServletContext()     得到servlet上下文对象

  java.lang.String getServletName()       得到servlet的名称

代码练习:

package com.servlet.context;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;

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

public class contextExercise extends HttpServlet {

    /**
     * Constructor of the object.
     */
    public contextExercise() {
        super();
    }

    /**
     * The doDelete method of the servlet. <br>
     *
     * This method is called when a HTTP delete request is received.
     * 
     * @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 doDelete(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {

        // Put your code here
    }

    /**
     * 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 {
        
        ServletContext context = this.getServletContext();
        String contextPath = context.getContextPath();
        System.out.println(contextPath);
        System.out.println(context.getInitParameter("AAA"));
        
        Enumeration<String> names = context.getInitParameterNames();
        while(names.hasMoreElements()){
            String name = names.nextElement();
            System.out.println(name + ":" + context.getInitParameter(name));
        }
        
    }

    /**
     * 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();
    }

}

10 ServletContext对象

  10.1 引入

    ServletContext对象 ,叫做Servlet的上下文对象。表示一个当前的web应用环境。一个web应用中只有一 ServletContext对象。

  10.2 对象创建和得到

    创建时机:加载web应用时创建ServletContext对象。

    得到对象: ServletConfig对象的getServletContext方法得到

    我们设计:

    创建ServletConfig对象

    public void init( ServletConfig configServletContext context ){  多了一个参数

    得到ServletConfig对象

    得到ServletContext对象;

    }

  Sun公司设计

    1)创建ServletContext对象   ServletContext  context = new ServletContext()

    2)创建ServletConfig对象   ServetConfig config = new ServletConfig();

                                              config.setServletContxt(context);

                class  ServletConfig{

                    ServletContext context;

                    public ServletContext getServletContxt(){

                    return contxt;

                  }

                }

      public void init( ServletConfig config ){

        得到ServletConfig对象

        从ServletConfig对象中得到ServletContext对象

        SerlvetContext context = config.getServletContext();

       }

10.1 ServletContext对象的核心API(作用)

  java.lang.String getContextPath()   --得到当前web应用的路径

  java.lang.String getInitParameter(java.lang.String name)  --得到web应用的初始化参数

  java.util.Enumeration getInitParameterNames()  

  void setAttribute(java.lang.String name, java.lang.Object object) --域对象有关的方法

  java.lang.Object getAttribute(java.lang.String name)  

  void removeAttribute(java.lang.String name)  

  RequestDispatcher getRequestDispatcher(java.lang.String path)   --转发(类似于重定向)

  java.lang.String getRealPath(java.lang.String path)     --得到web应用的资源文件

  java.io.InputStream getResourceAsStream(java.lang.String path)  

10.3 得到web应用路径

  java.lang.String getContextPath()  用在请求重定向的资源名称中

10.4得到web应用的初始化参数(全局)

  java.lang.String getInitParameter(java.lang.String name)  --得到web应用的初始化参数

  java.util.Enumeration getInitParameterNames()  

  web应用参数可以让当前web应用的所有servlet获取!!!

10.5域对象有关的方法

  域对象:作用是用于保存数据,获取数据。可以在不同的动态资源之间共享数据

案例:   

Servlet1                   Servlet2

        name=eric                     

response.sendRedirect("/Servlet2?name=eric")             String request.getParameter("name");

保存到域对象中            从域对象获取

Student                  

方案1: 可以通过传递参数的形式,共享数据。局限:只能传递字符串类型。

方案2: 可以使用域对象共享数据,好处:可以共享任何类型的数据!!!!!

ServletContext就是一个域对象!!!!

保存数据:void setAttribute(java.lang.String name, java.lang.Object object)

获取数据: java.lang.Object getAttribute(java.lang.String name)  

删除数据: void removeAttribute(java.lang.String name)  

ServletContext域对象:作用范围在整个web应用中有效!!!

所有域对象:

HttpServletRequet 域对象

ServletContext域对象

HttpSession 域对象

PageContext域对象

10.6 转发

 RequestDispatcher getRequestDispatcher(java.lang.String path)

1)转发

   a)地址栏不会改变

   b)转发只能转发到当前web应用内的资源

  c)可以在转发过程中,可以把数据保存到request域对象中

2)重定向

  a)地址栏会改变,变成重定向到地址。

  b)重定向可以跳转到当前web应用,或其他web应用,甚至是外部域名网站。

  c)不能再重定向的过程,把数据保存到request中。

结论: 如果要使用request域对象进行数据共享,只能用转发技术!!!

 代码1:

package com.servlet.context;

import java.io.IOException;
import java.io.PrintWriter;

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

public class demo1 extends HttpServlet {

    /**
     * Constructor of the object.
     */
    public demo1() {
        super();
    }

    /**
     * The doDelete method of the servlet. <br>
     *
     * This method is called when a HTTP delete request is received.
     * 
     * @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 doDelete(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {

        // Put your code here
    }

    /**
     * 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 {

//        func1();
        request.setAttribute("name", "lisi");
        this.getServletContext().getRequestDispatcher("/demo2").forward(request, response);
        
    }

    private void func1() {
        ServletContext context = this.getServletContext();
        Student student = new Student("张三", 15, "男");
        context.setAttribute("zs", student);
    }
    class Student{
        private String name;
        private int age;
        private String sex;
        public String getName() {
            return name;
        }
        public void setName(String name) {
            this.name = name;
        }
        public int getAge() {
            return age;
        }
        public void setAge(int age) {
            this.age = age;
        }
        public String getSex() {
            return sex;
        }
        public void setSex(String sex) {
            this.sex = sex;
        }
        public Student(String name, int age, String sex) {
            super();
            this.name = name;
            this.age = age;
            this.sex = sex;
        }
        @Override
        public String toString() {
            return "Student [name=" + name + ", age=" + age + ", sex=" + sex
                    + "]";
        }
        
    }

    /**
     * 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();
    }

}

代码2:

package com.servlet.context;

import java.io.IOException;
import java.io.PrintWriter;

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

import com.servlet.context.demo1.Student;

public class demo2 extends HttpServlet {

    /**
     * Constructor of the object.
     */
    public demo2() {
        super();
    }

    /**
     * The doDelete method of the servlet. <br>
     *
     * This method is called when a HTTP delete request is received.
     * 
     * @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 doDelete(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {

        // Put your code here
    }

    /**
     * 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 {

//        func2();
        System.out.println(request.getAttribute("name"));
    }

    private void func2() {
        ServletContext context = this.getServletContext();
        Student zs = (Student)context.getAttribute("zs");
        System.out.println(zs);
    }

    /**
     * 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();
    }

}

总结:

  Servlet编程:

  Servlet生命周期(重点)

  其他都是应用的东西(敲代码练习)

作业:

  改造通讯录程序

  servlet+xml版本

要求:

  1)使用浏览器操作系统

  提示:

  添加联系人:

  设计一个添加联系人html页面

  保存逻辑:

    AddServlet  (接收页面数据(getParameter()),使用dom4j保存到xml

  修改联系人

    QueryServlet xml查询修改的联系人, 把联系人显示到一个html页面(response.getWriter.write("<html></html>")));

  修改保存逻辑:

    UpdateServlet ( 接收页面数据,把数据保存xml )

  删除联系人:

      输入删除idhtml页面

  删除逻辑:

    DeleteServle( 接收id, 在xml文件中删除对应的联系人)