2022年Servlect课时六——:案例 servlet的常用对象-阿里云开发者社区

要点复习

1 Servlet的定义？

Servlet是Java Servlet的简称，称为小服务程序或服务连接器，用Java编写的服务器端程序，主要功能在于交互式地浏览和修改数据，生成动态Web内容。

狭义的Servlet是指Java语言实现的一个接口，广义的Servlet是指任何实现了这个Servlet接口的类，一般情况下，人们将Servlet理解为后者。

Servlet运行于支持Java的应用服务器中。

从原理上讲，Servlet可以响应任何类型的请求，但绝大多数情况下Servlet只用来扩展基于HTTP协议的Web服务器。最早支持Servlet标准的是JavaSoft的Java Web Server，一些其它的基于Java的Web服务器开始支持标准的Servlet。

2Servlet的定义的四种形式？

public class OneServlet implements Servlet { } //采用接口

public class TwoServlet extends GenericServlet {}//采用继承

public class ThreeServlet extends HttpServlet{}//采用继承

@WebServlet(urlPatterns="/d")

public class fourServlect extends HttpServlet {}采用快键

ALT+/ 在写代码中常用

3 Servlet get与post的区别？

第一点：get请求和post请求的区别:

浏览器使用get请求访问servlet服务器的时候doget方法接收

浏览器使用post请求访问servlet服务器的时候dopost方法接收

第二点

get请求所带的数据是拼接在地址上的，地址的长度是有限的，1kb=1024 一个字母2个字节 512字母

post传输数据是不受限制的

第三点

登录功能一律不允许使用get请求给服务器发送数据

浏览器默认为get请求

4 Servlet的周期？

servlet周期

构造方法（创建servlet 对象执行）

Servlet 初始化后调用 init () 方法。

Servlet 调用 service() 方法来处理客户端的请求。

Servlet 销毁前调用 destroy() 方法长时间未访问。

最后，Servlet 是由 JVM 的垃圾回收器进行垃圾回收的。

5 Servlet的注册在哪里？

web.xml文件

<!-- 注册oneServlet -->
  <!--  第一部分 注册OneServlet-->
  <servlet>
  <!--  srvlet 增加名字  -->
  <servlet-name>OneServlet</servlet-name>
  <!--注册servlet地址  -->
  <servlet-class>com.servlet.OneServlet</servlet-class>
  <load-on-startup>4</load-on-startup>
  </servlet>
  <!--第二部分 :设置一个浏览器可以访问的servlet的地址 -->
  <servlet-mapping>
  <servlet-name>OneServlet</servlet-name>
  <!--设置浏览器地址  -->
  <url-pattern>/a</url-pattern>
  <!-- 设置地址访问一定加/asd -->
  </servlet-mapping>

7 Servlet的常用对象有哪些?

ServletConfig

ServletContext 方法的作用

HttpServlet

HttpServletRequest

HttpServletResponseHttpServletRequest

ServletConfig

获取静态数据的二个方式

在web.xml文件中写

<!-- 注意<init-param>写在<servlet>里面 -->
 <init-param>
 <param-name>home</param-name>
 <param-value>二家酒店</param-value>
 </init-param>

方式二

/**
 * Servlet implementation class Servlet2
 */
@WebServlet(urlPatterns = "/Servlet2",initParams = {
        @WebInitParam(name="aaaa",value="张三"),
        @WebInitParam(name="age",value="23"),
        @WebInitParam(name="height",value="179cm"),
        @WebInitParam(name="weight",value="60kg")
})
public class Servlet2 extends HttpServlet {

ServletContext 方法的作用

ServletContext {con 上下文 }

tomcat 服务器为每个项目创建一个对象

ServletContext

1个web项目只有一个ServletContext对象

ServletContext 服务器开始创建结束而消失

ServletContext 作用同一个项目共享数据。

1 共享静态数据

2 共享动态数据写在java代码

3 共享文件数据

* 创建对象

* ServletContext sc=getServletContext();获取对象

* sc.setAttribute("pq", "排球"); 接收对象

* 删除对象 sc.removeAttribute("pq");

HttpServle

HttpServlet首先必须读取Http请求的内容。Servlet容器负责创建HttpServlet对象，并把Http请求直接封装到HttpServlet对象中，大大简化了HttpServlet解析请求数据的工作量。HttpServlet容器响应Web客户请求流程如下：

创建项目下图所示

package Aservlet;
import java.io.IOException;
import java.util.Enumeration;
import javax.servlet.Servlet;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.xml.ws.Response;
public class OneServlet  implements Servlet{
  public OneServlet() {
    System.out.println(" Servlet构造方法");
  }
  @Override
  public void destroy() {
    System.out.println("Servlet的销毁，释放cpu");
  }
  @Override
  public ServletConfig getServletConfig() {
    // TODO Auto-generated method stub
    return null;
  }
  @Override
  public String getServletInfo() {
    // TODO Auto-generated method stub
    return null;
  }
  @Override
  public void init(ServletConfig config) throws ServletException {
    //增加静态数据;到web.html去定义
    /*
     * 第一种方式
     */
    String a=config.getInitParameter("hont");
    System.out.println(a+"输入值为？？？");
    System.out.println("加载数据信息");
    /*
     * 第二种方式
     */
    Enumeration<String> e=config.getInitParameterNames();
    while (e.hasMoreElements()) {
      String key = (String) e.nextElement();
      String value=config.getInitParameter(key);
      System.out.println(key+"@@@@@@"+value);
    }
  }
  @Override
  public void service(ServletRequest arg0, ServletResponse arg1) throws ServletException, IOException {
    System.out.println("Servlet处于运行状态");
  }
}

package Aservlet;
import java.io.IOException;
import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebInitParam;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
 * Servlet implementation class Servlet1
 */
@WebServlet(urlPatterns = "/TwoServlet",initParams = {
    //增加静态数据的第一个学生
    @WebInitParam(name="a",value="胡一伤悲"),
    @WebInitParam(name="age",value="30岁"),
    @WebInitParam(name="height",value="179cm"),
    @WebInitParam(name="weight",value="60kg")
})
public class TwoServlet extends HttpServlet {
  private static final long serialVersionUID = 1L;
    /**
     * Default constructor. 
     */
    public TwoServlet() {
        // TODO Auto-generated constructor stub
    }
  /**
   * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
   */
    @Override
    public void init() throws ServletException {
      // TODO Auto-generated method stub
      super.init();
      //定义4个静态数据
      ServletConfig config=getServletConfig();
      String a=config.getInitParameter("a");
      String b=config.getInitParameter("age");
      String c=config.getInitParameter("height");
      String e=config.getInitParameter("weight");
      System.out.println(a+"===="+b+"#######"+c+"-----"+e);
      System.out.println(e);
    }
  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    //设置 发送给浏览器的文本信息HTML文本格式
    //response.setContentType("text/html");
    response.setContentType("text/html");
    //设置发送给浏览器文本utf-8
    //response.setCharacterEncoding("UTF-8");
    response.setCharacterEncoding("UTF-8");
    //因为浏览器是使用get请求
    //所以Servlet do-get
    //servlet1相打篮球
    //1获取ServletContext对象
    ServletContext  sc=getServletContext();
    //获取web.xml文件中的镜头数据
    String a=sc.getInitParameter("LQ");
    //获得servlet4共享的排球
    String b= (String) sc.getAttribute("PQ");
    //删除排球
    sc.removeAttribute("PQ");
    //给浏览器发送数据
    response.getWriter().append("Servlet1获得静态数据用来访问lq:"+a);
    response.getWriter().append("response.getWriter().append方法打印内容");
    response.getWriter().append("Servlet1获得静态数据用来访问pq:"+b);
  }
  /**
   * @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);
  }
}

package Aservlet;
import java.io.IOException;
import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebInitParam;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
 * Servlet implementation class Servlet3
 */
@WebServlet(urlPatterns = "/TreeServlet",initParams = {
    @WebInitParam(name="aaa",value="胡三定"),
    @WebInitParam(name="age",value="67岁"),
    @WebInitParam(name="height",value="180cm"),
    @WebInitParam(name="weight",value="60kg"),
})
public class TreeServlet extends HttpServlet {
  private static final long serialVersionUID = 1L;
    /**
     * Default constructor. 
     */
    public TreeServlet() {
        // TODO Auto-generated constructor stub
    }
    @Override
    public void init() throws ServletException {
      // TODO Auto-generated method stub
      super.init();
      ServletConfig config=getServletConfig();
      String a=config.getInitParameter("aaa");
      String b=config.getInitParameter("age");
      String c=config.getInitParameter("height");
      String e=config.getInitParameter("weight");
      System.out.println(a+"===="+b+"========"+c+"======="+e);
    }
  /**
   * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
   */
  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // TODO Auto-generated method stub
    //设置 发送给浏览器的文本信息HTML文本格式
        //response.setContentType("text/html");
        response.setContentType("text/html");
        //设置发送给浏览器文本utf-8
        //response.setCharacterEncoding("UTF-8");
        response.setCharacterEncoding("UTF-8");
        //因为浏览器是使用get请求
        //所以Servlet do-get
        //servlet1相打篮球
        //1获取ServletContext对象
        ServletContext  sc=getServletContext();
        //获取web.xml文件中的镜头数据
        String a=sc.getInitParameter("LQ");
        //给浏览器发送数据
        response.getWriter().append("Servlet3获得静态数据用来访问lq:"+a);
  }
  /**
   * @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);
  }
}

package Aservlet;
/*
 * ServletContext {con 上下文  }
tomcat 服务器为每个项目创建一个对象 
 ServletContext
1个web项目只有一个ServletContext对象
ServletContext 服务器开始创建    结束是 没有
ServletContext 作用   同一个项目共享数据。
1  共享静态数据
2  共享动态数据 写在java代码
3  共享文件数据
 * 创建对象
 *  ServletContext sc=getServletContext();获取对象
 * sc.setAttribute("pq", "排球"); 接收对象 
 *   删除对象 sc.removeAttribute("pq");
 */
import java.io.IOException;
import java.io.OutputStream;
import javax.servlet.ServletContext;
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 Servlet4
 */
@WebServlet("/fourServlet")
public class fourServlet extends HttpServlet {
  private static final long serialVersionUID = 1L;
    /**
     * @see HttpServlet#HttpServlet()
     * 由个人共享出来的动态数据
     */
    public fourServlet() {
        super();
        // TODO Auto-generated constructor stub
    }
  /**
   * 创建对象 ServletContext sc=getServletContext();获取对象
   * sc.setAttribute("pq", "排球"); 接收对象 
   * 删除对象 sc.removeAttribute("pq");
   * 
   * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
   */
  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    //servlet4共享班级 共享数据
    //共享动态数据
    response.setContentType("text/html");
    //设置发送给浏览器文本utf-8
    //response.setCharacterEncoding("UTF-8");
    response.setCharacterEncoding("UTF-8");
    //获取ServletContext 对象
    ServletContext sc=getServletContext();
    //将排球共享数据 setAttribute方法共享数据。
    //在java中object是任何数据类型的父类。
    //身份的多种类型；向上转型
    sc.setAttribute("pq", "排球");
    sc.setAttribute("yq", "羽毛球");
    sc.setAttribute("rd", "读书");
    //身份的多种类型；向上转型(强制转型)
    //获得动态数据
    //疯狂java讲义
    //getimitParameter只能获得静态数据
     String  a= (String) sc.getAttribute("pq");
     String  b= (String) sc.getAttribute("yq");
     String  c= (String) sc.getAttribute("rd");
    response.getWriter().append("Servlet4获得动态数据 "+a);
    response.getWriter().append("Servlet4获得动态数据 "+b);
    response.getWriter().append("Servlet4获得动态数据 "+c);
  }
  /**
   * @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);
  }
}

package Aservlet;
import java.io.IOException;
import java.io.InputStream;
import java.util.Set;
import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebInitParam;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
 * Servlet implementation class Servlet1
 */
@WebServlet(urlPatterns = "/FiveServlet5", initParams = {
    // 增加静态数据的第一个学生
    @WebInitParam(name = "a", value = "文件下载"),
})
public class FiveServlet5 extends HttpServlet {
  private static final long serialVersionUID = 1L;
  /**
   * Default constructor.
   */
  public FiveServlet5() {
    // TODO Auto-generated constructor stub
  }
  /**
   * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
   *      response)
   */
  @Override
  public void init() throws ServletException {
    // TODO Auto-generated method stub
    super.init();
    // 定义4个静态数据
    ServletConfig config = getServletConfig();
    String a = config.getInitParameter("a");
    System.out.println(a);
  }
  protected void doGet(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
    response.setContentType("text/html");
    response.setCharacterEncoding("UTF-8");
    // 获得text.txt完整路径
    ServletContext sc = getServletContext();
    // 指定文件名称获取完整路径
    String path = sc.getRealPath("text.txt");
    // 控制台打印输出文件完整路径
    System.out.println(path);
    // 指定文件夹
    Set<String> oSet = sc.getResourcePaths("/WEB-INF");
    for (String string : oSet) {
      System.out.println(string);
    }
    // response.getWriter().append("Served at: ").append(request.getContextPath());
    response.getWriter().append("Servlet1获得静态数据用来访问lq:");
    response.getWriter().append("response.getWriter().append方法打印内容");
    response.getWriter().append("Servlet1获得静态数据用来访问pq:");
  }
  /**
   * @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);
  }
}

package Aservlet;
import java.awt.image.RescaleOp;
import java.io.IOException;
import java.io.OutputStream;
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 Servlet1
 */
@WebServlet("/SxiServlet")
public class SxiServlet extends HttpServlet {
  private static final long serialVersionUID = 1L;
    /**
     * @see HttpServlet#HttpServlet()
     */
    public SxiServlet() {
        super();
        // TODO Auto-generated constructor stub
    }
  /**
   * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
   */
  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // response  回复  当浏览器根据地址发送请求servlet.servlet 使用response对象回复对象
    //设置servlet发送的数据支撑HTML格式
    response.setContentType("text/html");
    //设置发送servlet 浏览html格式 utf-8
    response.setCharacterEncoding("UTF-8");
    //response  回复  内容/数据/消息
    String info="hellow world java";
    String info1="你好,<span style='color:yellow'> java jsp</span>";
    //使用response获得输出
    OutputStream  os =response.getOutputStream();
    os.write(info.getBytes());
    os.write(info1.getBytes());
  }
  /*
   * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
   * 
   */
  }

package Aservlet;
import java.io.IOException;
import java.io.InputStream;
import java.util.Set;
import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebInitParam;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
 * Servlet implementation class Servlet1
 */
@WebServlet(urlPatterns = "/SevenServlet",initParams = {
    //增加静态数据的第一个学生
    @WebInitParam(name="a",value="胡五伤悲"),
    @WebInitParam(name="age",value="47岁"),
    @WebInitParam(name="height",value="169cm"),
    @WebInitParam(name="weight",value="60kg")
})
public class SevenServlet extends HttpServlet {
  private static final long serialVersionUID = 1L;
    /**
     * Default constructor. 
     */
    public SevenServlet() {
        // TODO Auto-generated constructor stub
    }
  /**
   * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
   */
    @Override
    public void init() throws ServletException {
      // TODO Auto-generated method stub
      super.init();
      //定义4个静态数据
      ServletConfig config=getServletConfig();
      String a=config.getInitParameter("a");
      String b=config.getInitParameter("age");
      String c=config.getInitParameter("height");
      String e=config.getInitParameter("weight");
      System.out.println(a+"===="+b+"#######"+c+"-----"+e);
      System.out.println(e);
      System.out.println("创建静态数据的方法");
      System.out.println("ServletConfig config=getServletConfig();");
      System.out.println("访问静态数据的方法");
      System.out.println("String a=config.getInitParameter(\"a\");");
    }
  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    response.setContentType("text/html");
    response.setCharacterEncoding("UTF-8");
    // 获得text.txt完整路径
        ServletContext sc=getServletContext();
        //指定文件名称获取完整路径
        String path=sc.getRealPath("A.txt");
        //控制台打印输出文件完整路径
        System.out.println(path);
      //  指定文件夹
      Set<String> oSet=sc.getResourcePaths("/WEB-INF");
      for (String string : oSet) {
        System.out.println(string);
      }
      //response.getWriter().append("Served at: ").append(request.getContextPath());
    response.getWriter().append("Servlet1获得静态数据用来访问lq:");
    response.getWriter().append("response.getWriter().append方法打印内容");
    response.getWriter().append("Servlet1获得静态数据用来访问pq:");
  }
  /**
   * @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);
  }
}