Servlet 2 生命周期 ServletConfig 自定义缺省Servlet

目录:

Servlet 主要作用 通过程序来生成 网页
Servlet 生命周期
读取本地工程下的文件
读取web工程发布后的文件
获得输入字符串，统计字母次数
使用ServletConfig对象 向Servlet传递初始化信息
读取 全局初始化参数
统计浏览器访问次数案例
自定义缺省Servlet

*注:web.xml配置文件在最下面,注意查看

Servlet 主要作用 通过程序来生成 网页

package cn.itcast.servlet;

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

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

/**
 * Servlet 主要作用 通过程序来生成 网页
 * 
 * 继承 HttpServlet
 * 
 * 覆盖 doGet 和 doPost
 * 
 * @author seawind
 * 
 */
public class HelloServlet extends HttpServlet {
    @Override
    public void init() throws ServletException {
    }

    @Override
    public void init(ServletConfig config) throws ServletException {
    }

    @Override
    // 处理 HTTP GET方式请求
    protected void doGet(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {

        System.out.println("hello servlet do get ...");
        // 处理中文字符集
        response.setContentType("text/html;charset=utf-8");
        // 生成网页 需要使用 response
        PrintWriter out = response.getWriter();

        // 通过响应输出流 生成一个网页
        out.println("<html>"); // 生成的HTML 源代码
        out.println("<body>");
        out.println("<h1>Hello Servlet</h1>");
        out.println("当前的时间是：" + new Date().toLocaleString());
        out.println("</body>");
        out.println("</html>");
    }

    @Override
    // 处理 HTTP POST 方式请求
    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        System.out.println("hello servlet do post ...");
    }
}

Servlet 生命周期

package cn.itcast.servlet;

import java.io.IOException;

import javax.servlet.Servlet;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

/**
 * Servlet 生命周期
 * 
 * @author seawind
 * 
 */
public class InitServlet implements Servlet {
    // 构造函数
    public InitServlet() {
        System.out.println("init servlet 创建对象");
    }

    @Override
    // Servlet对象销毁操作
    public void destroy() {
        System.out.println("destroy...");
    }

    @Override
    // Servlet对象初始化操作
    public void init(ServletConfig config) throws ServletException {
        System.out.println("init...");
    }

    @Override
    // Servlet对象 提供服务
    public void service(ServletRequest req, ServletResponse res)
            throws ServletException, IOException {
        System.out.println("service ...");
    }

    @Override
    public ServletConfig getServletConfig() {
        return null;
    }

    @Override
    public String getServletInfo() {
        return null;
    }

}

读取本地工程下的文件

package cn.itcast.io;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class FileReaderTest {
    public static void main(String[] args) throws IOException {
        // 编写四个文件 路径，调用readfile方法 完成文件读取
        // 读取1.txt
        String filename1 = "1.txt";
        readfile(filename1);
        // 读取2.txt
        String filename2 = "WebRoot/2.txt";
        readfile(filename2);
        // 读取3.txt
        String filename3 = "WebRoot/WEB-INF/3.txt";
        readfile(filename3);
        // 读取4.txt
        String filename4 = "src/4.txt";
        readfile(filename4);
        // 读取4.txt
        String filename5 = FileReaderTest.class.getResource("/4.txt").getFile();
        readfile(filename5);

    }

    public static void readfile(String filename) throws IOException {
        BufferedReader bufferedReader = new BufferedReader(new FileReader(
                filename));
        String line;
        while ((line = bufferedReader.readLine()) != null) {
            System.out.println(line);
        }

        bufferedReader.close();
    }
}

读取web工程发布后的文件

package cn.itcast.servlet.contextdemo3;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

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

/**
 * 读取 1.txt 2.txt 3.txt 4.txt
 * 
 * @author seawind
 * 
 */
public class ReadFileServlet extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 读取 1.txt （不会被发布到tomcat，没法读）
        // 读取 2.txt
        String filename1 = "/2.txt";
        // 根据相对于网站根目录绝对路径 ---- 获得磁盘绝对路径
        filename1 = getServletContext().getRealPath(filename1);
        System.out.println(filename1);
        readfile(filename1);

        // 读取3.txt
        String filename2 = getServletContext().getRealPath("/WEB-INF/3.txt");
        readfile(filename2);

        // 读取4.txt
        String filename3 = getServletContext().getRealPath(
                "/WEB-INF/classes/4.txt");
        readfile(filename3);

        // 读取4.txt 用类加载器读取
        String filename4 = ReadFileServlet.class.getResource("/4.txt")
                .getFile();
        readfile(filename4);
    }

    public static void readfile(String filename) throws IOException {
        BufferedReader bufferedReader = new BufferedReader(new FileReader(
                filename));
        String line;
        while ((line = bufferedReader.readLine()) != null) {
            System.out.println(line);
        }

        bufferedReader.close();
    }

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

}

获得输入字符串，统计字母次数

html

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
<h1>输入字符串，统计每个字母出现次数</h1>
<form action="/day5/countletter" method="post">
    请输入任意字符串 <textarea rows="5" cols="80" name="content"></textarea>
    <input type="submit" value="提交" />
</form>
</body>
</html>
package cn.itcast.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;

/**
 * 获得输入字符串，统计字母次数
 * 
 * @author seawind
 * 
 */
public class CountLetterServlet extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 获得输入字符串
        String content = request.getParameter("content");

        // 转换字符串小写
        content = content.toLowerCase();

        // 定义存放字母出现次数 数组
        int[] times = new int[26]; // 在0 位置存放 a次数，在1位置存放b次数

        // 遍历字符串
        for (int i = 0; i < content.length(); i++) {
            char c = content.charAt(i);
            // 判断c 必须是一个字母
            if (Character.isLetter(c)) {
                times[c - 'a']++;
            }
        }

        // 将统计字母出现次数 显示在浏览器上
        response.setContentType("text/html;charset=utf-8");// 设置字符串
        PrintWriter out = response.getWriter();

        for (int i = 0; i < times.length; i++) {
            int lettertimes = times[i];// 字母次数
            char letter = (char) ('a' + i);
            out.println(letter + "字母出现了" + lettertimes + "次<br/>");
        }
    }

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

}

使用ServletConfig对象 向Servlet传递初始化信息

package cn.itcast.servlet;

import java.io.IOException;
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;

/**
 * 使用ServletConfig对象 向Servlet传递初始化信息
 * 
 * @author seawind
 * 
 */
public class ConfigServlet extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 获得 Servlet对象 初始化信息
        ServletConfig config = getServletConfig();
        System.out.println(config.getInitParameter("company"));
        System.out.println(config.getInitParameter("address"));

        // 通过所有初始化参数名称 遍历 值
        Enumeration<String> names = config.getInitParameterNames();
        while (names.hasMoreElements()) {
            String name = names.nextElement();
            System.out.println(name + ":" + config.getInitParameter(name));
        }
    }

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

}

读取 全局初始化参数

package cn.itcast.servlet.contextdemo1;

import java.io.IOException;

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

/**
 * 读取 全局初始化参数
 * 
 * @author seawind
 * 
 */
public class ContextServlet1 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 获得 ServletContext对象
        // ServletContext context = getServletConfig().getServletContext();
        ServletContext context = getServletContext();

        System.out.println(context.getInitParameter("name"));

        // 输出文件 MIME类型
        System.out.println(context.getMimeType("1.html"));
        System.out.println(context.getMimeType("2.jpg"));
        System.out.println(context.getMimeType("3.ppt"));

        // 记录日志
        context.log("我很好，天晴了！");
    }

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

}

统计浏览器访问次数案例

package cn.itcast.servlet.contextdemo2;

import java.io.IOException;

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

/**
 * 每次请求 访问Servlet，将访问次数 +1 保存ServletContext
 * 
 * @author seawind
 * 
 */
public class VisitServlet extends HttpServlet {

    @Override
    // 对访问次数 进行初始化
    public void init() throws ServletException {
        ServletContext context = getServletContext();
        // 保存数据 到ServletContext
        context.setAttribute("times", 0);// 初始化访问次数为0
    }

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 有了一次请求，访问次数 +1
        ServletContext context = getServletContext();

        // 取出访问次数
        int times = (Integer) context.getAttribute("times");
        times++;
        // 将次数 放回去
        context.setAttribute("times", times);

        System.out.println("visitServlet 被访问了一次");
    }

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

}
package cn.itcast.servlet.contextdemo2;

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;

/**
 * 读取Context中保存访问次数，显示浏览器页面上
 * 
 * @author seawind
 * 
 */
public class ShowVisitTimesServlet extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 获得ServletContext对象
        ServletContext context = getServletContext();
        // 读取访问次数
        int times = (Integer) context.getAttribute("times");

        // 将次数显示在浏览器上
        response.setContentType("text/html;charset=utf-8");
        PrintWriter out = response.getWriter();

        out.println("<h1>VisitServlet被访问了的" + times + "次</h1>");
    }

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

}

自定义缺省Servlet

package cn.itcast.servlet;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

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

/**
 * 自定义缺省Servlet
 * 
 * @author seawind
 * 
 */
public class DefaultServlet extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        System.out.println("缺省Servlet 获得执行...");
        // 获得客户端访问资源路径
        String requestURI = request.getRequestURI(); // /day5/hello.html
        // getContextPath ----- /day5
        String path = requestURI.substring(request.getContextPath().length());
        // path ---- /hello.html

        // 将path 转换绝对磁盘路径
        String absolutePath = getServletContext().getRealPath(path);
        File file = new File(absolutePath);
        if (file.exists() && file.isFile()) {
            // 将文件内容返回客户端
            InputStream in = new FileInputStream(file);
            OutputStream out = response.getOutputStream();
            int b;
            while ((b = in.read()) != -1) {
                out.write(b);
            }
            in.close();
            out.close();
        } else {
            // 文件不存在，或者是一个目录
            response.setStatus(404);
        }
    }

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

}

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" 
    xmlns="http://java.sun.com/xml/ns/javaee" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
    http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
  <!-- 全局初始化参数 , 任何Servlet都可以读取-->
  <context-param>
      <param-name>name</param-name>
      <param-value>张三</param-value>
  </context-param>    
    
  <!-- 注册Servlet 程序, 为Servlet class 起一个名字 -->
  <servlet>
      <servlet-name>HelloServlet</servlet-name>
      <servlet-class>cn.itcast.servlet.HelloServlet</servlet-class>
  </servlet>
  
  <servlet>
      <servlet-name>InitServlet</servlet-name>
      <servlet-class>cn.itcast.servlet.InitServlet</servlet-class>
      <!-- 通过 load-on-startup 让Servlet 随服务器启动 加载，完成初始化 -->
      <!-- 中间值 是一个数字 取值 0-9 ，代表优先级 0最高 -->
      <load-on-startup>0</load-on-startup>
  </servlet>
  <servlet>
    <servlet-name>HelloServlet2</servlet-name>
    <servlet-class>cn.itcast.servlet.HelloServlet2</servlet-class>
  </servlet>
  <servlet>
    <servlet-name>HelloServlet3</servlet-name>
    <servlet-class>cn.itcast.servlet.HelloServlet3</servlet-class>
  </servlet>
  <servlet>
    <servlet-name>ConfigServlet</servlet-name>
    <servlet-class>cn.itcast.servlet.ConfigServlet</servlet-class>
    <!-- 通过 init-param 标签 传递初始化 信息 -->
    <init-param>
        <param-name>company</param-name>
        <param-value>传智播客</param-value>
    </init-param>
    <init-param>
        <param-name>address</param-name>
        <param-value>春生泰克</param-value>
    </init-param>
  </servlet>
  <servlet>
    <servlet-name>ContextServlet1</servlet-name>
    <servlet-class>cn.itcast.servlet.contextdemo1.ContextServlet1</servlet-class>
  </servlet>
  <servlet>
    <servlet-name>VisitServlet</servlet-name>
    <servlet-class>cn.itcast.servlet.contextdemo2.VisitServlet</servlet-class>
  </servlet>
  <servlet>
    <servlet-name>ShowVisitTimesServlet</servlet-name>
    <servlet-class>cn.itcast.servlet.contextdemo2.ShowVisitTimesServlet</servlet-class>
  </servlet>
  <servlet>
    <servlet-name>ReadFileServlet</servlet-name>
    <servlet-class>cn.itcast.servlet.contextdemo3.ReadFileServlet</servlet-class>
  </servlet>
  <servlet>
    <servlet-name>DefaultServlet</servlet-name>
    <servlet-class>cn.itcast.servlet.DefaultServlet</servlet-class>
  </servlet>
  <servlet>
    <servlet-name>CountLetterServlet</servlet-name>
    <servlet-class>cn.itcast.servlet.CountLetterServlet</servlet-class>
  </servlet>









  
  <!-- 配置Servlet 访问 路径 -->
  <servlet-mapping>
      <servlet-name>HelloServlet</servlet-name>
      <url-pattern>/hello</url-pattern>
  </servlet-mapping>
  
  <servlet-mapping>
      <servlet-name>InitServlet</servlet-name>
      <url-pattern>/init</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>HelloServlet2</servlet-name>
    <url-pattern>/hello2</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>HelloServlet3</servlet-name>
    <url-pattern>/hello3</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>ConfigServlet</servlet-name>
    <url-pattern>/config</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>ContextServlet1</servlet-name>
    <url-pattern>/context1</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>VisitServlet</servlet-name>
    <url-pattern>/visit</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>ShowVisitTimesServlet</servlet-name>
    <url-pattern>/show</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>ReadFileServlet</servlet-name>
    <url-pattern>/readfile</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>DefaultServlet</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>CountLetterServlet</servlet-name>
    <url-pattern>/countletter</url-pattern>
  </servlet-mapping>
  
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
</web-app>
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原文地址：https://www.cnblogs.com/vaer/p/3925112.html