Servlet 2 生命周期 ServletConfig 自定义缺省Servlet-白红宇

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Servlet 2 生命周期 ServletConfig 自定义缺省Servlet

阅读量：5059 次

发布时间：2019-06-12

本文共 16078 字，大约阅读时间需要 53 分钟。

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(""); // 生成的HTML 源代码        out.println("");        out.println("Hello Servlet
");        out.println("当前的时间是：" + new Date().toLocaleString());        out.println("");        out.println("");    }    @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


     Insert title here输入字符串，统计每个字母出现次数
     
          请输入任意字符串

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
");        }    }    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
     
       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("VisitServlet被访问了的" + times + "次
");    }    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


     
       
        
            
       
        name
             
       
        张三
         
                
        
            
       
        HelloServlet
             
       
        cn.itcast.servlet.HelloServlet
         
          
            
       
        InitServlet
             
       
        cn.itcast.servlet.InitServlet
             
             
             
       
        0
         
        
          
       
        HelloServlet2
           
       
        cn.itcast.servlet.HelloServlet2
         
        
          
       
        HelloServlet3
           
       
        cn.itcast.servlet.HelloServlet3
         
        
          
       
        ConfigServlet
           
       
        cn.itcast.servlet.ConfigServlet
           
           
               
        
         company
                
        
         传智播客
            
           
               
        
         address
                
        
         春生泰克
            
         
        
          
       
        ContextServlet1
           
       
        cn.itcast.servlet.contextdemo1.ContextServlet1
         
        
          
       
        VisitServlet
           
       
        cn.itcast.servlet.contextdemo2.VisitServlet
         
        
          
       
        ShowVisitTimesServlet
           
       
        cn.itcast.servlet.contextdemo2.ShowVisitTimesServlet
         
        
          
       
        ReadFileServlet
           
       
        cn.itcast.servlet.contextdemo3.ReadFileServlet
         
        
          
       
        DefaultServlet
           
       
        cn.itcast.servlet.DefaultServlet
         
        
          
       
        CountLetterServlet
           
       
        cn.itcast.servlet.CountLetterServlet
         
          
        
            
       
        HelloServlet
             
       
        /hello
         
          
            
       
        InitServlet
             
       
        /init
         
        
          
       
        HelloServlet2
           
       
        /hello2
         
        
          
       
        HelloServlet3
           
       
        /hello3
         
        
          
       
        ConfigServlet
           
       
        /config
         
        
          
       
        ContextServlet1
           
       
        /context1
         
        
          
       
        VisitServlet
           
       
        /visit
         
        
          
       
        ShowVisitTimesServlet
           
       
        /show
         
        
          
       
        ReadFileServlet
           
       
        /readfile
         
        
          
       
        DefaultServlet
           
       
        /
         
        
          
       
        CountLetterServlet
           
       
        /countletter
         
          
          
       
        index.jsp

转载于:https://www.cnblogs.com/vaer/p/3925112.html

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