Java Web 开发实战：创建服务器接收网页请求并实现不同功能

该题需要使用 Java Web 开发的相关知识，包括 Servlet、Tomcat 等，以下是代码示例：

首先创建一个 Servlet 类，命名为 MainServlet，实现 doGet 方法，根据请求路径的不同，调用不同的方法：

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.stream.Collectors;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class MainServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String path = req.getServletPath();
        if (path.equals("/print")) {
            print();
        } else if (path.equals("/zhishu")) {
            zhishu();
        } else if (path.equals("/sort")) {
            sort();
        } else if (path.equals("/string")) {
            string(req, resp);
        } else if (path.equals("/date")) {
            date(req, resp);
        } else if (path.equals("/arr")) {
            arr();
        } else if (path.equals("/set")) {
            set();
        } else if (path.equals("/map")) {
            map(req, resp);
        } else if (path.equals("/io")) {
            io();
        } else if (path.equals("/thread")) {
            thread();
        } else if (path.equals("/streamapi")) {
            streamapi();
        } else {
            resp.setContentType("text/plain");
            resp.setStatus(404);
            PrintWriter out = resp.getWriter();
            out.println("404 Not Found");
            out.close();
        }
    }

    private void print() {
        int num = 12345678;
        // 第一种方式
        String str = String.valueOf(num);
        for (int i = str.length() - 1; i >= 0; i--) {
            System.out.print(str.charAt(i));
        }
        System.out.println();

        // 第二种方式
        char[] arr = str.toCharArray();
        for (int i = arr.length - 1; i >= 0; i--) {
            System.out.print(arr[i]);
        }
        System.out.println();

        // 第三种方式
        List<Integer> list = Arrays.stream(arr).map(c -> Integer.parseInt(String.valueOf(c))).collect(Collectors.toList());
        Collections.reverse(list);
        list.forEach(System.out::print);
        System.out.println();
    }

    private void zhishu() {
        for (int i = 100; i <= 200; i++) {
            boolean flag = true;
            for (int j = 2; j <= Math.sqrt(i); j++) {
                if (i % j == 0) {
                    flag = false;
                    break;
                }
            }
            if (flag) {
                System.out.print(i + " ");
            }
        }
        System.out.println();
    }

    private void sort() {
        int[] arr = new int[10];
        for (int i = 0; i < arr.length; i++) {
            arr[i] = (int) (Math.random() * 100);
        }
        System.out.println("排序前：" + Arrays.toString(arr));
        for (int i = 0; i < arr.length - 1; i++) {
            for (int j = 0; j < arr.length - 1 - i; j++) {
                if (arr[j] > arr[j + 1]) {
                    int temp = arr[j];
                    arr[j] = arr[j + 1];
                    arr[j + 1] = temp;
                }
            }
        }
        System.out.println("排序后：" + Arrays.toString(arr));
    }

    private void string(HttpServletRequest req, HttpServletResponse resp) throws IOException {
        String host = req.getServerName();
        resp.setContentType("text/plain");
        PrintWriter out = resp.getWriter();
        out.println(host);
        out.close();
    }

    private void date(HttpServletRequest req, HttpServletResponse resp) throws IOException {
        resp.setContentType("text/plain");
        PrintWriter out = resp.getWriter();
        out.println("当前时间：" + new java.util.Date().toString());
        out.close();
    }

    private void arr() {
        int n = 20;
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) {
            arr[i] = i + 1;
        }
        int count = 0;
        int index = -1;
        while (count < n) {
            for (int i = 0; i < 3; i++) {
                index++;
                if (index == n) {
                    index = 0;
                }
                while (arr[index] == 0) {
                    index++;
                    if (index == n) {
                        index = 0;
                    }
                }
            }
            System.out.println("第" + (count + 1) + "轮删除：" + arr[index]);
            arr[index] = 0;
            count++;
        }
    }

    private void set() {
        String str = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < 4; i++) {
            int index = (int) (Math.random() * str.length());
            sb.append(str.charAt(index));
        }
        System.out.println(sb.toString());
    }

    private void map(HttpServletRequest req, HttpServletResponse resp) throws IOException {
        String str = req.getParameter("str");
        if (str == null) {
            resp.setContentType("text/html");
            PrintWriter out = resp.getWriter();
            out.println("<html><body>");
            out.println("<form method=\"GET\" action=\"/map\">");
            out.println("输入字符串：<input type=\"text\" name=\"str\">");
            out.println("<input type=\"submit\" value=\"统计\">");
            out.println("</form>");
            out.println("</body></html>");
            out.close();
        } else {
            int[] count = new int[256];
            for (int i = 0; i < str.length(); i++) {
                char c = str.charAt(i);
                count[c]++;
            }
            for (int i = 0; i < count.length; i++) {
                if (count[i] > 0) {
                    System.out.println((char) i + "：" + count[i]);
                }
            }
        }
    }

    private void io() throws IOException {
        FileInputStream fis = new FileInputStream("input.txt");
        FileOutputStream fos = new FileOutputStream("output.txt");
        byte[] buffer = new byte[1024];
        int length;
        while ((length = fis.read(buffer)) != -1) {
            fos.write(buffer, 0, length);
        }
        fis.close();
        fos.close();
    }

    private void thread() {
        int count = 100;
        int[] tickets = new int[count];
        for (int i = 0; i < count; i++) {
            tickets[i] = i + 1;
        }
        for (int i = 0; i < count; i++) {
            int index = i;
            new Thread(() -> {
                synchronized (MainServlet.class) {
                    int ticket = tickets[index];
                    try {
                        Thread.sleep((long) (Math.random() * 1000));
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println(Thread.currentThread().getName() + " 抢到了第" + ticket + "张票");
                }
            }, "用户" + (i + 1)).start();
        }
    }

    private void streamapi() {
        List<Integer> list = Arrays.stream(new int[100]).map(i -> (int) (Math.random() * 2000)).boxed().collect(Collectors.toList());
        System.out.println("原始数据：" + list);
        list = list.stream().filter(i -> i >= 100 && i <= 1000).distinct().collect(Collectors.toList());
        System.out.println("过滤后：" + list);
        list = list.stream().sorted().collect(Collectors.toList());
        System.out.println("排序后：" + list);
        list = list.stream().sorted(Collections.reverseOrder()).collect(Collectors.toList());
        System.out.println("倒序后：" + list);
        list = list.stream().limit(10).collect(Collectors.toList());
        System.out.println("取前10个：" + list);
        list = list.stream().skip(5).collect(Collectors.toList());
        System.out.println("跳过前5个：" + list);
        list = list.stream().map(i -> i * 2).collect(Collectors.toList());
        System.out.println("每个数乘以2：" + list);
        list = list.stream().distinct().collect(Collectors.toList());
        System.out.println("去重后：" + list);
        System.out.println("转换成Set集合：" + list.stream().collect(Collectors.toSet()));
    }
}

在 web.xml 文件中配置 Servlet：

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.0" 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_3_0.xsd">
    <servlet>
        <servlet-name>MainServlet</servlet-name>
        <servlet-class>MainServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>MainServlet</servlet-name>
        <url-pattern>/print</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>MainServlet</servlet-name>
        <url-pattern>/zhishu</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>MainServlet</servlet-name>
        <url-pattern>/sort</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>MainServlet</servlet-name>
        <url-pattern>/string</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>MainServlet</servlet-name>
        <url-pattern>/date</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>MainServlet</servlet-name>
        <url-pattern>/arr</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>MainServlet</servlet-name>
        <url-pattern>/set</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>MainServlet</servlet-name>
        <url-pattern>/map</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>MainServlet</servlet-name>
        <url-pattern>/io</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>MainServlet</servlet-name>
        <url-pattern>/thread</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>MainServlet</servlet-name>
        <url-pattern>/streamapi</url-pattern>
    </servlet-mapping>
</web-app>

最后启动 Tomcat 服务器，通过浏览器访问对应的请求路径即可看到效果。例如：http://localhost:9898/print