java web爬虫

目录

读取本地文件

从网站读取文件 

java爬虫 

 总结

读取本地文件

import java.io.File;
import java.io.PrintWriter;
import java.util.Scanner;

public class ReplaceText {
    public static void main() throws Exception{
        File file = new File("basic\\test.txt");
        if(!file.exists()) {
            System.exit(0);
        }

        File targetFile = new File("basic\\target.txt");
        if(targetFile.exists()) {
            System.exit(1);
        }

        String oldString = "case";
        String newString = "CASE";

        try(
            Scanner input = new Scanner(file);
            PrintWriter output = new PrintWriter(targetFile);
        ) {
            while (input.hasNext()) {
                String src = input.nextLine();
                String dist = src.replaceAll(oldString, newString);
                output.println(dist);
            }
            input.close();
            output.close();
        }
        
    }
}

输出结果： 

从网站读取文件 

import java.io.IOException;
import java.util.Scanner;

public class ReadFileFromUrl {
    public static void main() {
        System.out.println("Input the URL:");
        String addr = new Scanner(System.in).next();
        
        try {
            java.net.URL url = new java.net.URL(addr);
            int count = 0;
            Scanner input = new Scanner(url.openStream());

            while (input.hasNext()) {
                count = count + input.nextLine().length();
            }
            System.out.println("The website has " + count + " charactors.");
        } catch (java.net.MalformedURLException e) {
            // TODO: handle exception
            System.out.println("Invalid url!");
        } catch (IOException e) {
            System.out.println("No such file!");
        }
    }
}

 输出结果：

java爬虫 

package crawler;

import java.util.ArrayList;
import java.util.Scanner;

public class MyCrawler{

    public static void main() {
        String addr = new Scanner(System.in).next();

        crawler(addr);
    }

    private static void crawler(String url) {
        ArrayList<String> pendingUrls = new ArrayList<>();
        ArrayList<String> traversedUrls = new ArrayList<>();

        pendingUrls.add(url);
        while (!pendingUrls.isEmpty() && traversedUrls.size() < 100) {
            String urlString = pendingUrls.remove(0);
            if (!traversedUrls.contains(urlString)) {
                traversedUrls.add(urlString);
                System.out.println("crawl the website: " + urlString);
            }

            for(String s: getSubUrl(url)) {
                if(!traversedUrls.contains(s))
                pendingUrls.add(s);
            }

        }
    }

    private static ArrayList<String> getSubUrl(String urlString) {
        ArrayList<String> list = new ArrayList<>();

        try {
            java.net.URL url = new java.net.URL(urlString);
            int count = 0;
            Scanner input = new Scanner(url.openStream());

            while (input.hasNext()) {
                String line = input.nextLine();
                count = line.indexOf("http:", count);
                while (count > 0) {
                    int endIndex = line.indexOf("\"", count);

                    if (endIndex > 0) {
                        list.add(line.substring(count, endIndex));
                        count = line.indexOf("http:", endIndex);
                    } else {
                        count = -1;
                    }
                }

            }
        } catch (Exception e) {
            // TODO: handle exception
            System.out.println("Error : " + e.getMessage());
        }

        return list;
    }
    
}

 输出结果：

 总结

本文从读取本地文件，读取网站文件和爬虫，一步一步地实现简单的网络爬虫功能。