遇到找不到或无法加载主类错误的情况，有人可以帮助我修复该错误吗？ 我是Java新手

Question

I am trying to write a program that parses links and other media from a webpage, and i am having an error that i don't know how to deal with popping up when i try to run the code after compiling.

package org.jsoup.examples;

import org.jsoup.Jsoup;
import org.jsoup.helper.Validate;
import org.jsoup.nodes.Document;
import org.jsoup.nodes.Element;
import org.jsoup.select.Elements;

import java.io.IOException;
import java.io.*;

public class ListLinks{

    public static void main(String[] args) throws IOException {
        Validate.isTrue(args.length == 1, "usage: supply url to fetch");
        String url = args[0];

        File file = new File("save.txt");

        file.createNewFile();

        FileWriter writer = new FileWriter(file);

        print(writer,"Fetching %s...", url);

        Document doc = Jsoup.connect(url).get();
        Elements links = doc.select("a[href]");
        Elements media = doc.select("[src]");
        Elements imports = doc.select("link[href]");

        print(writer,"\nMedia: (%d)", media.size());
        for (Element src : media) {
            if (src.tagName().equals("img"))
                print(writer," * %s: <%s> %sx%s (%s)",
                        src.tagName(), src.attr("abs:src"), src.attr("width"), src.attr("height"),
                        trim(src.attr("alt"), 20));
            else
                print(writer," * %s: <%s>", src.tagName(), src.attr("abs:src"));
        }

        print(writer,"\nImports: (%d)", imports.size());
        for (Element link : imports) {
            print(writer," * %s <%s> (%s)", link.tagName(),link.attr("abs:href"), link.attr("rel"));
        }

        print(writer,"\nLinks: (%d)", links.size());
        for (Element link : links) {
            print(writer," * a: <%s>  (%s)", link.attr("abs:href"), trim(link.text(), 35));
        }
    }


    private static void print(FileWriter writer,String msg, Object... args) {
        try
        {
            writer.write(String.format(msg,args));
        }
        catch(IOException e){
            System.out.println("something went wrong");
        }
    }

    private static String trim(String s, int width) {
        if (s.length() > width)
            return s.substring(0, width-1) + ".";
        else
            return s;
    }

}

i am trying to run this from my command line, just parsing code from a web page.

I compiled the program by writing:

java -cp .;jsoup-1.9.2.jar ListLinks.java

then i am trying to run it by writing:

java -cp .jsoup-1.9.2.jar ListLinks

which gives me the error:

Error:could not find or load main class ListLinks

How do i fix this?

Answer 1

You should prepend your class name with a package org.jsoup.examples :

java -cp .jsoup-1.9.2.jar org.jsoup.examples.ListLinks

Without it java looks for this class in empty package (current directory) and it can't find it.

When you provide a package, java will look for this class inside org/jsoup/examples directory, you can see that actually the class file ( ListLinks.class ) is located there not in the current directory.