java - 将JSoup编译为Maven依赖关系的麻烦-Java

Question

我是新来的Java开发人员。
我在使用JSoup时遇到麻烦。几天后，我制作了一个Web爬网程序(其目的是练习和学习新东西)，但由于我必须解决的代码错误而使它无法正常运行，但至少在控制台上运行良好。我的意思是，它并没有给出预期的结果，而是在运行。但是现在我不明白发生了什么，并且遇到了与编译有关的麻烦。
这是输出中的错误:

Scanning for projects...

--------------< com.webcrawler.jsoupexample:jsoupexample >--------------
Building jsoupexample 1.0-SNAPSHOT
--------------------------------[ jar ]---------------------------------

--- maven-resources-plugin:2.6:resources (default-resources) @ jsoupexample ---
Using platform encoding (Cp1252 actually) to copy filtered resources, i.e. build is platform dependent!
Copying 0 resource

--- maven-compiler-plugin:3.1:compile (default-compile) @ jsoupexample ---
Changes detected - recompiling the module!
File encoding has not been set, using platform encoding Cp1252, i.e. build is platform dependent!
Compiling 2 source files to C:\Users\**\**\**\**\**\web-crawler-jsoup-example-master\webcrawler\target\classes
-------------------------------------------------------------
COMPILATION ERROR : 
-------------------------------------------------------------
com/webcrawler/jsoupexample/ParserEngine.java:[3,17] package org.jsoup does not exist
com/webcrawler/jsoupexample/ParserEngine.java:[4,23] package org.jsoup.nodes does not exist
com/webcrawler/jsoupexample/ParserEngine.java:[5,23] package org.jsoup.nodes does not exist
com/webcrawler/jsoupexample/ParserEngine.java:[6,24] package org.jsoup.select does not exist
com/webcrawler/jsoupexample/ParserEngine.java:[22,9] cannot find symbol
  symbol:   class Document
  location: class com.webcrawler.jsoupexample.ParserEngine
com/webcrawler/jsoupexample/ParserEngine.java:[22,24] cannot find symbol
  symbol:   variable Jsoup
  location: class com.webcrawler.jsoupexample.ParserEngine
com/webcrawler/jsoupexample/ParserEngine.java:[23,9] cannot find symbol
  symbol:   class Elements
  location: class com.webcrawler.jsoupexample.ParserEngine
com/webcrawler/jsoupexample/ParserEngine.java:[25,14] cannot find symbol
  symbol:   class Element
  location: class com.webcrawler.jsoupexample.ParserEngine
8 errors 
-------------------------------------------------------------
------------------------------------------------------------------------
BUILD FAILURE
------------------------------------------------------------------------
Total time:  3.465 s
Finished at: 2020-12-06T20:00:55-03:00
------------------------------------------------------------------------
Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.1:compile (default-compile) on project jsoupexample: Compilation failure: Compilation failure: 
com/webcrawler/jsoupexample/ParserEngine.java:[3,17] package org.jsoup does not exist
com/webcrawler/jsoupexample/ParserEngine.java:[4,23] package org.jsoup.nodes does not exist
com/webcrawler/jsoupexample/ParserEngine.java:[5,23] package org.jsoup.nodes does not exist
com/webcrawler/jsoupexample/ParserEngine.java:[6,24] package org.jsoup.select does not exist
com/webcrawler/jsoupexample/ParserEngine.java:[22,9] cannot find symbol
  symbol:   class Document
  location: class com.webcrawler.jsoupexample.ParserEngine
com/webcrawler/jsoupexample/ParserEngine.java:[22,24] cannot find symbol
  symbol:   variable Jsoup
  location: class com.webcrawler.jsoupexample.ParserEngine
com/webcrawler/jsoupexample/ParserEngine.java:[23,9] cannot find symbol
  symbol:   class Elements
  location: class com.webcrawler.jsoupexample.ParserEngine
com/webcrawler/jsoupexample/ParserEngine.java:[25,14] cannot find symbol
  symbol:   class Element
  location: class com.webcrawler.jsoupexample.ParserEngine
-> [Help 1]

To see the full stack trace of the errors, re-run Maven with the -e switch.
Re-run Maven using the -X switch to enable full debug logging.

For more information about the errors and possible solutions, please read the following articles:
[Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoFailureException 

这是我的 pom.mxl

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.webcrawler.jsoupexample</groupId>
    <artifactId>jsoupexample</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <!-- https://mvnrepository.com/artifact/org.jsoup/jsoup -->
        <dependency>
            <groupId>org.jsoup</groupId>
            <artifactId>jsoup</artifactId>
            <version>1.11.3</version>
        </dependency>
    </dependencies>
</project>

这是 ParserEngine.java类，我在导入中有错误(在我没有此错误之前)。

package com.webcrawler.jsoupexample;

import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
import org.jsoup.nodes.Element;
import org.jsoup.select.Elements; //this 4 imports has error now, days ago didn't have error

import java.io.IOException;
import java.util.ArrayList;

public class ParserEngine {

    private String baseUrl;
    private ArrayList<String> urlList;

    public ParserEngine(String baseUrl){
        this.baseUrl = baseUrl;
        this.urlList = new ArrayList<String>();
    }

    public void crawl(String url) throws IOException {
        Document doc = Jsoup.connect(url).ignoreContentType(true).get();
        Elements links = doc.select("a[href]");

        //here I found the problem why the crawler doesn't work as I want,         
        //but it isn't my actual issue, i want to be able to run it again in console
        for (Element link : links) {
            String actualUrl = link.attr("abs:href"); 

            if (!urlList.contains(actualUrl) & actualUrl.startsWith(baseUrl)){
                print(" * a: <%s>  (%s)", actualUrl, trim(link.text(), 35));
                urlList.add(actualUrl);
                crawl(actualUrl);
            }
        }
    }

    private static void print(String msg, Object... args) {
        System.out.println(String.format(msg, args));
    }

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

    public String getBaseUrl(){
        return baseUrl;
    }

    public void setBaseUrl(String url){
        baseUrl = url;
    }

    public ArrayList<String> getUrlList(){
        return urlList;
    }

}

这是 Main.Java

package com.webcrawler.jsoupexample;

import java.io.IOException;

public class Main {

    public static void main(String[] args) throws IOException {
        String url = "http://elfreneticoinformatico.com";
        ParserEngine parser = new ParserEngine(url);
        parser.crawl(parser.getBaseUrl());
        System.out.println("Crawler finished. Total URLs: " + parser.getUrlList().size());
    }

}

有人可以帮忙吗？

Answer 1

如果您使用的不是体面的Java IDE(集成开发环境)，建议您这样做。 NetBeans，IntelliJ IDEA，也许是Eclipse。 NetBeans可以更轻松地开始，因为它可以直接与Maven项目一起使用。 IDE甚至可以在构建之前就检测到问题。
...更新
我尝试使用Maven clean和compile目标构建它，并使用IntelliJ IDEA Community 2020.3和NetBeans 12.2运行它，并...
它可以正常运行，所以我不确定发生了什么。
NetBeans构建输出为:

cd P:\Users\infernoz\Documents\Java_Projects\infernoz\jsoup-question; "JAVA_HOME=C:\\Program Files\\AdoptOpenJDK\\jdk-8.0.275.1-hotspot" cmd /c "\"C:\\Program Files\\NetBeans-12.2\\netbeans\\java\\maven\\bin\\mvn.cmd\" -Dmaven.ext.class.path=\"C:\\Program Files\\NetBeans-12.2\\netbeans\\java\\maven-nblib\\netbeans-eventspy.jar\" --errors --errors clean compile"
[INFO] Error stacktraces are turned on.
[INFO] Scanning for projects...
[INFO] 
[INFO] --------------< com.webcrawler.jsoupexample:jsoupexample >--------------
[INFO] Building jsoupexample 1.0-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[INFO] 
[INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ jsoupexample ---
[INFO] Deleting P:\Users\infernoz\Documents\Java_Projects\rwperrott\jsoup-question\target
[INFO] 
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ jsoupexample ---
[WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] Copying 0 resource
[INFO] 
[INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ jsoupexample ---
[INFO] Changes detected - recompiling the module!
[WARNING] File encoding has not been set, using platform encoding Cp1252, i.e. build is platform dependent!
[INFO] Compiling 2 source files to P:\Users\infernoz\Documents\Java_Projects\rwperrott\jsoup-question\target\classes
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  4.496 s
[INFO] Finished at: 2020-12-22T02:06:04Z
[INFO] ------------------------------------------------------------------------

IntelliJ运行输出为:

"C:\Program Files\AdoptOpenJDK\jdk-8.0.275.1-hotspot\bin\java.exe" -javaagent:C:\Users\infernoz\AppData\Local\JetBrains\Toolbox\apps\IDEA-C\ch-1\203.5981.155\lib\idea_rt.jar=65151:C:\Users\infernoz\AppData\Local\JetBrains\Toolbox\apps\IDEA-C\ch-1\203.5981.155\bin -Dfile.encoding=UTF-8 -classpath "C:\Program Files\AdoptOpenJDK\jdk-8.0.275.1-hotspot\jre\lib\charsets.jar;C:\Program Files\AdoptOpenJDK\jdk-8.0.275.1-hotspot\jre\lib\ext\access-bridge-64.jar;C:\Program Files\AdoptOpenJDK\jdk-8.0.275.1-hotspot\jre\lib\ext\cldrdata.jar;C:\Program Files\AdoptOpenJDK\jdk-8.0.275.1-hotspot\jre\lib\ext\dnsns.jar;C:\Program Files\AdoptOpenJDK\jdk-8.0.275.1-hotspot\jre\lib\ext\jaccess.jar;C:\Program Files\AdoptOpenJDK\jdk-8.0.275.1-hotspot\jre\lib\ext\localedata.jar;C:\Program Files\AdoptOpenJDK\jdk-8.0.275.1-hotspot\jre\lib\ext\nashorn.jar;C:\Program Files\AdoptOpenJDK\jdk-8.0.275.1-hotspot\jre\lib\ext\sunec.jar;C:\Program Files\AdoptOpenJDK\jdk-8.0.275.1-hotspot\jre\lib\ext\sunjce_provider.jar;C:\Program Files\AdoptOpenJDK\jdk-8.0.275.1-hotspot\jre\lib\ext\sunmscapi.jar;C:\Program Files\AdoptOpenJDK\jdk-8.0.275.1-hotspot\jre\lib\ext\sunpkcs11.jar;C:\Program Files\AdoptOpenJDK\jdk-8.0.275.1-hotspot\jre\lib\ext\zipfs.jar;C:\Program Files\AdoptOpenJDK\jdk-8.0.275.1-hotspot\jre\lib\jce.jar;C:\Program Files\AdoptOpenJDK\jdk-8.0.275.1-hotspot\jre\lib\jfr.jar;C:\Program Files\AdoptOpenJDK\jdk-8.0.275.1-hotspot\jre\lib\jsse.jar;C:\Program Files\AdoptOpenJDK\jdk-8.0.275.1-hotspot\jre\lib\management-agent.jar;C:\Program Files\AdoptOpenJDK\jdk-8.0.275.1-hotspot\jre\lib\resources.jar;C:\Program Files\AdoptOpenJDK\jdk-8.0.275.1-hotspot\jre\lib\rt.jar;P:\Users\infernoz\Documents\Java_Projects\rwperrott\jsoup-question\target\classes;M:\Repository\org\jsoup\jsoup\1.13.1\jsoup-1.13.1.jar" com.webcrawler.jsoupexample.Main
Crawler finished. Total URLs: 0

Process finished with exit code 0