Using JSoup for Web scraping in Java API development

With the explosive growth of Internet information, more and more applications need to obtain relevant data from Web pages. JSoup is a Java HTML parser that can easily extract and manipulate data from web pages. In Java API development, JSoup is an important and commonly used tool. This article will introduce how to use JSoup for web scraping.

1. Introduction and basic usage of JSoup

1. Introduction of JSoup

JSoup is a Java HTML parser, developers can introduce it into the project through Maven , just add the following dependencies:

<dependency>
    <groupId>org.jsoup</groupId>
    <artifactId>jsoup</artifactId>
    <version>1.14.2</version>
</dependency>

2. Basic usage

Using JSoup requires first parsing the content of the HTML page into a Document object, and then you can use this object to Get various elements in the page. The following is an example of basic usage of JSoup:

String url = "https://www.baidu.com/";
Document document = Jsoup.connect(url).get(); // 通过 URL 加载页面

// 获取页面标题
String title = document.title();

// 获取页面所有超链接
Elements links = document.select("a[href]");

// 循环遍历页面中的所有链接
for(Element link: links){
    String linkHref = link.attr("href");
    String linkText = link.text();
}

2. Use JSoup for Web crawling

1. Obtain page information through URL

Method of using JSoup connect (url).get() You can obtain page information through the specified URL address, as shown below:

String url = "https://www.baidu.com/";
Document document = Jsoup.connect(url).get();

2. Parse HTML elements

According to the structure of the page, use select() method can quickly obtain the required elements. The following is an example of using JSoup to get all links:

Elements links = document.select("a[href]");

for(Element link: links){
    String linkHref = link.attr("href");
    String linkText = link.text();
    System.out.println(linkHref + " , " + linkText);
}

3. Filtering

Using selector syntax, you can get elements in the page that meet specified conditions. For example, use the following code to obtain all input elements with class "s_ipt":

Elements inputs = document.select("input[class=s_ipt]");

Supported selector syntax also includes: label selector, class selector, ID selector, attribute selector, and combination selection selector, pseudo-selector, etc.

4. Event processing

JSoup can easily handle events on the page. For example, you can use the following code to obtain the required input element and bind an event listener to it:

Element input = document.select("input[type=text").first();

input.attr("oninput", "console.log('input value has changed')");

5. Submit the form

JSoup can also help us submit the form. For example, you can use the following code to complete the submission to the Baidu search box:

String url = "https://www.baidu.com/s";
String keyword = "Java";
Document document = Jsoup.connect(url)
                        .data("wd", keyword)
                        .post();

3. Summary

This article introduces how to use JSoup for web crawling, and the basic usage of JSoup. Use JSoup to easily obtain page elements, filter, event handle, submit forms, etc. Of course, when using JSoup, you need to pay attention to comply with relevant laws, regulations and ethics, and you cannot obtain other people's information in an illegal and disciplinary manner.

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