Java URL Handling

URL (Uniform Resource Locator), also known as a web address, represents resources on the Internet, such as web pages or FTP addresses.

In this section, we will introduce how Java handles URLs. A URL can be divided into the following parts.

protocol://host:port/path?query#fragment

The protocol can be HTTP, HTTPS, FTP, and File; port is the port number; path is the file path and file name.

An example of an HTTP protocol URL is as follows:

http://www.example.com/index.html?language=cn#j2se

URL parsing:

• Protocol:http
• Host (host:port)：www.example.com
• Port number:80. The above URL example does not specify a port, because the default port number for the HTTP protocol is 80.
• File path (path):/index.html
• Query parameters (query)：language=cn
• Fragment (fragment):j2se, locating the position of the HTML element with the id attribute j2se in the web page.

URL Class Methods

The URL class is defined in the java.net package, and it is used to handle URL-related content. The creation and use of the URL class are introduced separately below.

java.net.URL provides various ways to construct URLs, and resources can be obtained through java.net.URL.

The URL class contains many methods for accessing various parts of a URL. The specific methods and descriptions are as follows:

Example

The above example demonstrates using the URL class of java.net to obtain various part parameters of a URL:

The compilation and running result of the above example is as follows:

URL 为：http://www.example.com/index.html?language=cn#j2se
协议为：http
验证信息：www.example.com
文件名及请求参数：/index.html?language=cn
主机名：www.example.com
路径：/index.html
端口：-1
默认端口：80
请求参数：language=cn
定位位置：j2se

URLConnections Class Methods

openConnection() returns a java.net.URLConnection.

For example:

• If you connect to a URL with the HTTP protocol, the openConnection() method returns an HttpURLConnection object.

• If the URL you connect to is a JAR file, the openConnection() method will return a JarURLConnection object.

• And so on...

The URLConnection method list is as follows:

Example

In the following example, the URL uses the HTTP protocol. openConnection returns an HttpURLConnection object.

The compilation and running result of the above example is as follows:

$ javac URLConnDemo.java 
$ java URLConnDemo
.....这里会输出Example首页(http://www.example.com)的 HTML 内容.....