Java URLConnection Class - Performing HTTP Communication

Performing HTTP Communication - URLConnection Class

URL(String spec)
URL(String protocol, String host, int port, String file)
  spec: URL string
  protocol: protocol name
  host: host name
  port: port number
  file: file name

You can access web pages through HTTP by using the URLConnection class (java.net package). A URLConnection object can be obtained with the URL#openConnection method.

Main Methods of the URLConnection Class

The main methods available in the URLConnection class are as follows.

Method	Overview
`void connect()`	Connects to the current URL.
`int getConnectTimeout()`	Gets the connection timeout.
`Object getContent()`	Gets the content.
`String getContentEncoding()`	Gets the value of the content-encoding header.
`int getContentLength()`	Gets the value of the content-length header.
`String getContentType()`	Gets the value of the content-type header.
`long getDate()`	Gets the value of the date header.
`String getHeaderField(String name)`	Gets the value of the specified header.
`long getHeaderFieldDate(String name, long Default)`	Gets the value of the specified header interpreted as a date.
`int getHeaderFieldInt(String name, int Default)`	Gets the value of the specified header interpreted as a number.
`InputStream getInputStream()`	Gets an input stream for reading from the current connection.
`OutputStream getOutputStream()`	Gets an output stream for writing to the current connection.
`void setConnectTimeout(int timeout)`	Sets the connection timeout.

URLConnection Example

The following example retrieves content from the specified URL and prints it.

UrlConnect.java

package com.devkuma.basic.http;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URL;
import java.net.URLConnection;

public class UrlConnect {
    public static void main(String[] args) {
        try {
            URL url = new URL("http://devkuma.com/");
            URLConnection con = url.openConnection();
            try (BufferedReader reader = new BufferedReader(new InputStreamReader(con.getInputStream(), "UTF-8"))) {
                while (reader.ready()) {
                    System.out.println(reader.readLine());
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Result:

<html>
<head><title>301 Moved Permanently</title></head>
<body>
<center><h1>301 Moved Permanently</h1></center>
<hr><center>nginx</center>
</body>
</html>

You can get an input stream with the URLConnection#getInputStream method, and the rest simply reads input according to normal stream operation steps. For more details, refer to “Streams”.