URL openConnection(Proxy) in Java

openConnection(Proxy): This method is available in the java.net.URL class of Java.

Syntax:

URLConnection java.net.URL.openConnection(Proxy proxy) throws IOException

This method takes one argument. This method returns a URLConnection instance that represents a connection to the remote object referred to by the URL with Proxy.

Protocol handlers that do not support proxying will ignore the proxy parameter and make a normal connection.

Invoking this method preempts the system's default ProxySelector settings.

Parameters: One parameter is required for this method.

proxy: the Proxy through which this connection will be made. If a direct connection is desired, Proxy.NO_PROXY should be specified.

Returns: a URLConnection to the URL.

Throws:

1. IOException - if an I/O exception occurs.

2. SecurityException - if a security manager is present and the caller doesn't have permission to connect to the proxy.

3. IllegalArgumentException - will be thrown if the proxy is null, or the proxy has the wrong type.

4. UnsupportedOperationException - if the subclass that implements the protocol handler doesn't support this method.

Approach 1: When no exception

Java

package com.URL;

import java.io.IOException;
import java.net.Proxy;
import java.net.URL;

public class URLopenConnection2 {
    public static void main(String[] args) throws IOException {

        String protocol = "http", host = "localhost", file = "/hello";
        int port = 8089;
        URL url = new URL(protocol, host, port, file);

        System.out.println(url.openConnection(Proxy.NO_PROXY));
    }
}

Output:

sun.net.www.protocol.http.HttpURLConnection:http://localhost:8089/hello

Approach 2: IllegalArgumentException 

Java

package com.URL;

import java.io.IOException;
import java.net.URL;

public class URLopenConnection2 {
    public static void main(String[] args) throws IOException {

        String protocol = "http", host = "localhost", file = "/hello";
        int port = 8089;
        URL url = new URL(protocol, host, port, file);

        System.out.println(url.openConnection(null));
    }
}

Output:

Exception in thread "main" java.lang.IllegalArgumentException: proxy can not be null
	at java.base/java.net.URL.openConnection(URL.java:1136)
	at com.URL.URLopenConnection2.main(URLopenConnection2.java:13)

Some other methods of the URL class

URL(String): This method creates a URL object from the String representation.

URL(URL, String): This method creates a URL by parsing the given spec within a specified context.

URL(String, String, String): This method creates a URL from the specified protocol name, hostname, and file name.

URL(URL, String, URLStreamHandler): This method creates a URL by parsing the given spec with the specified handler within a specified context.

URL(String, String, int, String): This method creates a URL object from the specified protocol, host, port number, and file. host can be expressed as a hostname or a literal IP address.

URL(String, String, int, String, URLStreamHandler): This method creates a URL object from the specified protocol, host, port number, file, and handler.

equals(Object): This method compares this URL for equality with another object.

getAuthority(): This method gets the authority part of this URL.

getContent(): This method gets the contents of this URL.

getContent(Class<?>[]): This method gets the contents of this URL.

getDefaultPort(): This method gets the default port number of the protocol associated with this URL.

getFile(): This method gets the file name of this URL. 

getHost(): This method gets the hostname of this URL, if applicable.

getPath(): This method gets the path part of this URL.

getPort(): This method gets the port number of this URL.

getProtocol(): This method gets the protocol name of this URL.

getQuery(): This method gets the query part of this URL.

getRef(): This method gets the anchor (also known as the "reference") of this URL.

getUserInfo(): This method gets the userInfo part of this URL.

hashCode(): This method creates an integer suitable for hash table indexing.

openConnection(): This method returns a URLConnection instance that represents a connection to the remote object referred to by the URL.

openConnection(Proxy): This method returns a URLConnection instance that represents a connection to the remote object referred to by the URL with Proxy.

openStream(): This method opens a connection to this URL and returns an InputStream for reading from that connection.

sameFile(URL): This method compares two URLs, excluding the fragment component.

URL.setURLStreamHandlerFactory(URLStreamHandlerFactory): This method sets an application's URLStreamHandlerFactory.This method can be called at most once in a given Java VirtualMachine.

toExternalForm(): This method constructs a string representation of this URL. 

toString(): This method constructs a string representation of this URL. The string is created by calling the toExternalForm method of the stream protocol handler for this object.

toURI(): This method returns a java.net.URI equivalent to this URL.