How to Use java.net.URLConnection to Fire and Handle HTTP Requests?

java.net.URLConnection in Java is used for handling HTTP requests in Java. With this class, you can send HTTP requests, manage connections, and also process responses, without using the external libraries

Whether you’re new to HTTP in Java, or looking for an efficient solution to handle HTTP requests, we’ll guide you in using URLConnection to make HTTP requests, handle responses, and manage connections.

Table of Contents:

• What is URLConnection in Java?
• Steps to Establish a URL Connection in Java
• What is HttpURLConnection?
• Making an HTTP GET Request (Firing a Request)
• Making a POST Request (Handling a Request)
• Methods of the java.net.HttpURLConnection Class in Java
• Other Popular Third-Party Java HTTP Libraries
• Conclusion

What is URLConnection in Java?

The URLConnection in Java is used to connect to the Internet. It is an abstract class that allows Java applications to talk to a resource or to read the data from a URL. It acts as a bridge between your Java code and the Internet.

In this abstract class, we can connect to a website, download data like HTML or files, and send data to a server.

Features of the URLConnection class

1. It is an abstract class and provides communication between the Java program and a URL resource.
2. It has 2 main subclasses
   • HttpURLConnection: For handling HTTP connections.
   • JarURLConnection: For accessing JAR file resources.
3. It supports different protocols like FTP and file URLs.
4. It can read and write a resource.

Steps to Establish a URL Connection in Java

To establish a connection using URLConnection in Java, follow these steps:

1. Create a URL Object

Define the URL of the resource you want to connect to.

URL url = new URL("https://jsonplaceholder.typicode.com/posts/1");  

2. Open a Connection

Use the openConnection() method to get a URLConnection object.

HttpURLConnection conn = (HttpURLConnection) url.openConnection();

3. Establish the Connection

Use connect() to start the connection

conn.connect();

4. Read Data from the Server

Use an InputStream to read the response from the server. If sending data, use an OutputStream.

BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));
String line;
while ((line = reader.readLine()) != null) {
    System.out.println(line); 
}

5. Close the Connection

If using streams, always close the connection to free up the resources.

reader.close();
conn.disconnect();

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What is HttpURLConnection?

The HttpURLConnection is a Java class used to communicate between an application and a URL. It is used to read and write data.

It has two components:

1. Client-Side / Request

Sends a request to the server using HTTP methods like GET and POST. The request from the client is sent to the server. It uses methods like GET, POST, etc, and sends the data to the server side.

2. Server Side / Response 

The request is sent by the client and received by the server, and according to that, the response is sent back to the client. 

Making an HTTP GET Request (Firing a Request)

The GET method is used to retrieve the data from the server. They do not send any optional data with the request body. During GET requests, multiple requests to the same URL can return the same result as long as the data remains unchanged on the server.

Example:

Output:

Explanation: In the above Java program, the data is obtained from an API. It first defines the URL and opens an HTTP connection. The request method is set to “GET”, due to which no additional data will be sent in the request body. The program sets connection timeouts and checks the server’s response code. If the response is successful, it reads and prints the data using a BufferedReader. The response contains JSON data from the server.

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Making a POST Request (Handling a Request)

The POST request is used to send data to the server. The data here is sent in the request body.

 It is also used to create a new resource.

Example:

Output:

Explanation: In the above Java program, the program sends the data to the server. It makes a connection with the API and sets the request method to “POST”. It also has headers to show JSON data Content-Type: application/json. After sending a request, it checks the response code; if it is 201, it is successful, after which it reads the response from the server. Hence, the server data is changed by adding new information.

Methods of the java.net.HttpURLConnection Class in Java

There are various methods in the java.net.HttpURLConnection class in Java, which are used to perform different tasks related to HTTP communication. Some of the commonly used methods are as follows:

Other Popular Third-Party Java HTTP Libraries

Other than Java’s built-in library for the HttpURLConnection, there are many third-party libraries. Some of these are:

1. Apache HTTPClient

It is a popular, open-source Java library used for building the Http-based client applications. They are used for authentication and handling requests/responses.

2. OkHttp

It was developed by Square. OkHttp is a powerful and efficient HTTP client known for its speed. It gives better performance.

3. Retrofit

It is built on top of OkHttp. It is a REST client for both Java and Android. It converts HTTP APIs into Java interfaces and makes API calls readable and maintainable. It also supports JSON parsing, authentication, and asynchronous requests.

For the Maven projects, one has to add the dependency on it in the pom.xml file.

Conclusion

From above, we learnt how to use HttpURLConnection in Java to send and receive data from websites. We have learned how to connect to a URL, get data (GET request), send data (POST request), and read responses. We have also looked at easy-to-use libraries like Apache HttpClient, OkHttp, and Retrofit, which can help make web requests easier and faster.

To learn more about this topic, you can refer to our Java Course.

How to Use java.net.URLConnection to Fire and Handle HTTP Requests? – FAQs