How to get HTTP response code for a URL in Java?

In Java, obtaining the HTTP response code for a URL can be achieved through multiple methods, with the most common approach being the use of the HttpURLConnection class from Java's standard library or third-party libraries such as Apache HttpClient. Below, I will detail the implementation steps for both methods.

Method One: Using HttpURLConnection

1. Create URL Object First, convert the string URL address into a URL object.

   java
   URL url = new URL("http://example.com");

2. Open Connection Use the openConnection() method of the URL object to create an HttpURLConnection object.

   java
   HttpURLConnection connection = (HttpURLConnection) url.openConnection();

3. Set Request Method You can set the HTTP request method (GET, POST, etc.), with GET being the default.

   java
   connection.setRequestMethod("GET");

4. Connect to Server Call the connect() method to establish a connection with the server.

   java
   connection.connect();

5. Get Response Code Use the getResponseCode() method to obtain the HTTP response status code.

   java
   int responseCode = connection.getResponseCode();
   System.out.println("HTTP Response Code: " + responseCode);

6. Close Connection Close the connection after completion.

   java
   connection.disconnect();

Method Two: Using Apache HttpClient

First, add the Apache HttpClient library dependency to your project. For Maven, add the following to your pom.xml:

xml
<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.13</version>
</dependency>

Next, the steps to obtain the HTTP response code using Apache HttpClient:

1. Create HttpClient Object Create a default client instance using the HttpClients class.

   java
   CloseableHttpClient httpClient = HttpClients.createDefault();

2. Create HttpGet Object Create an HttpGet object to set the target URL.

   java
   HttpGet request = new HttpGet("http://example.com");

3. Execute Request Execute the request using the execute() method, which returns a CloseableHttpResponse object.

   java
   CloseableHttpResponse response = httpClient.execute(request);

4. Get Response Code Retrieve the status line from the response object and then get the status code.

   java
   int responseCode = response.getStatusLine().getStatusCode();
   System.out.println("HTTP Response Code: " + responseCode);

5. Close Resources Finally, close the HttpResponse and HttpClient.

   java
   response.close();
   httpClient.close();

The above are the two common methods for obtaining the HTTP response code for a URL in Java. Both methods are practical, and the choice depends on personal or team preference and project requirements.