What is the difference between CloseableHttpClient and HttpClient in Apache HttpClient API?

• The main entry point of the HttpClient API is the HttpClient interface.
• The most essential function of HttpClient is to execute HTTP methods.
• Execution of an HTTP method involves one or several HTTP request / HTTP response exchanges, usually handled internally by HttpClient.

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• CloseableHttpClient is an abstract class which is the base implementation of HttpClient that also implements java.io.Closeable.

• Here is an example of request execution process in its simplest form:

  CloseableHttpClient httpclient = HttpClients.createDefault();
  HttpGet httpget = new HttpGet("http://localhost/");
  CloseableHttpResponse response = httpclient.execute(httpget);
  try {
      //do something
  } finally {
      response.close();
  }

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• HttpClient resource deallocation: When an instance CloseableHttpClient is no longer needed and is about to go out of scope the connection manager associated with it must be shut down by calling the CloseableHttpClient#close() method.

  CloseableHttpClient httpclient = HttpClients.createDefault();
  try {
      //do something
  } finally {
      httpclient.close();
  }

see the Reference to learn fundamentals.

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@Scadge
Since Java 7, Use of try-with-resources statement ensures that each resource is closed at the end of the statement. It can be used both for the client and for each response

try(CloseableHttpClient httpclient = HttpClients.createDefault()){

    // e.g. do this many times
    try (CloseableHttpResponse response = httpclient.execute(httpget)) {
    //do something
    }

    //do something else with httpclient here
}