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

Question

I m studying an application developed by our company  It uses the Apache HttpClient library  In the source code it uses the HttpClient class to create instances to connect to a server    I want to learn about Apache HttpClient and I ve gone trough this set of examples  All the examples use CloseableHttpClient instead of HttpClient  So I think CloseableHttpClient is an extended version of HttpClient  If this is the case I have two questions    What is the difference between these two  Which class is recommended to use for my new development

User · Answer

CloseableHttpClient is the base class of the httpclient library  the one all implementations use  Other subclasses are for the most part deprecated   The HttpClient is an interface for this class and other classes   You should then use the CloseableHttpClient in your code  and create it using the HttpClientBuilder  If you need to wrap the client to add specific behaviour you should use request and response interceptors instead of wrapping with the HttpClient   This answer was given in the context of httpclient-4 3

User · Answer

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       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           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      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

User · Answer

HttpClient is not a class  it is an interface  You cannot use it for development in the way you mean    What you want is a class that implements the HttpClient interface  and that is CloseableHttpClient

User · Answer

Had the same question   The other answers don t seem to address why close   is really necessary   Also  Op seemed to be struggling to figure out the preferred way to work with HttpClient  et al     According to Apache      The underlying HTTP connection is still held by the response object    to allow the response content to be streamed directly from the network socket     In order to ensure correct deallocation of system resources    the user MUST call CloseableHttpResponse close   from a finally clause    In addition  the relationships go as follows      HttpClient  interface            implemented by                  CloseableHttpClient - ThreadSafe               DefaultHttpClient - ThreadSafe BUT deprecated  use HttpClientBuilder instead               HttpClientBuilder - NOT ThreadSafe  BUT creates ThreadSafe CloseableHttpClient                   Use to create CUSTOM CloseableHttpClient               HttpClients - NOT ThreadSafe  BUT creates ThreadSafe CloseableHttpClient                 Use to create DEFAULT or MINIMAL CloseableHttpClient            The preferred way according to Apache   CloseableHttpClient httpclient   HttpClients createDefault      The example they give does httpclient close   in the finally clause  and also makes use of ResponseHandler as well     As an alternative  the way mkyong does it is a bit interesting  as well   HttpClient client   HttpClientBuilder create   build      He doesn t show a client close   call but I would think it is necessary  since client is still an instance of CloseableHttpClient

User · Answer

The other answers don t seem to address why close   is really necessary    2   Doubt on the answer  HttpClient resource deallocation    It is mentioned in old 3 x httpcomponents doc  which is long back and has a lot difference from 4 x HC  Besides the explanation is so brief that doesn t say what this underlying resource is   I did some research on 4 5 2 release source code  found the implementations of CloseableHttpClient close   basically only closes its connection manager     FYI  That s why when you use a shared PoolingClientConnectionManager and call client close    exception java lang IllegalStateException  Connection pool shut down will occur  To avoid  setConnectionManagerShared works   I prefer not do CloseableHttpClient close   after every single request  I used to create a new http client instance when doing request and finally close it  In this case  it d better not to call close    Since  if connection manager doesn t have  shared  flag  it ll be shutdown  which is too expensive for a single request   In fact  I also found in library clj-http  a Clojure wrapper over Apache HC 4 5  doesn t call close   at all  See func request in file core clj

User · Answer

In the next major version of the library HttpClient interface is going to extend Closeable  Until then it is recommended to use CloseableHttpClient if compatibility with earlier 4 x versions  4 0  4 1 and 4 2  is not required

User · Answer

Jon skeet said   The documentation seems pretty clear to me   Base implementation of HttpClient that also implements Closeable  - HttpClient is an interface  CloseableHttpClient is an abstract class  but because it implements AutoCloseable you can use it in a try-with-resources statement    But then Jules asked    JonSkeet That much is clear  but how important is it to close HttpClient instances  If it s important  why is the close   method not part of the basic interface   Answer for Jules      close need not be part of basic interface since underlying connection   is released back to the connection manager automatically after every execute   To accommodate the  try-with-resources statement  It is mandatory to implement Closeable  Hence included it in CloseableHttpClient   Note   close method in AbstractHttpClient which is extending CloseableHttpClient is deprecated  I was not able to find the source code for that

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

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