Class HttpClient

java.lang.Object
java.net.http.HttpClient
All Implemented Interfaces:
AutoCloseable
public abstract class HttpClient extends Object implements AutoCloseable
An HTTP Client.

An HttpClient can be used to send requests and retrieve their responses. An HttpClient is created through a builder. The newBuilder method returns a builder that creates instances of the default HttpClient implementation. The builder can be used to configure per-client state, like: the preferred protocol version ( HTTP/1.1 or HTTP/2 ), whether to follow redirects, a proxy, an authenticator, etc. Once built, an HttpClient is immutable, and can be used to send multiple requests.

An HttpClient provides configuration information, and resource sharing, for all requests sent through it. An HttpClient instance typically manages its own pools of connections, which it may then reuse as and when necessary. Connection pools are typically not shared between HttpClient instances. Creating a new client for each operation, though possible, will usually prevent reusing such connections.

A BodyHandler must be supplied for each HttpRequest sent. The BodyHandler determines how to handle the response body, if any. Once an HttpResponse is received, the headers, response code, and body (typically) are available. Whether the response body bytes have been read or not depends on the type, T, of the response body.

Requests can be sent either synchronously or asynchronously:

  • send(HttpRequest, BodyHandler) blocks until the request has been sent and the response has been received.
  • sendAsync(HttpRequest, BodyHandler) sends the request and receives the response asynchronously. The sendAsync method returns immediately with a CompletableFuture<HttpResponse>. The CompletableFuture completes when the response becomes available. The returned CompletableFuture can be combined in different ways to declare dependencies among several asynchronous tasks.

Synchronous Example 

HttpClient client = HttpClient.newBuilder()
     .version(Version.HTTP_1_1)
     .followRedirects(Redirect.NORMAL)
     .connectTimeout(Duration.ofSeconds(20))
     .proxy(ProxySelector.of(new InetSocketAddress("proxy.example.com", 80)))
     .authenticator(Authenticator.getDefault())
     .build();
HttpResponse<String> response = client.send(request, BodyHandlers.ofString());
System.out.println(response.statusCode());
System.out.println(response.body());

Asynchronous Example 

 HttpRequest request = HttpRequest.newBuilder()
     .uri(URI.create("https://foo.com/"))
     .timeout(Duration.ofMinutes(2))
     .header("Content-Type", "application/json")
     .POST(BodyPublishers.ofFile(Paths.get("file.json")))
     .build();
client.sendAsync(request, BodyHandlers.ofString())
     .thenApply(HttpResponse::body)
     .thenAccept(System.out::println);

Security checks

If a security manager is present then security checks are performed by the HTTP Client's sending methods. An appropriate URLPermission is required to access the destination server, and proxy server if one has been configured. The form of the URLPermission required to access a proxy has a method parameter of "CONNECT" (for all kinds of proxying) and a URL string of the form "socket://host:port" where host and port specify the proxy's address.

API Note:
Resources allocated by the HttpClient may be reclaimed early by closing the client.
Implementation Note:

The HttpResponse.BodyHandlers and HttpResponse.BodySubscribers classes provide some streaming or publishing BodyHandler and BodySubscriber implementations which allow to stream body data back to the caller. In order for the resources associated with these streams to be reclaimed, and for the HTTP request to be considered completed, a caller must eventually obtain the streaming response body and close, cancel, or read the returned streams to exhaustion. Likewise, a custom HttpResponse.BodySubscriber implementation should either request all data until onComplete or onError is signalled, or eventually cancel its subscription.

The JDK built-in implementation of the HttpClient overrides close(), shutdown(), shutdownNow(), awaitTermination(Duration), and isTerminated() to provide a best effort implementation. Failing to close, cancel, or read streaming or publishing bodies to exhaustion may stop delivery of data while leaving the request open, and stall an orderly shutdown. The shutdownNow() method, if called, will attempt to cancel any such non-completed requests, but may cause abrupt termination of any on going operation.

If not explicitly closed, the JDK built-in implementation of the HttpClient releases its resources when an HttpClient instance is no longer strongly reachable, and all operations started on that instance have eventually completed. This relies both on the garbage collector to notice that the instance is no longer reachable, and on all requests started on the client to eventually complete. Failure to properly close streaming or publishing bodies may prevent the associated requests from running to completion, and prevent the resources allocated by the associated client from being reclaimed by the garbage collector.

If an explicit executor has not been set for an HttpClient, and a security manager has been installed, then the default executor will execute asynchronous and dependent tasks in a context that is granted no permissions. Custom request body publishers, response body handlers, response body subscribers, and WebSocket Listeners, if executing operations that require privileges, should do so within an appropriate privileged context.

Since:
11

  • Constructor Details

    • HttpClient

      protected HttpClient()
      Creates an HttpClient.

  • Method Details

    • newHttpClient

      public static HttpClient newHttpClient()
      Returns a new HttpClient with default settings.

      Equivalent to newBuilder().build().

      The default settings include: the "GET" request method, a preference of HTTP/2, a redirection policy of NEVER, the default proxy selector, and the default SSL context.

      Implementation Note:
      The system-wide default values are retrieved at the time the HttpClient instance is constructed. Changing the system-wide values after an HttpClient instance has been built, for instance, by calling ProxySelector.setDefault(ProxySelector) or SSLContext.setDefault(SSLContext), has no effect on already built instances.
      Returns:
      a new HttpClient
      Throws:
      UncheckedIOException - if necessary underlying IO resources required to build a new HttpClient cannot be allocated.

    • newBuilder

      public static HttpClient.Builder newBuilder()
      Creates a new HttpClient builder.

      Builders returned by this method create instances of the default HttpClient implementation.

      Returns:
      an HttpClient.Builder

    • cookieHandler

      public abstract Optional<CookieHandler> cookieHandler()
      Returns an Optional containing this client's CookieHandler. If no CookieHandler was set in this client's builder, then the Optional is empty.
      Returns:
      an Optional containing this client's CookieHandler

    • connectTimeout

      public abstract Optional<Duration> connectTimeout()
      Returns an Optional containing the connect timeout duration for this client. If the connect timeout duration was not set in the client's builder, then the Optional is empty.
      Returns:
      an Optional containing this client's connect timeout duration

    • followRedirects

      public abstract HttpClient.Redirect followRedirects()
      Returns the follow redirects policy for this client. The default value for client's built by builders that do not specify a redirect policy is NEVER.
      Returns:
      this client's follow redirects setting

    • proxy

      public abstract Optional<ProxySelector> proxy()
      Returns an Optional containing the ProxySelector supplied to this client. If no proxy selector was set in this client's builder, then the Optional is empty.

      Even though this method may return an empty optional, the HttpClient may still have a non-exposed default proxy selector that is used for sending HTTP requests.

      Returns:
      an Optional containing the proxy selector supplied to this client.

    • sslContext

      public abstract SSLContext sslContext()
      Returns this client's SSLContext.

      If no SSLContext was set in this client's builder, then the default context is returned.

      Returns:
      this client's SSLContext

    • sslParameters

      public abstract SSLParameters sslParameters()
      Returns a copy of this client's SSLParameters.

      If no SSLParameters were set in the client's builder, then an implementation specific default set of parameters, that the client will use, is returned.

      Returns:
      this client's SSLParameters

    • authenticator

      public abstract Optional<Authenticator> authenticator()
      Returns an Optional containing the Authenticator set on this client. If no Authenticator was set in the client's builder, then the Optional is empty.
      Returns:
      an Optional containing this client's Authenticator

    • version

      public abstract HttpClient.Version version()
      Returns the preferred HTTP protocol version for this client. The default value is HttpClient.Version.HTTP_2
      Implementation Note:
      Constraints may also affect the selection of protocol version. For example, if HTTP/2 is requested through a proxy, and if the implementation does not support this mode, then HTTP/1.1 may be used
      Returns:
      the HTTP protocol version requested

    • executor

      public abstract Optional<Executor> executor()
      Returns an Optional containing this client's Executor. If no Executor was set in the client's builder, then the Optional is empty.

      Even though this method may return an empty optional, the HttpClient may still have an non-exposed default executor that is used for executing asynchronous and dependent tasks.

      Returns:
      an Optional containing this client's Executor

    • send

      public abstract <T> HttpResponse<T> send(HttpRequest request, HttpResponse.BodyHandler<T> responseBodyHandler) throws IOException, InterruptedException
      Sends the given request using this client, blocking if necessary to get the response. The returned HttpResponse<T> contains the response status, headers, and body ( as handled by given response body handler ).

      If the operation is interrupted, the default HttpClient implementation attempts to cancel the HTTP exchange and InterruptedException is thrown. No guarantee is made as to exactly when the cancellation request may be taken into account. In particular, the request might still get sent to the server, as its processing might already have started asynchronously in another thread, and the underlying resources may only be released asynchronously.

      • With HTTP/1.1, an attempt to cancel may cause the underlying connection to be closed abruptly.
      • With HTTP/2, an attempt to cancel may cause the stream to be reset, or in certain circumstances, may also cause the connection to be closed abruptly, if, for instance, the thread is currently trying to write to the underlying socket.
      Type Parameters:
      T - the response body type
      Parameters:
      request - the request
      responseBodyHandler - the response body handler
      Returns:
      the response
      Throws:
      IOException - if an I/O error occurs when sending or receiving, or the client has shut down
      InterruptedException - if the operation is interrupted
      IllegalArgumentException - if the request argument is not a request that could have been validly built as specified by HttpRequest.Builder.
      SecurityException - If a security manager has been installed and it denies access to the URL in the given request, or proxy if one is configured. See security checks for further information.

    • sendAsync

      public abstract <T> CompletableFuture<HttpResponse<T>> sendAsync(HttpRequest request, HttpResponse.BodyHandler<T> responseBodyHandler)
      Sends the given request asynchronously using this client with the given response body handler.

      Equivalent to: sendAsync(request, responseBodyHandler, null).

      Type Parameters:
      T - the response body type
      Parameters:
      request - the request
      responseBodyHandler - the response body handler
      Returns:
      a CompletableFuture<HttpResponse<T>>
      Throws:
      IllegalArgumentException - if the request argument is not a request that could have been validly built as specified by HttpRequest.Builder.

    • sendAsync

      public abstract <T> CompletableFuture<HttpResponse<T>> sendAsync(HttpRequest request, HttpResponse.BodyHandler<T> responseBodyHandler, HttpResponse.PushPromiseHandler<T> pushPromiseHandler)
      Sends the given request asynchronously using this client with the given response body handler and push promise handler.

      The returned completable future, if completed successfully, completes with an HttpResponse<T> that contains the response status, headers, and body ( as handled by given response body handler ).

      Push promises received, if any, are handled by the given pushPromiseHandler. A null valued pushPromiseHandler rejects any push promises.

      The returned completable future completes exceptionally with:

      The default HttpClient implementation returns CompletableFuture objects that are cancelable. CompletableFuture objects derived from cancelable futures are themselves cancelable. Invoking cancel(true) on a cancelable future that is not completed, attempts to cancel the HTTP exchange in an effort to release underlying resources as soon as possible. No guarantee is made as to exactly when the cancellation request may be taken into account. In particular, the request might still get sent to the server, as its processing might already have started asynchronously in another thread, and the underlying resources may only be released asynchronously.

      • With HTTP/1.1, an attempt to cancel may cause the underlying connection to be closed abruptly.
      • With HTTP/2, an attempt to cancel may cause the stream to be reset.
      Type Parameters:
      T - the response body type
      Parameters:
      request - the request
      responseBodyHandler - the response body handler
      pushPromiseHandler - push promise handler, may be null
      Returns:
      a CompletableFuture<HttpResponse<T>>
      Throws:
      IllegalArgumentException - if the request argument is not a request that could have been validly built as specified by HttpRequest.Builder.

    • newWebSocketBuilder

      public WebSocket.Builder newWebSocketBuilder()
      Creates a new WebSocket builder (optional operation).

      Example 

      HttpClient client = HttpClient.newHttpClient();
CompletableFuture<WebSocket> ws = client.newWebSocketBuilder()
   .buildAsync(URI.create("ws://websocket.example.com"), listener);

      Finer control over the WebSocket Opening Handshake can be achieved by using a custom HttpClient.

      Example 

      InetSocketAddress addr = new InetSocketAddress("proxy.example.com", 80);
HttpClient client = HttpClient.newBuilder()
        .proxy(ProxySelector.of(addr))
        .build();

CompletableFuture<WebSocket> ws = client.newWebSocketBuilder()
        .buildAsync(URI.create("ws://websocket.example.com"), listener);
      Implementation Requirements:
      The default implementation of this method throws UnsupportedOperationException. Clients obtained through newHttpClient() or newBuilder() return a WebSocket builder.
      Implementation Note:
      Both builder and WebSockets created with it operate in a non-blocking fashion. That is, their methods do not block before returning a CompletableFuture. Asynchronous tasks are executed in this HttpClient's executor.

      When a CompletionStage returned from Listener.onClose completes, the WebSocket will send a Close message that has the same code the received message has and an empty reason.

      Returns:
      a WebSocket.Builder
      Throws:
      UnsupportedOperationException - if this HttpClient does not provide WebSocket support

    • shutdown

      public void shutdown()
      Initiates an orderly shutdown in which requests previously submitted with send or sendAsync are run to completion, but no new request will be accepted. Running a request to completion may involve running several operations in the background, including waiting for responses to be delivered, which will all have to run to completion until the request is considered completed. Invocation has no additional effect if already shut down.

      This method does not wait for previously submitted request to complete execution. Use awaitTermination or close to do that.

      Implementation Requirements:
      The default implementation of this method does nothing. Subclasses should override this method to implement the appropriate behavior.
      Since:
      21
      See Also:

    • awaitTermination

      public boolean awaitTermination(Duration duration) throws InterruptedException
      Blocks until all operations have completed execution after a shutdown request, or the duration elapses, or the current thread is interrupted, whichever happens first. Operations are any tasks required to run a request previously submitted with send or sendAsync to completion.

      This method does not wait if the duration to wait is less than or equal to zero. In this case, the method just tests if the thread has terminated.

      Implementation Requirements:
      The default implementation of this method checks for null arguments, but otherwise does nothing and returns true. Subclasses should override this method to implement the proper behavior.
      Parameters:
      duration - the maximum time to wait
      Returns:
      true if this client terminated and false if the timeout elapsed before termination
      Throws:
      InterruptedException - if interrupted while waiting
      Since:
      21
      See Also:

    • isTerminated

      public boolean isTerminated()
      Returns true if all operations have completed following a shutdown. Operations are any tasks required to run a request previously submitted with send or sendAsync to completion.

      Note that isTerminated is never true unless either shutdown or shutdownNow was called first.

      Implementation Requirements:
      The default implementation of this method does nothing and returns false. Subclasses should override this method to implement the proper behavior.
      Returns:
      true if all tasks have completed following a shutdown
      Since:
      21
      See Also:

    • shutdownNow

      public void shutdownNow()
      This method attempts to initiate an immediate shutdown. An implementation of this method may attempt to interrupt operations that are actively running. Operations are any tasks required to run a request previously submitted with send or sendAsync to completion. The behavior of actively running operations when interrupted is undefined. In particular, there is no guarantee that interrupted operations will terminate, or that code waiting on these operations will ever be notified.
      Implementation Requirements:
      The default implementation of this method simply calls shutdown(). Subclasses should override this method to implement the appropriate behavior.
      Since:
      21
      See Also:

    • close

      public void close()
      Initiates an orderly shutdown in which requests previously submitted to send or sendAsync are run to completion, but no new request will be accepted. Running a request to completion may involve running several operations in the background, including waiting for responses to be delivered. This method waits until all operations have completed execution and the client has terminated.

      If interrupted while waiting, this method may attempt to stop all operations by calling shutdownNow(). It then continues to wait until all actively executing operations have completed. The interrupt status will be re-asserted before this method returns.

      If already terminated, invoking this method has no effect.

      Specified by:
      close in interface AutoCloseable
      Implementation Requirements:
      The default implementation invokes shutdown() and waits for tasks to complete execution with awaitTermination.
      Since:
      21
      See Also: