Class HttpClient

public abstract class HttpClient
extends Object

An HTTP Client.

An HttpClient can be used to send requests and retrieve their responses. An HttpClient is created through a builder. 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.

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.

Implementation Note:
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

Nested Classes

Modifier and Type Class Description
static interface  HttpClient.Builder

A builder of HTTP Clients.
static class  HttpClient.Redirect

Defines the automatic redirection policy.
static class  HttpClient.Version

The HTTP protocol version.

Constructors

Modifier Constructor Description
protected HttpClient()

Creates an HttpClient.

Methods

Modifier and Type Method Description
abstract Optional<Authenticator> authenticator()

Returns an Optional containing the Authenticator set on this client.
abstract Optional<Duration> connectTimeout()

Returns an Optional containing the connect timeout duration for this client.
abstract Optional<CookieHandler> cookieHandler()

Returns an Optional containing this client's CookieHandler.
abstract Optional<Executor> executor()

Returns an Optional containing this client's Executor.
abstract HttpClient.Redirect followRedirects()

Returns the follow redirects policy for this client.
static HttpClient.Builder newBuilder()

Creates a new HttpClient builder.
static HttpClient newHttpClient()

Returns a new HttpClient with default settings.
WebSocket.Builder newWebSocketBuilder()

Creates a new WebSocket builder (optional operation).
abstract Optional<ProxySelector> proxy()

Returns an Optional containing the ProxySelector supplied to this client.
abstract <T> HttpResponse<T> send​(HttpRequest request, HttpResponse.BodyHandler<T> responseBodyHandler)

Sends the given request using this client, blocking if necessary to get the response.
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.
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.
abstract SSLContext sslContext()

Returns this client's SSLContext.
abstract SSLParameters sslParameters()

Returns a copy of this client's SSLParameters.
abstract HttpClient.Version version()

Returns the preferred HTTP protocol version for this client.

Methods declared in class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructors

HttpClient

protected HttpClient()

Creates an HttpClient.

Methods

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

newBuilder

public static HttpClient.Builder newBuilder()

Creates a new HttpClient builder.

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 ).

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
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:

  • IOException - if an I/O error occurs when sending or receiving
  • 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.
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

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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
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https://docs.oracle.com/en/java/javase/11/docs/api/java.net.http/java/net/http/HttpClient.html