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本文主要研究一下Java11的HttpClient的基本使用。

变化

从java9的jdk.incubator.httpclient模块迁移到java.net.http模块，包名由jdk.incubator.http改为java.net.http
原来的诸如HttpResponse.BodyHandler.asString()方法变更为HttpResponse.BodyHandlers.ofString()，变化一为BodyHandler改为BodyHandlers，变化二为asXXX()之类的方法改为ofXXX()，由as改为of

实例

设置超时时间

    @Test
    public void testTimeout() throws IOException, InterruptedException {
        //1.set connect timeout
        HttpClient client = HttpClient.newBuilder()
                .connectTimeout(Duration.ofMillis(5000))
                .followRedirects(HttpClient.Redirect.NORMAL)
                .build();

        //2.set read timeout
        HttpRequest request = HttpRequest.newBuilder()
                .uri(URI.create("http://openjdk.java.net/"))
                .timeout(Duration.ofMillis(5009))
                .build();

        HttpResponse<String> response =
                client.send(request, HttpResponse.BodyHandlers.ofString());

        System.out.println(response.body());

    }

HttpConnectTimeoutException实例

Caused by: java.net.http.HttpConnectTimeoutException: HTTP connect timed out
	at java.net.http/jdk.internal.net.http.ResponseTimerEvent.handle(ResponseTimerEvent.java:68)
	at java.net.http/jdk.internal.net.http.HttpClientImpl.purgeTimeoutsAndReturnNextDeadline(HttpClientImpl.java:1248)
	at java.net.http/jdk.internal.net.http.HttpClientImpl$SelectorManager.run(HttpClientImpl.java:877)
Caused by: java.net.ConnectException: HTTP connect timed out
	at java.net.http/jdk.internal.net.http.ResponseTimerEvent.handle(ResponseTimerEvent.java:69)
	... 2 more

HttpTimeoutException实例

java.net.http.HttpTimeoutException: request timed out

	at java.net.http/jdk.internal.net.http.HttpClientImpl.send(HttpClientImpl.java:559)
	at java.net.http/jdk.internal.net.http.HttpClientFacade.send(HttpClientFacade.java:119)
	at com.example.HttpClientTest.testTimeout(HttpClientTest.java:40)

设置authenticator

    @Test
    public void testBasicAuth() throws IOException, InterruptedException {
        HttpClient client = HttpClient.newBuilder()
                .connectTimeout(Duration.ofMillis(5000))
                .authenticator(new Authenticator() {
                    @Override
                    protected PasswordAuthentication getPasswordAuthentication() {
                        return new PasswordAuthentication("admin","password".toCharArray());
                    }
                })
                .build();

        HttpRequest request = HttpRequest.newBuilder()
                .uri(URI.create("http://localhost:8080/json/info"))
                .timeout(Duration.ofMillis(5009))
                .build();

        HttpResponse<String> response =
                client.send(request, HttpResponse.BodyHandlers.ofString());

        System.out.println(response.statusCode());
        System.out.println(response.body());
    }

authenticator可以用来设置HTTP authentication，比如Basic authentication
虽然Basic authentication也可以自己设置header，不过通过authenticator省得自己去构造header

设置header

    @Test
    public void testCookies() throws IOException, InterruptedException {
        HttpClient client = HttpClient.newBuilder()
                .connectTimeout(Duration.ofMillis(5000))
                .build();
        HttpRequest request = HttpRequest.newBuilder()
                .uri(URI.create("http://localhost:8080/json/cookie"))
                .header("Cookie","JSESSIONID=4f994730-32d7-4e22-a18b-25667ddeb636; userId=java11")
                .timeout(Duration.ofMillis(5009))
                .build();
        HttpResponse<String> response =
                client.send(request, HttpResponse.BodyHandlers.ofString());

        System.out.println(response.statusCode());
        System.out.println(response.body());
    }

通过request可以自己设置header

GET

同步

    @Test
    public void testSyncGet() throws IOException, InterruptedException {
        HttpClient client = HttpClient.newHttpClient();
        HttpRequest request = HttpRequest.newBuilder()
                .uri(URI.create("https://www.baidu.com"))
                .build();

        HttpResponse<String> response =
                client.send(request, HttpResponse.BodyHandlers.ofString());

        System.out.println(response.body());
    }

异步

    @Test
    public void testAsyncGet() throws ExecutionException, InterruptedException {
        HttpClient client = HttpClient.newHttpClient();
        HttpRequest request = HttpRequest.newBuilder()
                .uri(URI.create("https://www.baidu.com"))
                .build();

        CompletableFuture<String> result = client.sendAsync(request, HttpResponse.BodyHandlers.ofString())
                .thenApply(HttpResponse::body);
        System.out.println(result.get());
    }

POST表单

    @Test
    public void testPostForm() throws IOException, InterruptedException {
        HttpClient client = HttpClient.newBuilder().build();
        HttpRequest request = HttpRequest.newBuilder()
                .uri(URI.create("http://www.w3school.com.cn/demo/demo_form.asp"))
                .header("Content-Type","application/x-www-form-urlencoded")
                .POST(HttpRequest.BodyPublishers.ofString("name1=value1&name2=value2"))
                .build();

        HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());
        System.out.println(response.statusCode());
    }

header指定内容是表单类型，然后通过BodyPublishers.ofString传递表单数据，需要自己构建表单参数

POST JSON

    @Test
    public void testPostJsonGetJson() throws ExecutionException, InterruptedException, JsonProcessingException {
        ObjectMapper objectMapper = new ObjectMapper();
        StockDto dto = new StockDto();
        dto.setName("hj");
        dto.setSymbol("hj");
        dto.setType(StockDto.StockType.SH);
        String requestBody = objectMapper
                .writerWithDefaultPrettyPrinter()
                .writeValueAsString(dto);

        HttpRequest request = HttpRequest.newBuilder(URI.create("http://localhost:8080/json/demo"))
                .header("Content-Type", "application/json")
                .POST(HttpRequest.BodyPublishers.ofString(requestBody))
                .build();

        CompletableFuture<StockDto> result = HttpClient.newHttpClient()
                .sendAsync(request, HttpResponse.BodyHandlers.ofString())
                .thenApply(HttpResponse::body)
                .thenApply(body -> {
                    try {
                        return objectMapper.readValue(body,StockDto.class);
                    } catch (IOException e) {
                        return new StockDto();
                    }
                });
        System.out.println(result.get());
    }

post json的话，body自己json化为string，然后header指定是json格式

文件上传

    @Test
    public void testUploadFile() throws IOException, InterruptedException, URISyntaxException {
        HttpClient client = HttpClient.newHttpClient();
        Path path = Path.of(getClass().getClassLoader().getResource("body.txt").toURI());
        File file = path.toFile();

        String multipartFormDataBoundary = "Java11HttpClientFormBoundary";
        org.apache.http.HttpEntity multipartEntity = MultipartEntityBuilder.create()
                .addPart("file", new FileBody(file, ContentType.DEFAULT_BINARY))
                .setBoundary(multipartFormDataBoundary) //要设置，否则阻塞
                .build();

        HttpRequest request = HttpRequest.newBuilder()
                .uri(URI.create("http://localhost:8080/file/upload"))
                .header("Content-Type", "multipart/form-data; boundary=" + multipartFormDataBoundary)
                .POST(HttpRequest.BodyPublishers.ofInputStream(() -> {
                    try {
                        return multipartEntity.getContent();
                    } catch (IOException e) {
                        e.printStackTrace();
                        throw new RuntimeException(e);
                    }
                }))
                .build();

        HttpResponse<String> response =
                client.send(request, HttpResponse.BodyHandlers.ofString());

        System.out.println(response.body());
    }

官方的HttpClient并没有提供类似WebClient那种现成的BodyInserters.fromMultipartData方法，因此这里需要自己转换
这里使用org.apache.httpcomponents(httpclient及httpmime)的MultipartEntityBuilder构建multipartEntity，最后通过HttpRequest.BodyPublishers.ofInputStream来传递内容
这里header要指定Content-Type值为multipart/form-data以及boundary的值，否则服务端可能无法解析

文件下载

    @Test
    public void testAsyncDownload() throws ExecutionException, InterruptedException {
        HttpClient client = HttpClient.newHttpClient();
        HttpRequest request = HttpRequest.newBuilder()
                .uri(URI.create("http://localhost:8080/file/download"))
                .build();

        CompletableFuture<Path> result = client.sendAsync(request, HttpResponse.BodyHandlers.ofFile(Paths.get("/tmp/body.txt")))
                .thenApply(HttpResponse::body);
        System.out.println(result.get());
    }

使用HttpResponse.BodyHandlers.ofFile来接收文件

并发请求

    @Test
    public void testConcurrentRequests(){
        HttpClient client = HttpClient.newHttpClient();
        List<String> urls = List.of("http://www.baidu.com","http://www.alibaba.com/","http://www.tencent.com");
        List<HttpRequest> requests = urls.stream()
                .map(url -> HttpRequest.newBuilder(URI.create(url)))
                .map(reqBuilder -> reqBuilder.build())
                .collect(Collectors.toList());

        List<CompletableFuture<HttpResponse<String>>> futures = requests.stream()
                .map(request -> client.sendAsync(request, HttpResponse.BodyHandlers.ofString()))
                .collect(Collectors.toList());
        futures.stream()
                .forEach(e -> e.whenComplete((resp,err) -> {
                    if(err != null){
                        err.printStackTrace();
                    }else{
                        System.out.println(resp.body());
                        System.out.println(resp.statusCode());
                    }
                }));
        CompletableFuture.allOf(futures
                .toArray(CompletableFuture<?>[]::new))
                .join();
    }

sendAsync方法返回的是CompletableFuture，可以方便地进行转换、组合等操作
这里使用CompletableFuture.allOf组合在一起，最后调用join等待所有future完成

错误处理

    @Test
    public void testHandleException() throws ExecutionException, InterruptedException {
        HttpClient client = HttpClient.newBuilder()
                .connectTimeout(Duration.ofMillis(5000))
                .build();
        HttpRequest request = HttpRequest.newBuilder()
                .uri(URI.create("https://twitter.com"))
                .build();

        CompletableFuture<String> result = client.sendAsync(request, HttpResponse.BodyHandlers.ofString())
//                .whenComplete((resp,err) -> {
//                    if(err != null){
//                        err.printStackTrace();
//                    }else{
//                        System.out.println(resp.body());
//                        System.out.println(resp.statusCode());
//                    }
//                })
                .thenApply(HttpResponse::body)
                .exceptionally(err -> {
                    err.printStackTrace();
                    return "fallback";
                });
        System.out.println(result.get());
    }

HttpClient异步请求返回的是CompletableFuture<HttpResponse>，其自带exceptionally方法可以用来做fallback处理
另外值得注意的是HttpClient不像WebClient那样，它没有对4xx或5xx的状态码抛出异常，需要自己根据情况来处理，手动检测状态码抛出异常或者返回其他内容

HTTP2

    @Test
    public void testHttp2() throws URISyntaxException {
        HttpClient.newBuilder()
                .followRedirects(HttpClient.Redirect.NEVER)
                .version(HttpClient.Version.HTTP_2)
                .build()
                .sendAsync(HttpRequest.newBuilder()
                                .uri(new URI("https://http2.akamai.com/demo"))
                                .GET()
                                .build(),
                        HttpResponse.BodyHandlers.ofString())
                .whenComplete((resp,t) -> {
                    if(t != null){
                        t.printStackTrace();
                    }else{
                        System.out.println(resp.version());
                        System.out.println(resp.statusCode());
                    }
                }).join();
    }

执行之后可以看到返回的response的version为HTTP_2

WebSocket

    @Test
    public void testWebSocket() throws InterruptedException {
        HttpClient client = HttpClient.newHttpClient();
        WebSocket webSocket = client.newWebSocketBuilder()
                .buildAsync(URI.create("ws://localhost:8080/echo"), new WebSocket.Listener() {

                    @Override
                    public CompletionStage<?> onText(WebSocket webSocket, CharSequence data, boolean last) {
                        // request one more
                        webSocket.request(1);

                        // Print the message when it's available
                        return CompletableFuture.completedFuture(data)
                                .thenAccept(System.out::println);
                    }
                }).join();
        webSocket.sendText("hello ", false);
        webSocket.sendText("world ",true);

        TimeUnit.SECONDS.sleep(10);
        webSocket.sendClose(WebSocket.NORMAL_CLOSURE, "ok").join();
    }

HttpClient支持HTTP2，也包含了WebSocket，通过newWebSocketBuilder去构造WebSocket
传入listener进行接收消息，要发消息的话，使用WebSocket来发送，关闭使用sendClose方法

reactive streams

HttpClient本身就是reactive的，支持reactive streams，这里举ResponseSubscribers.ByteArraySubscriber的源码看看： java.net.http/jdk/internal/net/http/ResponseSubscribers.java

public static class ByteArraySubscriber<T> implements BodySubscriber<T> {
        private final Function<byte[], T> finisher;
        private final CompletableFuture<T> result = new MinimalFuture<>();
        private final List<ByteBuffer> received = new ArrayList<>();

        private volatile Flow.Subscription subscription;

        public ByteArraySubscriber(Function<byte[],T> finisher) {
            this.finisher = finisher;
        }

        @Override
        public void onSubscribe(Flow.Subscription subscription) {
            if (this.subscription != null) {
                subscription.cancel();
                return;
            }
            this.subscription = subscription;
            // We can handle whatever you've got
            subscription.request(Long.MAX_VALUE);
        }

        @Override
        public void onNext(List<ByteBuffer> items) {
            // incoming buffers are allocated by http client internally,
            // and won't be used anywhere except this place.
            // So it's free simply to store them for further processing.
            assert Utils.hasRemaining(items);
            received.addAll(items);
        }

        @Override
        public void onError(Throwable throwable) {
            received.clear();
            result.completeExceptionally(throwable);
        }

        static private byte[] join(List<ByteBuffer> bytes) {
            int size = Utils.remaining(bytes, Integer.MAX_VALUE);
            byte[] res = new byte[size];
            int from = 0;
            for (ByteBuffer b : bytes) {
                int l = b.remaining();
                b.get(res, from, l);
                from += l;
            }
            return res;
        }

        @Override
        public void onComplete() {
            try {
                result.complete(finisher.apply(join(received)));
                received.clear();
            } catch (IllegalArgumentException e) {
                result.completeExceptionally(e);
            }
        }

        @Override
        public CompletionStage<T> getBody() {
            return result;
        }
    }

BodySubscriber接口继承了Flow.Subscriber<List>接口
这里的Subscription来自Flow类，该类是java9引入的，里头包含了支持Reactive Streams的实现

小结

HttpClient在Java11从incubator变为正式版，相对于传统的HttpUrlConnection其提升可不是一点半点，不仅支持异步，也支持reactive streams，同时也支持了HTTP2以及WebSocket，非常值得大家使用。

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