Java11 HttpClient小試牛刀

序

本文主要研究一下Java11的HttpClient的基本使用。

變化

• 從java9的jdk.incubator.httpclient模組遷移到java.net.http模組，包名由jdk.incubator.http改為java.net.http
• 原來的諸如HttpResponse.BodyHandler.asString()方法變更為HttpResponse.BodyHandlers.ofString()，變化一為BodyHandler改為BodyHandlers，變化二為asXXX()之類的方法改為ofXXX()，由as改為of

例項

設定超時時間

    @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());

    }
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• HttpConnectTimeoutException例項

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
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• HttpTimeoutException例項

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)
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設定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());
    }
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• authenticator可以用來設定HTTP authentication，比如Basic authentication
• 雖然Basic authentication也可以自己設定header，不過通過authenticator省得自己去構造header

設定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());
    }
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• 通過request可以自己設定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());
    }
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• 非同步

    @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());
    }
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POST表單

    @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());
    }
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• header指定內容是表單型別，然後通過BodyPublishers.ofString傳遞表單資料，需要自己構建表單引數

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());
    }
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• post json的話，body自己json化為string，然後header指定是json格式

檔案上傳

    @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) //要設定，否則阻塞
                .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());
    }
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• 官方的HttpClient並沒有提供類似WebClient那種現成的BodyInserters.fromMultipartData方法，因此這裡需要自己轉換
• 這裡使用org.apache.httpcomponents(httpclient及httpmime)的MultipartEntityBuilder構建multipartEntity，最後通過HttpRequest.BodyPublishers.ofInputStream來傳遞內容
• 這裡header要指定Content-Type值為multipart/form-data以及boundary的值，否則服務端可能無法解析

檔案下載

    @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());
    }
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• 使用HttpResponse.BodyHandlers.ofFile來接收檔案

併發請求

    @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();
    }
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• sendAsync方法返回的是CompletableFuture，可以方便地進行轉換、組合等操作
• 這裡使用CompletableFuture.allOf組合在一起，最後呼叫join等待所有future完成

錯誤處理

    @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());
    }
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• HttpClient非同步請求返回的是CompletableFuture<HttpResponse>，其自帶exceptionally方法可以用來做fallback處理
• 另外值得注意的是HttpClient不像WebClient那樣，它沒有對4xx或5xx的狀態碼丟擲異常，需要自己根據情況來處理，手動檢測狀態碼丟擲異常或者返回其他內容

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();
    }
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• 執行之後可以看到返回的response的version為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();
    }
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• HttpClient支援HTTP2，也包含了WebSocket，通過newWebSocketBuilder去構造WebSocket
• 傳入listener進行接收訊息，要發訊息的話，使用WebSocket來傳送，關閉使用sendClose方法

reactive streams

HttpClient本身就是reactive的，支援reactive streams，這裡舉ResponseSubscribers.ByteArraySubscriber的原始碼看看：
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;
        }
    }
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• BodySubscriber介面繼承了Flow.Subscriber<List>介面
• 這裡的Subscription來自Flow類，該類是java9引入的，裡頭包含了支援Reactive Streams的實現

小結

HttpClient在Java11從incubator變為正式版，相對於傳統的HttpUrlConnection其提升可不是一點半點，不僅支援非同步，也支援reactive streams，同時也支援了HTTP2以及WebSocket，非常值得大家使用。

doc

• java.net.http javadoc
• Examples and Recipes
• Java 11: Standardized HTTP Client API
• Exploring the New HTTP Client in Java 9
• Introduction to the New HTTP Client in Java 9
• Getting Started With Java 9`s New HTTP Client
• java9系列(六)HTTP/2 Client (Incubator)
• Java 9 HttpClient send a multipart/form-data request
• Java 9: High level HTTP and WebSocket API
• WebSocket Client API in Java 9 with Example