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我正在尝试从服务器加载数据。然后通过 JavaFX 视图显示加载的数据。我正在使用服务来执行网络操作，为此我正在使用 Apache HttpClients。最初，我认为这个错误与网络有关。我做了一些穴居人风格的调试，并意识到这个错误与服务相关联。奇怪的是，该服务在第二个运行时调用 onSucceeded() 方法（不同的实例，我没有重新启动服务）。我无法弄清楚为什么服务仅第二次调用 onSucceeded() 方法。

这是我为执行网络操作而实现的服务类。

public class HttpClientService extends Service<String> {

    private static final String TAG = HttpClientService.class.getName();
    private static final Logger logger = Logger.getLogger(TAG);

    private ObjectProperty<URL> url = new SimpleObjectProperty<>();
    private ObservableList<NameValuePair> parameters = FXCollections.observableArrayList();

    public HttpClientService(String url, Map<String, String> map) throws MalformedURLException {
        setUrl(new URL(url));
        for (String name : map.keySet()) {
            String value = map.get(name);
            parameters.add(new BasicNameValuePair(name, value));
        }
    }

    public HttpClientService(String url, NameValuePair ... parameters) throws MalformedURLException {
        setUrl(new URL(url));
        getParameters().addAll(parameters);
    }

    public HttpClientService(URL url, NameValuePair ... parameters) {
        setUrl(url);
        getParameters().addAll(parameters);
    }

    protected Task<String> createTask() {
        return new HttpClientTask(getUrl(), getParameters());
    }

    public URL getUrl() {
        return url.get();
    }

    public ObjectProperty<URL> urlProperty() {
        return url;
    }

    public void setUrl(URL url) {
        this.url.set(url);
    }

    public ObservableList<NameValuePair> getParameters() {
        return parameters;
    }

    public void setParameters(ObservableList<NameValuePair> parameters) {
        this.parameters = parameters;
    }

    @Override
    protected void succeeded() {
        System.out.println("## Successful...");
    }

    @Override
    protected void failed() {
        Throwable exception = getException();

        System.out.println("Error: Failed to download guest profiles.");
        exception.printStackTrace();
    }

    @Override
    protected void cancelled() {
        System.out.println("HttpClientService was stopped.");
    }

    @Override
    protected void running() {
        logger.log(Level.INFO, "Running service...");
    }
}

这是调用服务并将数据注入视图的方法。

private void loadBlocks() {
    try {
        // TODO: Get the property identifier and set!
        Integer propertyIdentifier = 1;

        Map<String, String> parameters = new HashMap<>();
        parameters.put("property", propertyIdentifier.toString());

        HttpClientService service = new HttpClientService(UrlPath.ADMINISTRATION_PROPERTY_BLOCK_LIST_ALL, parameters);
        service.setOnSucceeded(workerStateEvent -> {
            logger.log(Level.INFO, "Successfully loaded blocks");

            try {
                String result = (String)workerStateEvent.getSource().getValue();
                logger.log(Level.INFO, result);

                List<Block> blocks = mapper.readValue(result, new TypeReference<ArrayList<Block>>(){});

                ObservableList<Block> items = blocksTableView.getItems();
                items.clear();
                items.addAll(blocks);

                NotificationHelper.postNotification(eventBus, "Successfully loaded blocks", 500);
            }
            catch (IOException exception) {
                exception.printStackTrace();
            }
        });
        service.stateProperty().addListener((observableValue, state, t1) -> System.out.println(t1));
        service.start();
    }
    catch (MalformedURLException exception) {
        exception.printStackTrace();
    }
}

这是应用程序的日志。

SCHEDULED
RUNNING
Nov 10, 2018 2:28:26 PM com.onecube.pms.client.service.HttpClientService running
INFO: Running service...
Nov 10, 2018 2:28:26 PM com.onecube.pms.client.task.HttpClientTask call
INFO: [Content-Type: application/x-www-form-urlencoded,Content-Length: 10,Chunked: false]
14:28:26.778 [Thread-3] DEBUG org.apache.http.client.protocol.RequestAddCookies - CookieSpec selected: default
14:28:26.794 [Thread-3] DEBUG org.apache.http.client.protocol.RequestAuthCache - Auth cache not set in the context
14:28:26.796 [Thread-3] DEBUG org.apache.http.impl.conn.PoolingHttpClientConnectionManager - Connection request: [route: {}->http://localhost:8080][total kept alive: 0; route allocated: 0 of 100; total allocated: 0 of 200]
14:28:26.809 [Thread-3] DEBUG org.apache.http.impl.conn.PoolingHttpClientConnectionManager - Connection leased: [id: 0][route: {}->http://localhost:8080][total kept alive: 0; route allocated: 1 of 100; total allocated: 1 of 200]
14:28:26.810 [Thread-3] DEBUG org.apache.http.impl.execchain.MainClientExec - Opening connection {}->http://localhost:8080
14:28:26.829 [Thread-3] DEBUG org.apache.http.impl.conn.DefaultHttpClientConnectionOperator - Connecting to localhost/127.0.0.1:8080
14:28:26.830 [Thread-3] DEBUG org.apache.http.impl.conn.DefaultHttpClientConnectionOperator - Connection established 127.0.0.1:63671<->127.0.0.1:8080
14:28:26.831 [Thread-3] DEBUG org.apache.http.impl.execchain.MainClientExec - Executing request POST /administration/property/block/listAll HTTP/1.1
14:28:26.831 [Thread-3] DEBUG org.apache.http.impl.execchain.MainClientExec - Target auth state: UNCHALLENGED
14:28:26.834 [Thread-3] DEBUG org.apache.http.impl.execchain.MainClientExec - Proxy auth state: UNCHALLENGED
14:28:26.836 [Thread-3] DEBUG org.apache.http.headers - http-outgoing-0 >> POST /administration/property/block/listAll HTTP/1.1
14:28:26.836 [Thread-3] DEBUG org.apache.http.headers - http-outgoing-0 >> Content-Length: 10
14:28:26.836 [Thread-3] DEBUG org.apache.http.headers - http-outgoing-0 >> Content-Type: application/x-www-form-urlencoded
14:28:26.836 [Thread-3] DEBUG org.apache.http.headers - http-outgoing-0 >> Host: localhost:8080
14:28:26.836 [Thread-3] DEBUG org.apache.http.headers - http-outgoing-0 >> Connection: Keep-Alive
14:28:26.836 [Thread-3] DEBUG org.apache.http.headers - http-outgoing-0 >> User-Agent: Apache-HttpClient/4.5.6 (Java/11.0.1)
14:28:26.836 [Thread-3] DEBUG org.apache.http.headers - http-outgoing-0 >> Accept-Encoding: gzip,deflate
14:28:26.837 [Thread-3] DEBUG org.apache.http.wire - http-outgoing-0 >> "POST /administration/property/block/listAll HTTP/1.1[\r][\n]"
14:28:26.837 [Thread-3] DEBUG org.apache.http.wire - http-outgoing-0 >> "Content-Length: 10[\r][\n]"
14:28:26.837 [Thread-3] DEBUG org.apache.http.wire - http-outgoing-0 >> "Content-Type: application/x-www-form-urlencoded[\r][\n]"
14:28:26.837 [Thread-3] DEBUG org.apache.http.wire - http-outgoing-0 >> "Host: localhost:8080[\r][\n]"
14:28:26.837 [Thread-3] DEBUG org.apache.http.wire - http-outgoing-0 >> "Connection: Keep-Alive[\r][\n]"
14:28:26.837 [Thread-3] DEBUG org.apache.http.wire - http-outgoing-0 >> "User-Agent: Apache-HttpClient/4.5.6 (Java/11.0.1)[\r][\n]"
14:28:26.837 [Thread-3] DEBUG org.apache.http.wire - http-outgoing-0 >> "Accept-Encoding: gzip,deflate[\r][\n]"
14:28:26.837 [Thread-3] DEBUG org.apache.http.wire - http-outgoing-0 >> "[\r][\n]"
14:28:26.838 [Thread-3] DEBUG org.apache.http.wire - http-outgoing-0 >> "property=1"
14:28:26.845 [Thread-3] DEBUG org.apache.http.wire - http-outgoing-0 << "HTTP/1.1 200 [\r][\n]"
14:28:26.846 [Thread-3] DEBUG org.apache.http.wire - http-outgoing-0 << "Content-Type: application/json;charset=UTF-8[\r][\n]"
14:28:26.846 [Thread-3] DEBUG org.apache.http.wire - http-outgoing-0 << "Transfer-Encoding: chunked[\r][\n]"
14:28:26.846 [Thread-3] DEBUG org.apache.http.wire - http-outgoing-0 << "Date: Sat, 10 Nov 2018 08:58:26 GMT[\r][\n]"
14:28:26.846 [Thread-3] DEBUG org.apache.http.wire - http-outgoing-0 << "[\r][\n]"
14:28:26.846 [Thread-3] DEBUG org.apache.http.wire - http-outgoing-0 << "2[\r][\n]"
14:28:26.846 [Thread-3] DEBUG org.apache.http.wire - http-outgoing-0 << "[][\r][\n]"
14:28:26.846 [Thread-3] DEBUG org.apache.http.wire - http-outgoing-0 << "0[\r][\n]"
14:28:26.846 [Thread-3] DEBUG org.apache.http.wire - http-outgoing-0 << "[\r][\n]"
14:28:26.850 [Thread-3] DEBUG org.apache.http.headers - http-outgoing-0 << HTTP/1.1 200 
14:28:26.850 [Thread-3] DEBUG org.apache.http.headers - http-outgoing-0 << Content-Type: application/json;charset=UTF-8
java.lang.Throwable
    at com.onecube.pms.client.task.HttpClientTask.call(HttpClientTask.java:81)
    at com.onecube.pms.client.task.HttpClientTask.call(HttpClientTask.java:32)
    at javafx.concurrent.Task$TaskCallable.call(Task.java:1425)
    at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
    at javafx.concurrent.Service.lambda$executeTask$6(Service.java:725)
    at java.base/java.security.AccessController.doPrivileged(Native Method)
    at javafx.concurrent.Service.lambda$executeTask$7(Service.java:724)
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
    at java.base/java.lang.Thread.run(Thread.java:834)
14:28:26.850 [Thread-3] DEBUG org.apache.http.headers - http-outgoing-0 << Transfer-Encoding: chunked
14:28:26.850 [Thread-3] DEBUG org.apache.http.headers - http-outgoing-0 << Date: Sat, 10 Nov 2018 08:58:26 GMT
14:28:26.856 [Thread-3] DEBUG org.apache.http.impl.execchain.MainClientExec - Connection can be kept alive indefinitely
14:28:26.860 [Thread-3] DEBUG org.apache.http.impl.conn.PoolingHttpClientConnectionManager - Connection [id: 0][route: {}->http://localhost:8080] can be kept alive indefinitely
14:28:26.861 [Thread-3] DEBUG org.apache.http.impl.conn.DefaultManagedHttpClientConnection - http-outgoing-0: set socket timeout to 0
14:28:26.861 [Thread-3] DEBUG org.apache.http.impl.conn.PoolingHttpClientConnectionManager - Connection released: [id: 0][route: {}->http://localhost:8080][total kept alive: 1; route allocated: 1 of 100; total allocated: 1 of 200]
SCHEDULED
RUNNING
Nov 10, 2018 2:28:43 PM com.onecube.pms.client.service.HttpClientService running
INFO: Running service...
Nov 10, 2018 2:28:43 PM com.onecube.pms.client.task.HttpClientTask call
INFO: [Content-Type: application/x-www-form-urlencoded,Content-Length: 10,Chunked: false]
14:28:43.429 [Thread-4] DEBUG org.apache.http.client.protocol.RequestAddCookies - CookieSpec selected: default
14:28:43.430 [Thread-4] DEBUG org.apache.http.client.protocol.RequestAuthCache - Auth cache not set in the context
14:28:43.431 [Thread-4] DEBUG org.apache.http.impl.conn.PoolingHttpClientConnectionManager - Connection request: [route: {}->http://localhost:8080][total kept alive: 0; route allocated: 0 of 100; total allocated: 0 of 200]
14:28:43.431 [Thread-4] DEBUG org.apache.http.impl.conn.PoolingHttpClientConnectionManager - Connection leased: [id: 1][route: {}->http://localhost:8080][total kept alive: 0; route allocated: 1 of 100; total allocated: 1 of 200]
14:28:43.431 [Thread-4] DEBUG org.apache.http.impl.execchain.MainClientExec - Opening connection {}->http://localhost:8080
14:28:43.431 [Thread-4] DEBUG org.apache.http.impl.conn.DefaultHttpClientConnectionOperator - Connecting to localhost/127.0.0.1:8080
14:28:43.432 [Thread-4] DEBUG org.apache.http.impl.conn.DefaultHttpClientConnectionOperator - Connection established 127.0.0.1:63675<->127.0.0.1:8080
14:28:43.432 [Thread-4] DEBUG org.apache.http.impl.execchain.MainClientExec - Executing request POST /administration/property/block/listAll HTTP/1.1
14:28:43.432 [Thread-4] DEBUG org.apache.http.impl.execchain.MainClientExec - Target auth state: UNCHALLENGED
14:28:43.433 [Thread-4] DEBUG org.apache.http.impl.execchain.MainClientExec - Proxy auth state: UNCHALLENGED
14:28:43.433 [Thread-4] DEBUG org.apache.http.headers - http-outgoing-1 >> POST /administration/property/block/listAll HTTP/1.1
14:28:43.434 [Thread-4] DEBUG org.apache.http.headers - http-outgoing-1 >> Content-Length: 10
14:28:43.434 [Thread-4] DEBUG org.apache.http.headers - http-outgoing-1 >> Content-Type: application/x-www-form-urlencoded
14:28:43.434 [Thread-4] DEBUG org.apache.http.headers - http-outgoing-1 >> Host: localhost:8080
14:28:43.434 [Thread-4] DEBUG org.apache.http.headers - http-outgoing-1 >> Connection: Keep-Alive
14:28:43.434 [Thread-4] DEBUG org.apache.http.headers - http-outgoing-1 >> User-Agent: Apache-HttpClient/4.5.6 (Java/11.0.1)
14:28:43.434 [Thread-4] DEBUG org.apache.http.headers - http-outgoing-1 >> Accept-Encoding: gzip,deflate
14:28:43.434 [Thread-4] DEBUG org.apache.http.wire - http-outgoing-1 >> "POST /administration/property/block/listAll HTTP/1.1[\r][\n]"
14:28:43.434 [Thread-4] DEBUG org.apache.http.wire - http-outgoing-1 >> "Content-Length: 10[\r][\n]"
14:28:43.434 [Thread-4] DEBUG org.apache.http.wire - http-outgoing-1 >> "Content-Type: application/x-www-form-urlencoded[\r][\n]"
14:28:43.434 [Thread-4] DEBUG org.apache.http.wire - http-outgoing-1 >> "Host: localhost:8080[\r][\n]"
14:28:43.434 [Thread-4] DEBUG org.apache.http.wire - http-outgoing-1 >> "Connection: Keep-Alive[\r][\n]"
14:28:43.434 [Thread-4] DEBUG org.apache.http.wire - http-outgoing-1 >> "User-Agent: Apache-HttpClient/4.5.6 (Java/11.0.1)[\r][\n]"
14:28:43.434 [Thread-4] DEBUG org.apache.http.wire - http-outgoing-1 >> "Accept-Encoding: gzip,deflate[\r][\n]"
14:28:43.435 [Thread-4] DEBUG org.apache.http.wire - http-outgoing-1 >> "[\r][\n]"
14:28:43.435 [Thread-4] DEBUG org.apache.http.wire - http-outgoing-1 >> "property=1"
java.lang.Throwable
    at com.onecube.pms.client.task.HttpClientTask.call(HttpClientTask.java:81)
    at com.onecube.pms.client.task.HttpClientTask.call(HttpClientTask.java:32)
    at javafx.concurrent.Task$TaskCallable.call(Task.java:1425)
    at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
    at javafx.concurrent.Service.lambda$executeTask$6(Service.java:725)
    at java.base/java.security.AccessController.doPrivileged(Native Method)
    at javafx.concurrent.Service.lambda$executeTask$7(Service.java:724)
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
    at java.base/java.lang.Thread.run(Thread.java:834)
Nov 10, 2018 2:28:43 PM com.onecube.pms.client.controller.administration.room.ManageBlocksController lambda$loadBlocks$2
INFO: Successfully loaded blocks
Nov 10, 2018 2:28:43 PM com.onecube.pms.client.controller.administration.room.ManageBlocksController lambda$loadBlocks$2
INFO: []
14:28:43.444 [Thread-4] DEBUG org.apache.http.wire - http-outgoing-1 << "HTTP/1.1 200 [\r][\n]"
14:28:43.449 [Thread-4] DEBUG org.apache.http.wire - http-outgoing-1 << "Content-Type: application/json;charset=UTF-8[\r][\n]"
14:28:43.449 [Thread-4] DEBUG org.apache.http.wire - http-outgoing-1 << "Transfer-Encoding: chunked[\r][\n]"
14:28:43.449 [Thread-4] DEBUG org.apache.http.wire - http-outgoing-1 << "Date: Sat, 10 Nov 2018 08:58:43 GMT[\r][\n]"
14:28:43.449 [Thread-4] DEBUG org.apache.http.wire - http-outgoing-1 << "[\r][\n]"
14:28:43.449 [Thread-4] DEBUG org.apache.http.wire - http-outgoing-1 << "2[\r][\n]"
14:28:43.449 [Thread-4] DEBUG org.apache.http.wire - http-outgoing-1 << "[][\r][\n]"
14:28:43.449 [Thread-4] DEBUG org.apache.http.wire - http-outgoing-1 << "0[\r][\n]"
14:28:43.449 [Thread-4] DEBUG org.apache.http.wire - http-outgoing-1 << "[\r][\n]"
14:28:43.450 [Thread-4] DEBUG org.apache.http.headers - http-outgoing-1 << HTTP/1.1 200 
14:28:43.450 [Thread-4] DEBUG org.apache.http.headers - http-outgoing-1 << Content-Type: application/json;charset=UTF-8
14:28:43.450 [Thread-4] DEBUG org.apache.http.headers - http-outgoing-1 << Transfer-Encoding: chunked
14:28:43.451 [Thread-4] DEBUG org.apache.http.headers - http-outgoing-1 << Date: Sat, 10 Nov 2018 08:58:43 GMT
14:28:43.452 [Thread-4] DEBUG org.apache.http.impl.execchain.MainClientExec - Connection can be kept alive indefinitely
14:28:43.453 [Thread-4] DEBUG org.apache.http.impl.conn.PoolingHttpClientConnectionManager - Connection [id: 1][route: {}->http://localhost:8080] can be kept alive indefinitely
14:28:43.453 [Thread-4] DEBUG org.apache.http.impl.conn.DefaultManagedHttpClientConnection - http-outgoing-1: set socket timeout to 0
14:28:43.453 [Thread-4] DEBUG org.apache.http.impl.conn.PoolingHttpClientConnectionManager - Connection released: [id: 1][route: {}->http://localhost:8080][total kept alive: 1; route allocated: 1 of 100; total allocated: 1 of 200]
## Successful...
SUCCEEDED
4

1 回答 1

1

从您向我们展示的内容来看，您的代码对HttpClientService任何地方都没有强引用。这让我相信在它完成之前HttpClientService正在被垃圾收集。HttpClientTask一些快速测试证实这是可能的。事实上，文档特别警告了这一点：

一旦服务启动，它将调度其任务并监听任务状态的变化。Task 不包含对启动它的 Service 的引用，这意味着正在运行的 Task 不会阻止 Service 被垃圾收集。

要解决这个问题，您需要保持对HttpClientService实例的强引用。这可以通过将其存储在loadBlocks()所属类中的某个位置来完成（假设所述类的实例也被强引用）。然后，当服务终止时，您可以删除该引用（因为您当前没有重用该服务）。另一种解决方案是HttpClientTask直接使用，只有HttpClientService在你准备好时才使用。

请注意，不是HttpClientTask垃圾收集。这是因为从执行它可以很容易地到达它。因此，您的后台任务正常完成，但不再有通知您。ThreadHttpClientService

此外，第一次运行此代码与任何后续时间之间没有区别。它适用于第二次调用的事实只是运气。HttpClientService每次调用此方法时都会进行垃圾收集；但是，不能保证垃圾回收周期会运行，这意味着您会不时走运。

于 2018-11-11T04:18:57.070 回答