Android 上的 Restlet 服务器：客户端正在获取空对象

Question

我实现了一个简单的 Android Restlet 服务器演示，它可以向 Restlet 客户端提供传感器值。 然而，当 restlet 客户端收到对象时，它是空的。我想没有太多遗漏，因为事务显示它在服务器中正确完成logcat:

D/SensorTemperature: GET temperature: 20.0
W/System.err: 2015-10-23    20:28:37    192.168.2.129   -   -   8080    GET /sensors/temperature    -   200 -   0   198 http://192.168.2.94:8080    Restlet-Framework/2.3.5 -

并且在客户端，ClientResource 打印 (logcat):

ClientProxy for resource: GET http://192.168.2.94:8080/sensors/temperature HTTP/1.1 => HTTP/1.1 - OK (200) - The request has succeeded

此外，当使用 restlet request/response 时，浏览器界面按预期工作（参见下面的“/test”：）。

我遵循了官方的Restlet教程： http://restlet.com/technical-resources/restlet-framework/guide/2.2/introduction/first-steps/first-application

git: https://github.com/restlet/restlet-tutorial/tree/master/modules/org.restlet.tutorial.webapi/src/main/java/org/restlet/tutorial

连同这个例子： http://maxrohde.com/2011/09/02/restlet-quickstart/

代码：

这里是 restlet 服务器：

public class ServerFactory {

    static {
        // Get NIO engines, instead of defaults
        Engine.getInstance().getRegisteredServers().add(new HttpsServerHelper(null));
        Engine.getInstance().getRegisteredServers().add(new HttpServerHelper(null));
        // Engine.setLogLevel(Level.FINEST);
        Engine.getInstance().getRegisteredConverters().add(new JacksonConverter());
    }

    private static Restlet restlet = new Restlet() {
        @Override
        public void handle(Request request, Response response) {
            Date date = new Date();
            float temp = WSDataProvider.getInstance().getTemperature();
            response.setEntity("Hello World!\nTime: " + date + "\nTemp: " + temp, MediaType.TEXT_PLAIN);
        }
    };

    public static Server createServer(int port, final String rootUri) {
        Component component = new Component();

        Server server = component.getServers().add(Protocol.HTTP, port);

        // Attach the sample application.
        component.getDefaultHost().attach("/test", restlet);

        SensorsApplication sensorsApp = new SensorsApplication();
        component.getDefaultHost().attach("/sensors", sensorsApp);

        return server;  // server.start() and server.stop() called via Android buttons
    }
}

而客户：

Thread thread = new Thread(new Runnable(){
    @Override
    public void run() {
        try {
            Engine.getInstance().getRegisteredConverters().add(new JacksonConverter());

            // Initialize the resource proxy.
            final ClientResource cr = new ClientResource("http://192.168.2.94:8080/sensors/temperature");
            final SensorResource resource = cr.wrap(SensorResource.class);

            // Get the remote temperature sensor
            final SensorBase sensorBase = resource.retrieve();
            if (sensorBase != null)
                Log.e(TAG, "sensorBase.getData() = " + sensorBase.data);
            else
                Log.e(TAG, "sensorBase is null !!");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
});

thread.start();

SensorBaseclass：（客户端+服务器）

public class SensorBase implements Serializable {

    private static final long serialVersionUID = 1L;

    public static final int TYPE_UNKNOWN = 0;
    public static final int TYPE_TEMPERATURE = 1;
    public static final int TYPE_HUMIDITY = 2;

    public int type;
    public float data;

    public SensorBase(final int type) {
        super();
        this.type = type;
    }
}

传感器资源class：（客户端+服务器）

public interface SensorResource {
    @Get
    public SensorBase retrieve();
}

传感器温度class:

public class SensorTemperature extends ServerResource implements SensorResource {

    private static final String TAG = "SensorTemperature";
    private static volatile SensorBase sensorBase = new SensorBase(SensorBase.TYPE_TEMPERATURE);

    public SensorBase retrieve() {
        float temp = WSDataProvider.getInstance().getTemperature();
        Log.d(TAG, "GET temperature: " + temp);
        sensorBase.data = temp;
        return sensorBase;
    }
}

传感器应用程序class:

public class SensorsApplication extends Application {
    public Restlet createInboundRoot() {
        Router router = new Router(getContext());
        router.attach("/temperature", SensorTemperature.class);
        //TODO add more sensors
        return router;
    }
}

更新

我已通过包含 jackson jar 文件 com.fasterxml.jackson.core.jar 修复了空指针异常。 class 未找到错误仅在 Restlet 客户端使用 Engine.setLogLevel(Level.FINEST); !

时显示

但是，我现在从客户端收到以下异常：

org.restlet.resource.ResourceException: Unprocessable Entity (422) - The server understands the content type of the request entity and the syntax of the request entity is correct but was unable to process the contained instructions

谢谢！

Answer 1

其实不是Restlet的问题，而是Jackson的问题。如果查看 422 错误的根本原因，您会看到：

Caused by: com.fasterxml.jackson.databind.JsonMappingException: No suitable constructor found for type [simple type, class SensorBase]: can not instantiate from JSON object (need to add/enable type information?)
 at [Source: sun.nio.ch.ChannelInputStream@1eb0d79; line: 1, column: 2]
 at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:148)
 at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromObjectUsingNonDefault(BeanDeserializerBase.java:1071)
 at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:264)
 at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:124)
 at com.fasterxml.jackson.databind.ObjectReader._bindAndClose(ObjectReader.java:1269)
 at com.fasterxml.jackson.databind.ObjectReader.readValue(ObjectReader.java:864)
 at org.restlet.ext.jackson.JacksonRepresentation.getObject(JacksonRepresentation.java:299)
 at org.restlet.ext.jackson.JacksonConverter.toObject(JacksonConverter.java:208)
 at org.restlet.service.ConverterService.toObject(ConverterService.java:229)
 at org.restlet.resource.Resource.toObject(Resource.java:889)
 ... 3 more

Jackson 对你的对象 SensorBase 的反序列化需要一个空构造函数 class:

public class SensorBase implements Serializable {
    private static final long serialVersionUID = 1L;

    public static final int TYPE_UNKNOWN = 0;
    public static final int TYPE_TEMPERATURE = 1;
    public static final int TYPE_HUMIDITY = 2;

    public int type;
    public float data;

    public SensorBase() {

    }

    public SensorBase(final int type) {
        super();
        this.type = type;
    }

    (...)
}

希望对你有帮助，蒂埃里

Android 上的 Restlet 服务器：客户端正在获取空对象

Restlet server on Android: client is getting a null object

android

restlet

restlet-2.0