使用 Jetty Websockets 的通用编码器和解码器

Question

如果我使用的是 resteasy，我可以使用 resteasy-jackson-provider 来处理将我的对象编组为 JSON 并返回到我的 rest 端点，例如：

@GET
@Path("/")
@Produces({MediaType.APPLICATION_JSON})
public MyThing getSingle() {
    return new MyThing();
}

这很好，因为这意味着我不需要为每种类型指定编码器 - Jackson 只需处理它。

我现在正在学习websockets，我发现我必须提供编码器：

@ServerEndpoint(value = "/websocket", encoders = {MyThingEncoder.class}, decoders = {MyThingDecoder.class})
public class Websocket {

    @OnOpen
    public void onOpen(Session session) {
            session.getBasicRemote().sendObject(new MyThing());
    }
}

这令人沮丧，因为我不想为每个单独的实体类型提供编码器/解码器，尤其是当它们只使用 Jackson 时。现在，我的编码器/解码器看起来像：

public class MyThingEncoder implements Encoder.Text<MyThing> {

    private static final ObjectMapper MAPPER = new ObjectMapper();

    @Override
    public void init(EndpointConfig endpointConfig) {
    }

    @Override
    public void destroy() {
    }

    @Override
    public String encode(MyThing t) throws EncodeException {
        try {
            return MAPPER.writeValueAsString(t);
        } catch (IOException e) {
            throw new EncodeException(t, "Could not encode.", e);
        }
    }
}

我尝试通过将类定义更改为 MyThingEncoder（下）来使用泛型，但它引发了异常（也在下）：

package com.jetnuts.serv.encoders;

import org.codehaus.jackson.map.ObjectMapper;
import org.jboss.resteasy.util.Encode;

import javax.websocket.*;
import java.io.IOException;

public class MyThingEncoder<T> implements Encoder.Text<T> {

    private static final ObjectMapper MAPPER = new ObjectMapper();

    Class<T> typeOf;

    @Override
    public void init(EndpointConfig endpointConfig) {
    }

    @Override
    public void destroy() {
    }

    @Override
    public String encode(T t) throws EncodeException {
        try {
            return MAPPER.writeValueAsString(t);
        } catch (IOException e) {
            throw new EncodeException(t, "Could not encode.", e);
        }
    }
}

例外：

org.eclipse.jetty.websocket.api.InvalidWebSocketException: Invalid type declared for interface javax.websocket.Encoder$Text on class class com.jetnuts.serv.encoders.MyThingEncoder
    at org.eclipse.jetty.websocket.jsr356.metadata.EncoderMetadataSet.getEncoderType(EncoderMetadataSet.java:82)
    at org.eclipse.jetty.websocket.jsr356.metadata.EncoderMetadataSet.discover(EncoderMetadataSet.java:50)
    at org.eclipse.jetty.websocket.jsr356.metadata.CoderMetadataSet.addAll(CoderMetadataSet.java:78)
    at org.eclipse.jetty.websocket.jsr356.server.AnnotatedServerEndpointMetadata.<init>(AnnotatedServerEndpointMetadata.java:51)
    at org.eclipse.jetty.websocket.jsr356.server.ServerContainer.getServerEndpointMetadata(ServerContainer.java:162)
    at org.eclipse.jetty.websocket.jsr356.server.ServerContainer.addEndpoint(ServerContainer.java:87)
    at org.eclipse.jetty.websocket.jsr356.server.ServerContainer.doStart(ServerContainer.java:139)
    at org.eclipse.jetty.util.component.AbstractLifeCycle.start(AbstractLifeCycle.java:68)
    at org.eclipse.jetty.util.component.ContainerLifeCycle.start(ContainerLifeCycle.java:132)
    at org.eclipse.jetty.util.component.ContainerLifeCycle.doStart(ContainerLifeCycle.java:106)
    at org.eclipse.jetty.server.handler.AbstractHandler.doStart(AbstractHandler.java:61)
    at org.eclipse.jetty.server.handler.ScopedHandler.doStart(ScopedHandler.java:120)
    at org.eclipse.jetty.server.handler.ContextHandler.startContext(ContextHandler.java:803)
    at org.eclipse.jetty.servlet.ServletContextHandler.startContext(ServletContextHandler.java:344)
    at org.eclipse.jetty.webapp.WebAppContext.startWebapp(WebAppContext.java:1379)
    at org.eclipse.jetty.webapp.WebAppContext.startContext(WebAppContext.java:1341)
    at org.eclipse.jetty.server.handler.ContextHandler.doStart(ContextHandler.java:772)
    at org.eclipse.jetty.servlet.ServletContextHandler.doStart(ServletContextHandler.java:261)
    at org.eclipse.jetty.webapp.WebAppContext.doStart(WebAppContext.java:517)
    at org.eclipse.jetty.util.component.AbstractLifeCycle.start(AbstractLifeCycle.java:68)
    at org.eclipse.jetty.deploy.bindings.StandardStarter.processBinding(StandardStarter.java:41)
    at org.eclipse.jetty.deploy.AppLifeCycle.runBindings(AppLifeCycle.java:188)
    at org.eclipse.jetty.deploy.DeploymentManager.requestAppGoal(DeploymentManager.java:499)
    at org.eclipse.jetty.deploy.DeploymentManager.addApp(DeploymentManager.java:147)
    at org.eclipse.jetty.deploy.providers.ScanningAppProvider.fileAdded(ScanningAppProvider.java:180)
    at org.eclipse.jetty.deploy.providers.WebAppProvider.fileAdded(WebAppProvider.java:458)
    at org.eclipse.jetty.deploy.providers.ScanningAppProvider$1.fileAdded(ScanningAppProvider.java:64)
    at org.eclipse.jetty.util.Scanner.reportAddition(Scanner.java:610)
    at org.eclipse.jetty.util.Scanner.reportDifferences(Scanner.java:529)
    at org.eclipse.jetty.util.Scanner.scan(Scanner.java:392)
    at org.eclipse.jetty.util.Scanner$1.run(Scanner.java:329)
    at java.util.TimerThread.mainLoop(Timer.java:555)
    at java.util.TimerThread.run(Timer.java:505)

如何避免需要一个编码器/解码器，它对我想要发送/接收的每种类型的对象执行完全相同的操作？

Answer 1

import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;

import javax.websocket.DecodeException;
import javax.websocket.Decoder;
import javax.websocket.EndpointConfig;
import java.io.IOException;
import java.io.Reader;

public class DataDecoder implements    Decoder.TextStream<Object> {

@Override
public Object decode(Reader reader) throws DecodeException, IOException {

    ObjectMapper mapper = new ObjectMapper();
    return mapper.readValue(reader, new TypeReference<Object>() {
    });

}

@Override
public void init(EndpointConfig config) {

}

@Override
public void destroy() {

}
}



@ClientEndpoint (decoders = { DataDecoder.class })
public class SomeClass  {


private WebSocketContainer container;

private Session session;
private Object objectModel;

@Override
public SomeType getAimedJobs() throws DatabaseException, ModuleNotLoadException, NamingException {



    SomeType someType = new SomeType ();
    ObjectMapper mapper = new ObjectMapper();
    try {
        String jsonInString =    mapper.writeValueAsString(this.objectModel);
        someType = mapper.readValue(jsonInString, SomeType.class);
    } catch (IOException e) {
        e.printStackTrace();
    }
    return someType ;
}


@OnOpen
public void onOpen(Session session) {

    this.session = session;
}

@OnMessage
public void onMessage(Object o) {

    this.objectModel = o;
}

@OnClose
public void onClose(CloseReason reason) {

    System.out.println("WebSocket connection closed with CloseCode: " + reason.getCloseCode());
    this.session.Close();
}

}